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Title: The potential relaxation instability in a helicon plasma

Abstract

High positive grid biasing (>10T e) in a large-scale helicon plasma at the University of New Mexico has led to the excitation of large fluctuations (>50%) in ion saturation current and floating potential at a low frequency (100–300 Hz). Additionally, these fluctuations have been identified as an instability and have been studied under a variety of conditions, including variations in the bias voltage, magnetic field strength, and the length of the plasma column. A series of measurements with Langmuir probes has been used to analyze the characteristics of the fluctuations. The instability has been found to travel predominately along the axis with a speed of 1–3c s, where c s is the ion sound speed. The frequency of the mode is found to be dependent on the bias voltage. Increasing the grid bias leads to an increase in the frequency until a second critical voltage causes the fluctuations to disappear. The magnetic field and plasma length are found to affect the amplitude of the mode and the voltage range over which it exists. Finally, this mode has been identified as the potential relaxation instability.

Authors:
ORCiD logo [1];  [1]
  1. Univ. of New Mexico, Albuquerque, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE; National Science Foundation (NSF)
OSTI Identifier:
1469551
Report Number(s):
[LA-UR-18-22463]
[Journal ID: ISSN 1070-664X]
Grant/Contract Number:  
[AC52-06NA25396]
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
[ Journal Volume: 25; Journal Issue: 6]; 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

Citation Formats

Desjardins, Tiffany R., and Gilmore, Mark. The potential relaxation instability in a helicon plasma. United States: N. p., 2018. Web. doi:10.1063/1.5030430.
Desjardins, Tiffany R., & Gilmore, Mark. The potential relaxation instability in a helicon plasma. United States. doi:10.1063/1.5030430.
Desjardins, Tiffany R., and Gilmore, Mark. Fri . "The potential relaxation instability in a helicon plasma". United States. doi:10.1063/1.5030430. https://www.osti.gov/servlets/purl/1469551.
@article{osti_1469551,
title = {The potential relaxation instability in a helicon plasma},
author = {Desjardins, Tiffany R. and Gilmore, Mark},
abstractNote = {High positive grid biasing (>10Te) in a large-scale helicon plasma at the University of New Mexico has led to the excitation of large fluctuations (>50%) in ion saturation current and floating potential at a low frequency (100–300 Hz). Additionally, these fluctuations have been identified as an instability and have been studied under a variety of conditions, including variations in the bias voltage, magnetic field strength, and the length of the plasma column. A series of measurements with Langmuir probes has been used to analyze the characteristics of the fluctuations. The instability has been found to travel predominately along the axis with a speed of 1–3cs, where cs is the ion sound speed. The frequency of the mode is found to be dependent on the bias voltage. Increasing the grid bias leads to an increase in the frequency until a second critical voltage causes the fluctuations to disappear. The magnetic field and plasma length are found to affect the amplitude of the mode and the voltage range over which it exists. Finally, this mode has been identified as the potential relaxation instability.},
doi = {10.1063/1.5030430},
journal = {Physics of Plasmas},
number = [6],
volume = [25],
place = {United States},
year = {2018},
month = {6}
}

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