Beam dynamics experiments in support of relativistic klystrons

Experiments to study beam dynamics for relativistic klystrons (RK) are being performed with a 1-MeV, 600-A induction accelerator beam. The RK is a RF power source based on induction accelerator technology and conventional resonant output structures. Capable of generating 100´s of MW/m at frequencies up to the K-band, the RK has been proposed as a driver for a future linear collider in one version of a two-beam accelerator. A critical feasibility issue remaining to be demonstrated is suppression of the transverse instability of the drive beam. This kiloampere beam must transit about a hundred resonance output structures and many hundreds of induction accelerator cavities for the RK to achieve competitive efficiency and cost with respect to other proposed power sources. The RK´s strong focusing used to contain the beam in the small aperture resonant structures, repetitive geometry, and reacceleration allow the resonant output structures to be spaced at a betatron phase advance of 360°. This phase advance (or any integral multiple of 180°) is beneficial in linear accelerators as the instability growth changes from exponential to linear. In our experiment the beam is contained in a solenoidal focusing channel, RF cavities are spaced every 60 cm, and growth in the transverse motion is measured as a function of phase advance. Details of the experiments and results are presented