Review of transport investigations with ECRH

Abstract

Localised heating of the electron component of plasmas using electron cyclotron waves has been used in a number of devices in an attempt to determine energy and particle transport. Results have been obtained from conventional power and particle balance analyses, analysis of sawteeth heat pulse propagation and by using phase sensitive detection of plasma perturbations induced by modulated ECRF power. Global particle confinement is generally degraded during ECRH; in most cases, a drop in ne is observed despite an increase in the edge particle source. Increased gas puffing can, however, maintain or raise ne. Local analysis of particle transport indicates higher particle diffusion and, possibly, a reduction of inward convection. Increases in the amplitude of fluctuations of poloidal magnetic field and plasma density in the scrape-off layer seem to be correlated with degradations in particle confinement. Global energy content typically follows an L-mode type of scaling but H-modes have been generated in diverted discharges. Some sensitivity to the shape of the power deposition profile is seen with localised central deposition being favoured. At low ne, when strongly non-Maxwellian electron distributions can be produced, tau E may be increased above the ohmic value. Analysis of temperature waves produced by modulating the ECRH power at frequencies approximately 1/ tau E gives values of the effective thermal diffusivity close to those obtained by other techniques.