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 between the first beam and the wall. It is possible by this means to bring the persistent axial current to zero, but only under rather restricted conditions because the propagation of the second beam is adversely affected by the peripheral plasma produced by the first beam. However, the principal of this novel method of producing a magnetically confined plasma was effectively demonstrated.