Properties of convective cells generated in magnetized toroidal plasmas

Abstract

Parallel resistivity and ohmic heating of laboratory dipole plasmas Phys. Plasmas 19, 082509 (2012) Influence of charging process and size distribution of dust grain on the electric conductivity of dusty plasma Phys. Plasmas 19, 083703 (2012) Stationary electron velocity distribution function in crossed electric and magnetic fields with collisions Phys. Plasmas 19, 083503 (2012) Measurements of parallel electron velocity distributions using whistler wave absorption Rev. Sci. Instrum. 83, 083503 (2012) Additional information on Phys. Plasmas Convective cells for turbulence control, generated by means of biased electrodes, are investigated in the simple magnetized toroidal plasmas of TORPEX. A two-dimensional array of 24 electrodes is installed on a metal limiter to test different biasing schemes. This allows influencing significantly both radial and vertical blob velocities. It is shown that these changes agree quantitatively with the flows deduced from the time averaged potential perturbations induced by the biasing. Detailed measurements along and across the magnetic field provide a rather clear picture of the effect of biasing on time averaged profiles. The biased electrodes produce perturbations of the plasma potential and density profiles that are fairly uniform along the magnetic field. Background flows influence the location where potential variations are induced. The magnitude of the achievable potential variations in the plasma is strongly limited by cross-field currents and saturates at large bias voltages once the electrodes draw electron saturation current. A quantitative discussion on the origin of cross-field currents is presented, considering contributions related with diamagnetic drifts, ion inertia, collisions with neutrals, and viscosity.

Edge sheared flows and the dynamics of blob-filaments

“…Judiciously driven sheared flows in the SOL could increase the SOL width, likely at the expense of edge confinement, such as the 'reverse' flows shown in figure 6(e) which enhance the blob ejection velocity due to polarization charge interactions. These flows could be produced by toroidally symmetric biasing, in contrast to the toroidally dependent biasing studied elsewhere [78][79][80].…”

Plasma turbulence, suprathermal ion dynamics and code validation on the basic plasma physics device TORPEX

“…Analytical estimates, based on the drift-reduced Braginskii ordering valid in TORPEX, have been performed to evaluate the magnitude of the cross-field currents that presumably underlie the reduction of the potential variations with respect to the applied bias. These estimates show that the high level of cross-field currents necessary to explain the experimental observations cannot be accounted for by ion polarization currents, diamagnetic currents, or currents due to ion/electron-neutral collisions and gyro-viscous effects (Theiler et al 2012b;Fasoli et al 2013). …”

Validation of edge turbulence codes in a magnetic X-point scenario in TORPEX

“…Cross-talk among neighboring probe tips was evaluated to be negligible [41]. We also measured time-averaged fields by means of SLP (Slow Langmuir Probes) [42]. SLP is a radially-movable vertical array of 8 Langmuir probes spaced by 1.8 cm, each with a collecting area A SLP = 18.9 mm 2 .…”