The potential relaxation instability in a helicon plasma

Journal Article · 15 June 2018 · Physics of Plasmas

DOI: https://doi.org/10.1063/1.5030430 · OSTI ID:1469551

Desjardins, Tiffany R.  ^[1]; Gilmore, Mark ^[1]

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1. Univ. of New Mexico, Albuquerque, NM (United States)

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.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE; National Science Foundation (NSF)
• Grant/Contract Number: AC52-06NA25396
• OSTI ID: 1469551
• Report Number(s): LA-UR--18-22463
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 6 Vol. 25; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English