ORCID Profile
0000-0002-2822-4108
Current Organisation
The University of Auckland
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Publisher: AIP Publishing
Date: 12-2021
DOI: 10.1063/5.0070924
Abstract: A radio frequency plasma device is presented in which the regions of plasma creation and maximum plasma magnetization can be separated along a 1.5-m tube. Measurements of the plasma density, plasma potential, and electron temperature in the device successfully reproduce previously reported plasma features. These validate the ability of the experiment to continue the investigation of a regime of operation in which the axial plasma density follows the profile of the applied magnetic field, as long as the ions are magnetized under the antenna. The density is shown to increase on axis owing to the decreasing cross section of the converging magnetic funnel connecting the antenna region to the solenoids. When the funnel pinching is increased, stronger magnetic fields are required to inhibit cross-field diffusion and to bring the density on axis in the expected 1012 cm−3 range. Collisionless transport of hot electron populations is observed along the field lines which intersect the area under the antenna and coincides with the presence of high-density conics more than 0.5 m away from the antenna for magnetic fields ≥600 G.
Publisher: AIP Publishing
Date: 04-2023
DOI: 10.1063/5.0133840
Abstract: Retarding field energy analyzers and Langmuir probes are routinely used to obtain ion and electron-energy distribution functions (IEDF and EEDF). These typically require knowledge of the first and second derivatives of the current–voltage characteristics, both of which can be obtained using analog and numerical techniques. A frequent problem with electric-probe plasma diagnostics is the noise from the plasma environment and measurement circuits. This poses challenges inherent to differentiating noisy signals, which often require prior filtering of the raw current–voltage data before evaluating the distribution functions. A review of commonly used filtering and differentiation techniques is presented. It covers analog differentiator circuits, polynomial fitting (Savitzky–Golay filter and B-spline fitting), window filtering (Gaussian and Blackman windows) methods as well as the AC superimposition and Gaussian deconvolution routines. The application of each method on experimental datasets with signal-to-noise ratios ranging from 44 to 66 dB is evaluated with regard to the dynamic range, energy resolution, and signal distortion of the obtained IEDF and EEDF as well as to the deduced plasma parameters.
Publisher: IOP Publishing
Date: 07-2023
Abstract: To improve the efficiency of radio-frequency magnetic nozzle plasma thrusters, it is important to better understand the coupling between plasma expansion and a convergent– ergent magnetic field. This study explores the effects of magnetic field strength and orientation on plasma expansion in a magnetic nozzle. Two-dimensional measurements of the plasma characteristics obtained both in the source and in the expansion region are presented to investigate the influence of magnetic field strength on the formation of high-density conics in a symmetric magnetic nozzle. The measurements are repeated in a deflected magnetic nozzle using a novel magnetic steering system. Measurements of the ion saturation current and floating potential profiles are used respectively to qualitatively assess the plasma density distribution and the presence of high-energy electrons for the magnetic field configurations analysed. In the symmetric magnetic nozzle configuration, it is observed that the ion saturation current peaks on axis in the plasma source, but downstream of the nozzle throat, a double-peaked hollow profile is observed for all cases studied. The location of the high-density conics structure matches the most radial field lines that intersect the antenna and can freely expand downstream outside the source. Negative values of the floating potential are measured in the same peripheral regions, which could be a sign of the presence of high-energy electrons. When the magnetic field is deflected, the ion saturation current profile shows only a single peak centred around the bent field line that reconnects to the antenna. Again, a region of negative floating potential is measured at the location of the maximum ion current. Thus, it is shown how, independent of magnetic field strength and orientation, the magnetic field lines interacting with the antenna dictate the local plasma profiles downstream from the magnetic nozzle.
No related grants have been discovered for Félicien Filleul.