Investigation of a Helium cooling circulation loop on a 1.3 GHz cavity structure

Abstract This paper presents a novel cryogenic cooling method for Superconducting Radio Frequency (SRF) cavities, utilizing a cold helium flow passed through a brazed capillary for their cooling. Such novel and drastically reduced helium content cooling scheme can be applied to a wide variety of superconducting cavities, and it has many advantages compared to the traditional cooling method of SRF cavities in a liquid helium bath. The paper describes cooling options and configurations concerning helium forced flow heat transfer at the capillary surface plus the resulting temperature distribution in the cavity itself. The results from the cold commissioning of the experimental system are outlined, demonstrating that the cavity could reach a minimum temperature of 6.5 K with an applied heat load of 1 W, with a He circulation loop based on a 1.8 W @ 4.2 K cryocooler. A LHe booster heat exchanger has been introduced to achieve even lower temperatures and ensure consistent inlet conditions for further evaluation of cavity cooling efficiency. The upgraded setup allows to apply up to 7 W heat load in the 1.3 GHz Cu cavity and reaching stable operating conditions below 6.5 K.