USE OF AN ACTIVE WIRE B-THETA CELL FOR ELECTRON-BEAM CONDITIONING

The propagation of intense, relativistic electron beams in air is subj ect to the resistive hose instability. Conditioning the beam prior to injecting it into the air can extend its range by reducing the hose gr owth rate and by reducing the initial spatial perturbations that seed the hose instability. Experiments have been performed using the SuperI BEX accelerator (I-peak=10-30 kA, E=4.5 MeV, 40 ns full width at half- maximum) to develop conditioning cells that suppress the hose. This pa per describes the performance of an active wire B-theta cell that is u sed in conjunction with an ion focused regime (IFR) cell. The IFR cell detunes the instability by producing a head-to-tail radius taper on t he beam. The wire eel maintains this radius taper while producing an e mittance taper that is necessary to suppress the hose growth. In addit ion, the wire cell reduces the initial beam perturbations through the anharmonic centering force associated with the wire current and its az imuthal magnetic field B-theta. The ability of the B-theta cell to red uce the beam offset with a minimal increase in the beam radius gives i t several advantages over the use of a simple, thick scattering foil t o perform the radius taper to emittance taper conversion. The SuperIBE X beam propagation distance, in terms of the betatron oscillation scal e length, was extended to similar to 10 lambda(beta) using these cells . (C) 1996 American Institute of Physics.