Development of Laser Based Techniques for In-situ Characterization of the First Wall in ITER and Future Fusion Devices

In situ methods to measure the fuel retention and to characterize the material deposition on the wall are highly important for ITER and future fusion devices. Laser-based methods are the most promising candidates (for non-invasive applications) and their feasibility is assessed in a cooperative undertaking in various European associations under EFDA coordination. The work concentrates on three different laser techniques in which the laser light is guided from outside the biological shield by a mirror system through a window onto special wall areas: i) laser induced desorption spectroscopy (LIDS) in which ms laser pulses thermally desorbs the retained fuel from a wall area of about 1cm2 and this fuel is spectroscopically detected in the edge of a running plasma, ii) laser induced ablation spectroscopy (LIAS) in which ns laser pulses ablates material from a small wall spot and the ablated material together with the incorporated fuel is detected in a similar way as in LIDS and iii) laser induced breakdown spectroscopy (LIBS) in which ns (or even ps ) laser pulses produce in front of the irradiated wall spot a plasma plume which (in proper conditions) emits line radiation being a fingerprint of the chemical composition of the ablated materials. The aims are to compare the pros and cons of the methods and propose an optimized solution for ITER. LIDS and LIAS have been developed in the TEXTOR tokamak to a prototype-like status for application in ITER. LIBS has been investigated in several EU laboratories in dedicated lab experiments with a focus on the particular conditions in ITER, including pilot experiments in the TEXTOR tokamak. To enable a clear and fair quantification of the methods, standard deposits of diamond like carbon (DLC) and mixed W/Al/C (with Al mimicing Be) with thicknesses of 2-3 μm deposited on rough and polished W substrates with a known D inventory were prepared using magnetron sputtering and vacuum arc deposition. They were used as reference samples in studies