Head-to-tail velocity tilt in an ion induction LINAC

Abstract

In the earlier stages of acceleration in a heavy‐ion‐induction linac, acceleration and bunching rates are constrained by the allowable value of head‐to‐tail velocity tilt at a given location. If focusing parameters at a given location are fixed, the velocity tilt should be less than a certain upper bound to avoid too much envelope variation and consequent beam losses. For space charge dominated beams, we found some favorable particle distributions in longitudinal phase space for which the maximum‐matched‐beam envelope at a given location is almost constant with respect to time, in spite of the presence of a large velocity tilt. Mismatch oscillations can be reduced by slow variation of the velocity tilt and slow current amplification. Under these circumstances, the velocity tilt can be as large as allowed by the usable range of σ0. Behavior of Cs ion beams with very large velocity tilts (up to 40%) are studied experimentally in MBE‐4 and the results are presented.