Pulse Risetime and Corkscrew Excitation of Beam Breakup in Linear Induction Accelerators

Beam breakup (BBU) in linear induction accelerators (LIA) used for flash radiography is problematic because the high-frequency beam motion can blur the source spot, thereby degrading resolution. BBU can be excited by the fast risetime of an offset current pulse, it can grow from noise due to other sources of RF, or it can be excited by the corkscrew motion of the beam head. In this article, numerical experiments are used to examine BBU excited by the fast risetime of the current pulse expected to be injected into an advanced LIA. Excitation by high-frequency corkscrew on the beam head is also investigated. The results of these simulations indicate that BBU can be expected to be excited by both fast risetimes and corkscrew.