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 Thermonuclear Experimental Reactor (ITER) is the creation of a low-pressure (∼10-mTorr) gaseous divertor. The divertor would have a long channel over which energy would be removed from the plasma by radiation, and the plasma pressure would be balanced by a change in flow velocities and neutral pressures entering the sides of the channel. This combination should substantially reduce the ion energy and ion flux that impact the eventual end of the divertor channel. For this concept to work, momentum must be removed from the plasma by the neutral atoms and molecules. Plasma parameters were taken from a DDC83 code solution. A Monte Carlo treatment of the plasma-neutral interactions has been obtained using DEGAS, which includes charge-exchange, recombination, ion-neutral, and neutral-neutral elastic collisions. Results show that the momentum transferred to the side walls is insufficient by two orders of magnitude to achieve the pressure reduction needed. Each molecule that enters the plasma makes hundreds of elastic and inelastic collisions in the plasma and then is more likely to be ionized (transferring the momentum back to the plasma) than to travel to a wall.