LN2-free Operation of the MEG Liquid Xenon Calorimeter by using a High-power Pulse Tube Cryocooler

A high‐power coaxial pulse tube cryocooler, originally developed in KEK and technology‐transferred to Iwatani Industrial Gases Corp (IIGC), has been installed in a large liquid xenon calorimeter to evaluate liquid nitrogen‐free (LN2‐free) operation of the rare μ‐particle decay experiment (MEG). Features of this pulse tube cryocooler include the cold‐end heat exchanger, designed with sufficient surface area to ensure high‐power cooling, and a cylindrical regenerator placed inside the pulse tube giving compact design and ease of fabrication. This production‐level cryocooler provides a cooling power of ∼200 W at 165 K, using a 6 kW Gifford‐McMahon (GM)‐type compressor. The paper describes the detailed configuration of the cryocooler, and the results of the continuous LN2‐free operation of the large prototype liquid xenon calorimeter, which ran for more than 40 days without problems.