Transit time instabilities in an inverted fireball. II. Mode jumping and nonlinearities

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

doi:10.1063/1.3533440

Cited by 33 publications

(18 citation statements)

References 21 publications

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“…Stenzel et al [236,237] have also investigated an "inverted fireball" configuration where a spherical high density plasma is generated inside of a wire grid formed into a sphere. This has some similar properties to fireballs on the surface of electrodes, such as being produced by increased ionization due to energetic electrons and having a double layer electric field, but it is also particular to the transparent anode grid geometry.…”

Section: Multiple Fireballsmentioning

confidence: 99%

“…This instability is associated with a variety of nonlinear behaviors such as amplitude clipping of the collected electron current and bursty transient behavior as indicated by the fluctuations in electrode current. A high frequency transit time instability has also been extensively studied in inverted fireballs which are present on the interior of large gridded spherical electrodes [236,237,276]. The instability frequency in such cases is related to the electron transit time across the fireball.…”

Section: 52mentioning

confidence: 99%

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Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs

Baalrud

Scheiner

Yee

et al. 2020

Plasma Sources Sci. Technol.

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Biased electrodes are common components of plasma sources and diagnostics. The plasma-electrode interaction is mediated by an intervening sheath structure that influences properties of the electrons and ions contacting the electrode surface, as well as how the electrode influences properties of the bulk plasma. A rich variety of sheath structures have been observed, including ion sheaths, electron sheaths, double sheaths, double layers, anode glow, and fireballs. These represent complex self-organized responses of the plasma that depend not only on the local influence of the electrode, but also on the global properties of the plasma and the other boundaries that it is in contact with. This review summarizes recent advances in understanding the conditions under which each type of sheath forms, what the basic stability criteria and steady-state properties of each are, and the ways in which each can influence plasma-boundary interactions and bulk plasma properties. These results may be of interest to a number of application areas where biased electrodes are used, including diagnostics, plasma modification of materials, plasma sources, electric propulsion, and the interaction of plasmas with objects in space.

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Section: Multiple Fireballsmentioning

confidence: 99%

Section: 52mentioning

confidence: 99%

Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs

Baalrud

Scheiner

Yee

et al. 2020

Plasma Sources Sci. Technol.

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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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“…The impact on the grid ejects secondary electrons which become confined inside the sphere. Ionization in an electron-rich sheath can produce sheath modifications which affect many other instabilities [22]. Negatively biased permanent magnets also form sheaths, secondary electrons and plasmas, known as magnetrons and used for sputtering [23,24].…”

Section: Introductionmentioning

confidence: 99%

Untitled

2021

J. Technol. Space Plasmas

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The properties of sheaths and associated potential structures and instabilities cover a broad field which even a review cannot cover everything. Thus, the focus will be on about a dozen examples, describe their observations and focus on the basic physical explanations for the effects, while further details are found in the references. Due to familiarity the review focuses mainly on the authors work but compared and referenced related work. The topics start with a high frequency oscillation near the electron plasma frequency. Low frequency instabilities also occur at the ion plasma frequency. The injection of ions into an electron-rich sheath widens the sheath and forms a double layer. Likewise, the injection of electrons into an ion rich sheath widens and establishes a double layer which occurs in free plasma injection into vacuum. The sheath widens and forms a double layer by ionization in an electron rich sheath. When particle fluxes in "fireballs" gets out of balance the double layer performs relaxation instabilities which has been studied extensively. Fireballs inside spherical electrodes create a new instability due to the transit time of trapped electrons. On cylindrical and spherical electrodes the electron rich sheath rotates in magnetized plasmas. Electrons rotate due to E × B 0 which excites electron drift waves with azimuthal eigenmodes. Conversely a permanent magnetic dipole has been used as a negative electrode. The impact of energetic ions produces secondary electron emission, forming a ring of plasma around the magnetic equator. Such "magnetrons" are subject to various instabilities. Finally, the current to a positively biased electrode in a uniformly magnetized plasma is unstable to relaxation oscillations, which shows an example of global effects. The sheath at the electrode raises the potential in the flux tube of the electrode thereby creating a radial sheath which moves unmagnetized ions radially. The ion motion creates a density perturbation which affects the electrode current. If the electrode draws large currents the current disruptions create large inductive voltages on the electrode, which again produce double layers. This phenomenon has been seen in reconnection currents. Many examples of sheath properties will be explained. Although the focus is on the physics some examples of applications will be suggested such as neutral gas heating and accelerating, sputtering of plasma magnetrons and rf oscillators.

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Transit time instabilities in an inverted fireball. II. Mode jumping and nonlinearities

Cited by 33 publications

References 21 publications

Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs

Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs

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

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