Emissivity toroidal asymmetries induced by ECRH driven convective fluxes in the TJ-II stellarator

Abstract

Intermittent toroidal asymmetries in the plasma edge emissivity have been detected in the TJ-II stellarator. During the toroidal radiation asymmetry phase (TRAP), sharp up and down jumps in electron cyclotron emission and total radiation are observed. The time resolved soft x-ray spectra also show changes in the suprathermal electron population. Given that the asymmetries reveal a variation in the wall desorption near the gyrotron port, TRAP is interpreted as a sudden increase of electron cyclotron resonance heating (ECRH) driven convective flux of ripple-trapped suprathermal electrons. This effect occurs in most of the magnetic configurations explored to date and is strongly affected by the presence of low order rational surfaces. A first assessment of the implications of TRAPs for confinement in ECRH plasmas of the TJ-II device is presented.