Ion beam analysis of surface probes used to study plasma boundary phenomena and first-wall interactions in JET

This paper describes a 1.6 MV tandem accelerator-based facility which has been used to measure deposit levels on collector probes that are exposed to plasma discharges in the JET tokamak. The region probed is at the edge of the plasma, of which the central temperature and current may be ∽108 K and 7 MA, respectively. The probes are transported entirely under ultrahigh vacuum conditions to the analysis chamber, wherein Rutherford backscattering, Nuclear reaction analysis, elastic recoil detection and particle induced X-ray emission may be performed. A second chamber in the same vacuum system offers the more surface specific techniques of Auger electron spectroscopy and X-ray photoelectron spectroscopy. The complete system enables the determination of time-resolved information (during the plasma pulse) and radial profiles of all the elements of interest (such as hydrogen, deuterium, carbon, oxygen, chromium, iron and nickel). The particular example cited is a study of erosion/deposition during a 3 MA ohmically heated reference discharge.