Gas release from metals under irradiation with elliptic Gaussian laser beam during LID-QMS analysis

Abstract Laser-induced-desorption quadrupole-mass-spectrometry (LID-QMS) diagnostics is considered as one of the candidate methods for the remote control of tritium inventory in the ITER first wall. Studies involving LID-QMS generally assume the circular shape of the laser spot on the analyzed surface. At the same time, the diagnostics laser source cannot be always positioned so as to irradiate tokamak tiles under normal angles, which results in the laser spot shape differing from the circular one. In this contribution, we analyze the tritium removal under sample irradiation by an elliptic Gaussian laser beam, extending the results of our previous analysis [A. A. Stepanenko and Y. M. Gasparyan, Phys. Scr. , vol. 99, no. 8, 2024, Art. no. 085604]. The thermal desorption model governing the heat transport and tritium removal from the solid is formulated. The new analytical expression describing the sample temperature dynamics is derived. The developed model is used to examine the impact of the laser beam/spot ellipticity on the tritium desorption from a tungsten sample. The conditions, under which the elliptic beam can be approximated with the circular one for the rapid assessment of the amount of desorbed tritium, are assessed.