AN OVERVIEW OF THE CRYOMODULE FOR THE CORNELL ERL INJECTOR H. Padamsee, B.Barstow, I. Bazarov, S. Belomestnykh, M. Liepe, V. Medjidzade, R. L. Geng, V. Shemelin, C. Sinclair, K. Smolenski, M. Tigner and V. Vescherevich Laboratory for Elementary-Particle Physics, Cornell University, Ithaca, NY 14853 Abstract The first stage of the Cornell ERL project will be a 100 MeV, 100 mA (CW) prototype machine to study the energy recovery concept with high current, low emittance beams. In the injector, a bunched 100 mA, 500 keV beam of a DC gun will be compressed in a normal-conducting copper cavity and subsequently accelerated by five superconducting 2-cell cavities to an energy of 5.5 MeV. We present an overview of the cryomodule design along with the status of the 2-cell HOM-free cavity, the twin- input coupler and the ferrite HOM dampers. 1 INTRODUCTION The Laboratory of Elementary-Particle Physics, Cornell University, in collaboration with Jefferson Lab is exploring the potential of a Synchrotron Radiation User Facility based on a multi-GeV, low emittance, Energy- Recovery Linac (ERL) with a 100 mA CW beam[1]. The first stage will be a 100 MeV, 100 mA (CW) prototype machine to study the energy recovery concept with high current, low emittance beams[2]. A key element of this machine is a high brightness injector with every bunch filled , i.e. 77 pC/bunch at 1300 MHz [3]. The injector system needs to deliver 500 kW to the beam through input coupling devices, typically antennae that protrude into the beam pipe. . Beam energy is not recovered in the injector. More than a hundred watts per cavity of beam induced power must be removed through HOM couplers. Both power delivery and extraction must be accomplished without introducing emittance-diluting asymmetries. Fig 1 gives an overview of the cavity string of the injector cryomodule. Fig. 1 The cavity string consists of five 2-cell cavities, dual input couplers and beam pipe HOM loads. 2 INJECTOR CAVITIES Fig.2 shows the basic cavity design and Table 1 lists the properties of the superconducting 2-cell niobium structures [4]. Most parts of the cavity assembly are complete and await electron beam welding. A copper model is also underway for HOM mode and damping evaluations. Fig.2: 2-cell injector cavity, input coupler ports and helium vessel disk. Table 1: RF properties of 2-cell superconducting cavities Frequency 1300 MHz Number of cells 2 R/Q 218 Ohm acc pk E E 1.94 acc pk E H 42.8 Oe/(MV/m) Coupling cell to cell 0.7 % Q0 at 2 K > 5!10 9 Twin-Input coupler Qext 4.6!10 4 / 4.1!10 5 Accelerating voltage 1 MV / 3 MV Max. power transferred to beam 100 kW Despite the presence of a large beam pipe to propagate out HOMs, the main cavity parameters are similar to those of the TESLA cavity. This was accomplished through the additional freedom of the cell length. The injector cavity has a thicker iris than for the TESLA cavity. The resulting cell-to-cell coupling is weaker (0.7 %), but still sufficient for two-cells. . 3 INPUT COUPLER Each cavity has two coaxial couplers (Fig.3 and Fig. 4), to minimize the coupler kick and keep the power delivered per coupler at a conservative 50 kW CW[5]. The couplers are variable, allowing the external Q to be Proceedings of EPAC 2004, Lucerne, Switzerland 491