STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
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<strong>STUDIES</strong> <strong>OF</strong> <strong>ENERGY</strong> <strong>RECOVERY</strong> <strong>LINACS</strong> <strong>AT</strong> JEFFERSON LABOR<strong>AT</strong>ORY<br />
1 GeV Demonstration of Energy Recovery at CEBAF and Studies of the Multibunch, Multipass<br />
Beam Breakup Instability in the 10 kW FEL Upgrade Driver<br />
ABSTRACT<br />
An energy recovering linac (ERL) offers an attractive alternative for generating intense elec-<br />
tron beams by approaching the operational efficiency of a storage ring while maintaining the<br />
superior beam quality typical of a linear accelerator. Two primary physics challenges exist in<br />
pushing the frontier of ERL performance. The first is energy recovering a high energy beam while<br />
demonstrating operational control of two coupled beams in a common transport channel. The sec-<br />
ond is controlling the high average current effects in ERLs, specifically a type of beam instability<br />
called multipass beam breakup (BBU). This work addresses each of these issues.<br />
A successful 1 GeV energy recovery demonstration with a maximum-to-injection energy ratio<br />
of 51:1 was carried out on the Continuous Electron Beam Accelerator Facility at Jefferson Labo-<br />
ratory in an effort to address issues related to beam quality preservation in a large scale system.<br />
With a 1.3 km recirculation length and containing 312 superconducting radio frequency (SRF)<br />
cavities, this experiment has demonstrated energy recovery on the largest scale, and through the<br />
largest SRF environment, to date.<br />
The BBU instability imposes a potentially severe limitation to the average current that can<br />
be accelerated in an ERL. Simulation results for Jefferson Laboratory’s 10 kW free electron laser<br />
(FEL) Upgrade Driver predict the occurrence of BBU below the nominal operating current. Mea-<br />
surements of the threshold current are described and shown to agree to within 10% of predictions<br />
from BBU simulation codes. This represents the first time the codes have been benchmarked with<br />
experimental data. With BBU limiting the beam current, several suppression schemes were de-<br />
veloped. These include direct damping of the higher-order mode using two different cavity-based<br />
feedbacks and modifying the electron beam optics. Each method increased the threshold current<br />
for stability. Beam optical control methods proved to be so effective that they are routinely used<br />
in normal operation of the 10 kW FEL Upgrade.<br />
CHRISTOPHER D. TENNANT<br />
DEPARTMENT <strong>OF</strong> PHYSICS<br />
THE COLLEGE <strong>OF</strong> WILLIAM AND MARY IN VIRGINIA<br />
KEITH GRIFFIOEN<br />
PR<strong>OF</strong>ESSOR <strong>OF</strong> PHYSICS