EXPERIMENTAL SIMULATION OF THE GASEOUS DIVERTOR CONCEPT IN PISCES-A

The concept of the reentrant divertor (or gaseous divertor) has been suggested as a possible solution to the divertor heat load problem in next generation tokamaks. The idea of the reentrant divertor is to redistribute the divertor heat flux over a large surface area by radiation and/or elastic and inelastic collisions with neutral particles. Simulation experiments are performed in the PISCES-A linear plasma device to test the basic concept and to evaluate the axial and radial particle and heat transport. To date, data have been obtained in steady state hydrogen and argon plasmas at densities of up to 2 x 10(13) cm-3 and electron temperatures of 5-30 eV. With moderate gas feed (10 mTorr) to a simulated divertor slot (length 90 cm) we have observed the electron temperature to decrease axially from 25 eV to 3 eV. At higher neutral pressure (> 25 mTorr) a neutralizer regime is found, where the plasma density at the simulated divertor target can be reduced by more than two orders of magnitude. Radial plasma loss is proportional to the neutral pressure and greatly enhanced as compared to the Bohm rate and the classical diffusion rate. The axial plasma heat flux to the divertor target is reduced by a factor of up to 2 x 10(3).