Developments in the Physics of High Current Linear Ion Accelerators

Abstract

Linear ion accelerators have been proposed for both high peak and high average current applications.1 The design of high-intensity linacs is strongly influenced by the requirement of providing sufficient focusing (confinement) for the beam to balance the effects of the space-charge (self-field) forces, which become important for high beam current. Longitudinal focusing is obtained by operation on the rising rf electric field, where both acceleration and phase stability are obtained. Strong transverse focusing results from electric or magnetic quadrupole lenses arranged in a quasiperiodic structure; in the drift-tube linac (DTL), these individual quadrupole elements are installed within the drift tubes. In a smooth approximation, the quadrupole lenses produce an equivalent linear continuous focusing force upon which is superimposed the local forces of individual lenses that create a flutter in the beam envelope.