Effect of neutral density and electron temperature on drift-wave turbulence in LAPD

Drift waves arise in all magnetized plasmas with cross-field pressure gradients, and drift-wave turbulence contributes to cross-field particle and heat transport (Rutherford & Goldston 1995). At the Large Plasma Device (LAPD), electron density and temperature gradients were found to drive drift-wave turbulence in the plasma edge region (Tynan et al. 2009, Carter et al. 2006). Drift-wave density fluctuations were positively correlated with density gradients. Small temperature gradients damped density fluctuations and inverted the cross-phase between density and potential fluctuations, reversing the direction of particle flux, while varying neutral fill pressure shifted parallel flow profiles and resulting drift-wave potential fluctuations (Perks et al. 2022). Recent experiments at LAPD use a new LaB6 cathode to access higher electron densities and temperatures. The gas puffing was varied to study the effect of neutral density on parallel flows and density and potential fluctuations, while the cathode current was varied to investigate the roles of temperature and density gradients. Data analysis is ongoing, but has revealed steep parallel pressure gradients, consistent velocity shear in the edge region, and non-linear increases in temperature and density with cathode current.