Theory and simulation of anode spots in low pressure plasmas

Journal Article · Wed Nov 22 00:00:00 EST 2017 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4999477· OSTI ID:1464203

Scheiner, Brett ^[1]; Barnat, Edward V. ^[2]; Baalrud, Scott D. ^[1]; Hopkins, Matthew M. ^[2]; Yee, Benjamin Tong ^[2]

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1. Univ. of Iowa, Iowa City, IA (United States)
2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

When electrodes are biased above the plasma potential, electrons accelerated through the associated electron sheath can dramatically increase the ionization rate of neutrals near the electrode surface. It has previously been observed that if the ionization rate is great enough, a double layer separates a luminous high-potential plasma attached to the electrode surface (called an anode spot or fireball) from the bulk plasma. Here, results of the first 2D particle-in-cell simulations of anode spot formation are presented along with a theoretical model describing the formation process. It is found that ionization leads to the build-up of an ion-rich layer adjacent to the electrode, forming a narrow potential well near the electrode surface that traps electrons born from ionization. It is shown that anode spot onset occurs when a quasineutral region is established in the potential well and the density in this region becomes large enough to violate the steady-state Langmuir condition, which is a balance between electron and ion fluxes across the double layer. A model for steady-state properties of the anode spot is also presented, which predicts values for the anode spot size, double layer potential drop, and form of the sheath at the electrode by considering particle, power, and current balance. Furthermore, these predictions are found to be consistent with the presented simulation and previous experiments.

• Research Organization: Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000; AC04-94SL85000; AC05-06OR23100
• OSTI ID: 1464203
• Alternate ID(s): OSTI ID: 1409873
• Report Number(s): SAND-2017-8476J; 663066; TRN: US1902380
• Journal Information: Physics of Plasmas, Vol. 24, Issue 11; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY