The hydrogen plasma produced by a coaxialE × Bgun located in a magnetic mirror system was extensively studied. When the gun was externally shorted (crowbarred) at peak avalanche current, the magnitude of the reverse current due to the angular momentum of the rotating plasma was found to depend on the axial position of the gun with respect to the upstream magnetic mirror. Microwave measurements gave a maximum electron density of 1.7 × 1013cm−3in the presence of neutrals of 1014cm−3with electron decay times of 300 to 400 &mgr;sec in the 1011to 1012per cm3range. Analysis of the optical spectra showed the presence of H, H2, Fe, Fe+, Cr, Cr+, Mn, Mn+, and Mo, and indicated that the electron temperature was approximately 5 eV. Evidence is presented which indicates that internal shorting of the discharge is the result of a low‐resistance path developing along the axial magnetic field lines to the downstream chamber walls. Floating probe measurements revealed that the electric field depended both on current and radial position, and showed little evidence of an anode sheath. Some measurements were also taken with helium and nitrogen as working gases.