NEUTRAL ATOM AND MOLECULAR-TRANSPORT IN A GASEOUS DIVERTOR

The Monte Carlo code DEGAS with the addition of ion-neutral elastic co llisions was used to evaluate the ability of a dynamic gaseous diverto r to remove power to the side waifs through charge exchange and ion-ne utral elastic collisions. The geometry simulated was a louvered ITER d ivertor. The plasma parameters for each of the four toroidal slices si mulated was taken from PLANET, a 2D plasma fluid code. Results show th at only in the initial hottest region of the plasma extending into the divertor throat do neutrals carry away significant energy. Even in th is 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 propose d area of the side walls and 30 cm of hot region extending into the di vertor channel, less than 10 MW of the 200-300 MW of input power are r emoved. This occurs because an individual atom undergoes many charge e xchange and ion elastic collisions before returning to the wall. The c hance for ionization during the multiple charge exchange and elastic c ollisions is higher in general than the chance of exiting the plasma r egion.