MOMENTUM AND ENERGY-TRANSFER VIA NEUTRAL ATOMS AND MOLECULES IN AN INTERNATIONAL THERMONUCLEAR EXPERIMENTAL REACTOR LOW-PRESSURE (10-MTORR)GAS-TARGET DIVERTOR

One option for particle and power handling in the International Thermo nuclear Experimental Reactor (ITER) is the creation of a low-pressure (similar to 10-mTorr) gaseous divertor. The divertor would have a long channel over which energy would be removed from the plasma by radiati on, and the plasma pressure would be balanced by a change in flow velo cities and neutral pressures entering the sides of the channel. This c ombination should substantially reduce the ion energy and ion flux tha t impact the eventual end of the divertor channel. For this concept to work, momentum must be removed from the plasma by the neutral atoms a nd molecules. Plasma parameters were taken from a DDC83 code solution. A Monte Carlo treatment of the plasma-neutral interactions has been o btained using DEGAS, which includes charge-exchange, recombination, io n-neutral, and neutral-neutral elastic collisions. Results show that t he momentum transferred to the side walls is insufficient by two order s of magnitude to achieve the pressure reduction needed Each molecule that enters the plasma makes hundreds of elastic and inelastic collisi ons in the plasma and then is more likely to be ionized (transferring the momentum back to the plasma) than to travel to a wall.