Theoretical studies of the ion-hose instability in a plasma-focused free-electron laser

摘要

An 'ion-focused' relativistic electron beam traversing a magnetic wiggler is subject to a transverse two-steam or 'in-hose' instability, resulting from the coupling of transverse displacements of the beam centroid to the 'slosh' motion of the (beam-focused) nonneutral ion plasma, and driven by the 'V*B' deflection in the wiggler field. The equations of motion are resolved into an inhomogeneous 'beam breakup' equation, and asymptotic growth is computed in the limit of linear focusing. The effect of nonlinearities is assessed numerically with a 'distributed-mass' model. As examples, ion-hose growth is considered in a UV FEL and a microwave FEL two-beam accelerator.