Simulation of the Alcator C‐Mod Divertor with an Improved Neutral Fluid Model

We have simulated detachment in Alcator C‐Mod, using an improved neutral fluid model. It features a parallel neutral momentum equation, fully coupled to the ions, allowing parallel plasma momentum to be converted into neutral momentum, which is dispersed to the material walls due to the high neutral viscosity. The simulations reproduce the pervasive experimental feature that the plasma detaches gradually, starting at the strike point, while always remaining attached above the nose of the divertor channel. The strike point heat flux and current drop by an order of magnitude as 0.5% of carbon is introduced to induce partial detachment. The plate temperature remains at or above about 1 eV all the way out to the divertor nose, in agreement with the experimental data.