NEUTRAL ATOM AND MOLECULAR-TRANSPORT IN A GASEOUS DIVERTOR

The Monte Carlo code DEGAS with the addition of ion-neutral elastic collisions was used to evaluate the ability of a dynamic gaseous divertor to remove power to the side waifs through charge exchange and ion-neutral elastic collisions. The geometry simulated was a louvered ITER divertor. The plasma parameters for each of the four toroidal slices simulated was taken from PLANET, a 2D plasma fluid code. Results show that only in the initial hottest region of the plasma extending into the divertor throat do neutrals carry away significant energy. Even in this region at most 0.1 MW/m(2) is removed to the side walls by neutral atoms for a pressure behind the louvers of 10 mTorr. Given the proposed area of the side walls and 30 cm of hot region extending into the divertor channel, less than 10 MW of the 200-300 MW of input power are removed. This occurs because an individual atom undergoes many charge exchange and ion elastic collisions before returning to the wall. The chance for ionization during the multiple charge exchange and elastic collisions is higher in general than the chance of exiting the plasma region.