Title: Theory and simulation of anode spots in low pressure plasmas

Abstract

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,more » and current balance. Furthermore, these predictions are found to be consistent with the presented simulation and previous experiments.« less

Authors:

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

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+ Show Author Affiliations

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

Publication Date:

Wed Nov 22 00:00:00 EST 2017

Research Org.:

Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1464203

Alternate Identifier(s):

OSTI ID: 1409873

Report Number(s):

SAND-2017-8476J
Journal ID: ISSN 1070-664X; 663066; TRN: US1902380

Grant/Contract Number:  

AC04-94AL85000; AC04-94SL85000; AC05-06OR23100

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 24; Journal Issue: 11; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY