Boyd Blackwell

Dynamic behaviour of the low-to-high confinement transitions in the H-1 heliac

Publisher: IOP Publishing

Date: 16-03-2001

DOI: 10.1088/0741-3335/43/4/312

Determination of error field sources by accurate mapping of the magnetic geometry of the H-1 heliac

Publisher: IOP Publishing

Date: 02-02-2009

DOI: 10.1088/0029-5515/49/3/035001

Abstract: High precision mapping of the vacuum flux surfaces of the H-1NF heliac is carried out using electron-beam multi-wire tomography for various magnetic configurations and field strengths. The extreme accuracy of this technique has been exploited to understand the nature of error fields and to determine the best-fit empirical values for the H-1NF coil parameters, by point-by-point matching experimental surface data with computer modelling results. This has helped in developing a highly accurate computer model for H-1NF magnetic configurations.

Effects of resistivity and rotation on the linear plasma response to non-axisymmetric magnetic perturbations on DIII-D

Publisher: IOP Publishing

Date: 05-01-2015

DOI: 10.1088/0741-3335/57/2/025015

Studies of resonantly produced plasmas in the H-1NF heliac using a far-infrared scanning interferometer

Publisher: AIP Publishing

Date: 03-2003

DOI: 10.1063/1.1538360

Abstract: The H-1NF heliac regularly operates using the ion cyclotron range of frequencies at 0.5 T to produce plasmas with a mixture of hydrogen and helium gases. Due to the complex three-dimensional structure of the magnetic flux surfaces, these plasmas require sophisticated diagnostic systems, with good spatial coverage, to extract meaningful physical information. This article presents a study of the dependence of the plasma density profile on resonant heating conditions and magnetic configuration, using a far-infrared scanning interferometer. Recent modifications to the system and data that illustrate the performance of the interferometer will be discussed.

A supersonic gas injection system for fuelling and probing fusion plasmas

Publisher: IOP Publishing

Date: 09-2006

DOI: 10.1088/0963-0252/15/4/025

Spontaneous transition of core radial electric field driven by magnetic islands in the H-1NF heliac

Publisher: IOP Publishing

Date: 23-06-2011

DOI: 10.1088/0029-5515/51/8/083003

Abstract: This paper reports an experimental observation of spontaneous transition of the core radial electric field to a large positive value ( E r ∼ 5 kV m −1 ), with a strong electric-field shear (∼700 kV m −2 ) in a low temperature ( T e ∼ 10 eV) radio frequency generated argon plasma in the H-1NF heliac stellarator. The transition, which seems to be driven by a spontaneous excitation of m = 2 magnetic islands near the core, is associated with a localized increase in the plasma density and excitation of coherent low frequency (∼3 kHz) oscillations possibly due to unstable E r shear driven modes. Evidence suggests development of the core electron-root scenario, which previously has been observed only at high temperature electron cyclotron heated plasmas.

Algorithms for real time magnetic field tracing and optimization

Publisher: Elsevier BV

Date: 12-2001

DOI: 10.1016/S0010-4655(01)00326-5

Ideal-magnetohydrodynamic theory of low-frequency Alfvén waves in the H-1 Heliac

Publisher: IOP Publishing

Date: 12-04-2012

DOI: 10.1088/0741-3335/54/5/055009

Ion Detachment in the Helicon Double-Layer Thruster Exhaust Beam

Publisher: American Institute of Aeronautics and Astronautics (AIAA)

Date: 2006

DOI: 10.2514/1.13914

Magnetic field mapping system on the H-1 heliaca)

Publisher: AIP Publishing

Date: 02-1995

DOI: 10.1063/1.1145998

Abstract: The H-1 heliac recently brought into operation is a medium-sized 3-field-period heliac with major radius R0=1 m, plasma mean minor radius 〈a〉≤0.2 m and a wide range of rotational transforms 0.6≤ι–(0)≤2.0. Electron beam mapping of the vacuum magnetic field was performed using new type of a fluorescent target (movable fluorescent rod array having a transparency about 98%). Up to 150–200 toroidal transits were observed at each electron gun position. The spatial resolution of the system was about 3 mm. Electron collector probes were used for monitoring the positions of the magnetic surfaces in different toroidal field periods. Visible paths of the electron beam due to the excitation of the background gas (p∼10−4 Torr) were used for identification of the toroidal transit numbers. This newly developed method gives an accuracy in measurement of the rotational transform of about 1.5%. Experimental surfaces and measured ι/ profiles show very good agreement with the computer model results.

Tomographic interferometry of a filtered high-current vacuum arc plasma

Publisher: AIP Publishing

Date: 04-2007

DOI: 10.1063/1.2714677

Abstract: Tomography of a plasma enables the distribution of electron density to be visualized. We report on the design of two tomographic interferometer systems used to measure plasma electron density distributions in a high-current pulsed cathodic vacuum arc. The method is shown to be capable of microsecond time resolution. The spatial resolution of the quasioptical interferometer operating at 2 mm wavelength is 20 mm and the spatial resolution of the waveguide-based interferometer operating at 8 mm wavelength is 50 mm. In both cases the resolution achieved depends on the launching and receiving geometries. We developed criteria for assessing the tomogram for artifacts arising from limited s ling. First results of the spatial and temporal history of plasma in a high-current vacuum arc guided by a curved magnetic filter are presented and indicate poloidal field fluctuations reminiscent of magnetohydrodynamic instabilities in pinches. The applicability of the tomographic interferometry method to optimize plasma transport through the filter is also demonstrated.

Design and characterization of the Magnetized Plasma Interaction Experiment (MAGPIE): A new source for plasma-material interaction studies

Publisher: IOP Publishing

Date: 10-2012

DOI: 10.1088/0963-0252/21/5/055033

The H-1 radio frequency system and an initial study of plasma formation

Publisher: Elsevier BV

Date: 1995

DOI: 10.1016/0920-3796(94)00186-B

Wave modeling in a cylindrical non-uniform helicon discharge

Publisher: AIP Publishing

Date: 08-2012

DOI: 10.1063/1.4748874

Abstract: A radio frequency field solver based on Maxwell's equations and a cold plasma dielectric tensor is employed to describe wave phenomena observed in a cylindrical non-uniform helicon discharge. The experiment is carried out on a recently built linear plasma-material interaction machine: The magnetized plasma interaction experiment [Blackwell et al., Plasma Sources Sci. Technol. (submitted)], in which both plasma density and static magnetic field are functions of axial position. The field strength increases by a factor of 15 from source to target plate, and the plasma density and electron temperature are radially non-uniform. With an enhancement factor of 9.5 to the electron-ion Coulomb collision frequency, a 12% reduction in the antenna radius, and the same other conditions as employed in the experiment, the solver produces axial and radial profiles of wave litude and phase that are consistent with measurements. A numerical study on the effects of axial gradient in plasma density and static magnetic field on wave propagations is performed, revealing that the helicon wave has weaker attenuation away from the antenna in a focused field compared to a uniform field. This may be consistent with observations of increased ionization efficiency and plasma production in a non-uniform field. We find that the relationship between plasma density, static magnetic field strength, and axial wavelength agrees well with a simple theory developed previously. A numerical scan of the enhancement factor to the electron-ion Coulomb collision frequency from 1 to 15 shows that the wave litude is lowered and the power deposited into the core plasma decreases as the enhancement factor increases, possibly due to the stronger edge heating for higher collision frequencies.

Linear ideal MHD predictions forn= 2 non-axisymmetric magnetic perturbations on DIII-D

Publisher: IOP Publishing

Date: 05-02-2014

DOI: 10.1088/0741-3335/56/3/035005

The use of Bayesian inversion to resolve plasma equilibrium

Publisher: AIP Publishing

Date: 10-2010

DOI: 10.1063/1.3491044

Abstract: Recently, Bayesian probability theory has been used at a number of experiments to fold uncertainties and interdependencies in the diagnostic data and forward models, together with prior knowledge of the state of the plasma, to increase accuracy of inferred physics variables. A new probabilistic framework, MINERVA, based on Bayesian graphical models, has been used at JET and W7-AS to yield predictions of internal magnetic structure. A feature of the framework is the Bayesian inversion for poloidal magnetic flux without the need for an explicit equilibrium assumption. Building on this, we discuss results from a new project to develop Bayesian inversion tools that aim to (1) distinguish between competing equilibrium theories, which capture different physics, using the MAST spherical tokamak, and (2) test the predictions of MHD theory, particularly mode structure, using the H-1 Heliac. Specifically, we report on correction of the motional Stark effect, pickup coils, flux-loop constrained Bayesian inferred equilibrium for varying toroidal flux.

Wire tomography in the H-1NF heliac for investigation of fine structure of magnetic islands

Publisher: AIP Publishing

Date: 2007

DOI: 10.1063/1.2424453

Abstract: Electron beam wire tomography in the H-1NF heliac enables high resolution mapping of vacuum flux surfaces with minimal disruption of the plasma operations schedule. Recent experimental results have proven this technique to be a highly accurate and high resolution method for mapping vacuum magnetic islands. Islands of width as small as δ∼8mm have been measured, providing estimates of the internal rotational transform of the island. Point-to-point comparison of the mapping results with computer tracing, in conjunction with an image warping technique, enables systematic exploration of magnetic islands and surfaces of interest. Recent development of a fast mapping technique significantly reduced the mapping time and made this technique suitable for mapping at higher magnetic fields. This article presents recent experimental results and associated techniques.

A reduced global Alfvén eigenmodes model for Mirnov array data on the H-1NF heliac

Publisher: IOP Publishing

Date: 23-06-2011

DOI: 10.1088/0741-3335/53/8/085023

Clustering of periodic multichannel timeseries data with application to plasma fluctuations

Publisher: Elsevier BV

Date: 06-2014

DOI: 10.1016/J.CPC.2014.03.008

A multichannel magnetic probe system for analysing magnetic fluctuations in helical axis plasmas

Publisher: AIP Publishing

Date: 09-2013

DOI: 10.1063/1.4819250

Abstract: The need to understand the structure of magnetic fluctuations in H-1NF heliac [S. Hamberger et al., Fusion Technol. 17, 123 (1990)] plasmas has motivated the installation of a sixteen former, tri-axis helical magnetic probe Mirnov array (HMA). The new array complements two existing poloidal Mirnov arrays by providing polarisation information, higher frequency response, and improved toroidal resolution. The helical placement is ideal for helical axis plasmas because it positions the array as close as possible to the plasma in regions of varying degrees of favourable curvature in the magnetohydrodynamic sense, but almost constant magnetic angle. This makes phase variation with probe position near linear, greatly simplifying the analysis of the data. Several of the issues involved in the design, installation, data analysis, and calibration of this unique array are presented including probe coil design, frequency response measurements, mode number identification, orientation calculations, and mapping probe coil positions to magnetic coordinates. Details of specially designed digitally programmable pre- lifiers, which allow gains and filters to be changed as part of the data acquisition initialisation sequence and stored with the probe signals, are also presented. The low shear heliac geometry [R. Jiménez-Gómez et al., Nucl. Fusion 51, 033001 (2011)]10.1088/0029-5515/51/3/033001, flexibility of the H-1NF heliac, and wealth of information provided by the HMA create a unique opportunity for detailed study of Alfvén eigenmodes, which could be a serious issue for future fusion reactors.

Selected papers from the Joint 18th International Stellarator Heliotron Workshop and the 10th Asia Pacific Plasma Theory Conference

Publisher: IOP Publishing

Date: 17-12-2012

DOI: 10.1088/0741-3335/55/1/010201

Core magnetic islands and plasma confinement in the H-1NF heliac

Publisher: AIP Publishing

Date: 08-2010

DOI: 10.1063/1.3474946

Plasma parameters and electron energy distribution functions in a magnetically focused plasma

Publisher: AIP Publishing

Date: 03-2013

DOI: 10.1063/1.4794841

Abstract: Spatially resolved measurements of ion density, electron temperature, floating potential, and the electron energy distribution function (EEDF) are presented for a magnetically focused plasma. The measurements identify a central plasma column displaying Maxwellian EEDFs at an electron temperature of about 5 eV indicating the presence of a significant fraction of electrons in the inelastic energy range (energies above 15 eV). It is observed that the EEDF remains Maxwellian along the axis of the discharge with an increase in density, at constant electron temperature, observed in the region of highest magnetic field strength. Both electron density and temperature decrease at the plasma radial edge. Electron temperature isotherms measured in the downstream region are found to coincide with the magnetic field lines.

Three view electronically scanned interferometer for plasma electron density measurements on the H-1 heliac

Publisher: AIP Publishing

Date: 27-09-2006

DOI: 10.1063/1.2218839

Abstract: We report the development of a three view electronically scanned millimeter-wave interferometer for plasma electron density profile measurement on the H-1 heliac. The system utilizes an electronically tunable backward-wave oscillator whose output is incident on a fixed blazed diffraction grating such that sweeping the source frequency effects a spatial scan of the plasma cross section. Two diagonal views essentially span most of the plasma cross section, while the horizontal arm views the lower half of the plasma. The diffracted beams traverse the plasma in & ms with a spatial resolution ∼20mm. A study of the density projection dependence on magnetic configuration shows that the presence of low-order rational surfaces in the plasma gives rise to sharp density gradients in the vicinity of the surface.

RF compensation of double Langmuir probes: modelling and experiment

Publisher: IOP Publishing

Date: 05-06-2015

DOI: 10.1088/0963-0252/24/3/035024

Initial damage processes for diamond film exposure to hydrogen plasma

Publisher: Elsevier BV

Date: 12-2013

DOI: 10.1016/J.FUSENGDES.2013.08.010

Fluctuations and stability of plasmas in the H-1NF heliac

Publisher: IOP Publishing

Date: 12-01-2004

DOI: 10.1088/0029-5515/44/2/008

Experimental investigation of the magnetic structure in the H-1 heliac

Publisher: IOP Publishing

Date: 12-1994

DOI: 10.1088/0029-5515/34/12/I09

Imaging photomultiplier array with integrated amplifiers and high-speed USB interface

Publisher: AIP Publishing

Date: 10-2008

DOI: 10.1063/1.2965013

Abstract: Multianode photomultiplier tube (PMT) arrays are finding application as convenient high-speed light sensitive devices for plasma imaging. This paper describes the development of a USB-based “plug-n-play” 16-channel PMT camera with 16bits simultaneous acquisition of 16 signal channels at rates up to 2MS∕s per channel. The pre lifiers and digital hardware are packaged in a compact housing which incorporates magnetic shielding, on-board generation of the high-voltage PMT bias, an optical filter mount and slits, and F-mount lens adaptor. Triggering, timing, and acquisition are handled by four field-programmable gate arrays (FPGAs) under instruction from a master FPGA controlled by a computer with a LABVIEW interface. We present technical design details and specifications and illustrate performance with high-speed images obtained on the H-1 heliac at the ANU.

Synchronous imaging of coherent plasma fluctuations

Publisher: AIP Publishing

Date: 03-2014

DOI: 10.1063/1.4868504

Abstract: A new method for imaging high frequency plasma fluctuations is described. A phase locked loop and field programmable gate array are used to generate gating triggers for an intensified CCD camera. A reference signal from another diagnostic such as a magnetic probe ensures that the triggers are synchronous with the fluctuation being imaged. The synchronous imaging technique allows effective frame rates exceeding millions per second, good signal to noise through the accumulation of multiple exposures per frame, and produces high resolution images without generating excessive quantities of data. The technique can be used to image modes in the MHz range opening up the possibility of spectrally filtered high resolution imaging of MHD instabilities that produce sufficient light fluctuations. Some ex les of projection images of plasma fluctuations on the H-1NF heliac obtained using this approach are presented here.

Visible light tomography of MHD eigenmodes in the H-1NF stellarator using magnetic coordinates

Publisher: IOP Publishing

Date: 23-07-2014

DOI: 10.1088/0029-5515/54/8/083031

Discovery Projects - Grant ID: DP0344361

Start Date: 2003

End Date: 12-2005

Amount: $162,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0453732

Start Date: 01-2004

End Date: 12-2005

Amount: $726,164.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP110102881

Start Date: 2011

End Date: 12-2014

Amount: $255,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0451960

Start Date: 2004

End Date: 12-2008

Amount: $195,000.00

Funder: Australian Research Council