Observation of self-steering effects on the ITS 6-MeV linac

Beam centroid oscillations were induced in the ITS eightcell linear induction accelerator (LIA) by steering the beam near the entrance, and position measurement were then made at four locations through the linac. Measurements were in good agreement with code predictions, using the nominal accelerator values, for a collimated beam of ~0.3 kA, but to get reasonable agreement for the full 3-kA beam, it was necessary to increase the code value of injection voltage from its known value of ~3.7 MeV by ~300 kV, approximately the edge beam-potential depression (bpd). Subsequent simulations with the 3D PIC code LSP showed that centroid steering is described more accurately by the total rather than the kinetic energy of the beam. Modification of the beam dynamics code to eliminate the bpd resulted in good agreement with measurement for both 0.3- and 3-kA beams