LASER-ABLATION IONIZATION MASS-SPECTROMETRY ON TOKAMAK DEPOSITION PROBES

Laser ablation-ionization mass spectrometric surface analysis was appl ied in plasma diagnostic experiments on the MT-IM tokamak. Non-intrins ic impurities were injected into the discharges using laser blow-off i n order to study the impurity transport processes. High purity silicon samples were used as deposition probes in the edge plasma of the toka mak. The distributions of the impurities deposited on the probe surfac es during the discharges were measured after the exposures by laser io nization mass spectrometry. In the first experiments with sodium impur ities the surface distributions showed a considerable poloidal depende nce besides the well known decrease with increasing minor radius. The poloidal dependence showed mirror-like symmetry on the probes facing t he ion and electron sides. In the second experimental series carried o ut with tungsten impurities even more localized deposit distributions were obtained. The results are explained assuming that the impurities propagate in confined packets along the magnetic field Lines even for several toroidal turns.