Pulsating fireballs with high-frequency sheath–plasma instabilities

Stenzel, R. L.; Gruenwald, J.; Ioniţă, C.; Schrittwieser, R.

doi:10.1088/0963-0252/20/4/045017

Cited by 25 publications

(24 citation statements)

References 29 publications

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“…Fireballs are just one of the several forms of sheath structure that are possible near positively biased electrodes 2 and are of interest due to their application in dust confinement, 7 plasma contactors, 8 as an ion source 9 including those which can be used in the fabrication of nanodots, 10 and as a platform to study plasma self organization 11 and nonlinear processes. 12 Fireballs also bare a resemblance to similar phenomena that occur near hollow cathode plasma sources 13,14 and may contribute to the understanding of their operation.…”

Section: Introductionmentioning

confidence: 95%

Measurements of fireball onset

et al. 2018

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Laser-based measurements of the characteristic features of fireball onset and stabilization in response to a stepped voltage applied to an anode immersed in a low pressure (100 mTorr) helium afterglow are reported. These include spatial and temporal evolution of metastable species, electron density, and electric field magnitude as measured by planar laser induced fluorescence, lasercollision induced fluorescence, and laser-induced fluorescence-dip spectroscopy, respectively. These measurements are found to be in qualitative agreement with recent particle-in-cell simulations and theoretical models [Scheiner et al., Phys. Plasmas 24, 113520 (2017)]. The measurements validate the simulations and models in which fireball onset was predicted to follow from the trapping of electrons born from electron impact ionization within a potential well created by a buildup of ions in the sheath. The experimental measurements also demonstrate transient features following the onset that were not present in previous simulations. New simulation results are presented which demonstrate that these features are associated with the abruptness of the voltage step used to initiate fireball onset. An abrupt step in the anode bias causes rapid displacement of ions and an associated plasma potential response following the sheath and fireball expansion.

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Section: Introductionmentioning

confidence: 95%

Measurements of fireball onset

et al. 2018

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“…Similar types of oscillations have been reported in studies on anode spots and "fireballs." [16][17][18][19][20][21]…”

Section: A Anode Size and Mode Transitionsmentioning

confidence: 99%

Response of the plasma to the size of an anode electrode biased near the plasma potential

Barnat

Laity

2014

Physics of Plasmas

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As the size of a positively biased electrode increases, the nature of the interface formed between the electrode and the host plasma undergoes a transition from an electron-rich structure (electron sheath) to an intermediate structure containing both ion and electron rich regions (double layer) and ultimately forms an electron-depleted structure (ion sheath). In this study, measurements are performed to further test how the size of an electron-collecting electrode impacts the plasma discharge the electrode is immersed in. This is accomplished using a segmented disk electrode in which individual segments are individually biased to change the effective surface area of the anode. Measurements of bulk plasma parameters such as the collected current density, plasma potential, electron density, electron temperature and optical emission are made as both the size and the bias placed on the electrode are varied. Abrupt transitions in the plasma parameters resulting from changing the electrode surface area are identified in both argon and helium discharges and are compared to the interface transitions predicted by global current balance [S. D. Baalrud, N. Hershkowitz, and B. Longmier, Phys. Plasmas 14, 042109 (2007)]. While the size-dependent transitions in argon agree, the size-dependent transitions observed in helium systematically occur at lower electrode sizes than those nominally derived from prediction. The discrepancy in helium is anticipated to be caused by the finite size of the interface that increases the effective area offered to the plasma for electron loss to the electrode. V

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“…It is worth mentioning here that in this study, there was no noticable influence of instabilities on the LCIF measurements of the plasma structure or the current-voltage characteristics. Instabilities have been observed in similar 'fireball' plasma structures at the surface of positively biased anodes, which have been thoroughly studied by Stenzel et al [28][29][30][31]. Instabilities can cause oscillations in the current and voltage waveforms at the anode, as well as extinction of the plasma structure.…”

Section: Resultsmentioning

confidence: 99%

Two-dimensional laser collision-induced fluorescence measurements of plasma properties near an RF plasma cathode extraction aperture

Weatherford

Barnat

Foster

2012

Plasma Sources Sci. Technol.

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A dense plasma structure was observed to form near the extraction aperture of a helium RF plasma cathode. Laser collision-induced fluorescence was used to generate two-dimensional spatial maps of the electron density and the effective electron temperature within the structure over a range of operating conditions. The aperture plasma reached densities nearly an order of magnitude higher than the surrounding bulk plasma. The sharp spatial change in density at the plasma structure boundary suggests the presence of a double layer sheath. Higher temperature electrons were also observed at the periphery of the plasma structure. Variations in the observed plasma structure with extracted electron current were found to be consistent with reported low pressure anode spot behavior. Measurements of plasma density within and at the boundary of the structure, and the dependence of these on the current extracted across the external gap, are compared with calculations and discussed.

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Pulsating fireballs with high-frequency sheath–plasma instabilities

Cited by 25 publications

References 29 publications

Measurements of fireball onset

Measurements of fireball onset

Response of the plasma to the size of an anode electrode biased near the plasma potential

Two-dimensional laser collision-induced fluorescence measurements of plasma properties near an RF plasma cathode extraction aperture

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