Plasma and neutral dynamics in a simulated tokamak gas target divertor

Abstract

A stationary, detached ionization front is observed in an experimentally simulated divertor plasma (nG3X 1019 mW3, kT,G20 eV) interacting with a hydrogen gas target. with a neutral hydrogen density, n0=2X 10Z1 me3, the electron temperature at the simulated divertor target is reduced to kTe tigrt w 2.5 eV. Up to 97% of the ele&on heat flux (G7 MW/m') is dissipated by dissociation and ionization losses and 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 $D) coupled plasma-neutral fluid model (incorporating radial particle transpo& 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 coefficient. 0 1995 American Institute of Physics.

Asymmetry of the Electron Distribution Function in the PISCES‐A Linear Divertor Simulator

“…The PISCES-A device is a linear reflex arc plasma source producing a magnetized (Bz10.02 T) plasma column of 1.3 m length [2]. The source plasma parameters (n 12x 1018 m-3, kTe S 20 eV) are similar to a typical tokamak scrape-off layer.…”

“…This code has been used to model the electron energy distribution function in the PISCES-A linear divertor simulator. Atomic and molecular neutral density profiles arc taken from measurements as well as fluid modeling reconstructions of PISCES-A experimental data [2]. Coulomb self-collisions of electrons are taken into account without approximation, while electron-ion collisions are linearized [3].…”

“…In this paper, we discuss measurements and modeling results of the upstreanddownstream asymmetry of the electron distribution function in the PISCES-A linear divertor simulator. The PISCES-A detached plasma experiments [2] are modeled with the kinetic lD2V-code ALLA [3]. We present a preliminary comparison of code results and electron energy measurements in PISCES-A made by two-sided Langmuir probes.…”

Observations of macroscopic oscillations of the detachment front for injection of H2, He, and Ne into the simulated baffled divertor

“…In this configuration, denoted herein as a baffled/closed divertor, the neutral leakage through the opening of the baffle is reduced by friction due to ion-neutral collisions. The friction effectively decreases the gas conductance of the opening, which is the so-called Ôplasma pluggingÕ effect [2,3]. This effect depends on the upstream plasma pressure at the opening of the baffle.…”

“…The plasma-gas interaction enhances plasma momentum loss along the field lines, and finally results in plasma detachment from the divertor plate. A number of studies on linear plasma devices concerning plasma detachment have been performed [2][3][4][5]. There is a potential issue that the gas-target divertor method may have negative effects on the high-confinement modes (H-modes) of core tokamak plasmas.…”