e-/H- Plasmas: Enhanced Centrifugal Separation and Other Disparate Mass Effects

Recent experiments quantify the strong centrifugal separation effects in e-/H- plasmas, here cylindrical columns with ne~10^7/cm3, Bz~10.kG, T~25.meV, and H- fraction 1% to 20%. Most striking is the outward transport of H- on the sub-second timescale, substantially faster than the 10^4 sec predicted for collisional drag between species. [1]  Here, the H- ions couple to the collective diocotron mode, causing algebraic damping of the mode at a rate proportional to the H- creation and outward transport.  The thermalization of axially hot H- ions onto cold electrons is observed to be 20-40 times slower than expected for radially-overlapping species.  In contrast, H- ions perp-heated by ICRH couple energy rapidly to parallel e- motion, suggesting a collective process. Similarly, the "inter-species drag" damping of excited TG waves depends strongly on their radial mode number.  The recently developed "plasma modes thermometer" comparing diocotron and T-G mode frequencies provides quantitative non-destrictive information on the plasma temperature and H- fraction evolutions;  but quantitative analysis of collisional and collective species couplings necessitates a MCP dump diagnostic imaging H-.  [1] A.A. Kabantsev et al, AIP Conf. Proc. 1928, 020008 (2018).