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\ifmmode^\circ\else\textdegree\fi{}. 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.

Highlights

  • The relativistic klystron (RK) is a rf power source based on induction accelerator technology and conventional resonant output structures

  • Significant theoretical studies and experiments have been accomplished in support of the relativistic klystron two-beam accelerator concept since it was initially described by Sessler and Yu in 1987 [2,3]

  • The relativistic klystron two-beam accelerator (RTA) program was established at LBNL in 1996 to study engineering and physics issues related to the construction of RK’s suitable as rf power sources for TBA applications

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Summary

INTRODUCTION

The relativistic klystron (RK) is a rf power source based on induction accelerator technology and conventional resonant output structures. A critical feasibility issue is the 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 if the RK is to achieve competitive efficiency and cost with respect to other proposed power sources. The relativistic klystron two-beam accelerator (RTA) program was established at LBNL in 1996 to study engineering and physics issues related to the construction of RK’s suitable as rf power sources for TBA applications. The experiment described below studied a technique for suppressing the growth of the transverse instability for the beam line geometry of an RK.

BETATRON NODE SCHEME
10 R1 r pr
DESCRIPTION OF BNS EXPERIMENT
Injector
BNS section
RF COMPONENT DESCRIPTIONS
Dipole pillbox cavities
Capacitive button beam position monitors
50 Ω Coaxial Line
Cavity mode parameters
General comments on rf components
MEASUREMENTS
Growth as function of focusing
Growth along the beam line
Determining beam energy
CONCLUSIONS
Full Text
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