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

A stationary, detached ionization front is observed in an experimental ly 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 tar get. With a neutral hydrogen -3, the electron temperature at the simul ated divertor target is reduced to density, n(0) approximate to 2X10(2 1) m(-3) kT(e) (target) approximate to 2.5 eV. Up to 97% of the electr on heat flux (less than or equal to 7 MW/m(2)) is dissipated by dissoc iation and ionization losses ind hydrogen line radiation. The plasma p ressure is observed to peak near the ionization front, and a plasma fl ow reversal is observed in the region of reversed pressure gradient. C lassical momentum flow parallel to the magnetic held and anomalous cro ss-field particle transport are found. The plasma flow is strongly dam ped 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 th at the electron heat flow is classical and well described by a harmoni c flux limit. The scale length of the parallel plasma pressure gradien t in a gas target is found to depend on the neutral density, the elect ron temperature, and the cross-field diffusion coefficient. (C) 1995 A merican Institute of Physics.