Beam dynamics experiments to study the suppression of transverse instabilities

Abstract

Two-beam accelerators based upon relativistic klystron's (RK's) have been proposed as power sources for future generation linear electron-positron colliders. These drivers are susceptible to several transverse beam breakup (BBU) instabilities. An experiment to study a particular technique (the ''betatron node scheme'') for ameliorating the high-frequency BBU has been performed at LBNL on a 1 MeV, 500 A induction accelerator beam. The results of this experiment are particularly important for RK, but apply to any system where the betatron phase advance between perturbing structures is an integral multiple of 180 . This phase advance is beneficial in linear accelerators as the instability growth changes from exponential to linear. In the experiment described below, the beam is contained in a solenoidal focusing channel, rf cavities are spaced every 60 cm, and growth in the transverse motion was measured as a function of phase advance. Details of the experiment and results are presented.

Cumulative beam breakup in linear accelerators with arbitrary beam current profile

“…In some high-current, low-energy accelerators [17,18] the BBU growth length is comparable to the cavity spacing. In those cases the continuum model would not be valid and the discreteness of the accelerator needs to be taken into account; thus they fall outside the scope of this work.…”