Simulation of Neutral Atoms and Molecules in an International Thermonuclear Experimental Reactor High-Pressure (1-Torr) Ultrahigh Recycling Divertor

The Monte Carlo code DEGAS was used to investigate the neutral atom and molecular interactions for a high-pressure (∼1-Torr) gaseous divertor in the International Thermonuclear Experimental Reactor (ITER). Energy is removed from the plasma by radiation while the plasma pressure is balanced predominantly by a high neutral pressure at the end of the divertor. Plasma parameters were taken from the two-dimensional fluid code PLANET. Neutral sources from both ions recycling off the walls and recombination were included. The neutral density peak calculated with DEGAS of 3.43 ± 0.01 × 10²² m⁻³ occurred 4.5 cm from the divertor channel end. The ion and neutral atom energy fluxes were calculated to determine the heat load onto the divertor walls. A code was written to calculate the radiation distribution onto the side walls, not including any radiative absorption or reemission. The total energy flux peak (including ions, neutrals, and radiation) was 4.28 ± 0.30 MW/m². This falls below the design criteria of 5 MW/m². These results may help determine the wall material, heat removal, and the vacuum pumping requirements for the ITER divertor design and show the importance of a full treatment of neutral atoms and molecules in these regimes.