Turbulent Particle And Thermal Transport In Magnetized Plasmas PDF Download

Three experiments are conducted to study the effect of the turbulent waves on the transport of fast ions and thermal plasmas. In the first experiment, strong drift wave turbulence with linear geometry is observed in the Large Plasma Device (LAPD) on density gradients produced by a plate limiter. Energetic lithium ions orbit through the turbulent region. Scans with a collimated ion analyzer and with Langmuir probes give detailed profiles of the fast ion spatial distribution and the fluctuating fields. The fast-ion transport decreases rapidly with increasing fast-ion gyroradius. Unlike the diffusive transport caused by Coulomb collisions, in this case the turbulent transport is super-diffusive. Analysis and simulation suggest that such super-diffusive transport is due to the interaction of the fast ions with the low-frequency two-dimensional electrostatic turbulence. The second experiment studies the dependence of the fast ion transport on the nature of the turbulent waves. Strong turbulent waves with cylindrical geometry are observed in the LAPD on density gradients produced by an annular obstacle. The characteristics of the fluctuations are modified by changing the plasma species from helium to neon, and by modifying the bias on the obstacle. Different spatial structure sizes and correlation lengths (Lcorr) of the wave potential fields alter the fast ion transport. The effects of electrostatic fluctuations are reduced due to gyro-averaging, which explains the difference in the fast-ion transport. A transition from super-diffusive to sub-diffusive transport is observed when the fast ion interacts with the waves for most of a wave period, which agrees with theoretical predictions. The transport of thermal plasmas under electrostatic waves is explored in the third experiment. Sheared azimuthal flow is driven at the edge of a magnetized plasma cylinder through edge biasing. Strong fluctuations of density and potential are observed at the plasma edge, accompanied by large density gradient. Edge turbulence and cross-field transport are modified by changing the bias voltage on the obstacle and the axial magnetic field strength. In cases with low V bias and large Bz, improved plasma confinement is observed, along with steeper edge density gradients. The radially sheared flow induced by E x B dramatically changes the cross-phase between density and potential fluctuations, which causes the wave-induced particle flux to reverse its direction across the shear layer and forms a transport barrier. In cases with higher bias voltage or smaller Bz large radial transport and rapid depletion of the central plasma density are observed. Two-dimensional cross-correlation measurement shows that a mode with azimuthal mode number m=1 and large radial correlation length dominates the outward transport in these cases. Linear analysis based on a two-fluid Braginskii model suggests that the fluctuations are driven by both density gradient and flow shear at the plasma edge.