G. C. Goldenbaum

Spectroscopic Investigation of Enhanced Plasma Oscillations in a High‐Voltage Theta Pinch

Intensity and frequency of fluctuating electric fields are obtained from a “plasma satellite” on the 21P ‐ 41D line of helium observed in the piston field of a collisionless shock. In contrast to second‐order perturbation theory only one satellite is seen. The perturbation theory is developed, therefore, to higher orders. Agreement between this theory and experiment is achieved. From the observed level of electric field fluctuations an effective collision frequency of about one‐fourth of the ion plasma frequency can be deduced.

Experimental studies of spheromak formation

Studies in the PS‐1 spheromak configuration can be effectively formed by a combined z‐ and θ‐pinch technique on both a fast (τformation≂τAlfven) and a much slower timescale. The gross tilt and shift instability of the toroid can be suppressed by a combination of conduction walls, shaping the separatrix by externally applied fields, and the use of ‘‘figure‐eight’’ coils. Optimum stabilty is obtained for almost spherical toroids. Maximum field‐reversal times for stable, well‐confined toroids are ≥40 /μsec, consistent with resistive decay. Temperatures during the stable decay are 5–10 eV; impurity radiation is an important energy‐loss mechanism.

Experimental spheromak MHD stability studies

Abstract The n = 1 tilt and radial shift instability of spheromaks is shown to be stabilized by the use of conducting wall ( r w r s ≅1.2) and stabilization coils.

Poloidal ion motion during formation of toroidal high beta plasmas

Spectroscopic measurements of the ion motion in a fast compression high beta tokamak experiment show paramagnetic ion motion. This motion is initially caused by magnetic field gradient drift, which does not produce any net paramagnetic current opposing the plasma diamagnetic current. After the crowbar of the fast rising toroidal magnetic field a larger paramagnetic polarization drift develops, which contributes to the disappearance of the diamagnetic well.

Critical field index for passive coil stabilization of the spheromak shift instability

The physics of a shifting spheromak plasma inside a passive stabilization coil is examined. Criteria for the design of these coils are derived for various spheromak current distributions. For realistic coils and force‐free plasmas a critical field index is derived, above which the coils are ineffective.

Electron and ion heating in a high‐voltage toroidal theta pinch with parallel or antiparallel bias fields

Rapid heating of electrons and ions has been observed in a high‐voltage toroidal theta pinch with initial bias fields either parallel or antiparallel to the fast rising toroidal field. The elimination of rapid end losses has permitted higher electron temperatures to be attained. In contrast to the results of linear theta pinches in which Te≲0.3 Ti, it is now found that Te∼Ti. The ion heating is similar to that observed in the linear case indicating that the effective microinstability heating process is maintained in a toroidal system. Higher temperatures were observed with antiparallel bias fields, but in both cases superthermal electron populations were observed indicating that the turbulent heating process involves electron tail formation.

Observations of a highly collisional toroidal plasma equilibrium

The time evolution of temperature and density profiles in a finite beta, noncircular cross section (b/a=2) toroidal plasma (R0/a=2) has been measured. Measurements show ion temperatures decreasing as the density is increasing along the major radius at the z=0 midplane. For these conditions, the electron temperature remains approximately uniform over the cross section. A recent theoretical model for highly collisional circular cross section plasma predicts qualitatively similar temperature and density profiles which are different from those for the less collisional Pfirsch–Schluter regime.

Observations of the nonlinear phase of a noncircular cross section toroidal kink instability

A low pressure region is observed to propagate from the boundary to the interior in the nonlinear phase of a toroidal kink instability.

Plasma heating in a high-voltage toroidal theta pinch

Rapid heating of ions and electrons to keV temperatures in approximately-less-than 1 ..mu..sec has been observed at densities of 1 x 10/sup 14/ cm/sup -3/. This is to be compared with experiments in which energy losses along the magnetic field limit the electron temperature. The most striking difference is in the electron- to ion-temperature ratio which is now approximately-greater-than 2 rather than approximately-less-than 0.3 as in comparable open-ended theta pinches.