ORCID Profile
0000-0001-8322-9983
Current Organisation
Swinburne University of Technology
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Optical Physics | Photonics, Optoelectronics and Optical Communications | Plasma Physics; Fusion Plasmas; Electrical Discharges | Nanomaterials | Nanotechnology | Lasers and Quantum Electronics | Condensed Matter Imaging | Atomic and Molecular Physics | Nanofabrication, Growth and Self Assembly
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Technology | Scientific Instruments | Expanding Knowledge in Engineering |
Related Links
Publications
Streaked radiography measurements of convergent ablator performance (invited)
Publisher: AIP Publishing
Date: 10-2010
DOI: 10.1063/1.3475727
Abstract: The velocity and remaining ablator mass of an imploding capsule are critical metrics for assessing the progress toward ignition of an inertially confined fusion experiment. These and other ablator rocket parameters have been measured using a single streaked x-ray radiograph. A regularization technique has been used to determine the ablator density profile ρ(r) at each time step moments of ρ(r) then provide the areal density, average radius, and mass of the unablated, or remaining, ablator material, with the velocity determined from the time derivative of the average radius. The technique has been implemented on experiments at the OMEGA laser facility.
Comparisons of NIF convergent ablation simulations with radiograph data
Publisher: AIP Publishing
Date: 06-08-2012
DOI: 10.1063/1.4738653
Abstract: A technique for comparing simulation results directly with radiograph data from backlit capsule implosion experiments will be discussed. Forward Abel transforms are applied to the kappa*rho profiles of the simulation. These provide the transmission ratio (optical depth) profiles of the simulation. Gaussian and top hat blurs are applied to the simulated transmission ratio profiles in order to account for the motion blurring and imaging slit resolution of the experimental measurement. Comparisons between the simulated transmission ratios and the radiograph data lineouts are iterated until a reasonable backlighter profile is obtained. This backlighter profile is combined with the blurred, simulated transmission ratios to obtain simulated intensity profiles that can be directly compared with the radiograph data. Ex les will be shown from recent convergent ablation (backlit implosion) experiments at the NIF.
High-precision measurements of the equation of state of hydrocarbons at 1–10 Mbar using laser-driven shock waves
Publisher: AIP Publishing
Date: 31-03-2010
DOI: 10.1063/1.3358144
Abstract: The equation of state (EOS) of polystyrene and polypropylene were measured using laser-driven shock waves with pressures from 1 to 10 Mbar. Precision data resulting from the use of α-quartz as an impedance-matching (IM) standard tightly constrains the EOS of these hydrocarbons, even with the inclusion of systematic errors inherent to IM. The temperature at these high pressures was measured, which, combined with kinematic measurements, provide a complete shock EOS. Both hydrocarbons were observed to reach similar compressions and temperatures as a function of pressure. The materials were observed to transition from transparent insulators to reflecting conductors at pressures of 1 to 2 Mbar.
Laser-driven single shock compression of fluid deuterium from 45 to 220 GPa
Publisher: American Physical Society (APS)
Date: 26-01-2009
Differences between morphological and electrophysiological retinal ganglion cell classes
Publisher: IEEE
Date: 07-2018
Parameter estimation and identifiability in a neural population model for electro-cortical activity
Publisher: Cold Spring Harbor Laboratory
Date: 10-12-2018
DOI: 10.1101/492504
Abstract: Electroencephalography (EEG) provides a non-invasive measure of brain electrical activity. Neural population models, where large numbers of interacting neurons are considered collectively as a macroscopic system, have long been used to understand features in EEG signals. By tuning dozens of input parameters describing the excitatory and inhibitory neuron populations, these models can reproduce prominent features of the EEG such as the alpha-rhythm. However, the inverse problem, of directly estimating the parameters from fits to EEG data, remains unsolved. Solving this multi-parameter non-linear fitting problem will potentially provide a real-time method for characterizing average neuronal properties in human subjects. Here we perform unbiased fits of a 22-parameter neural population model to EEG data from 82 in iduals, using both particle swarm optimization and Markov chain Monte Carlo s ling. We estimate how much is learned about in idual parameters by computing Kullback-Leibler ergences between posterior and prior distributions for each parameter. Results indicate that only a single parameter, that determining the dynamics of inhibition, is directly identifiable, while other parameters have large, though correlated, uncertainties. We show that the eigenvalues of the Fisher information matrix are roughly uniformly spaced over a log scale, indicating that the model is sloppy, like many of the regulatory network models in systems biology. These eigenvalues indicate that the system can be modeled with a low effective dimensionality, with inhibition being prominent in driving system behavior. Electroencephalography (EEG), where electrodes are used to measure electric potential on the outside of the scalp, provides a simple, non-invasive way to study brain activity. Physiological interpretation of features in EEG signals has often involved use of collective models of neural populations. These neural population models have dozens of input parameters to describe the properties of inhibitory and excitatory neurons. Being able to estimate these parameters by direct fits to EEG data holds the promise of providing a real-time non-invasive method of inferring neuronal properties in different in iduals. However, it has long been impossible to fit these nonlinear, multi-parameter models effectively. Here we describe fits of a 22-parameter neural population model to EEG spectra from 82 different subjects, all exhibiting alpha-oscillations. We show how only one parameter, that describing inhibitory dynamics, is constrained by the data, although all parameters are correlated. These results indicate that inhibition plays a central role in the generation and modulation of the alpha-rhythm in humans.
Progress towards ignition on the National Ignition Facility
Publisher: IOP Publishing
Date: 31-08-2011
DOI: 10.1088/0029-5515/51/9/094024
Abstract: The National Ignition Facility at Lawrence Livermore National Laboratory was formally dedicated in May 2009. The hohlraum energetics c aign with all 192 beams began shortly thereafter and ran until early December 2009. These experiments explored hohlraum-operating regimes in preparation for experiments with layered cryogenic targets. The hohlraum energetic series culminated with an experiment that irradiated an ignition scale hohlraum with 1 MJ. The results demonstrated the ability to produce a 285 eV radiation environment in an ignition scale hohlraum while meeting ignition requirements for symmetry, backscatter and hot electron production. Complementary scaling experiments indicate that with ∼1.3 MJ, the capsule drive temperature will reach 300 eV, the point design temperature for the first ignition c aign. Preparation for cryo-layered implosions included installation of a variety of nuclear diagnostics, cryogenic layering target positioner, advanced optics and facility modifications needed for tritium operations and for routine operation at laser energy greater than 1.3 MJ. The first cyro-layered experiment was carried out on 29 September 2010. The main purpose of this shot was to demonstrate the ability to integrate all of the laser, target and diagnostic capability needed for a successful cryo-layered experiment. This paper discusses the ignition point design as well as findings and conclusions from the hohlraum energetics c aign carried out in 2009. It also provides a brief summary of the initial cryo-layered implosion.
Acylase I catalysed hydrolysis of para-substituted (S)-phenylalanine derivatives from mixtures of the racemic ortho- and para-substituted isomers
Publisher: Elsevier BV
Date: 07-1998
Line-imaging velocimeter for shock diagnostics at the OMEGA laser facility
Publisher: AIP Publishing
Date: 11-2004
DOI: 10.1063/1.1807008
Abstract: A line-imaging velocity interferometer has been implemented at the OMEGA laser facility of the Laboratory for Laser Energetics, University of Rochester. This instrument is the primary diagnostic for a variety of experiments involving laser-driven shock-wave propagation, including high-pressure equation of state experiments, materials characterization experiments, shock characterization for Rayleigh–Taylor experiments, and shock timing experiments for inertial confinement fusion research. Using a laser probe beam to illuminate a target, the instrument measures shock breakout times at temporal resolutions as low as 20 ps, and spatial resolution ∼4 μm. For velocity measurements the detection limit is & .1 km/s, and velocities of interfaces, free surfaces, and shock fronts traveling through transparent media can be measured with accuracies ∼1% over the range from 4 km/s to greater than 50 km/s. Quantitative measurements of the optical reflectance of ionizing shock fronts can also be obtained simultaneously with the velocity measurements.
Absolute measurements of neutron yields from DD and DT implosions at the OMEGA laser facility using CR-39 track detectors
Publisher: AIP Publishing
Date: 21-06-2002
DOI: 10.1063/1.1487889
Abstract: The response of CR-39 track detectors to neutrons has been characterized and used to measure neutron yields from implosions of DD- and DT-filled targets at the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], and the scaling of neutron fluence with R (the target-to-detector distance) has been used to characterize the fluence of backscattered neutrons in the target chamber. A Monte-Carlo code was developed to predict the CR-39 efficiency for detecting DD neutrons, and it agrees well with the measurements. Neutron detection efficiencies of (1.1±0.2)×10−4 and (6.0±0.7)×10−5 for the DD and DT cases, respectively, were determined for standard CR-39 etch conditions. In OMEGA experiments with both DD and DT targets, the neutron fluence was observed to decrease as R−2 up to about 45 cm at larger distances, a significant backscattered neutron component was seen. The measured backscattered component appears to be spatially uniform, and agrees with predictions of a neutron-transport code. As an additional application of the calibration results, it is shown that the neutron-induced signal in CR-39 used in charged-particle spectrometers on OMEGA can be used to determine DD and DT yields ranging from about 1010 up to 1014. With further improvements in the processing and analysis of CR-39, this upper limit can be increased by at least two orders of magnitude.
Shock Compressing Diamond to a Conducting Fluid
Publisher: American Physical Society (APS)
Date: 05-11-2004
Progress towards ignition on the National Ignition Facility
Publisher: AIP Publishing
Date: 07-2013
DOI: 10.1063/1.4816115
Abstract: The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory includes a precision laser system now capable of delivering 1.8 MJ at 500 TW of 0.35-μm light to a target. NIF has been operational since March 2009. A variety of experiments have been completed in support of NIF's mission areas: national security, fundamental science, and inertial fusion energy. NIF capabilities and infrastructure are in place to support its missions with nearly 60 X-ray, optical, and nuclear diagnostic systems. A primary goal of the National Ignition C aign (NIC) on the NIF was to implode a low-Z capsule filled with ∼0.2 mg of deuterium-tritium (DT) fuel via laser indirect-drive inertial confinement fusion and demonstrate fusion ignition and propagating thermonuclear burn with a net energy gain of ∼5–10 (fusion yield/input laser energy). This requires assembling the DT fuel into a dense shell of ∼1000 g/cm3 with an areal density (ρR) of ∼1.5 g/cm2, surrounding a lower density hot spot with a temperature of ∼10 keV and a ρR ∼0.3 g/cm2, or approximately an α-particle range. Achieving these conditions demand precise control of laser and target parameters to allow a low adiabat, high convergence implosion with low ablator fuel mix. We have demonstrated implosion and compressed fuel conditions at ∼80–90% for most point design values independently, but not at the same time. The nuclear yield is a factor of ∼3–10× below the simulated values and a similar factor below the alpha dominated regime. This paper will discuss the experimental trends, the possible causes of the degraded performance (the off-set from the simulations), and the plan to understand and resolve the underlying physics issues.
Investigation of ion kinetic effects in direct-drive exploding-pusher implosions at the NIF
Publisher: AIP Publishing
Date: 12-2014
DOI: 10.1063/1.4905064
Progress in the study of warm dense matter
Publisher: IOP Publishing
Date: 08-11-2005
Evidence for a Phase Transition in Silicate Melt at Extreme Pressure and Temperature Conditions
Publisher: American Physical Society (APS)
Date: 08-02-2012
Parameter estimation and identifiability in a neural population model for electro-cortical activity
Publisher: Public Library of Science (PLoS)
Date: 30-05-2019
Inferring a simple mechanism for alpha-blocking by fitting a neural population model to EEG spectra
Publisher: Public Library of Science (PLoS)
Date: 30-04-2020
Electronic conduction in shock-compressed water
Publisher: AIP Publishing
Date: 25-06-2004
DOI: 10.1063/1.1758944
Abstract: The optical reflectance of a strong shock front in water increases continuously with pressure above 100 GPa and saturates at ∼45% reflectance above 250 GPa. This is the first evidence of electronic conduction in high pressure water. In addition, the water Hugoniot equation of state up to 790 GPa (7.9 Mbar) is determined from shock velocity measurements made by detecting the Doppler shift of reflected light. From a fit to the reflectance data we find that an electronic mobility gap ∼2.5 eV controls thermal activation of electronic carriers at pressures in the range of 100–150 GPa. This suggests that electronic conduction contributes significantly to the total conductivity along the Neptune isentrope above 150 GPa.
Systematic uncertainties in shock-wave impedance-match analysis and the high-pressure equation of state of Al
Publisher: AIP Publishing
Date: 12-2005
DOI: 10.1063/1.2140077
Abstract: A method for producing quantitative estimates of systematic uncertainties generated in the analysis of impedance-match shock-wave data is described. Central to the method is an analytic representation of the principal Hugoniot of the standard which incorporates a description of data-dependent uncertainties of the principal Hugoniot and model-dependent uncertainties of the off-Hugoniot states. Expressions for the sound speed and Grüneisen coefficient along the principal Hugoniot are also derived with uncertainties. An accurate impedance-match shock-wave equation of state for Al to shock pressure of 3TPa is given and is used to estimate the systematic uncertainties of several previously published experimental results.
Proton Radiography of a Laser-Driven Implosion
Publisher: American Physical Society (APS)
Date: 24-07-2006
Shock vaporization of silica and the thermodynamics of planetary impact events
Publisher: American Geophysical Union (AGU)
Date: 09-2012
DOI: 10.1029/2012JE004082
Optimal foil shape for neutron time-of-flight measurements using elastic recoils
Publisher: AIP Publishing
Date: 2001
DOI: 10.1063/1.1321002
Abstract: The basis for a time-of-flight neutron spectrometer for inertial confinement fusion (ICF) experiments using recoils from a shaped scattering foil is presented. It is shown that the number of elastic recoils can be substantially increased by utilizing a large scattering foil in the shape of an ellipsoid, with the curvature of the ellipsoid being determined by the mass of the recoil particle. This shape allows the time-of-flight dispersion — present originally in the neutrons — to be maintained in the recoils despite the large foil area. The feasibility of using this design on current ICF experiments is discussed.
Laser-produced protons and their application as a particle probe
Publisher: Hindawi Limited
Date: 04-2002
DOI: 10.1017/S0263034602202177
Abstract: One of the most exciting results recently obtained in the ultraintense interaction research area is the observation of beams of protons with energies up to several tens of megaelectron volts, generated during the interaction of ultraintense picosecond pulses with solid targets. The particular properties of these beams (high brilliance, small source size, high degree of collimation, short duration) make them of exceptional interest in view of diagnostic applications. In a series of experiments carried out at the Rutherford Appleton Laboratory (RAL) and at the Lawrence Livermore National Laboratory (LLNL), the laser-produced proton beams have been characterized in view of their application as a particle probe for high-density matter, and applied to diagnose ultraintense laser–plasma interactions. In general, the intensity cross section of a proton beam traversing matter will be modified both by collisional stopping/scattering, and deflections caused by electric/magnetic fields. With a suitable choice of irradiation geometry and target parameters, the proton probe can be made mainly sensitive to the electric field distribution in the object probed. Therefore, point projection proton imaging appears as a powerful and unique technique for electric field detection in laser-irradiated targets and plasmas. The first measurements of transient electric fields in high-intensity laser-plasma interactions have been obtained with this technique.
Multiple spherically converging shock waves in liquid deuterium
Publisher: AIP Publishing
Date: 09-2011
DOI: 10.1063/1.3640805
A direct-drive exploding-pusher implosion as the first step in development of a monoenergetic charged-particle backlighting platform at the National Ignition Facility
Publisher: Elsevier BV
Date: 03-2016
Proton Moiré fringes for diagnosing electromagnetic fields in opaque materials and plasmas
Publisher: AIP Publishing
Date: 12-05-2003
DOI: 10.1063/1.1569416
Experimental studies of ICF indirect-drive Be and high density C candidate ablators
Publisher: IOP Publishing
Date: 05-2008
Influence and measurement of mass ablation in ICF implosions
Publisher: IOP Publishing
Date: 05-2008
Self-consistent measurement of the equation of state of liquid deuterium
Publisher: Elsevier BV
Date: 03-2012
Insulator-to-Conducting Transition in Dense Fluid Helium
Publisher: American Physical Society (APS)
Date: 05-05-2010
Performance of High-Convergence, Layered DT Implosions with Extended-Duration Pulses at the National Ignition Facility
Publisher: American Physical Society (APS)
Date: 19-11-2013
Diamond at 800 GPa
Publisher: American Physical Society (APS)
Date: 18-02-2009
Streaked optical pyrometer system for laser-driven shock-wave experiments on OMEGA
Publisher: AIP Publishing
Date: 03-2007
DOI: 10.1063/1.2712189
Abstract: The temperature of laser-driven shock waves is of interest to inertial confinement fusion and high-energy-density physics. We report on a streaked optical pyrometer that measures the self-emission of laser-driven shocks simultaneously with a velocity interferometer system for any reflector (VISAR). Together these diagnostics are used to obtain the temporally and spatially resolved temperatures of approximately megabar shocks driven by the OMEGA laser. We provide a brief description of the diagnostic and how it is used with VISAR. Key spectral calibration results are discussed and important characteristics of the recording system are presented.
Ignition tuning for the National Ignition Campaign
Publisher: EDP Sciences
Date: 2013
Novel Diagnostic of Shock Fronts in Low-Z Dense Plasmas
Publisher: Springer Science and Business Media LLC
Date: 07-2005
Coupling static and dynamic compressions: first measurements in dense hydrogen
Publisher: Informa UK Limited
Date: 2004
Demonstration of the shock-timing technique for ignition targets on the National Ignition Facility
Publisher: AIP Publishing
Date: 27-02-2009
DOI: 10.1063/1.3078422
Abstract: A high-performance inertial confinement fusion capsule is compressed by multiple shock waves before it implodes. To minimize the entropy acquired by the fuel, the strength and timing of those shock waves must be accurately controlled. Ignition experiments at the National Ignition Facility (NIF) will employ surrogate targets designed to mimic ignition targets while making it possible to measure the shock velocities inside the capsule. A series of experiments on the OMEGA laser facility [Boehly et al., Opt. Commun. 133, 495 (1997)] validated those targets and the diagnostic techniques proposed. Quartz was selected for the diagnostic window and shock-velocity measurements were demonstrated in Hohlraum targets heated to 180 eV. Cryogenic experiments using targets filled with liquid deuterium further demonstrated the entire timing technique in a Hohlraum environment. Direct-drive cryogenic targets with multiple spherical shocks were used to further validate this technique, including convergence effects at relevant pressures (velocities) and sizes. These results provide confidence that shock velocity and timing can be measured in NIF ignition targets, allowing these critical parameters to be optimized.
Study of direct-drive, deuterium–tritium gas-filled plastic capsule implosions using nuclear diagnostics at OMEGA
Publisher: AIP Publishing
Date: 11-2001
DOI: 10.1063/1.1405016
Abstract: Implosions of direct-drive, deuterium–tritium (DT) gas-filled plastic capsules are studied using nuclear diagnostics at the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. In addition to traditional neutron measurements, comprehensive sets of spectra of deuterons, tritons, and protons elastically scattered from the fuel and shell by primary DT neutrons (“knock-on” particles) are, for the first time, obtained and used for characterizing target performance. It is shown with these measurements that, for 15-atm DT capsules with 20-μm CH shells, improvement of target performance is achieved when on-target irradiation nonuniformity is reduced. Specifically, with a two-dimensional (2D) single-color-cycle, 1-THz-bandwidth smoothing by spectral dispersion (SSD), plus polarization smoothing (PS), a primary neutron yield of ∼1×1013, a fuel areal density of ∼15 mg/cm2, and a shell areal density of ∼60 mg/cm2 are obtained these are, respectively, ∼80%, ∼60%, and ∼35% higher than those achieved using 0.35-THz, 3-color-cycle, 2D SSD without PS. (In determining fuel areal density we assume the fuel to have equal numbers of D and T.) With full beam smoothing, implosions with moderate radial convergence (∼10–15) are shown to have ρR performance close to one-dimensional-code predictions, but a ratio of measured-to-predicted primary neutron yield of ∼0.3. Other capsules that are predicted to have much higher radial convergence (3.8-atm DT gas with 20-μm CH shell) are shown to have ρRfuel∼3 mg/cm2, falling short of prediction by about a factor of 5. The corresponding convergence ratios are similar to the values for 15-atm capsules. This indicates, not surprisingly, that the effects of mix are more deleterious for high-convergence implosions. A brief comparison of these moderate- and high-convergence implosions to those of similar deuterium–deuterium (D2) gas-filled capsules shows comparable hydrodynamic performance.
Measurement of the sound speed in dense fluid deuterium along the cryogenic liquid Hugoniot
Publisher: AIP Publishing
Date: 2019
DOI: 10.1063/1.5053994
Abstract: Many experimental studies, spanning several decades of research and using various dynamic compression schemes, have been conducted to investigate cryogenic liquid deuterium under strong shock compression. The consensus emerging from these studies is that of a progressive dissociation of the D2 molecules into an electrically conducting, atomic plasma, when subjected to shock pressures exceeding ∼50 GPa. While state-of-the-art numerical simulations based on density-functional-theory or quantum Monte-Carlo techniques capture this behavior quite well, subtle differences subsist between these simulations and the available experimental data regarding the pressure-density compressibility. Here, leveraging a recently developed analysis method for high-resolution Doppler interferometric velocity data, we present Eulerian sound speed measurements in compressed deuterium to shock pressures between 50 and 200 GPa. These results, extracted from laser-driven shockwave experiments, are found to agree with several of the most accurate equation of state models for deuterium at those conditions up to ∼150 GPa. However, the data indicate that these models fail to reproduce the experimentally observed sound speed at higher pressures, approaching 200 GPa. In particular, we unveil a discrepancy between the experimental results and the equation of state model that is most commonly used in inertial confinement fusion at the National Ignition Facility.
Capsule implosion optimization during the indirect-drive National Ignition Campaign
Publisher: AIP Publishing
Date: 05-2011
DOI: 10.1063/1.3592170
Abstract: Capsule performance optimization c aigns will be conducted at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, 228 (2004)] to substantially increase the probability of ignition. The c aigns will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models using a variety of ignition capsule surrogates before proceeding to cryogenic-layered implosions and ignition experiments. The quantitative goals and technique options and down selections for the tuning c aigns are first explained. The computationally derived sensitivities to key laser and target parameters are compared to simple analytic models to gain further insight into the physics of the tuning techniques. The results of the validation of the tuning techniques at the OMEGA facility [J. M. Soures et al., Phys. Plasmas 3, 2108 (1996)] under scaled hohlraum and capsule conditions relevant to the ignition design are shown to meet the required sensitivity and accuracy. A roll-up of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget. Finally, we show how the tuning precision will be improved after a number of shots and iterations to meet an acceptable level of residual uncertainty.
Alpha blocking and 1/fβ spectral scaling in resting EEG can be accounted for by a sum of damped alpha band oscillatory processes
Publisher: Public Library of Science (PLoS)
Date: 15-04-2022
DOI: 10.1371/JOURNAL.PCBI.1010012
Abstract: The dynamical and physiological basis of alpha band activity and 1/ f β noise in the EEG are the subject of continued speculation. Here we conjecture, on the basis of empirical data analysis, that both of these features may be economically accounted for through a single process if the resting EEG is conceived of being the sum of multiple stochastically perturbed alpha band d ed linear oscillators with a distribution of d ings (relaxation rates). The modulation of alpha-band and 1/ f β noise activity by changes in d ing is explored in eyes closed (EC) and eyes open (EO) resting state EEG. We aim to estimate the distribution of d ings by solving an inverse problem applied to EEG power spectra. The characteristics of the d ing distribution are examined across subjects, sensors and recording condition (EC/EO). We find that there are robust changes in the d ing distribution between EC and EO recording conditions across participants. The estimated d ing distributions are found to be predominantly bimodal, with the number and position of the modes related to the sharpness of the alpha resonance and the scaling ( β ) of the power spectrum (1/ f β ). The results suggest that there exists an intimate relationship between resting state alpha activity and 1/ f β noise with changes in both governed by changes to the d ing of the underlying alpha oscillatory processes. In particular, alpha-blocking is observed to be the result of the most weakly d ed distribution mode becoming more heavily d ed. The results suggest a novel way of characterizing resting EEG power spectra and provides new insight into the central role that d ed alpha-band activity may play in characterising the spatio-temporal features of resting state EEG.
Laser-driven shock waves for the study of extreme matter states
Publisher: IOP Publishing
Date: 13-11-2006
Analysis of extracellular spike waveforms and associated receptive fields of neurons in cat primary visual cortex
Publisher: Wiley
Date: 02-03-2021
DOI: 10.1113/JP280844
Abstract: Extracellular spikes recorded in the visual cortex (Area 17/18, V1) are commonly classified into either regular‐spiking (RS) or fast‐spiking (FS). Using multi‐electrode arrays positioned in cat V1 and a broadband stimulus, we show that there is also a distinct class with positive‐spiking (PS) waveforms. PS units were associated mainly with non‐oriented receptive fields while RS and FS units had orientation‐selective receptive fields. We suggest that PS units are recordings of axons originating from the thalamus. This conclusion was reinforced by our finding that we could record PS units after cortical silencing, but not record RS and FS units. The importance of our findings is that we were able to correlate spike shapes with receptive field characteristics with high precision using multi‐electrode extracellular recording techniques. This allows considerable increases in the amount of information that can be extracted from future cortical experiments. Extracellular spike waveforms from recordings in the visual cortex have been classified into either regular‐spiking (RS) or fast‐spiking (FS) units. While both these types of spike waveforms are negative‐dominant, we show that there are also distinct classes of spike waveforms in visual Area 17/18 (V1) of anaesthetised cats with positive‐dominant waveforms, which are not regularly reported. The spatial receptive fields (RFs) of these different spike waveform types were estimated, which objectively revealed the existence of oriented and non‐oriented RFs. We found that units with positive‐dominant spikes, which have been associated with recordings from axons in the literature, had mostly non‐oriented RFs (84%), which are similar to the centre‐surround RFs observed in the dorsal lateral geniculate nucleus (dLGN). Thus, we hypothesise that these positive‐dominant waveforms may be recordings from dLGN afferents. We recorded from V1 before and after the application of muscimol (a cortical silencer) and found that the positive‐dominant spikes (PS) remained while the RS and FS cells did not. We also noted that the PS units had spiking characteristics normally associated with dLGN units (i.e. higher response spike rates, lower response latencies and higher proportion of burst spikes). Our findings show quantitatively that it is possible to correlate the RF properties of cortical neurons with particular spike waveforms. This has implications for how extracellular recordings should be interpreted and complex experiments can now be contemplated that would have been very challenging previously, such as assessing the feedforward connectivity between brain areas in the same location of cortical tissue.
Capsule Ablator Inflight Performance Measurements Via Streaked Radiography Of ICF Implosions On The NIF*
Publisher: IOP Publishing
Date: 03-2016
The direct measurement of ablation pressure driven by 351-nm laser radiation
Publisher: AIP Publishing
Date: 10-2011
DOI: 10.1063/1.3646554
Abstract: The instantaneous scaling of ablation pressure to laser intensity is directly inferred for r compression of diamond targets irradiated by 351-nm light. Continuously increasing pressure profiles from 100 to 970 GPa are produced by direct-drive laser ablation at intensities up to 7 × 1013 W/cm2. The free-surface velocity on the rear of the target is used to directly infer the instantaneous ablation-pressure profile at the front of the target. The laser intensity on target is determined by laser power measurements and fully characterized laser spots. The ablation pressure is found to depend on the laser intensity as P(GPa)=42(±3)[I(TW/cm2)]0.71(±0.01).
The velocity campaign for ignition on NIF
Publisher: AIP Publishing
Date: 28-03-2012
DOI: 10.1063/1.3694840
Abstract: Achieving inertial confinement fusion ignition requires a symmetric, high velocity implosion. Experiments show that we can reach 95 ± 5% of the required velocity by using a 420 TW, 1.6 MJ laser pulse. In addition, experiments with a depleted uranium hohlraum show an increase in capsule performance which suggests an additional 18 ± 5 μm/ns of velocity with uranium hohlraums over gold hohlraums. Combining these two would give 99 ± 5% of the ignition velocity. Experiments show that we have the ability to tune symmetry using crossbeam transfer. We can control the second Legendre mode (P2) by changing the wavelength separation between the inner and outer cones of laser beams. We can control the azimuthal m = 4 asymmetry by changing the wavelength separation between the 23.5 and 30 degree beams on NIF. This paper describes our “first pass” tuning the implosion velocity and shape on the National Ignition Facility laser [Moses et al., Phys. Plasmas, 16, 041006 (2009)].
Strength effects in diamond under shock compression from 0.1 to 1 TPa
Publisher: American Physical Society (APS)
Date: 22-01-2010
Observation of strong electromagnetic fields around laser-entrance holes of ignition-scale hohlraums in inertial-confinement fusion experiments at the National Ignition Facility
Publisher: IOP Publishing
Date: 27-02-2013
Direct-drive high-convergence-ratio implosion studies on the OMEGA laser system
Publisher: AIP Publishing
Date: 05-2000
DOI: 10.1063/1.874032
Abstract: A series of direct-drive implosion experiments, using room-temperature, gas-filled CH targets, are performed on the University of Rochester’s OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. The target performance at stagnation and its dependence on beam smoothing and pulse shaping is investigated. Compressed core conditions are diagnosed using x-ray and neutron spectroscopy, and x-ray imaging. The in idual beams of OMEGA are smoothed by spectral dispersion in two dimensions (2D SSD) with laser bandwidths up to ∼0.3 THz, with 1 ns square to 2.5 ns shaped pulses. A clear dependence of target performance on pulse shape and beam smoothing is seen, with the target performance (yield, areal density, and shell integrity) improving as SSD bandwidth is applied.
Powder diffraction from solids in the terapascal regime
Publisher: AIP Publishing
Date: 11-2012
DOI: 10.1063/1.4766464
Abstract: A method of obtaining powder diffraction data on dynamically compressed solids has been implemented at the Jupiter and OMEGA laser facilities. Thin powdered s les are sandwiched between diamond plates and r compressed in the solid phase using a gradual increase in the drive-laser intensity. The pressure history in the s le is determined by back-propagation of the measured diamond free-surface velocity. A pulse of x rays is produced at the time of peak pressure by laser illumination of a thin Cu or Fe foil and collimated at the s le plane by a pinhole cut in a Ta substrate. The diffracted signal is recorded on x-ray sensitive material, with a typical d-spacing uncertainty of ∼0.01 Å. This diagnostic has been used up to 0.9 TPa (9 Mbar) to verify the solidity, measure the density, constrain the crystal structure, and evaluate the strain-induced texturing of a variety of compressed s les spanning atomic numbers from 6 (carbon) to 82 (lead). Further refinement of the technique will soon enable diffraction measurements in solid s les at pressures exceeding 1 TPa.
Refractive index of lithium fluoride ramp compressed to 800 GPa
Publisher: AIP Publishing
Date: 15-06-2011
DOI: 10.1063/1.3599884
Abstract: We report the highest pressure under which a transparent insulator has been observed. The refractive index of r -compressed lithium fluoride (LiF) is measured up to a pressure of 800 GPa and is observed to maintain its linear dependence on density. An effective single-oscillator model infers that the bandgap monotonically closes with increasing density, indicating that metallization of LiF should occur at pressures above 4000 GPa, and that LiF should remain transparent at extremely high pressures.
Equation of state of CH1.36
Publisher: American Physical Society (APS)
Date: 25-09-2012
Ultrafast Dynamic Compression Technique to Study the Kinetics of Phase Transformations in Bismuth
Publisher: American Physical Society (APS)
Date: 08-08-2008
Cryogenic thermonuclear fuel implosions on the National Ignition Facility
Publisher: AIP Publishing
Date: 05-2012
DOI: 10.1063/1.4719686
Abstract: The first inertial confinement fusion implosion experiments with equimolar deuterium-tritium thermonuclear fuel have been performed on the National Ignition Facility. These experiments use 0.17 mg of fuel with the potential for ignition and significant fusion yield conditions. The thermonuclear fuel has been fielded as a cryogenic layer on the inside of a spherical plastic capsule that is mounted in the center of a cylindrical gold hohlraum. Heating the hohlraum with 192 laser beams for a total laser energy of 1.6 MJ produces a soft x-ray field with 300 eV temperature. The ablation pressure produced by the radiation field compresses the initially 2.2-mm diameter capsule by a factor of 30 to a spherical dense fuel shell that surrounds a central hot-spot plasma of 50 μm diameter. While an extensive set of x-ray and neutron diagnostics has been applied to characterize hot spot formation from the x-ray emission and 14.1 MeV deuterium-tritium primary fusion neutrons, thermonuclear fuel assembly is studied by measuring the down-scattered neutrons with energies in the range of 10 to 12 MeV. X-ray and neutron imaging of the compressed core and fuel indicate a fuel thickness of (14 ± 3) μm, which combined with magnetic recoil spectrometer measurements of the fuel areal density of (1 ± 0.09) g cm–2 result in fuel densities approaching 600 g cm–3. The fuel surrounds a hot-spot plasma with average ion temperatures of (3.5 ± 0.1) keV that is measured with neutron time of flight spectra. The hot-spot plasma produces a total fusion neutron yield of 1015 that is measured with the magnetic recoil spectrometer and nuclear activation diagnostics that indicate a 14.1 MeV yield of (7.5±0.1)×1014 which is 70% to 75% of the total fusion yield due to the high areal density. Gamma ray measurements provide the duration of nuclear activity of (170 ± 30) ps. These indirect-drive implosions result in the highest areal densities and neutron yields achieved on laser facilities to date. This achievement is the result of the first hohlraum and capsule tuning experiments where the stagnation pressures have been systematically increased by more than a factor of 10 by fielding low-entropy implosions through the control of radiation symmetry, small hot electron production, and proper shock timing. The stagnation pressure is above 100 Gbars resulting in high Lawson-type confinement parameters of Pτ≃10 atm s. Comparisons with radiation-hydrodynamic simulations indicate that the pressure is within a factor of three required for reaching ignition and high yield. This will be the focus of future higher-velocity implosions that will employ additional optimizations of hohlraum, capsule and laser pulse shape conditions.
Dissociation of Liquid Silica at High Pressures and Temperatures
Publisher: American Physical Society (APS)
Date: 13-07-2006
Shock-Induced Transformation ofA l
Publisher:
American Physical Society (APS)
Date:
18-07-2003
Publisher: American Physical Society (APS)
Date: 18-07-2003
The effect of shock dynamics on compressibility of ignition-scale National Ignition Facility implosions
Publisher: AIP Publishing
Date: 11-2014
DOI: 10.1063/1.4900621
Abstract: The effects of shock dynamics on compressibility of indirect-drive ignition-scale surrogate implosions, CH shells filled with D3He gas, have been studied using charged-particle spectroscopy. Spectral measurements of D3He protons produced at the shock-bang time probe the shock dynamics and in-flight characteristics of an implosion. The proton shock yield is found to vary by over an order of magnitude. A simple model relates the observed yield to incipient hot-spot adiabat, suggesting that implosions with rapid radiation-power increase during the main drive pulse may have a 2× higher hot-spot adiabat, potentially reducing compressibility. A self-consistent 1-D implosion model was used to infer the areal density (ρR) and the shell center-of-mass radius (Rcm) from the downshift of the shock-produced D3He protons. The observed ρR at shock-bang time is substantially higher for implosions, where the laser drive is on until near the compression bang time (“short-coast”), while longer-coasting implosions have lower ρR. This corresponds to a much larger temporal difference between the shock- and compression-bang time in the long-coast implosions (∼800 ps) than in the short-coast (∼400 ps) this will be verified with a future direct bang-time diagnostic. This model-inferred differential bang time contradicts radiation-hydrodynamic simulations, which predict constant 700–800 ps differential independent of coasting time this result is potentially explained by uncertainties in modeling late-time ablation drive on the capsule. In an ignition experiment, an earlier shock-bang time resulting in an earlier onset of shell deceleration, potentially reducing compression and, thus, fuel ρR.
A high-resolution integrated model of the National Ignition Campaign cryogenic layered experiments
Publisher: AIP Publishing
Date: 05-2012
DOI: 10.1063/1.4718595
Abstract: A detailed simulation-based model of the June 2011 National Ignition C aign cryogenic DT experiments is presented. The model is based on integrated hohlraum-capsule simulations that utilize the best available models for the hohlraum wall, ablator, and DT equations of state and opacities. The calculated radiation drive was adjusted by changing the input laser power to match the experimentally measured shock speeds, shock merger times, peak implosion velocity, and bangtime. The crossbeam energy transfer model was tuned to match the measured time-dependent symmetry. Mid-mode mix was included by directly modeling the ablator and ice surface perturbations up to mode 60. Simulated experimental values were extracted from the simulation and compared against the experiment. Although by design the model is able to reproduce the 1D in-flight implosion parameters and low-mode asymmetries, it is not able to accurately predict the measured and inferred stagnation properties and levels of mix. In particular, the measured yields were 15%–40% of the calculated yields, and the inferred stagnation pressure is about 3 times lower than simulated.
Progress in the indirect-drive National Ignition Campaign
Publisher: IOP Publishing
Date: 21-11-2021
Ghost fringe removal techniques using Lissajous data presentation
Publisher: AIP Publishing
Date: 03-2016
DOI: 10.1063/1.4943563
Abstract: A VISAR (Velocity Interferometer System for Any Reflector) is a Doppler velocity interferometer which is an important optical diagnostic in shockwave experiments at the national laboratories, used to measure equation of state (EOS) of materials under extreme conditions. Unwanted reflection of laser light from target windows can produce an additional component to the VISAR fringe record that can distort and obscure the true velocity signal. Accurately removing this so-called ghost artifact component is essential for achieving high accuracy EOS measurements, especially when the true light signal is only weakly reflected from the shock front. Independent of the choice of algorithm for processing the raw data into a complex fringe signal, we have found it beneficial to plot this signal as a Lissajous and seek the proper center of this path, even under time varying intensity which can shift the perceived center. The ghost contribution is then solved by a simple translation in the complex plane that recenters the Lissajous path. For continuous velocity histories, we find that plotting the fringe magnitude vs nonfringing intensity and optimizing linearity is an invaluable tool for determining accurate ghost offsets. For discontinuous velocity histories, we have developed graphically inspired methods which relate the results of two VISARs having different velocity per fringe proportionalities or assumptions of constant fringe magnitude to find the ghost offset. The technique can also remove window reflection artifacts in generic interferometers, such as in the metrology of surfaces.
Modeling of laser-driven proton radiography of dense matter
Publisher: Elsevier BV
Date: 04-2008
Imaging VISAR diagnostic for the National Ignition Facility (NIF)
Publisher: SPIE
Date: 17-03-2005
DOI: 10.1117/12.579285
A neutron spectrometer for precise measurements of DT neutrons from 10 to 18 MeV at OMEGA and the National Ignition Facility
Publisher: AIP Publishing
Date: 2001
DOI: 10.1063/1.1323243
Abstract: A model independent method to determine fuel 〈ρR〉 is to measure the energy spectrum and yield of elastically scattered primary neutrons in deuterium–tritium (DT) plasmas. As is the case for complementary methods to measure fuel 〈ρR〉 (in particular from knock-on deuterons and tritons [S. Skupsky and S. Kacenjar, J. Appl. Phys. 52, 2608 (1981) C. K. Li et al. (unpublished)]), minimizing the background is critical for successful implementation. To achieve this objective, a novel spectrometer for measurements of neutrons in the energy range 10–18 MeV is proposed. From scattered neutrons (10–13 MeV), the DT fuel 〈ρR〉 will be measured from primary neutrons (∼14 MeV), the ion temperature and neutron yield will be determined and from secondary neutrons, in the energy range 12–18 MeV, the fuel 〈ρR〉 in deuterium plasmas will be inferred at the National Ignition Facility. The instrument is based on a magnetic spectrometer with a neutron-to-deuteron (nd) conversion foil for production of deuteron recoils at nearly forward scattered angles. In its initial phase of implementation, CR-39 track detectors will be used in the focal plane to detect the recoil deuterons with extremely high spatial resolution. Besides simplicity, CR-39 track detectors will facilitate a highly accurate energy calibration. However, in a later implementation of the spectrometer design, the recoils will also be detected by an array of fast scintillation counters functioning in current mode. In either detection scheme, the detection efficiency is about 10−9 for measuring 14 MeV neutrons with an energy resolution of about 3%. Due to its large dynamic range, its relatively high efficiency, and a compliant design that allows for significant background rejection, this spectrometer can be effectively used, with very high resolution, at both OMEGA and the National Ignition Facility.
Novel diagnostic of low-Z shock compressed material
Publisher: Elsevier BV
Date: 06-2006
High-precision measurements of the diamond Hugoniot in and above the melt region
Publisher: American Physical Society (APS)
Date: 04-11-2008
Nuclear diagnostics for the National Ignition Facility (invited)
Publisher: AIP Publishing
Date: 2001
DOI: 10.1063/1.1319356
Abstract: The National Ignition Facility (NIF), currently under construction at the Lawrence Livermore National Laboratory, will provide unprecedented opportunities for the use of nuclear diagnostics in inertial confinement fusion experiments. The completed facility will provide 2 MJ of laser energy for driving targets, compared to the approximately 40 kJ that was available on Nova and the approximately 30 kJ available on Omega. Ignited NIF targets are anticipated to produce up to 1019 DT neutrons. In addition to a basic set of nuclear diagnostics based on previous experience, these higher NIF yields are expected to allow innovative nuclear diagnostic techniques to be utilized, such as neutron imaging, recoil proton techniques, and gamma-ray-based reaction history measurements.
Laser-produced protons and their application as a particle probe
Publisher: Hindawi Limited
Date: 10-2002
DOI: 10.1017/S0263034602204322
Abstract: Due to an error, the published version of the paper differed from the final version submitted by the authors. The section starting at page 271 with “The beams are well collimated …” and finishing at the end of the page, and the caption for figure 4 were to be replaced with an updated version, submitted on 20 May 2002, which follows underneath.
11 TOPS photonic convolutional accelerator for optical neural networks
Publisher: Springer Science and Business Media LLC
Date: 06-01-2202
The first experiments on the national ignition facility
Publisher: EDP Sciences
Date: 06-2006
The first target experiments on the National Ignition Facility
Publisher: Springer Science and Business Media LLC
Date: 18-05-2006
Maps of variability in cell lineage trees
Publisher: Cold Spring Harbor Laboratory
Date: 18-02-2018
DOI: 10.1101/267450
Abstract: New approaches to lineage tracking allow the study of cell differentiation over many generations of cells during development in multicellular organisms. Understanding the variability observed in these lineage trees requires new statistical methods. Whereas invariant cell lineages, such as that for the nematode Caenorhabditis elegans , can be described using a lineage map, defined as the fixed pattern of phenotypes overlaid onto the binary tree structure, the variability of cell lineages from higher organisms makes it impossible to draw a single lineage map. Here, we introduce lineage variability maps which describe the pattern of second-order variation throughout the lineage tree. These maps can be undirected graphs of the partial correlations between every lineal position or directed graphs showing the dynamics of bifurcated patterns in each subtree. By using the symmetry invariance of a binary tree to develop a generalized spectral analysis for cell lineages, we show how to infer these graphical models for lineages of any depth from s le sizes of only a few pedigrees. When tested on pedigrees from C. elegans expressing a marker for pharyngeal differentiation potential, the maps recover essential features of the known lineage map. When applied to highly-variable pedigrees monitoring cell size in T lymphocytes, the maps show how most of the phenotype is set by the founder naive T cell. Lineage variability maps thus elevate the concept of the lineage map to the population level, addressing questions about the potency and dynamics of cell lineages and providing a way to quantify the progressive restriction of cell fate with increasing depth in the tree. Multicellular organisms develop from a single fertilized egg by sequential cell isions. The progeny from these isions adopt different traits that are transmitted and modified through many generations. By tracking how cell traits change with each successive cell ision throughout the family, or lineage, tree, it has been possible to understand where and how these modifications are controlled at the single-cell level, thereby addressing questions about, for ex le, the developmental origin of tissues, the sources of differentiation in immune cells, or the relationship between primary tumors and metastases. Such lineages often show large variability, with apparently identical founder cells giving rise to different patterns of descendants. Fundamental scientific questions, such as about the range of possible cell types a cell can give rise to, are often about this variability. To characterize this variation, and thus understand the lineage at the population level, we introduce lineage variability maps. Using data from worm and mammalian cell lineages we show how these maps provide quantifiable answers to questions about any developing lineage, such as the potency of founder cells and the progressive restriction of cell fate at each stage in the tree.
Charged-particle acceleration and energy loss in laser-produced plasmas
Publisher: AIP Publishing
Date: 12-2000
DOI: 10.1063/1.1320467
Abstract: Spectral measurements have been made of charged fusion products produced in deuterium + helium-3 filled targets irradiated by the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Comparing the energy shifts of four particle types has allowed two distinct physical processes to be probed: Electrostatic acceleration in the low-density corona and energy loss in the high-density target. When the fusion burn occurred during the laser pulse, particle energy shifts were dominated by acceleration effects. Using a simple model for the accelerating field region, the time history of the target electrostatic potential was found and shown to decay to zero soon after laser irradiation was complete. When the fusion burn occurred after the pulse, particle energy shifts were dominated by energy losses in the target, allowing fundamental charged-particle stopping-power predictions to be tested. The results provide the first experimental verification of the general form of stopping power theories over a wide velocity range.
Onset of Hydrodynamic Mix in High-Velocity, Highly Compressed Inertial Confinement Fusion Implosions
Publisher: American Physical Society (APS)
Date: 23-08-2013
X-ray driven implosions at ignition relevant velocities on the National Ignition Facility
Publisher: AIP Publishing
Date: 05-2013
DOI: 10.1063/1.4803915
Abstract: Backlit convergent ablator experiments on the National Ignition Facility [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)] are indirect drive implosions that study the inflight dynamics of an imploding capsule. Side-on, backlit radiography provides data used by the National Ignition C aign to measure time-dependent properties of the capsule ablator including its center of mass radius, velocity, and unablated mass. Previously, Callahan [D. A. Callahan et al., Phys. Plasmas 19, 056305 (2012)] and Hicks [D. H. Hicks et al., Phys. Plasmas 19, 122702 (2012)] reported backlit convergent ablator experiments demonstrating velocities approaching those required for ignition. This paper focuses on implosion performance data in the “rocket curve” plane, velocity vs. ablator mass. These rocket curve data, along with supporting numerical simulations, show that the nominal 195 μm-thick ignition capsule would reach the ignition velocity goal V = 370 km/s with low ablator mass remaining–below the goal of M = 0.25 mg. This finding led to experiments with thicker capsule ablators. A recent symmetry capsule experiment with a 20 μm thicker capsule driven by 520 TW, 1.86 MJ laser pulse (along with a companion backlit convergent ablator experiment) appears to have demonstrated V≥350 km/s with ablator mass remaining above the ignition goal.
Shock-timing experiments using double-pulse laser irradiation
Publisher: AIP Publishing
Date: 05-2006
DOI: 10.1063/1.2179057
Abstract: The timing of multiple shock waves is crucial to the performance of inertial confinement fusion ignition targets. Presented are measurements of velocities and optical self-emission from shock waves in polystyrene targets driven by two 90-ps pulses separated by 1.5–2ns. These pulses drive two shock waves that coalesce in the target, and the resultant velocity histories, coalescence times, and transit times are unambiguously observed in both velocity interferometry and self-emission data. These results are in good agreement with one-dimensional hydrodynamics code predictions.
Density Measurements of Shock Compressed Matter Using Short Pulse Laser Diagnostics
Publisher: Springer Science and Business Media LLC
Date: 08-01-2006
Refraction-enhanced x-ray radiography for density profile measurements at CH/Be interface
Publisher: IOP Publishing
Date: 20-09-2011
Multi-MeV Proton Source Investigations in Ultraintense Laser-Foil Interactions
Publisher: American Physical Society (APS)
Date: 05-02-2004
Hohlraum designs for high velocity implosions on NIF
Publisher: EDP Sciences
Date: 2013
High pressures generated by laser driven shocks: applications to planetary physics
Publisher: IOP Publishing
Date: 27-11-2004
Design of a streaked radiography instrument for ICF ablator tuning measurements
Publisher: AIP Publishing
Date: 10-2008
DOI: 10.1063/1.2965021
Abstract: A streaked radiography diagnostic has been proposed as a technique to determine the ablator mass remaining in an inertial confinement fusion ignition capsule at peak velocity. This instrument, the “HXRI-5,” has been designed to fit within a National Ignition Facility Diagnostic Instrument Manipulator. The HXRI-5 will be built at Sandia National Laboratories (SNL), and initial testing will be done at the SNL Z-Beamlet Facility. In this paper, we will describe the National Ignition C aign requirements for this diagnostic, the instrument design, and the planned test experiments.
High performance imaging streak camera for the National Ignition Facility
Publisher: AIP Publishing
Date: 12-2012
DOI: 10.1063/1.4769753
Abstract: An x-ray streak camera platform has been characterized and implemented for use at the National Ignition Facility. The camera has been modified to meet the experiment requirements of the National Ignition C aign and to perform reliably in conditions that produce high electromagnetic interference. A train of temporal ultra-violet timing markers has been added to the diagnostic in order to calibrate the temporal axis of the instrument and the detector efficiency of the streak camera was improved by using a CsI photocathode. The performance of the streak camera has been characterized and is summarized in this paper. The detector efficiency and cathode measurements are also presented.
Alpha blocking and 1/fβspectral scaling in resting EEG can be accounted for by a sum of damped alpha band oscillatory processes
Publisher: Cold Spring Harbor Laboratory
Date: 20-08-2021
DOI: 10.1101/2021.08.20.457060
Abstract: The dynamical and physiological basis of alpha band activity and 1/ f β noise in the EEG are the subject of continued speculation. Here we conjecture, on the basis of empirical data analysis, that both of these features may be economically accounted for through a single process if the resting EEG is conceived of being the sum of multiple stochastically perturbed alpha band d ed linear oscillators with a distribution of d ings (relaxation rates). The modulation of alpha-band and 1/ f β noise activity by changes in d ing is explored in eyes closed (EC) and eyes open (EO) resting state EEG. We aim to estimate the distribution of d ings by solving an inverse problem applied to EEG power spectra. The characteristics of the d ing distribution are examined across subjects, sensors and recording condition (EC/EO). We find that there are robust changes in the d ing distribution between EC and EO recording conditions across participants. The estimated d ing distributions are found to be predominantly bimodal, with the number and position of the modes related to the sharpness of the alpha resonance and the scaling ( β ) of the power spectrum (1/ f β ). The results suggest that there exists an intimate relationship between resting state alpha activity and 1/ f β noise with changes in both governed by changes to the d ing of the underlying alpha oscillatory processes. In particular, alpha-blocking is observed to be the result of the most weakly d ed distribution mode becoming more heavily d ed. The results suggest a novel way of characterizing resting EEG power spectra and provides new insight into the central role that d ed alpha-band activity may play in characterising the spatio-temporal features of resting state EEG. The resting human electroencephalogram (EEG) exhibits two dominant spectral features: the alpha rhythm (8-13 Hz) and its associated attenuation between eyes-closed and eyes-open resting state (alpha blocking), and the 1/ f β scaling of the power spectrum. While these phenomena are well studied a thorough understanding of their respective generative processes remains elusive. By employing a theoretical approach that follows from neural population models of EEG we demonstrate that it is possible to economically account for both of these phenomena using a singular mechanistic framework: resting EEG is assumed to arise from the summed activity of multiple uncorrelated, stochastically driven, d ed alpha band linear oscillatory processes having a distribution of relaxation rates or d ings. By numerically estimating these d ing distributions from eyes-closed and eyes-open EEG data, in a total of 136 participants, it is found that such d ing distributions are predominantly bimodal in shape. The most weakly d ed mode is found to account for alpha band power, with alpha blocking being driven by an increase in the d ing of this weakly d ed mode, whereas the second, and more heavily d ed mode, is able to explain 1/ f β scaling present in the resting state EEG spectra.
Hugoniot Data for Helium in the Ionization Regime
Publisher: American Physical Society (APS)
Date: 28-03-2008
Laser-driven shock experiments on precompressed water: Implications for “icy” giant planets
Publisher: AIP Publishing
Date: 05-07-2006
DOI: 10.1063/1.2207618
Abstract: Laser-driven shock compression of s les precompressed to 1GPa produces high-pressure-temperature conditions inducing two significant changes in the optical properties of water: the onset of opacity followed by enhanced reflectivity in the initially transparent water. The onset of reflectivity at infrared wavelengths can be interpreted as a semiconductor↔electronic conductor transition in water, and is found at pressures above ∼130GPa for single-shocked s les precompressed to 1GPa. Our results indicate that conductivity in the deep interior of “icy” giant planets is greater than realized previously because of an additional contribution from electrons.
D – 3 He proton spectra for diagnosing shell ρR and fuel Ti of imploded capsules at OMEGA
Publisher: AIP Publishing
Date: 06-2000
DOI: 10.1063/1.874099
Abstract: Recent work has resulted in the first high-resolution, spectroscopic measurements of energetic charged particles on OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 496 (1997)]. Energy spectra of charged fusion products have been obtained from two spectrometers, and have been used to deduce various physical quantities in imploded capsules. In this paper the first use of 14.7 MeV deuterium–helium3 (D–3He) proton spectra for diagnosing shell areal density (ρR) and fuel ion temperature (Ti) is discussed. For thick-plastic shell capsules, shell areal densities between 20 and 70 mg/cm2 and ion temperatures between 3 and 5 keV have been determined. The spectral linewidths associated with such capsules are found to be wider than the doppler widths. This effect, the focus of future study, is the result of ρR evolution during the burn or is the result of an extended burn region or results from nonuniformities in the shell. For thin-glass shell capsules, the spectral linewidths are dominated by the doppler width, and ion temperatures between 10 and 15 keV were determined. These measurements have been also compared and contrasted with the results from neutron measurements and from one-dimension hydrodynamic simulations.
Solid Iron Compressed Up to 560 GPa
Publisher: American Physical Society (APS)
Date: 05-08-2013
Capsule performance optimization in the National Ignition Campaign
Publisher: AIP Publishing
Date: 04-03-2010
DOI: 10.1063/1.3298882
Abstract: A capsule performance optimization c aign will be conducted at the National Ignition Facility [G. H. Miller et al., Nucl. Fusion 44, 228 (2004)] to substantially increase the probability of ignition by laser-driven hohlraums [J. D. Lindl et al., Phys. Plasmas 11, 339 (2004)]. The c aign will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models before proceeding to cryogenic-layered implosions and ignition attempts. The required tuning techniques using a variety of ignition capsule surrogates have been demonstrated at the OMEGA facility under scaled hohlraum and capsule conditions relevant to the ignition design and shown to meet the required sensitivity and accuracy. In addition, a roll-up of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget.
OMEGA ICF experiments and preparation for direct drive ignition on NIF
Publisher: IOP Publishing
Date: 10-2001
Spectral PCA for MANOVA and data over binary trees
Publisher: Elsevier BV
Date: 03-2022
Erratum: Evidence for a Phase Transition in Silicate Melt at Extreme Pressure and Temperature Conditions [Phys. Rev. Lett. 108 , 065701 (2012)]
Publisher: American Physical Society (APS)
Date: 29-09-2017
Time evolution of filamentation and self-generated fields in the coronae of directly driven inertial-confinement fusion capsules
Publisher: AIP Publishing
Date: 2012
DOI: 10.1063/1.3671908
Abstract: Time-gated radiography with monoenergetic 15-MeV protons, 3-MeV protons, and 4-MeV alpha particles has revealed a rich and complex evolution of electromagnetic field structures in and around imploding, directly driven inertial-confinement fusion (ICF) targets at the OMEGA laser facility. Plastic-shell capsules and solid plastic spheres were imaged during and after irradiation with ICF-relevant laser drive (up to 6 × 1014 W/cm2). Radial filaments appeared while the laser was on they filled, and were frozen into, the out-flowing corona, persisting until well after the end of the laser drive. Data from specially designed experiments indicate that the filaments were not generated by two-plasmon-decay instabilities or by Rayleigh-Taylor instabilities associated with shell acceleration. Before the onset of visible filamentation, quasi-spherical field structures appeared outside the capsule in the images in a form that suggests outgoing shells of net positive charge. We conjecture that these discrete shells are related to multiple peaks seen previously in the spectra of protons ablated from the targets.
A study of CR-39 track response to charged particles from NOVA implosions
Publisher: AIP Publishing
Date: 1997
DOI: 10.1063/1.1147662
Abstract: We have exposed CR-39 track recording material to a number of NOVA implosions. Radiation from the implosion passed through an array of ranging filters, which aided identification of the incident particles and their energies. The etching procedure was calibrated by including a piece of track exposed to DD protons from a small accelerator. For the same shots, we quantitatively compare the DD neutron yield with the DD proton yield determined from the track. In DT implosions, tracks produced by neutron interactions prevent observation of charged-particle tracks that are produced by the processes of knock on, secondary, or tertiary fusion.
Hohlraum energetics scaling to 520 TW on the National Ignition Facility
Publisher: AIP Publishing
Date: 05-2013
DOI: 10.1063/1.4803907
Abstract: Indirect drive experiments have now been carried out with laser powers and energies up to 520 TW and 1.9 MJ. These experiments show that the energy coupling to the target is nearly constant at 84% ± 3% over a wide range of laser parameters from 350 to 520 TW and 1.2 to 1.9 MJ. Experiments at 520 TW with depleted uranium hohlraums achieve radiation temperatures of ∼330 ± 4 eV, enough to drive capsules 20 μm thicker than the ignition point design to velocities near the ignition goal of 370 km/s. A series of three symcap implosion experiments with nearly identical target, laser, and diagnostics configurations show the symmetry and drive are reproducible at the level of ±8.5% absolute and ±2% relative, respectively.
Charged-coupled devices for charged-particle spectroscopy on OMEGA and NOVA
Publisher: AIP Publishing
Date: 1997
DOI: 10.1063/1.1147661
Abstract: Charge-coupled devices (CCDs) are to be utilized as charged-particle detectors for ρR and implosion symmetry diagnostics on OMEGA and NOVA. Using a large range of MeV charged particles, comprehensive studies have been performed on several back-illuminated CCDs in order to establish their utility for determining particle energy and identity (e.g., H, D, or T). Issues of signal and noise (i.e., especially from neutrons and gammas interacting with the CCDs) are also being investigated.
Shock formation and the ideal shape of ramp compression waves
Publisher: American Physical Society (APS)
Date: 29-12-2008
Design of an electronic charged particle spectrometer to measure 〈ρ𝓡〉 on inertial fusion experiments
Publisher: AIP Publishing
Date: 1997
DOI: 10.1063/1.1147660
Abstract: The design and fabrication of a new diagnostic that measures the energy spectra of charged particles from targets on the Omega Upgrade are actively underway. Using seven 512×512 charge coupled devices (CCDs) and a 7.5 kG permanent magnet, this instrument will uniquely determine particle identities and measure particle energies from 1 MeV up to the maximum charged particle energies of interest for ρR measurements (10.6 MeV knock-on tritons, 12.5 MeV knock-on deuterons and 30.8 MeV tertiary protons). The resolution of the diagnostic will be better than 5%. We have tested the response of SITe back-illuminated CCDs to 1.2–13.6 MeV protons from our Cockcroft–Walton accelerator and to alpha particles from an Am241 source, and the results agree extremely well with predictions. With its high density picture elements, each CCD has 105 single-hit detectors. In the case of a low DT yield of 109 neutrons, about 100 knock-on charged particles will be detected when the spectrometer aperture is 60 cm from the implosion. Measurements of ρR up to 150 mg/cm2 can be obtained from knock-on D and T spectra, and values up to 300 mg/cm2 can be determined from secondary proton spectra. The sensitivity of the CCDs to 14 and 2.5 MeV neutrons has been experimentally determined using our Cockcroft–Walton accelerator source and indicates that by incorporating neutron shielding, the signal to neutron noise ratio at a yield of 1011 will be better than 100:1. In the development phases of this program, we plan to utilize CR-39 track detectors concurrently with the CCDs.
Hot-spot mix in ignition-scale implosions on the NIF
Publisher: AIP Publishing
Date: 30-03-2012
DOI: 10.1063/1.3694057
Abstract: Ignition of an inertial confinement fusion (ICF) target depends on the formation of a central hot spot with sufficient temperature and areal density. Radiative and conductive losses from the hot spot can be enhanced by hydrodynamic instabilities. The concentric spherical layers of current National Ignition Facility (NIF) ignition targets consist of a plastic ablator surrounding a thin shell of cryogenic thermonuclear fuel (i.e., hydrogen isotopes), with fuel vapor filling the interior volume [S. W. Haan et al., Phys. Plasmas 18, 051001 (2011)]. The Rev. 5 ablator is doped with Ge to minimize preheat of the ablator closest to the DT ice caused by Au M-band emission from the hohlraum x-ray drive [D. S. Clark et al., Phys. Plasmas 17, 052703 (2010)]. Richtmyer–Meshkov and Rayleigh–Taylor hydrodynamic instabilities seeded by high-mode (50& ℓ& ) ablator-surface perturbations can cause Ge-doped ablator to mix into the interior of the shell at the end of the acceleration phase [B. A. Hammel et al., Phys. Plasmas 18, 056310 (2011)]. As the shell decelerates, it compresses the fuel vapor, forming a hot spot. K-shell line emission from the ionized Ge that has penetrated into the hot spot provides an experimental signature of hot-spot mix. The Ge emission from tritium–hydrogen–deuterium (THD) and deuterium–tritium (DT) cryogenic targets and gas-filled plastic-shell capsules, which replace the THD layer with a mass-equivalent CH layer, was examined. The inferred amount of hot-spot–mix mass, estimated from the Ge K-shell line brightness using a detailed atomic physics code [J. J. MacFarlane et al., High Energy Density Phys. 3, 181 (2006)], is typically below the 75-ng allowance for hot-spot mix [S. W. Haan et al., Phys. Plasmas 18, 051001 (2011)]. Predictions of a simple mix model, based on linear growth of the measured surface-mass modulations, are consistent with the experimental results.
Convergent ablator performance measurements
Publisher: AIP Publishing
Date: 10-2010
DOI: 10.1063/1.3486536
Abstract: The velocity and remaining ablator mass of an imploding capsule are critical metrics for assessing the progress toward ignition of an inertially confined fusion experiment. These and other convergent ablator performance parameters have been measured using a single streaked x-ray radiograph. Traditional Abel inversion of such a radiograph is ill-posed since backlighter intensity profiles and x-ray attenuation by the ablated plasma are unknown. To address this we have developed a regularization technique which allows the ablator density profile ρ(r) and effective backlighter profile I0(y) at each time step to be uniquely determined subject to the constraints that ρ(r) is localized in radius space and I0(y) is delocalized in object space. Moments of ρ(r) then provide the time-resolved areal density, mass, and average radius (and thus velocity) of the remaining ablator material. These results are combined in the spherical rocket model to determine the ablation pressure and mass ablation rate during the implosion. The technique has been validated on simulated radiographs of implosions at the National Ignition Facility [Miller et al., Nucl. Fusion 44, 228 (2004)] and implemented on experiments at the OMEGA laser facility [Boehly et al., Opt. Commun. 133, 495 (1997)].
NIF capsule performance modeling
Publisher: EDP Sciences
Date: 2013
Total energy loss to fast ablator-ions and target capacitance of direct-drive implosions on OMEGA
Publisher: AIP Publishing
Date: 10-09-2012
DOI: 10.1063/1.4752012
Abstract: Measurements of the total energy carried by fast ablator-ions in direct-drive implosions on OMEGA have been conducted using magnetic and Thomson Parabola spectrometers. It is shown that the total laser energy lost to fast ablator-ions for plastic and glass targets is comparable and that it is a modest fraction of the incident laser energy (≲1%). These measurements have been used to infer a non-linear, voltage-dependent target capacitance (∼0.1 nF) associated with the space-charge that accelerates the fast-ions.
Observations of fast protons above 1 MeV produced in direct-drive laser-fusion experiments
Publisher: AIP Publishing
Date: 02-2001
DOI: 10.1063/1.1335831
Abstract: Fast protons ≳1 MeV have been observed on the 60-beam, 30 kJ OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] at an intensity I≃1015 W/cm2 and a wavelength λ=0.35 μm. These energies are more than 5 times greater than those observed on previous, single-beam experiments at the same Iλ2. The total energy in the proton spectrum above 0.2 MeV is ∼0.1% of the laser energy. Some of the proton spectra display intense, regular lines which may be related to ion acoustic perturbations in the expanding plasma.
Spectrometry of charged particles from inertial-confinement-fusion plasmas
Publisher: AIP Publishing
Date: 24-01-2003
DOI: 10.1063/1.1518141
Abstract: High-resolution spectrometry of charged particles from inertial-confinement-fusion (ICF) experiments has become an important method of studying plasma conditions in laser-compressed capsules. In experiments at the 60-beam OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], utilizing capsules with D2, D3He, DT, or DTH fuel in a shell of plastic, glass, or D2 ice, we now routinely make spectral measurements of primary fusion products (p, D, T, He3, α), secondary fusion products (p), “knock-on” particles (p, D, T) elastically scattered by primary neutrons, and ions from the shell. Use is made of several types of spectrometers that rely on detection and identification of particles with CR-39 nuclear track detectors in conjunction with magnets and/or special ranging filters. CR-39 is especially useful because of its insensitivity to electromagnetic noise and its ability to distinguish the types and energies of in idual particles, as illustrated here by detailed calibrations of its response to 0.1–13.8 MeV protons from a Van de Graaff accelerator and to p, D, T, and α from ICF experiments at OMEGA. A description of the spectrometers is accompanied by illustrations of their operating principles using data from OMEGA. S le results and discussions illustrate the relationship of secondary-proton and knock-on spectra to capsule fuel and shell areal densities and radial compression ratios the relationship of different primary fusion products to each other and to ion temperatures the relationship of deviations from spherical symmetry in particle yields and energies to capsule structure the acceleration of fusion products and the spectra of ions from the shell due to external fields and other important physical characteristics of the laser-compressed capsules.
Hot-Spot Mix in Ignition-Scale Inertial Confinement Fusion Targets
Publisher: American Physical Society (APS)
Date: 22-07-2013
Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment
Publisher: American Physical Society (APS)
Date: 08-08-2022
Quasi-isentropic material property studies at extreme pressures: from omega to NIF
Publisher: IOP Publishing
Date: 05-2008
Publisher’s Note: “Laser-driven shock experiments on precompressed water: Implications for ‘icy’ giant planets” [J. Chem. Phys. 125, 014701 (2006)]
Publisher: AIP Publishing
Date: 09-02-2007
DOI: 10.1063/1.2434949
A novel particle time of flight diagnostic for measurements of shock- and compression-bang times in D3He and DT implosions at the NIF
Publisher: AIP Publishing
Date: 02-07-2012
DOI: 10.1063/1.4731000
Abstract: The particle-time-of-flight (pTOF) diagnostic, fielded alongside a wedge range-filter (WRF) proton spectrometer, will provide an absolute timing for the shock-burn weighted ρR measurements that will validate the modeling of implosion dynamics at the National Ignition Facility (NIF). In the first phase of the project, pTOF has recorded accurate bang times in cryogenic DT, DT exploding pusher, and D3He implosions using DD or DT neutrons with an accuracy better than ±70 ps. In the second phase of the project, a deflecting magnet will be incorporated into the pTOF design for simultaneous measurements of shock- and compression-bang times in D3He-filled surrogate implosions using D3He protons and DD-neutrons, respectively.
Proton radiography of a shock-compressed target
Publisher: American Physical Society (APS)
Date: 26-07-2010
Imaging Shock Waves in Diamond with Both High Temporal and Spatial Resolution at an XFEL
Publisher: Springer Science and Business Media LLC
Date: 18-06-2015
DOI: 10.1038/SREP11089
Abstract: The advent of hard x-ray free-electron lasers (XFELs) has opened up a variety of scientific opportunities in areas as erse as atomic physics, plasma physics, nonlinear optics in the x-ray range and protein crystallography. In this article, we access a new field of science by measuring quantitatively the local bulk properties and dynamics of matter under extreme conditions, in this case by using the short XFEL pulse to image an elastic compression wave in diamond. The elastic wave was initiated by an intense optical laser pulse and was imaged at different delay times after the optical pump pulse using magnified x-ray phase-contrast imaging. The temporal evolution of the shock wave can be monitored, yielding detailed information on shock dynamics, such as the shock velocity, the shock front width and the local compression of the material. The method provides a quantitative perspective on the state of matter in extreme conditions.
Radiative shocks produced from spherical cryogenic implosions at the National Ignition Facility
Publisher: AIP Publishing
Date: 05-2013
DOI: 10.1063/1.4805081
Abstract: Spherically expanding radiative shock waves have been observed from inertially confined implosion experiments at the National Ignition Facility. In these experiments, a spherical fusion target, initially 2 mm in diameter, is compressed via the pressure induced from the ablation of the outer target surface. At the peak compression of the capsule, x-ray and nuclear diagnostics indicate the formation of a central core, with a radius and ion temperature of ∼20 μm and ∼ 2 keV, respectively. This central core is surrounded by a cooler compressed shell of deuterium-tritium fuel that has an outer radius of ∼40 μm and a density of & g/cm3. Using inputs from multiple diagnostics, the peak pressure of the compressed core has been inferred to be of order 100 Gbar for the implosions discussed here. The shock front, initially located at the interface between the high pressure compressed fuel shell and surrounding in-falling low pressure ablator plasma, begins to propagate outwards after peak compression has been reached. Approximately 200 ps after peak compression, a ring of x-ray emission created by the limb-brightening of a spherical shell of shock-heated matter is observed to appear at a radius of ∼100 μm. Hydrodynamic simulations, which model the experiment and include radiation transport, indicate that the sudden appearance of this emission occurs as the post-shock material temperature increases and upstream density decreases, over a scale length of ∼10 μm, as the shock propagates into the lower density (∼1 g/cc), hot (∼250 eV) plasma that exists at the ablation front. The expansion of the shock-heated matter is temporally and spatially resolved and indicates a shock expansion velocity of ∼300 km/s in the laboratory frame. The magnitude and temporal evolution of the luminosity produced from the shock-heated matter was measured at photon energies between 5.9 and 12.4 keV. The observed radial shock expansion, as well as the magnitude and temporal evolution of the luminosity from the shock-heated matter, is consistent with 1-D radiation hydrodynamic simulations. Analytic estimates indicate that the radiation energy flux from the shock-heated matter is of the same order as the in-flowing material energy flux, and suggests that this radiation energy flux modifies the shock front structure. Simulations support these estimates and show the formation of a radiative shock, with a precursor that raises the temperature ahead of the shock front, a sharp μm-scale thick spike in temperature at the shock front, followed by a post-shock cooling layer.
OMEGA experiments and preparation for moderate-gain direct-drive experiments on NIF
Publisher: Elsevier BV
Date: 08-2000
Inferring a simple mechanism for alpha-blocking by fitting a neural population model to EEG spectra
Publisher: Cold Spring Harbor Laboratory
Date: 20-01-2020
DOI: 10.1101/2020.01.20.912386
Abstract: Alpha blocking, a phenomenon where the alpha rhythm is reduced by attention to a visual, auditory, tactile or cognitive stimulus, is one of the most prominent features of human electroencephalography (EEG) signals. Here we identify a simple physiological mechanism by which opening of the eyes causes attenuation of the alpha rhythm. We fit a neural population model to EEG spectra from 82 subjects, each showing different degrees of alpha blocking upon opening of their eyes. Although it is notoriously difficult to estimate parameters from fitting such models, we show that, by regularizing the differences in parameter estimates between eyes-closed and eyes-open states, we can reduce the uncertainties in these differences without significantly compromising fit quality. From this emerges a parsimonious explanation for the spectral changes between states: Just a single parameter, p ei , corresponding to the strength of a tonic, excitatory input to the inhibitory population, is sufficient to explain the reduction in alpha rhythm upon opening of the eyes. When comparing parameter estimates across different subjects we find that the inferred differential change in p ei for each subject increases monotonically with the degree of alpha blocking observed. In contrast, other parameters show weak or negligible differential changes that do not scale with the degree of alpha attenuation in each subject. Thus most of the variation in alpha blocking across subjects can be attributed to the strength of a tonic afferent signal to the inhibitory cortical population. One of the most striking features of the human electroencephalogram (EEG) is the presence of neural oscillations in the range of 8-13 Hz. It is well known that attenuation of these alpha oscillations, a process known as alpha blocking, arises from opening of the eyes, though the cause has remained obscure. In this study we infer the mechanism underlying alpha blocking by fitting a neural population model to EEG spectra from 82 different in iduals. Although such models have long held the promise of being able to relate macroscopic recordings of brain activity to microscopic neural parameters, their utility has been limited by the difficulty of inferring these parameters from fits to data. Our approach is to fit both eyes-open and eyes-closed EEG spectra together, minimizing the number of parameter changes required to transition from one spectrum to the other. Surprisingly, we find that there is just one parameter, the external input to the inhibitory neurons in cortex, that is responsible for attenuating the alpha oscillations. We demonstrate how the strength of this inhibitory input scales monotonically with the degree of alpha blocking observed over all 82 subjects.
A platform for x-ray absorption fine structure study of dynamically compressed materials above 1 Mbar
Publisher: AIP Publishing
Date: 12-2013
DOI: 10.1063/1.4841935
Abstract: A platform consisting of a multi-shock drive and an implosion backlighter has been developed for x-ray absorption fine structure (XAFS) measurements on materials compressed to multi-Mbar pressures. The experimental setup, target design, and backlighter characteristics are presented. Extended XAFS (EXAFS) measurements for various materials have been demonstrated. A quintuple-crystal design is described to enhance the efficiency of the x-ray spectrometer, enabling observation of very weak EXAFS signals in a single shot.
In-flight observations of low-mode ρR asymmetries in NIF implosions
Publisher: AIP Publishing
Date: 15-04-2015
DOI: 10.1063/1.4918355
Abstract: Charged-particle spectroscopy is used to assess implosion symmetry in ignition-scale indirect-drive implosions for the first time. Surrogate D3He gas-filled implosions at the National Ignition Facility produce energetic protons via D+3He fusion that are used to measure the implosion areal density (ρR) at the shock-bang time. By using protons produced several hundred ps before the main compression bang, the implosion is diagnosed in-flight at a convergence ratio of 3–5 just prior to peak velocity. This isolates acceleration-phase asymmetry growth. For many surrogate implosions, proton spectrometers placed at the north pole and equator reveal significant asymmetries with litudes routinely ≳10%, which are interpreted as ℓ=2 Legendre modes. With significant expected growth by stagnation, it is likely that these asymmetries would degrade the final implosion performance. X-ray self-emission images at stagnation show asymmetries that are positively correlated with the observed in-flight asymmetries and comparable in magnitude, contradicting growth models this suggests that the hot-spot shape does not reflect the stagnated shell shape or that significant residual kinetic energy exists at stagnation. More prolate implosions are observed when the laser drive is sustained (“no-coast”), implying a significant time-dependent asymmetry in peak drive.
Shock compression of quartz in the high-pressure fluid regime
Publisher: AIP Publishing
Date: 08-2005
DOI: 10.1063/1.2009528
Abstract: The Hugoniot of quartz has been measured using laser-driven shock waves with pressures from 2 to 15 Mbars. Within this pressure range silica transforms from a liquid near melt into a dense plasma. Results are in good agreement with previous studies in part of this range performed using explosive- and nuclear-driven shocks indicating the absence of time-dependent effects for time scales between several hundred picoseconds and several hundred microseconds. These data combined with earlier data at lower pressures clearly show the increasing compressibility of silica as it transitions from solid to liquid to dense plasma regimes.
Group-12 vdW dimers in free-jet supersonic beams: The legacy of Eugeniusz Czuchaj continues
Publisher: Springer Science and Business Media LLC
Date: 05-2007
Analysis of laser shock experiments on precompressed samples using a quartz reference and application to warm dense hydrogen and helium
Publisher: AIP Publishing
Date: 16-11-2015
DOI: 10.1063/1.4935295
Abstract: Megabar (1 Mbar = 100 GPa) laser shocks on precompressed s les allow reaching unprecedented high densities and moderately high ∼103–104 K temperatures. We describe here a complete analysis framework for the velocimetry (VISAR) and pyrometry (SOP) data produced in these experiments. Since the precompression increases the initial density of both the s le of interest and the quartz reference for pressure-density, reflectivity, and temperature measurements, we describe analytical corrections based on available experimental data on warm dense silica and density-functional-theory based molecular dynamics computer simulations. Using our improved analysis framework, we report a re-analysis of previously published data on warm dense hydrogen and helium, compare the newly inferred pressure, density, and temperature data with most advanced equation of state models and provide updated reflectivity values.
Proton radiography as an electromagnetic field and density perturbation diagnostic (invited)
Publisher: AIP Publishing
Date: 10-2004
DOI: 10.1063/1.1788893
Abstract: Laser driven proton beams have been used to diagnose transient fields and density perturbations in laser produced plasmas. Grid deflectometry techniques have been applied to proton radiography to obtain precise measurements of proton beam angles caused by electromagnetic fields in laser produced plasmas. Application of proton radiography to laser driven implosions has demonstrated that density conditions in compressed media can be diagnosed with million electron volt protons. This data has shown that proton radiography can provide unique insight into transient electromagnetic fields in super critical density plasmas and provide a density perturbation diagnostics in compressed matter.
Photonic Perceptron Based on a Kerr Microcomb for High‐Speed, Scalable, Optical Neural Networks
Publisher: Wiley
Date: 06-08-2020
First observation of Moiré fringes in a proton beam generated by a 100 fs laser pulse
Publisher: AIP Publishing
Date: 03-2003
DOI: 10.1063/1.1534900
Abstract: High contrast Moiré fringes have been observed when two gratings were inserted into a proton beam produced from the interaction of a 100 TW laser beam with a thin solid foil. Moiré fringes with modulation close to 20% were observed in protons with energies between 4 and 7 MeV. The fringes were rotated with respect to a collimated optical test beam, a finding consistent with the protons originating from a point source close to the original target surface. These important results indicate that proton Moiré can be used as a high precision diagnostic of proton beam deflections from electric and magnetic fields in plasmas.
Measurements of charged-particle fusion yields and ratios from Omega (abstract)
Publisher: AIP Publishing
Date: 1999
DOI: 10.1063/1.1149458
Abstract: We have recently conducted a series of experiments on Omega in which we utilized a charged-particle spectrometer. It consists of a 7.6 kG magnet, CR-39 track for particle detection, and an assortment of range filters to either discriminate against or emphasize certain particles. Because of excellent particle selectivity and energy resolution, the spectrometer can accurately measure the ratios of various fusion products from a single shot. Among other uses, these ratios will be used to determine ion temperatures.
Charged-particle spectroscopy for diagnosing shock ρR and strength in NIF implosions
Publisher: AIP Publishing
Date: 19-06-2012
DOI: 10.1063/1.4729672
Abstract: The compact Wedge Range Filter (WRF) proton spectrometer was developed for OMEGA and transferred to the National Ignition Facility (NIF) as a National Ignition C aign diagnostic. The WRF measures the spectrum of protons from D-3He reactions in tuning-c aign implosions containing D and 3He gas in this work we report on the first proton spectroscopy measurement on the NIF using WRFs. The energy downshift of the 14.7-MeV proton is directly related to the total ρR through the plasma stopping power. Additionally, the shock proton yield is measured, which is a metric of the final merged shock strength.
MASS-RADIUS RELATIONSHIPS FOR EXOPLANETS
Publisher: American Astronomical Society
Date: 13-12-2011
The F1F0-ATPase of Escherichia coli. Substitution of proline by leucine at position 64 in the c-subunit causes loss of oxidative phosphorylation
Publisher: Portland Press Ltd.
Date: 08-1983
DOI: 10.1042/BJ2130451
Abstract: The uncE410 allele differs from the normal uncE gene in that C leads to T base changes occur at nucleotides 190 and 191, resulting in proline at position 64 in the c-subunit of the F1F0-ATPase being replaced by leucine. Two partial-revertant strains were isolated in which alanine-20 of the c-subunit was replaced by proline, owing to a G leads to C base change at nucleotide 58. These c-subunits, coded for by the uncE501 and uncE502 alleles, therefore contained two amino acid changes, namely proline-64 leads to leucine, and alanine-20 leads to proline. Membranes prepared from the partial-revertant strains lacked ATP-dependent atebrin-fluorescence-quenching activity but were able to carry out oxidative phosphorylation. The ATPase activity of the F1-ATPase was inhibited when bound to membranes from strains carrying the uncE410, uncE501 and uncE502 alleles. It is concluded that a bend in the helix axis in one of the arms of the c-subunit hairpin structure is required for integration of the c-subunit into a functional F1F0-ATPase.
Properties of fluid deuterium under double-shock compression to several Mbar
Publisher: AIP Publishing
Date: 18-08-2004
DOI: 10.1063/1.1778164
Abstract: The compressibility of fluid deuterium up to several Mbar has been probed using laser-driven shock waves reflected from a quartz anvil. Combining high-precision (∼1%) shock velocity measurements with the double-shock technique, where differences in equation of state (EOS) models are magnified, has allowed better discrimination between theoretical predictions in the second-shock regime. Double-shock results are in agreement with the stiffer EOS models—which exhibit roughly fourfold single-shock compression—for initial shocks up to 1 Mbar and above 2 Mbar, but erge from these predictions in between. Softer EOS models—which exhibit sixfold single-shock compression at 1 Mbar—overestimate the reshock pressure for the entire range under study.
Velocity and Timing of Multiple Spherically Converging Shock Waves in Liquid Deuterium
Publisher: American Physical Society (APS)
Date: 13-05-2011
Diamond spheres for inertial confinement fusion
Publisher: IOP Publishing
Date: 30-09-2009
DOI: 10.1088/0029-5515/49/11/112001
Abstract: The National Ignition Facility (NIF) will allow scientists to prove the feasibility of inertial confinement fusion (ICF). The success of ICF experiments at NIF will critically depend on the availability of robust targets. Guided by computer simulations, we generated a new target design that takes advantage of the extreme atomic density of synthetic diamond, and developed a process that allows us to produce large quantities of these ultrahigh precision diamond targets via a low-cost batch process. Computer simulations were used to assess the performance and the robustness of these diamond targets. The results demonstrate that diamond has the potential to outperform other target materials in terms of energy efficiency and implosion stability, thus making successful ignition more likely.
Precision equation-of-state measurements on National Ignition Facility ablator materials from 1 to 12 Mbar using laser-driven shock waves
Publisher: AIP Publishing
Date: 05-2012
DOI: 10.1063/1.4712050
Abstract: A large uncertainty in the design of ignition capsules for use in the National Ignition C aign (NIC) is the ablator equation of state. In this article, we report equation-of-state measurements for two candidate NIC ablator materials, glow-discharge polymer (GDP), and germanium-doped GDP. These materials were driven to pressures of 1 to 12 Mbar using laser-driven shock waves. Hugoniot measurements were obtained using the impedance matching technique with an α-quartz standard. This article presents the first kinematic measurements in the high-pressure fluid regime for these materials, which show to be in close agreement with Livermore equation-of-state model predictions.
Trinity of Three-Dimensional (3D) Scaffold, Vibration, and 3D Printing on Cell Culture Application: A Systematic Review and Indicating Future Direction
Publisher: MDPI AG
Date: 23-07-2018
DOI: 10.3390/BIOENGINEERING5030057
Abstract: Cell culture and cell scaffold engineering have previously developed in two directions. First can be ‘static into dynamic’, with proven effects that dynamic cultures have benefits over static ones. Researches in this direction have used several mechanical means, like external vibrators or shakers, to approximate the dynamic environments in real tissue, though such approaches could only partly address the issue. Second, can be ‘2D into 3D’, that is, artificially created three-dimensional (3D) passive (also called ‘static’) scaffolds have been utilized for 3D cell culture, helping external culturing conditions mimic real tissue 3D environments in a better way as compared with traditional two-dimensional (2D) culturing. In terms of the fabrication of 3D scaffolds, 3D printing (3DP) has witnessed its high popularity in recent years with ascending applicability, and this tendency might continue to grow along with the rapid development in scaffold engineering. In this review, we first introduce cell culturing, then focus 3D cell culture scaffold, vibration stimulation for dynamic culture, and 3DP technologies fabricating 3D scaffold. Potential interconnection of these realms will be analyzed, as well as the limitations of current 3D scaffold and vibration mechanisms. In the recommendation part, further discussion on future scaffold engineering regarding 3D vibratory scaffold will be addressed, indicating 3DP as a positive bridging technology for future scaffold with integrated and localized vibratory functions.
The role of hot spot mix in the low-foot and high-foot implosions on the NIF
Publisher: AIP Publishing
Date: 05-2017
DOI: 10.1063/1.4983625
Abstract: Hydrodynamic mix of the ablator into the DT fuel layer and hot spot can be a critical performance limitation in inertial confinement fusion implosions. This mix results in increased radiation loss, cooling of the hot spot, and reduced neutron yield. To quantify the level of mix, we have developed a simple model that infers the level of contamination using the ratio of the measured x-ray emission to the neutron yield. The principal source for the performance limitation of the “low-foot” class of implosions appears to have been mix. Lower convergence “high-foot” implosions are found to be less susceptible to mix, allowing velocities of & km/s to be achieved.
Melting of magnesium oxide up to two terapascals using double-shock compression
Publisher: American Physical Society (APS)
Date: 12-07-2021
Using secondary-proton spectra to study the compression and symmetry of deuterium-filled capsules at OMEGA
Publisher: AIP Publishing
Date: 21-05-2002
DOI: 10.1063/1.1472502
Abstract: With new measurement techniques, high-resolution spectrometry of secondary fusion protons has been used to study compression and symmetry of imploded D2-filled capsules in direct-drive inertial-confinement-fusion experiments at the 60-beam OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Data from target capsules with ∼15 atmospheres of D2 fuel, in CH shells 19–27 μm thick, were acquired with a magnet-based, charged-particle spectrometer and with several new “wedge-range-filter”-based spectrometers incorporating special filters and CR39 nuclear track detectors. Capsules with 19-μm shells, imploded with similar laser energies (∼23 kJ) but different methods of single-beam laser smoothing, were studied and found to show different compression characteristics as indicated by the fuel areal density (determined by the ratio of secondary-proton yield to primary-neutron yield) and the total areal density (determined by the energy loss of protons due to slowing in the fuel and shell). In going from 0.3-THz SSD (smoothing by spectral dispersion) to 1-THz SSD and PS (polarization smoothing), the fuel areal density increased by at least 30%, while the total areal density increased by 40% (from ∼52 to ∼72 mg/cm2). In addition, significant low-mode-number spatial asymmetries in implosions were indicated by spectra measured at different angles with respect to the target. The mean energies of protons, measured at different angles during the same shot, varied by as much as 1 MeV, implying angular variations in areal density of order 30 mg/cm2. To the best of our knowledge, this is the first experimental demonstration that capsule symmetry can be sensitively studied by measuring the energy loss of charged particles.
First implosion experiments with cryogenic thermonuclear fuel on the National Ignition Facility
Publisher: IOP Publishing
Date: 21-03-2012
Collection of solid and gaseous samples to diagnose inertial confinement fusion implosions
Publisher: AIP Publishing
Date: 02-2012
DOI: 10.1063/1.3685250
Abstract: Collection of representative s les of debris following inertial confinement fusion implosions in order to diagnose implosion conditions and efficacy is a challenging endeavor because of the unique conditions within the target chamber such as unconverted laser light, intense pulse of x-rays, physical chunks of debris, and other ablative effects. We present collection of gas s les following an implosion for the first time. High collection fractions for noble gases were achieved. We also present collection of solid debris s les on flat plate collectors. Geometrical collection efficiencies for Au hohlraum material were achieved and collection of capsule debris (Be and Cu) was also observed. Asymmetric debris distributions were observed for Au and Be s les. Collection of Be capsule debris was higher for solid collectors viewing the capsule through the laser entrance hole in the hohlraum than for solid collectors viewing the capsule around the waist of the hohlraum. Collection of Au hohlraum material showed the opposite pattern: more Au debris was collected around the waist than through the laser entrance hole. The solid debris collectors were not optimized for minimal Cu backgrounds, which limited the conclusions about the symmetry of the Cu debris. The quality of the data limited conclusions on chemical fractionation effects within the burning, expanding, and then cooling plasma.
Implosion dynamics measurements at the National Ignition Facility
Publisher: AIP Publishing
Date: 12-2012
DOI: 10.1063/1.4769268
Abstract: Measurements have been made of the in-flight dynamics of imploding capsules indirectly driven by laser energies of 1–1.7 MJ at the National Ignition Facility [Miller et al., Nucl. Fusion 44, 228 (2004)]. These experiments were part of the National Ignition C aign [Landen et al., Phys. Plasmas 18, 051002 (2011)] to iteratively optimize the inputs required to achieve thermonuclear ignition in the laboratory. Using gated or streaked hard x-ray radiography, a suite of ablator performance parameters, including the time-resolved radius, velocity, mass, and thickness, have been determined throughout the acceleration history of surrogate gas-filled implosions. These measurements have been used to establish a dynamically consistent model of the ablative drive history and shell compressibility throughout the implosion trajectory. First results showed that the peak velocity of the original 1.3-MJ Ge-doped polymer (CH) point design using Au hohlraums reached only 75% of the required ignition velocity. Several capsule, hohlraum, and laser pulse changes were then implemented to improve this and other aspects of implosion performance and a dedicated effort was undertaken to test the sensitivity of the ablative drive to the rise time and length of the main laser pulse. Changing to Si rather than Ge-doped inner ablator layers and increasing the pulse length together raised peak velocity to 93% ± 5% of the ignition goal using a 1.5 MJ, 420 TW pulse. Further lengthening the pulse so that the laser remained on until the capsule reached 30% (rather than 60%–70%) of its initial radius, reduced the shell thickness and improved the final fuel ρR on companion shots with a cryogenic hydrogen fuel layer. Improved drive efficiency was observed using U rather than Au hohlraums, which was expected, and by slowing the rise time of laser pulse, which was not. The effect of changing the Si-dopant concentration and distribution, as well as the effect of using a larger initial shell thickness were also examined, both of which indicated that instabilities seeded at the ablation front are a significant source of hydrodynamic mix into the central hot spot. Additionally, a direct test of the surrogacy of cryogenic fuel layered versus gas-filled targets was performed. Together all these measurements have established the fundamental ablative-rocket relationship describing the dependence of implosion velocity on fractional ablator mass remaining. This curve shows a lower-than-expected ablator mass at a given velocity, making the capsule more susceptible to feedthrough of instabilities from the ablation front into the fuel and hot spot. This combination of low velocity and low ablator mass indicates that reaching ignition on the NIF will require & μm (∼10%) thicker targets and laser powers at or beyond facility limits.
Melting temperature of diamond at ultrahigh pressure
Publisher: Springer Science and Business Media LLC
Date: 08-11-2009
DOI: 10.1038/NPHYS1438
Phase Transformations and Metallization of Magnesium Oxide at High Pressure and Temperature
Publisher: American Association for the Advancement of Science (AAAS)
Date: 07-12-2012
Abstract: The interiors of Earth and other rocky planets generally consist of a few common minerals. Depending largely on the size of the planet, the distribution and relative abundance of these minerals varies for ex le, MgO is abundant in the mantles of Earth and large Earth-like planets, but is present in Jupiter's core. The properties of MgO also vary with planetary size as a function of temperature and pressure. McWilliams et al. (p. 1330 , published online 22 November) performed laser-shock experiments at pressures over three times higher than Earth's inner core. MgO underwent two phase transformations, first to a solid with a modified crystal structure, and then to a conductive liquid. In terrestrial planets greater than eight Earth masses, MgO in the mantle could generate a magnetic field–generating dynamo such as those that typically found in planetary cores.
Maps of variability in cell lineage trees
Publisher: Public Library of Science (PLoS)
Date: 12-02-2019
Related Organisations
Lawrence Livermore National Laboratory
Location: United States of America
Massachusetts Institute Of Technology
Location: United States of America
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