Thermal plasma and fast ion transport in electrostatic turbulence in the large plasma device

The transport of thermal plasma and fast ions in electrostatic microturbulence is studied. Strong density and potential fluctuations (delta n/n similar to delta phi/kT(e) similar to 0.5, f similar to 5-50 kHz) are observed in the large plasma device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky et al., Rev. Sci. Instrum. 62, 2875 (1991)] in density gradient regions produced by obstacles with slab or cylindrical geometry. Wave characteristics and the associated plasma transport are modified by driving sheared E x B drift through biasing the obstacle and by modification of the axial magnetic fields (B-z) and the plasma species. Cross-field plasma transport is suppressed with small bias and large B-z and is enhanced with large bias and small B-z. The transition in thermal plasma confinement is well explained by the cross-phase between density and potential fluctuations. Large gyroradius lithium fast ion beam (rho(fast)/rho(s) similar to 10) orbits through the turbulent region. Scans with a collimated analyzer give detailed profiles of the fast ion spatial-temporal distribution. Fast-ion transport decreases rapidly with increasing fast-ion energy and gyroradius. Background waves with different scale lengths also alter the fast ion transport. Experimental results agree well with gyro-averaging theory. When the fast ion interacts with the wave for most of a wave period, a transition from super-diffusive to sub-diffusive transport is observed, as predicted by diffusion theory. Besides turbulent-wave-induced fast-ion transport, the static radial electric field (E-r) from biasing the obstacle leads to drift of the fast-ion beam centroid. The drift and broadening of the beam due to static E-r are evaluated both analytically and numerically. Simulation results indicate that the E-r induced transport is predominately convective. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3695341]