Transport of high current, relativistic electron beams using active-wire BΘ cell techniques

The high-current, relativistic electron beam (10–20kA, 5MeV, 40ns) of the SuperIBEX accelerator is transported from its diode to an experimental chamber along a wire that has an externally driven current flowing in the same direction as the electron beam current. The magnetic field from the wire current both guides the beam and smears out coherent radial beam oscillations. The wire cell is used to damp the initial radial motion to decrease the growth of the resistive hose instability in the air propagation region following the wire cell. Experimental parameters varied in this study include wire cell current (Iw<Ib) and cell gas pressure (full atmospheric pressure or vacuum). The effects of these parameters on the cell transport efficiency (Iout/Iin) beam pulse length (tp), and beam radial profile (Ib(r, t)) were measured with an array of diagnostics. The beam spatial profile was measured optically using Čerenkov light generated as it passed through a thin FEP teflon foil at the cell exit using an ultra-fast, 4 channel framing camera and one or more streak cameras. Electrical measurements included non-interceptive beam position monitors at the input and exit of the wire cell and a 5-element, segmented, concentric Faraday collector which could be mounted to intercept the beam. The results of this experiment are compared with theory and numerical simulations.