Two stage pulse tube refrigerator with double rotary valves

We have constructed a two stage pulse tube refrigerator equipped with two rotary valves. The first stage regenerator was made of stainless steel tube 39 mm OD, 0.5 mm thickness and 180 mm long packed 1735 stainless steel screens of 200 mesh and the second stage regenerator was made of stainless steel tube 18 mm OD, 0.3 mm thickness and 250 mm long packed with stainless steel screen of 250 mesh and lead shots of about 0.3 mm diameter. The performance was investigated by changing the ratio of the stainless steel mesh and lead shots of the second regenerator and the volumes of first and second pulse tubes. The second stage cold end reached below 20 K.