Speaker
Description
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 4.25 K filling the inner vessel of the cryostat at an equivalent cooling power of 0.55 W. To reduce the transmission of vibration to the highly sensitive CCC the titanium support systems of the cryostat were optimised 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 conduction, techniques employed to reduce transmission of thermal radiation, and procedures used to reduce the diffusion of helium to the vacuum space through ceramic isolators. Finally the upgraded cryogenic performance of the cryostat is presented.