Development of laser-based diagnostics for surface characterisation of wall components in fusion devices

Abstract

Laser-based techniques in combination with spectroscopy are proposed for in situ characterization of the first wall in ITER. Three laser-based diagnostics, laser-induced desorption spectroscopy (LIDS), laser-induced ablation spectroscopy (LIAS) and laser-induced breakdown spectroscopy (LIBS) are under investigation in Forschungszentrum Jülich (FZJ) to determine the stored amount of tritium (“tritium retention”) and to characterize the layer deposition on the wall components in fusion devices (thickness, composition, growth rate). Demonstration experiments for LIDS, LIAS and LIBS were performed on TEXTOR and in the laboratory. An advanced ITER prototype version of these diagnostics is currently under preparation on TEXTOR based on coaxial laser beam injection and light detection with the possibility to scan certain wall areas in TEXTOR. It has been demonstrated that LIDS is a reliable diagnostic for the absolute determination of hydrogen isotopes retained on first wall components on the basis of a single laser shot in combination with local H α spectroscopy. LIAS and LIBS are presently under investigation with respect to their capability to monitor reliably in situ the thickness and composition of deposited layers on the first wall during and between plasma pulses, respectively. A preliminary design and the main parameters for the application of these methods at ITER are discussed.