Surface analysis in fusion devices

Abstract

Fusion devices with magnetic confinement of a hot plasma show a considerable amount of interaction of the plasma with material wall surfaces. This interaction strongly influences, for example, the plasma behavior due to recycling of the discharge gas (hydrogen isotopes) and release of impurity atoms from the wall surfaces. In order to assess the various effects caused by plasma–wall interactions, surface analysis techniques have been successfully applied. Among the problems studied are wall conditioning, erosion, and redeposition of material in the discharge vessel, erosion mechanisms such as sputtering or arcing, and measurement of particle fluxes into and out of the plasma by using surface probes. A variety of surface analysis techniques is used in these investigations: Rutherford backscattering, nuclear reaction analysis, proton- and electron-induced x rays, Auger electron spectroscopy, scanning electron microscopy, secondary ion mass spectroscopy, etc. Some achievements and problems of surface analysis in fusion devices are outlined and illustrated by a number of examples from tokamak experiments.