Divergence control experiments on the SABRE extraction ion diode

Summary form only given. To support the development of a high-power extraction geometry light ion driver module for ICF (inertial confinement fusion) applications, the authors are investigating techniques for ion beam divergence measurement and control with a high-impedance applied-B extraction ion diode on the SABRE ten-stage linear induction accelerator (6 MV, 300 kA) at Sandia National Laboratories. Initial experiments have concentrated on divergence and beam uniformity measurements with an annular 4-MeV proton beam generated from a passive wax flashover ion source. This beam is transported through the return flux of the cathode magnetic field coils inside a static fill gas cell containing argon or nitrogen at 1 to 20 Torr. Divergence accounting is in progress to evaluate the contributions to divergence growth from ion source divergence and nonuniformity, electromagnetic instabilities in the anode-cathode gap, instabilities in the gas cell transport region arising from incomplete charge neutralization in a strong transverse magnetic field, and additional contributions from foil scattering and gas transport.