Speaker
Description
Determining tritium concentration within plasma facing components (PFC) of a thermonuclear reactor is crucial in terms of safety. As an example, tritium implantation can be high at the material surface (10-2 % at in W) and low in the bulk of the PFC (10s of ppm). In addition, a simultaneous implantation of tritium, deuterium and helium takes place. An in situ technique used to measure concentrations must enable isotopic discrimination and the access to T/D/He concentration profiles. In these conditions, Laser-Induced Breakdown Spectroscopy (LIBS) seems to be an appropriate method.
LIBS is based on the interaction of a high energy laser pulse and the material. The irradiated material is ablated and transformed into low temperature thermal plasma whose spectroscopic analysis provides its composition and therefore that of the material.
LIBS using nanosecond pulses has been proved to be irrelevant [Mercadier et al, Journal of Nuclear Materials 414 (2011) 485] in determining the D/T ratio in metallic samples, a specific experimental setup has been elaborated based on the implementation of picosecond pulses. Results obtained on samples implanted with hydrogen isotopes will be presented. The depth of craters following the ablation has been measured. With pulse energy of ~ 20 mJ, low ablation rates (~ 100 nm/pulse) are obtained. The plasma spectroscopic analysis is performed on the [200, 800] nm spectral range for W (for fusion), Al (as Be substitute) and Si (as benchmark) implanted with mainly D+ ions produced by plasma discharges or ion beams. Temporal studies have been performed to identify the appropriate time window compatible with a plasma in thermochemical equilibrium. We will finally present concentration profiles obtained with a double pulse technique, when a second (5 ns) laser pulse is absorbed by the plasma to increase the signal to noise ratio and enables the measurement of He.
