Thermal load calculations at TJ-II vacuum vessel under neutral beam injection

The neutral beam power transmitted into the helical axis stellarator TJ-II is calculated for the final duct design of TJ-II The transmitted beam is in tercepted by the first toroidal field coil before reaching the plasma. The nontrapped fraction of the beam hits various vacuum vessel components. The adopted design of the graphite thermal shields used as vacuum vessel pr otection at TJ-II is presented. The design achieves a compromise between ma ximum power into the torus and minimum loads on sensitive parts. A three-dimensional version of the beam geometric code DENSE is set up to c alculate the power loads due to shine-through neutrals on the shields under these circumstances. Power load maps are the input to the finite element c ode ANSYS for the calculation of temperature distributions. For the usual duty cycle at TJ-II (300-ms pulses every 300 s), the peak sur face saturation temperatures at all surfaces remain under 650 degrees C, we ll below the tolerable limits for graphite.