Cryogenic sub-system for the 56 MHz SRF storage cavity for RHIC

Abstract A 56 MHz Superconducting RF Storage Cavity is being constructed for the RHIC collider. This cavity is a quarter wave resonator that will be operated in a liquid helium bath at 4.4 K. The cavity requires an extremely quiet environment to maintain its operating frequency. The cavity, besides being engineered for a mechanically quiet system, also requires a quiet cryogenic system. The helium is taken from RHIC’s main helium supply header at 3.5 atm, 5.3K at a phase separator tank. The boil-off is sent back to the RHIC refrigeration system to recover the cooling. To acoustically separate the RHIC helium supply and return lines, a condenser/boiler heat exchanger condenses the helium vapor generated in the RF cavity bath. A system description and operating parameters are given about the cryogen delivery system. INTRODUCTION A 56 MHz superconducting RF storage cavity is planned to be installed in the RHIC IP4 area to provide a large longitudinal bucket for stored bunches of ion beams and hence increase the luminosity of the RHIC machine. The RF cavity is cooled in a helium bath at 4.4 K. Two vacuum jacketed lines, one to the helium supply line (S) and another to the cold vapour return line (R), have been completed in summer 2009. The helium supply from S line always observes pressure fluctuations during normal operations due to changes in the cryogenic load requirements. The cold vapour return line is connected to the re-coolers around the two RHIC rings and the cold-box cold end. Its pressure also varies during normal operations. A warm helium gas return line (WR line) is for current lead flows and is connected to the main helium compressor skids. Its pressure also changes as the compressor loads change. The cryogenic system designed specifically for the 56 MHz RF cavity is described and the major component design and purchase schedule is also included. The pressures and temperatures in the RHIC distribution lines during normal operation are listed in Table 1. Table 1: RHIC Cryogenic System Parameters