Comparing Turbulence Characteristics by Finding Dimensionless Matches of Hydrogen and Helium Plasmas

This poster presents Langmuir and Mach probe data from UCLA’s Large Plasma Device (LAPD) to study change in electrostatic turbulence for dimensionless matching helium and hydrogen plasmas. Fully ionized dimensionlessly matched plasmas should have matching turbulence characteristics independent of plasma species. However, most astrophysical and experimental plasmas are either partially ionized or contain mixed-ion species where turbulence characteristics are less understood and studied. Plasmas in the LAPD are only about 50% ionized [1], which makes the LAPD an effective tool to evaluate the turbulence characteristics of partially ionized plasmas. Dimensionlessly matched experiments using hydrogen and helium from the LAPD are studied with a focus on the changes in normalized gradients, electrostatic turbulence and Mach flows. The dimensionless parameters used to match the helium and hydrogen plasmas are derived using a Buckingham Pi theorem-based method specific for the LAPD. Deviations in turbulence levels between plasma species can be attributed to differences in neutral content for hydrogen and helium due to strong differences in atomic and molecular interactions. Future work will focus on mixed-ion species to investigate how the turbulence growth rate changes in a mixed-ion plasma compared to partially ionized hydrogen or helium plasmas.

[1] Perks, Conor et al, Impact of the Electron Density and Temperature Gradient on Drift-Wave Turbulence in the Large Plasma Device, J. Plasma Physics, (2022)