Reversed field geometry generated with a rotating e-beam

A reversed magnetic field configuration has been produced by injecting a rotating relativistic e-beam (1.2 MeV, 50 kA) along a 1.8 kG guide field into 85 μ, neutral H₂ (Typically, T_e=5 eV, n_e =5×10¹⁵ cm^-3). End-on photography, radial scans with Thomson scattering, and CO₂ interferometry are in agreement with an MHD equilibrium model fitted to measurements of the excluded flux and the beam-induced axial (ΔB_z) and azimuthal (B_θ) fields. The resulting magnetic field configuration is similar to a belt pinch, with cross-section length-to-width ratio of 20, and midplane β≈.5. The absence of hard x-ray emission after beam passage shows these fields are induced by plasma currents, rather than trapped beam electrons. After beam passage, ΔB_z remains constant until B_θ becomes small, at which time the plasma collapses radially as ΔB_z decays. No unstable motion is observed. The observed decay times of 3-4 μsec, and concurrent two-fold increase in T_e (obtained from H_β line-to-continuum data) are consistent with classical dissipation of the induced currents.