Abstract
The Cryogenic Current Comparator (CCC) and its purpose built cryostat were installed in the low-energy Antiproton Decelerator (AD) at CERN in 2015. A pulse-tube cryocooler recondenses evaporated helium to liquid at 4.2 K filling the helium vessel of the cryostat at an equivalent cooling power of 0.69 W. To reduce the transmission of vibration to the highly sensitive CCC, the titanium support systems of the cryostat were optimized to be as stiff as possible while limiting the transmission of heat to the liquid helium vessel. During operation the liquid helium level in the cryostat was seen to reduce, indicating that heat load was higher than intended. To verify the reason for this additional heat load and improve the cryogenic performance of the cryostat, an upgrade was undertaken during the 2016 technical stop of the AD. This article presents the studies undertaken to understand the thermal performance of the cryostat and details the improvements made to reduce heat load on the liquid helium vessel. Also discussed are the procedures used to reduce the diffusion of helium to the vacuum space through ceramic insulators. Finally the upgraded cryogenic performance of the cryostat is presented.
Highlights
The Cryogenic Current Comparator (CCC) cryostat was installed in the Antiproton Decelerator (AD) at CERN during 2015 to house the cryogenic current comparator (CCC) [1]
The liquid helium (LHe) level in the helium vessel (HV) reduced by 16.7 liters, equating to a heat load of 0.59 W, a reduction of 43% when compared to the value of 1.04 W measured before the upgrade
Results from the CCC indicate that this result has been achieved without a significant reduction in mechanical performance
Summary
The CCC cryostat was installed in the Antiproton Decelerator (AD) at CERN during 2015 to house the cryogenic current comparator (CCC) [1]. During its first period of operation, it was not possible to keep a stable level of LHe in the cryostat due to a heat load of 1.04 W on the helium vessel (HV), 0.47 W higher than intended by design [1]. Gaseous helium (GHe) was found to be diffusing through the ceramic insulator integrated in the HV beam tube, reducing the performance of the insulation vacuum of the cryostat. This article discusses the improvements made to reduce heat load on the HV and thermal shield (TS), as well as the procedure put in place to manage the effect of diffusion of helium through the ceramic insulators. 2. Improvements to the thermal design of cryostat The following modifications were made to the cryostat to reduce heat load on the HV and TS: 2.1. It was decided to completely remove the strain gauges and all associated cables
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