CURRENT NEUTRALIZATION OF INTENSE MEV PROTON-BEAMS TRANSPORTED IN LOW-PRESSURE GAS

This paper reports on the first experiments designed to study ion-beam -induced gas ionization and subsequent conductivity growth using inten se proton beams transported through various gases in the 1-Torr pressu re regime. Net-current fractions of 2% to 8% are measured outside the beam channel. Ionization is confined predominantly to the beam channel with ionization fractions of a few percent. Analysis suggests that ne t currents are larger inside the beam channel and that fast electrons and their secondaries carry a significant fraction of the return curre nt in a halo outside the beam.