SIMS analysis of isolated graphite probes exposed to a tokamak plasma

Summary

Probes made of graphite were exposed to deuterium plasma of the tokamak discharges. The probes were highly polished and annealed in vacuum to about 900 ° C 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.