Abstract: Beam energy transfer and propagation in a fully ionized magnetized plasma

Abstract

The interaction of a relativistic electron beam (300–500 kV, 5–40 kA, ν/2<2) with a fully ionized magnetic mirror-confined plasma column (1012 cm−3<ne<5×1013 cm−3; 0.01<nb/ne<0.3) has been experimentally investigated. Beam density profiles have been obtained using a small Faraday cup with a thin foil-covered aperture, and by measuring the intensity of x rays generated in small targets. Spatially resolved current profiles have been measured with small magnetic flux loops. Beam energy has been determined by varying the foil thickness covering the Faraday-cup aperature and by graded-foil-absorber energy analysis of the target x-ray emission. The energy transfer to the plasma column has been measured with diamagnetic loops, and the ion energy distribution has been determined with a multichannel analyzer. Results indicate up to 8% transfer of the diode energy to heating of the plasma column with the energy per electron–ion pair increasing linearly with the beam to plasma density ratio nb/ne. Ion energy distribution with high energy tails is observed. Following beam injection, oscillations are observed on the plasma column which propagate with the Alven velocity. 80%–98% current neutralization is observed. From the decay of currents which persist after the passage of the beam, a plasma resistivity can be inferred for the plasma column which is three to four orders of magnitude greater than the Spitzer resistivity calculated for the plasma column.