Abstract
The transport of thermal plasma and fast ions in electrostatic microturbulence is studied. Strong density and potential fluctuations (δn/n∼δφ/kTe ∼ 0.5, f ∼ 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 × B drift through biasing the obstacle and by modification of the axial magnetic fields (Bz) and the plasma species. Cross-field plasma transport is suppressed with small bias and large Bz and is enhanced with large bias and small Bz. The transition in thermal plasma confinement is well explained by the cross-phase between density and potential fluctuations. Large gyroradius lithium fast ion beam (ρfast/ρs ∼ 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 (Er) from biasing the obstacle leads to drift of the fast-ion beam centroid. The drift and broadening of the beam due to static Er are evaluated both analytically and numerically. Simulation results indicate that the Er induced transport is predominately convective.
Highlights
Plasma transport in turbulent waves is very important both in fusion experiments and in space physics
Two experiments have been performed at the large plasma device20 (LAPD) to study the transport of both thermal plasma and fast ions in electrostatic turbulent waves
This paper summarizes the main results reported in earlier publications about the thermal22 and fast-ion23,24 transport in these LAPD experiments
Summary
Plasma transport in turbulent waves is very important both in fusion experiments and in space physics. It is demonstrated that the E Â B drift induced by external bias can trigger an H-mode like state in plasma The mechanism of this confinement transition has been further studied in experiments.. Two experiments have been performed at the large plasma device (LAPD) to study the transport of both thermal plasma and fast ions in electrostatic turbulent waves. This paper summarizes the main results reported in earlier publications about the thermal and fast-ion transport in these LAPD experiments. It includes new material on a possible source of uncertainty in the fast-ion transport experiment: the effect of the static electric field on the fast ion beam. The results of the thermal plasma and fast-ion transport in electrostatic turbulent waves are briefly reviewed in Secs.
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