Abstract
The RF operation of the about 800 superconducting 1.3 GHz 9-cell cavities of the XFEL linac requires helium II bath cooling at 2 K, corresponding to a vapor pressure of 3100 Pa. After the first cool-down of the XFEL linac to 4 K in December, 27th 2016 the operation of the 2 K cryogenic system was started in January, 2nd 2017. The 2 K cryogenic system consist of a 4-stage set of cold compressors to compress helium vapor at a mass flow of up to 100 g/s from 2400 Pa to about 110 kPa and a full flow bypass with an arrangement of heat exchangers and control valves.This paper describes the XFEL refrigerating plant, especially the 2 K cryogenic system, the tuning of the cold compressor regulation to adapt to the XFEL linac static and dynamic heat loads and experience of about 6 months of operation.
Highlights
The about 800 superconducting 9-cell 1.3 GHz niobium cavities of the XFEL linac are cooled in a helium II liquid bath at a temperature of 2 K
The CB44 is located in the XFEL shaft building XSE, close to the valve box XLVB, the XFEL linac and the injector in order to reduce the distance induced pressure drop in the 2K return flow .The CB44 is connected to the XFEL refrigerator by the transfer line XRTL [1]. 2 K operation of the XFEL linac started in January 2017
cold compressors (CCs)-operation: Recovery after shutdown In case of a cold compressor shutdown, the XFEL linac/injector can be kept cold at 3060 Pa at static heat loads using a system of warm helium pumps, located in the Accelerator Module Test Facility (AMTF), dedicated to be used for module and cavity performance tests
Summary
The about 800 superconducting 9-cell 1.3 GHz niobium cavities of the XFEL linac are cooled in a helium II liquid bath at a temperature of 2 K. 2. The 2 K vapor return flow from the XFEL linac passes the counterflow heat exchanger in the XLVB and enters the CB44 at a minimum pressure of 2400 Pa. The helium is compressed by the CCs from 2400 Pa at 3.4 K to 0.11 MPa at 25 K. Based on the total pressure ratio of the four cold compressor stages, the set-pressure as well as the deviation to the measured suction pressure, four reduced speeds without units are calculated. The reduced mass flow versus the pressure ratio of each cold compressor stage can be charted to evaluate the current operating conditions. The required mass flow for the operation of the CCs is calculated by a PLC process control and supplied by the 2 K return flow from the XFEL linac/injector plus the CC-bypass flow.
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More From: IOP Conference Series: Materials Science and Engineering
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