Predictions of hydrogen isotopes inventory in Break Even Axisymmetric Mirror (BEAM)*

In this work, the retention of deuterium (D) and tritium (T) in plasma-facing components (PFCs) of a Break-Even Axisymmetric Mirror (BEAM) [1] is estimated for the two potential material choices: tungsten (W) and tantalum (Ta). The macroscopic rate equation code FESTIM (Finite Element Simulation of Tritium In Materials) [2] is used for several temperature conditions which represent operations with and without cooling of the PFCs. Firstly, the code is used to reproduce experimental thermodesorption (TDS) data for 95 eV D ions implanted at 550 K up to the high fluence of 3x10²⁵ D m^-2 in the set of three samples: W bulk, Ta bulk and cold-sprayed Ta on stainless steel [3]. This enables determination of energy and density of the intrinsic traps for D in the three samples that were irradiated and outgassed during TDS in laboratory conditions. The results are used to predict hydrogen isotope retention in the 2D geometry of the PFCs of BEAM, without considering the damage caused by the high-energy ion irradiation and neutron impact. In the end, the numerical results are compared with the theoretical retention maximum obtained using the SRIM implantation probability for W and Ta for the given distribution of escaping fast ions in BEAM and for a plasma duration of one hour. Finally, the effect of physical sputtering of W and Ta by energetic ions is discussed.