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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Upgrade the ratio is approximately 20:1.<br />
With the injector set to provide 56 MeV into the linac, 80 µA of cw beam, ac-<br />
celerated to 1056 MeV and energy recovered at 56 MeV, was steered to the energy<br />
recovery dump. Electron source problems, and not issues related to the energy re-<br />
covery process, limited operation to below the typical 100 µA average beam current.<br />
Changing the injection energy to 20 MeV, 1 µA of cw beam was energy recovered,<br />
after being accelerated to 1020 MeV. The low average current does not represent a<br />
fundamental limit, rather it reflects the lack of time available to optimize the ma-<br />
chine for handling the increased beam losses observed at this lower injection energy.<br />
An understanding of how the emittance evolves can be gained by making mea-<br />
surements at several locations in the machine. The results for the two machine<br />
configurations, Einj = 56 MeV and Einj = 20 MeV, are summarized in Fig. 2.20 and<br />
Fig. 2.21, respectively. The arc 2 emittance data in Fig. 2.20 has been removed for<br />
reasons discussed in Section 2.4.5. Qualitatively, the emittances for each machine<br />
configuration evolve in a similar manner. Moreover, it can be concluded that the<br />
process of energy recovery does not degrade the transverse emittance, since the emit-<br />
tance growth on the accelerating pass is consistent with the growth on the energy<br />
recovery (decelerating) pass.<br />
Quantifying beam loss is vital for the next generation of ERLs which propose<br />
to operate with megawatt beam powers and where even small amounts of beam loss<br />
can severely damage machine components. While the beam loss in CEBAF-ER was<br />
not measured directly, an upper limit of 0.5 µA can be used due to the fact that a<br />
stable machine configuration with 80 µA of cw beam was established and did not<br />
cause machine trips due to the beam loss accounting system. As a result, the beam<br />
loss in CEBAF-ER is comparable to the beam loss in standard CEBAF operations<br />
[36]. A summary of beam loss in the FEL Demo, CEBAF and CEBAF with energy<br />
recovery is given in Table 2.6.<br />
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