CONSTRUCTION OF MAIN LINAC CRYOMODULE FOR COMPACT ERL PROJECT

A main linac cryomodule have been constructed for Compact ERL project. It contains two 9-cell cavities, mounted with HOM absorbers and input couplers. After cavity string assembly, they were installed into the vacuum vessel of the cryomodule. It was placed inside radiation shield of cERL and connected to a refrigerator system. The cryomodule was successfully cooled down to 2K and low power and high power measurements were carried out. COMPACT ERL PROJECT Compact ERL (cERL)[1, 2] is a test facility, which is now being constructed on the ERL Test Facility in KEK. Its aim is to demonstrate technologies needed for future multi GeV class ERL. One of critical issues for ERL is development of the superconducting cavities. Figure 1: Conceptual layout of the cERL project Table 1: Main Parameters for cERL Project Beam energy 35 – 245 MeV Beam current 10 – 100 mA Normalized emittance 0.1 – 1 mm mrad Bunch length 1 – 3 ps (usual) 100 fs (bunch compression) Conceptual layout of the cERL is shown in Figure 1 and its main parameters are shown in Table 1. At the first stage of cERL, minimum version of ERL will be constructed and electron beams of 10 mA will be accelerated up to 35 MeV. One main linac cryomodule with two 9-cell cavities have been constructed. MAIN LINAC CRYOMODULE Figure 2 shows a schematic view of the main linac cryomodule [3], which contains two 9-cell KEK ERL model-2 cavities [4] mounted with He jackets. Beampipetype ferrite HOM absorbers [5] are connected at both sides of cavities, to strongly damp HOMs. The HOM absorbers are placed on 80K region. Coaxial input couplers [6] with double ceramic windows feed RF power to the cavities. Frequency tuners [7] control cavity resonant frequencies. Cooling pipes of 80K, 5K and 2K are extended throughout the cryomodule. The 80K line was cooled by Nitrogen, and 5K and 2K lines were cooled by Helium. After filling with 4K liquid He, insides of the He jackets were pumped down and the cavities were cooled down to 2K. Figure 2: Schematic view of ERL main linac cryomodule