Abstract. Superconducting radio frequency (SRF) cavities for particle accelerators are at risk of failure due to sudden loss of vacuum (SLV) adjacent to liquid helium (LHe) spaces. To better understand this failure mode and its associated risks an experiment is designed to test the longitudinal effects of SLV within the beam tube of a scaled SRF cryomodule that has considerable length relative to beam tube cross section. The scaled cryomodule consists of six individual SRF cavities each roughly 350 mm long, initially cooled to 2 K by a superfluid helium bath and a beam tube pumped to vacuum. A fast-acting solenoid valve is used to simulate SLV on the beam tube, from which point it takes over 3 s for the beam tube pressure to equalize with atmosphere, and 30 s for the helium space to reach the relief pressure of 4 bara. A SLV longitudinal effect in the beam tube is evident in both pressure and temperature data, but interestingly the temperatures responds more quickly to SLV than do the pressures. It takes 500 ms (roughly 100 ms per cavity) for the far end of the 2 m long beam tube to respond to a pressure increase compared to 300 ms for temperature (approximately 50 ms per cavity). The paper expands upon these and other results to better understand the longitudinal effect for SRF cryomodules due to SLV.

Safe operation of superconducting radio frequency (SRF) cavities require design consideration of a sudden catastrophic loss of vacuum (SCLV) adjacent with liquid helium (LHe) vessels and subsequent dangers. An experiment is discussed to test the longitudinal effects of SCLV along the beam line of a string of scaled SRF cavities. Each scaled cavity includes one segment of beam tube within a LHe vessel containing 2 K saturated LHe, and a riser pipe connecting the LHe vessel to a common gas header. At the beam tube inlet is a fast acting solenoid valve to simulate SCLV and a high/low range orifice plate flow-meter to measure air influx to the cavity. The gas header exit also has an orifice plate flow-meter to measure helium venting the system at the relief pressure of 0.4 MPa. Each cavity is instrumented with Validyne pressure transducers and Cernox thermometers. The purpose of this experiment is to quantify the time required to spoil the beam vacuum and the effects of transient heat and mass transfer on the helium system. Heat transfer data is expected to reveal a longitudinal effect due to the geometry of the experiment. Details of the experimental design criteria and objectives are presented.

Abstract. This paper provides an overview of the current progress and near-future plans for the cryogenic system at the new Cryomodule Test Facility (CMTF) at Fermilab, which includes the helium compressors, refrigerators, warm vacuum compressors, gas and liquid storage, and a distribution system. CMTF will house the Project X Injector Experiment (PXIE), which is the front end of the proposed Project X. PXIE includes one 162.5 MHz half wave resonator (HWR) cryomodule and one 325 MHz single spoke resonator (SSR) cryomodule. Both cryomodules contain superconducting radio-frequency (SRF) cavities and superconducting magnets operated at 2.0 K. CMTF will also support the Advanced Superconducting Test Accelerator (ASTA), which is located in the adjacent New Muon Lab (NML) building. A cryomodule test stand (CMTS1) located at CMTF will be used to test 1.3 GHz cryomodules before they are installed in the ASTA cryomodule string. A liquid helium pump and transfer line will be used to provide supplemental liquid helium to ASTA.

Abstract. Superconducting spoke resonators (SSR1 and SSR2) envisioned for Project X will be developed in Fermilab and operated at temperatures down to 2 K in continuous wave (CW) mode. Each spoke cavity will be tested individually in a cryostat that replicates conditions in the longer multi-cavity cryomodules. This test cryostat has all the features of the longer cryomodules -magnetic shielding, 80 K thermal shield, multi-layer insulation, support post, and input coupler [1]. Fermilab is in the processing of retrofitting the existing test cryostat which was originally designed for operation at 4.5 K. This paper describes the design of the conversion of the current test cryostat, flexible transfer lines, helium relief system and cryogenics interface.

Abstract-The Linac Coherent Light Source (LCLS) atStanford Linear Accelerator Center (SLAC) is in the process of being upgraded to a superconducting radio frequency (SRF) accelerator and renamed LCLS-II. This upgrade requires thirtyfive 1.3 GHz SRF cryomodules (CM) and two 3.9 GHz CM. A cryogenic distribution system (CDS) is in development by Fermi National Accelerator Laboratory to interconnect the CM Linac with the cryogenic plant (CP). The CDS design utilizes cryogenic helium to support the CM operations with a high temperature thermal shield around 55 K, a low temperature thermal intercepts around 5 K, and a SRF cavity liquid helium supply and subatmospheric vapor return both around 2 K. Additionally the design must accommodate a Linac consisting of two parallel cryogenic strings, supported by two independent CP utilizing CDS components such as distribution boxes, transfer lines, feed caps and endcaps. The paper describes the overall layout of the cryogenic distribution system and the major thermodynamic factors which influence the CDS design including heat loads, pressure drops, temperature profiles, and pressure relieving requirements. In addition the paper describes how the models are created to perform the analyses. 