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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ized. And while it did not provide complete suppression, the local reflector is rou-<br />
tinely used in beam operations to achieve high average currents in the FEL Driver.<br />
In October 2006, the reflector was activated when the FEL achieved 14.3 kW of laser<br />
power at 1.6 microns by running 8 mA of average beam current in cw mode [92].<br />
Despite the ability of the rotator to stabilize the dangerous mode, caution<br />
should be exercised when intentionally introducing strong betatron coupling. While<br />
it is possible to manipulate the transfer matrix to create reflections and rotations,<br />
internal mismatch can generate beam loss that limits machine performance just as<br />
readily as BBU [93]. This proved to be the case when implementing the rotator and<br />
is the reason for the limited number of data points measured.<br />
Demonstrating through simulations that the threshold current can be made<br />
sufficiently high through the use of these coupled optics is one issue. An equally<br />
important issue is the operational ramifications of such schemes; that is, meeting<br />
the stringent requirements and maintaining sufficient control of a transversely cou-<br />
pled beam. Take for example the largest scale energy recovery experiment to date,<br />
CEBAF-ER, where coupled transverse motion was evident as a result of the fields in<br />
the cavity HOM couplers. As it was discovered, trying to thread a coupled, energy<br />
recovered beam through 200 m of linac, though possible, is a formidable task.<br />
While optical suppression techniques remain promising, ultimately, stronger<br />
HOM damping must be provided in future high current ERL applications.<br />
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