SIMS analysis of isolated graphite probes exposed to a tokamak plasma

Probes made of graphite were exposed to deuterium plasma of the tokamak discharges. The probes were highly polished and annealed in vacuum to about 9000C previously. They were kept isolated from the wall. Each set of probes was irradiated by the plasma only for a few shots. The probes were either kept floating or biased to -45 V or +45 V. The corresponding floating potential of or the net current to each probe was measured as a function of time during the pulsed discharge. Subsequently, the probes were removed from the ASDEX to the laboratory under the gas pressure of argon and placed in the SIMS-device UMPA. The mass spectra and depth profiles of different isotopes were obtained by using Ar+ ions of 2.4 keV and 1 nA. The impurities, recycling and other plasma parameters can be determined from these measurements. (orig.)