Performance of a single-stage 4K pulse tube cooler with neodymium regenerator precooled with a single-stage GM refrigerator

摘要

A study on the experimental performance of ahybrid cooler is presented. The two-stage unit consists of acommercial single-stage GM refrigerator to precool a pulse tubestage capable of reaching a minimum temperature of 2.2 K. Thepressure waves for both stages are generated separately byindependent rotary valves using the same 6 kW helium compressor.This allows one to run each stage at its optimum frequency. TheGM refrigerator operates at a fixed frequency of 2 Hz while theoptimum frequency for the pulse tube stage was experimentallyfound to be lower. Experiments were carried out with and withouta regenerative tube. Neodymium was used as regenerator materialin the coldest section. A cooling power of 0.26 W at 4.2 K wasachieved at the pulse tube stage with an additional heat load of 50W at the GM stage at 56 K.