Turbulent Fluctuations in a Flux-Rope Plasma at the Big Red Ball*

Observations of flux rope plasmas in the spherical BRB device at WiPPL are used to study turbulence and magnetic relaxation in plasma with beta between 0.25-1, flow speeds of approximately 20 km/s, and dB/B of approximately 12%. The flux ropes are generated via three plasma guns electrically biased relative to an anode on the opposite pole of the sphere, creating a current across the device.  Magnetic fields can be applied externally in either a solenoid or mirror geometry. We use zero-time-lag correlations of co-located density and parallel magnetic field measurements in order to study the character of MHD wave fluctuations in the plasma. Excitations are also observed in the ion-cyclotron range, pointing to possible ion heating from turbulent dissipation. We intend to measure ion temperature at various beta values in order to test predictions for ion heating to scale with beta [1] and are able to vary beta between 0.1 and 10 for these purposes. These measurements were taken along with similar density-magnetic field correlations at SSX.

[1] Kunz, M. W., et al. “Astrophysical Gyrokinetics: Turbulence in Pressure-Anisotropic Plasmas at Ion Scales and Beyond.” Journal of Plasma Physics, vol. 84, no. 2, 2018, p. 715840201.