Application of pulsed laser irradiation for removal of hydrogen retained in tungsten

Abstract

For the purpose of removal of tritium retained in tungsten (W), pulsed laser irradiation has been applied. The laser light used here was the fourth harmonic of Nd: YAG laser (wavelength; 266nm, pulse width; 20ps, pulse frequency; 10Hz, laser energy up to 3mJ/pulse). Samples were pure W plates and those saturated with D by D2+ ion implantation at room temperature with using a 2.5keV ion gun. Released ions and molecules by the laser irradiation were measured by a time-of-flight mass spectrometer (TOFMS) and a quadrupole mass spectrometer (Q-mass), respectively. Ablation of W was observed by the laser irradiation with a deposited power density above 1.5×1011W/cm2 (3J/cm2/pulse) (an ablation threshold) and D removals below and above the ablation threshold were quite different. The most effective removal of tritium retained in W could be realized by the pulsed laser irradiation with the power density of just below the ablation threshold.