Tokamak deposition probe analysis by laser ionization spectroscopy

Abstract

Laser analytical methods are used for the determination of surface sodium impurity distribution on silicon samples. In the first experiments, the spots on the surface of the sample were atomized by ruby laser pulses and the sodium atoms were selectively ionized by resonant ionization, thus the simple ion detection yielded the sodium surface contamination density. The second method applies excimer laser ablation, and the generated ions are analyzed and detected by a reflectron-type time-of-flight mass spectrometer. The analytical arrangements are applied for tokamak plasma investigations. Silicon plates as deposition probes located in the edge plasma region are exposed to several tokamak discharges, which are contaminated by pulsed sodium impurity injections. Surface analysis of the samples enables determining the sodium impurity fluxes in the tokamak edge plasma region, which are characteristic of particle transport properties. The high sensitivity of the method applying resonance ionization enables the analysis of single discharges, whereas the application of mass spectrometry offers the possibility of detecting several impurity materials.