A. E. Robson

Reversed‐field configuration generated by a rotating relativistic electron beam

A reversed‐field plasma confinement geometry has been produced by plasma currents induced by a rotating relativistic electron beam injected into 85 mTorr neutral hydrogen. The resulting belt‐pinch‐like configuration has a rectangular cross section, with length‐to‐width ratio of 20, and midplane β=0.5. An equilibrium model, fitted to measurements of the excluded flux and induced axial (ΔBz) and azimuthal (Bϑ) magnetic fields, is in agreement with the annular plasma observed with radial Thomson scattering scans, CO2 interferometry, and end‐on streak photographs. After beam passage, ΔBz remains constant for 5 μsec until Bϑ becomes small, at which time the plasma collapses radially. The observed decay times of 4 μsec and concurrent increase in Te (from 5 to 10 eV) are consistent with classical dissipation of the induced currents.

Formation of closed magnetic field line plasma systems using intense relativistic electron beams

Abstract Closed magnetic field plasma confinement geometries produced by plasma currents induced by rotating intense relativistic electron beams are discussed conceptually. Experimental evidence for the formation of such layers is presented.

Equilibrium and propagation of a rotating relativistic electron beam

This paper describes an experimental and theoretical study of a charge-neutralized, hollow, rotating relativistic electron beam propagating inside a metal tube in the absence of an external magnetic guide field. A model has been developed in which the radial equilibrium is derived from the force balance on the beam interacting with its self-field, and the velocity of propagation of the beam is derived from the power balance. The experimental results show close agreement with the predictions of the model.

The NRL frozen deuterium fiber Z‐pinch experiment

Previous experiments at NRL have shown z‐pinches formed from 60 to 125 micron diameter frozen D2 fibers were stable as long as the current was rising. At current peak the pinch went rapidly m=0 unstable and emitted 2.45 MeV neutrons whose total number scaled as I10. The maximum current was 640 kA with a rise time of 130 nsec. A new generator, called ZFX, has been built to increase the current through the pinch to up to 2 MA. In preliminary experiments with ZFX at currents of 450 kA, streak photos again shown the pinch is stable as long as the current is rising, except that the stable period has been extended to 300 nsec. X‐ray pinhole photos also show a straight, uniform pinch. The number of neutrons produced by the pinch when it goes unstable is consistent with the previously observed I10 scaling.

Compact toroid created by rotating relativistic electron beams

A hollow, rotating relativistic electron beam with ν/γ≫1 may be stably propagated inside an initially field‐free, closed metal tube containing neutral hydrogen at a pressure of about 100 mTorr. Under these circumstances the beam is charge neutralized but not current neutralized, and propagates at an equilibrium radius determined by the pressure balance of the self‐magnetic fields inside and outside the beam. The axial component of the magnetic field is in opposite directions inside and outside the beam, the total flux inside the tube being zero. During its passage the beam ionizes and heats the neutral gas such that when the beam pulse ends, the magnetic field of the beam is ‘‘frozen’’ into the resulting plasma. The plasma confinement configuration generated by a single beam is a reversed‐field linear pinch with an axial current which returns through the wall of the tube. To produce a completely closed plasma configuration, a second rotating electron beam is injected from the opposite end of the chamber b...