DESIGN OF AN ERL LINAC CRYOMODULE*

The Cornell Energy Recovery Linac (ERL) will nominally operate cw at 1.3 GHz, 2 ps bunch length, 100 mA average current in each of the accelerating and decelerating beams, normalized emittances of 0.3 mmmrad, and energy ranging from 5 GeV down to 10 MeV, at which point the spent beam is directed to a dump [1]. The cw duty and low emittance drive the choice of using superconducting RF. The cryomodule for the ERL will be based on TTF technology, but must have several unique features dictated by the ERL beam parameters. The main deviations from TTF are that the HOM loads must be on the beamline for sufficient damping, that the average power through the RF couplers is relatively low, and that cw beam operation introduces higher cryogenic heat loads. Several of these challenges were addressed for the Cornell ERL Injector, from which valuable fabrication and operational insight is being gained [2,3]. A cut-away CAD model showing the main features of the ERL Linac cryomodule is shown in Fig. 1. The present design incorporates six 7-cell SRF cavities, beamline HOM loads, one quadrupole, one set of X-Y steering coils, gate valves at each end, and is 9.82 m long. Details of a few aspects of the design at this early stage of development are presented below.