Characterizing Near-Field Modifications from an Antenna in the Alfven Wave Range of Frequencies in the LArge Plasma Device (LAPD)

The Large Plasma Device (LAPD) is an 18 m long, 1 m diameter cylindrical device that in this experiment produces a magnetized plasma (n = 10¹²-10¹³ cm^-3, Te= 1-6 eV B= 1 kG)¹ capable of supporting Alfvén waves. Recent experiments with large amplitude (𝛿b/B ~ 0.1%) Alfvén wave has revealed far-field density and temperature modifications of up to 100% during the active phase of the discharge, in which the waves are in a kinetic regime. Previous studies in the LAPD have attributed these modifications to mechanisms such as Landau damping, collisional heating, ionization or near-field effects, but nevertheless their origin remains poorly understood. To isolate the effects of the large-amplitude waves in the far field to those close to the antenna, plasma parameters such as density, temperature, parallel flow, floating potential and magnetic field were measured in close proximity to the antenna. Significant modifications to density and temperature are observed, accompanied by parallel flow reversal, ExB flows and low frequency fluctuations in I_sat. These will be presented in this poster. Ongoing analysis aims to determine the mechanisms driving these changes, and their potential role in the observed far-field modifications.

¹W. Gekelman, et al., Rev. Sci. Instr., 87, 025105 (2016)