H. Zwi

Observation of a steady‐state field‐reversed equilibrium

Steady‐state quiescent field‐reversed configurations are produced in the toroidal UCLA RACETRACK [Rev. Sci. Instrum. 57, 2720 (1986)] by rotating magnetic fields. Observed pressure and magnetic field profiles agree with high β, rigid electron rotor theory. Full penetration of the right‐hand component of the rotating field and slight ion drag by the electrons were observed for the first time.

Mirror ratio scaling of axial confinement of a mirror-trapped collisional plasma

The axial confinement time of a single cell mirror is found to be proportional to the mirror ratio over the range of 12–74 when the mean free path for Coulomb collisions is less than one‐third of the length of the device. The reduction in total end‐loss current is shown to correspond to the reduction of the cross‐sectional area of the plasma at the mirror throat as the mirror ratio is increased. The end‐loss current density is independent of the mirror ratio and is proportional to the product of the plasma density and the acoustic speed.

RACETRACK: Novel device for basic research on magnetized plasmas

The construction and operation of a novel magnetized plasma device are described. The device combines characteristics of both linear mirror and toroidal confinement. It opens up new areas of basic plasma physics research. Examples of experiments on potential formation are presented.

Observation of a stable high‐beta axisymmetric plasma equilibrium

Stable, steady‐state plasma equilibrium is generated in an axisymmetric configuration. The diamagnetic current is maintained by electromagnetic fields rotating in the electron diamagnetic sense. The stable, free‐standing equilibrium exists for all values of beta up to 0.98, limited only by the available rf power. The plasma is centered on the axis well removed from the metal chamber walls, the limiters, and the rf antenna. The equilibrium pressure balance, J×B=grad p, is quantitatively verified. Radial profiles of pressure and magnetic field show that the equilibrium is that of a rigid rotor.

Balance of angular momentum and energy in a rotating‐field generated plasma equilibrium

The balance of energy and angular momentum is modeled for a rigid‐rotor plasma equilibrium generated by a rotating magnetic field. The model predicts that deviation from circular polarization of the rotating field and the presence of transverse stationary error fields reduce the efficiency of the diamagnetic current drive. The error field in combination with low collision frequency can prevent electron fluid corotation. In the RACETRACK experiment [Rev. Sci. Instrum. 57, 2720 (1986)], the measured power balance is in agreement with the measured rotating field polarization and the estimated magnitude of the stationary error field.

Observation of radio‐frequency field induced plasma loss in a simple mirror

High‐frequency parallel electric fields applied to plasmas confined in a simple magnetic mirror cause enhanced plasma loss. The plasma potential rises because of a population of electrons in the magnetic loss cone that are accelerated to parallel energies significantly higher than the bulk electron temperature. The radio‐frequency induced plasma loss has a nonambipolar component, with ions lost predominantly in the radial direction.

Spatial localization of bursts of the drift cyclotron loss cone instability

Spatial localization of bursts of the drift cyclotron loss cone instability in a mirror machine is caused by asymmetric motion of the background plasma. The dynamic behavior of the plasma determines the appearance of the instability

Power deposition and field penetration in a field‐reversed configuration generated by rotating magnetic fields

Power deposition profiles derived from measured equlibrium and field‐penetration profiles in the RACETRACK rotating magnetic field drived FRC are presented. It is found, that significantly higher RF power can be deposited in the plasma than what is necessary to maintain the diamagnetic current. The Klima relations are reconciled with the higher power input because the excess power is delivered by waves possessing zero net angular momentum. Only the right‐hand rotating component of the RF field penetrates fully, and this results in correct circular polarization of the fields on axis regardless of the imposed polarization by the antennas.