PLASMA AND NEUTRAL DYNAMICS IN A SIMULATED TOKAMAK GAS-TARGET DIVERTOR

A stationary, detached ionization front is observed in an experimentally simulated divertor plasma (n less than or equal to 3x10(19) m(-3), kT(e) less than or equal to 20 eV) interacting with a hydrogen gas target. With a neutral hydrogen -3, the electron temperature at the simulated divertor target is reduced to density, n(0) approximate to 2X10(21) m(-3) kT(e) (target) approximate to 2.5 eV. Up to 97% of the electron heat flux (less than or equal to 7 MW/m(2)) is dissipated by dissociation and ionization losses ind hydrogen line radiation. The plasma pressure is observed to peak near the ionization front, and a plasma flow reversal is observed in the region of reversed pressure gradient. Classical momentum flow parallel to the magnetic field and anomalous cross-field particle transport are found. The plasma flow is strongly damped by ion-neutral collisions and is subsonic. Numerical results from a one-and-one-half dimensional (1 1/2-D) coupled plasma-neutral fluid model (incorporating radial particle transport, recycling, and neutral gas injection) agree well with the experimental data, and indicate that the electron heat flow is classical and well described by a harmonic flux limit. The scale length of the parallel plasma pressure gradient in a gas target is found to depend on the neutral density, the electron temperature, and the cross-field diffusion coefficient. (C) 1995 American Institute of Physics.