Title: Particle-in-cell study of the ion-to-electron sheath transition

Abstract

The form of a sheath near a small electrode, with bias changing from below to above the plasma potential, is studied using 2D particle-in-cell simulations. When the electrode is biased within T_e/2_e below the plasma potential, the electron velocity distribution functions (EVDFs) exhibit a loss-cone type truncation due to fast electrons overcoming the small potential difference between the electrode and plasma. No sheath is present in this regime, and the plasma remains quasineutral up to the electrode. The EVDF truncation leads to a presheath-like density and flow velocity gradients. Once the bias exceeds the plasma potential, an electron sheath is present. In this case, the truncation driven behavior persists, but is accompanied by a shift in the maximum value of the EVDF that is not present in the negative bias cases. In conclusion, the flow moment has significant contributions from both the flow shift of the EVDF maximum, and the loss-cone truncation.

Authors:

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

Tue Aug 09 00:00:00 EDT 2016

Research Org.:

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

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1326057

Alternate Identifier(s):

OSTI ID: 1287752

Report Number(s):

SAND-2016-3872J
Journal ID: ISSN 1070-664X; PHPAEN; 647402

Grant/Contract Number:  

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

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 23; Journal Issue: 8; 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; electrodes; plasma sheaths; plasma flows; tensor methods; Boltzmann equations