Studies of inelastic collision effects on the alpha particle flux with the FOCUS code

The effect of inelastic collisions on the alpha particle flux to the divertor is studied using the FOCUS code [1]. FOCUS calculates the exact orbits of the alpha particles including elastic and inelastic collisions. It is written in CUDA and runs on GPUs. FOCUS can read equilibria reconstructed by EFIT and use the information provided by SOL codes (i. e. SOLPS-ITER [2]). The results of simulations performed with FOCUS for an ITER equilibrium are presented. We find that for low energy alpha particles (E< 150 keV), the addition of inelastic collisions produces a dramatic change in distribution of the flux, reversing the asymmetry between the inner and outer targets and increasing the flux to the dome region. At intermediate energies (150 keV< E<1 MeV ) the addition of inelastic collisions spreads the flux over a larger area, including the dome and its supporting structure, but does not reverse the asymmetry. Finally, at high energies (E > 1 MeV), were the reaction rates for the inelastic processes decrease rapidly, both cases give approximately the same result.

[1] C. F. Clauser, R. Farengo, H. E. Ferrari. Comp. Phys. Comm., in press (2018).

[2] H. Pacher et al., J. Nucl. Mater. 463 (2015) 591.