In situ characterisation of hydrocarbon layers in TEXTOR by laser induced ablation and laser induced breakdown spectroscopy

Laser based methods in combination with spectroscopy are proposed for in situ characterisation of the first wall in ITER and are tested presently and applied in TEXTOR. A ruby laser is used to heat up a defined area at a surface of a test limiter, which then leads to ablation. The released particles are observed spectroscopically either at the surface or in the edge of the tokamak plasma. The absolute calibration affords the knowledge of the ablation process, especially the ablated debris compounds as a function of laser energy. Beyond that, the interaction of the released material with the edge plasma and the atomic and spectroscopic data of the species must be known, e.g. breakup of clusters and molecules, ionisation and excitation of atoms. In laboratory experiments the ablation process has been investigated in detail. Carbon test samples with known layer properties are exposed by laser radiation in laboratory and in TEXTOR with comparable power densities.