Electrostatic transport reduction induced by flow shear modification in a reversed field pinch plasma

Abstract

The E × B velocity and its shear have been modified in the edge of the RFX reversed field pinch experiment by a biasing experiment performed with electrodes inserted into the plasma. Causality between an increase in the E × B velocity shear and a decrease of the particle flux driven by electrostatic turbulence has been observed. The decrease of the particle flux has been found to be mainly due to a change of the relative phase between density and plasma potential fluctuations. The results confirm the role of sheared flow in transport suppression in reversed field pinches and show remarkable similarities with those found in other magnetic configurations.

Magnetic and electrostatic structures measured in the edge region of the RFX-mod experiment

“…The average features of these events have then been extracted by applying the conditional average method on time window widths adequate to their time scale. A frequency range of few hundreds of kHz has been used for the present analysis, close to the typical time scale which characterizes the particle transport flux measured in the edge region [15].…”

Experimental Evidence of Turbulent Transport Regulation by Zonal Flows

“…Thus, in the early phase of the ZF the cross phase α nE rather than the turbulent amplitudes is relevant for transport reduction as it was already emphasized in theoretical [34,35] works. Also biasing experiments indicated that shear flows mainly act on the cross phase [36,37,25].…”

Effects of a non-monotonic safety factor on the particle transport and diffusion in the case of a reversed magnetic shear

“…The particle diffusion coefficients are computed for different values of applied potential and compared to the ones of the monotonic profile of the safety factor [9,10,12]. Figure 2 shows the time evolution of the ratio of two diffusion coefficients calculated with the NMSF and the monotonic safety factor (MSF); for any value of applied potential the ratio Dr rnmp /Dr rmp (rnmp: reversed-non monotonic profile; rmp: reversed monotonic profile) is always less than one.…”