High current proton beams in multi-stage linear induction accelerators

A 1-MV, 6-kA, 50-ns annular proton beam has been generated in a full-cusp-geometry diode and transported along a 0.6-T solenoidal magnetic field. The radial profile and transport efficiency were measured under different drift tube conditions using carbon activation. Faraday cup arrays gave time-resolved measurements of the net and ion current densities. The measurements showed that successful transport can be achieved by using a fast puff valve to fill the drift region immediately downstream of the full cusp with neutral gas. The exact neutralization process is still being studied, but it is thought that the plasma created from the neutral gas allows electrons to be pulled from the drift tube walls, neutralizing the space charge of the ion beam. Results have demonstrated beam transport efficiencies of 99% and maintenance of the annular beam profile throughout the drift region. The results have implications for the development of multistage induction accelerators.<>