Title: Analysis of the Transition Time between the Space-Charge-Limited and Inverse Regimes

Abstract

Accumulation of cold ions trapped within a space-charge-limited sheath collapses the sheath, causing a transition to the inverse sheath mode. A driving mechanism creating trapped ions is charge-exchange collisions which occur between fast ions and cold neutrals. Due to the complex nature of the temporally evolving sheath, it is difficult to predict how long the transition takes. Depending on the properties of the plasma, emitted electrons, and neutrals, the time scale can range from microseconds to hours. For experimental situations, it is important to understand whether the sheath will transition to an inverse mode within the observation time allotted. We establish a theoretical basis for defining transition time of the sheath in terms of plasma properties. Calculations include an analytical approximation for the length of the virtual cathode, the amount of charged particles in each layer of the space-charge-limited sheath, and a time for its transition to the inverse sheath. The theoretical model is then compared to 1D kinetic simulations of a space-charge-limited sheath with charge-exchange collisions present. The results are applied to estimate transition time scales for applications in laboratory plasma experiments, the lunar sheath, and tokamaks.

Authors:

Johnson, G. R. ^[1]; Campanell, M. D. ^[1]

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+ Show Author Affiliations

1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Publication Date:

Tue Apr 09 00:00:00 EDT 2019

Research Org.:

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1515340

Report Number(s):

LLNL-JRNL-749737
Journal ID: ISSN 1063-780X; 934698

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Accepted Manuscript

Journal Name:

Plasma Physics Reports

Additional Journal Information:

Journal Volume: 45; Journal Issue: 1; Journal ID: ISSN 1063-780X

Publisher:

Pleiades Publishing

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY