(IT/P1-15) Laser Methods Development for in situ ITER Walls Detritiation and Deposition Layers Characterisation
1) CEA Saclay, Gif sur Yvette, France
2) Association Euratom-CEA, Cadarache, DSM/DRFC/SIPP, Saint Paul lez Durance, France
3) Association Euratom-Forschungszentrum Jülich, IPP, Jülich, Germany
4) Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, UK
Abstract. Laser methods for tokamak surface detritiation and characterisation have been under thorough multiaspect experimental and theoretical study in LILM laboratory (CEA Saclay, France). The graphite surface characterisation and cleaning with the pulsed repetition rate Nd-YAG laser systems were successfully realised. Heating and ablation regimes were distinguished by ablation threshold fluence. It was demonstrated that due to the significant difference in ablation thresholds for graphite (25 kJ per square meter) and a deposited layer (4 kJ per square meter), it was possible to decontaminate the graphite surface without its damage, if the laser fluence is lower than the ablation threshold for graphite. The ablation rate of the TEXTOR deposited layer was determined as 0.2 micrometer per laser shot. Thus, with the pulsed repetition rate lasers of 250 W mean power, a deposited layer of 20 micrometers can be removed with the rate of one square meter per hour. The developed laser facilities are very flexible and can be easily fixed on a robot for in situ surface characterisation and detritiation. The developed laser system will be installed onto AIA (Articulated Inspection Arm) robot on TORE SUPRA. The ablated matter will be aspirated by the nozzle fixed on AIA and collected on the aspirator filters. The integrated pyrometer system will be applied to record the surface temperature in laser heating regime (laser fluence below 4 kJ per square meter) with a high repetition rate Nd-YAG laser. The flexibility of the developed laser system is an important advantage. The same laser system (by adjusting appropriately the laser beam energy and spot) may allow to switch from heating regime (deposited layer depth estimation by pyrometer method) to ablation (where the layer depth is directly measured from the total ablation time) and to Laser Induced Breakdown Spectroscopy (LIBS) with laser plasma plume formation. A good agreement was demonstrated between the experimental results and the developed theoretical 3D model of surface heating (graphite + layer) that allowed to determine the deposited layer depth with micrometric accuracy. The preliminary studies have shown that analysis by LIBS method might be suggested to estimate tritium concentration in the material. Further goals and tasks to satisfy ITER requirements are discussed.
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