Pulse tube refrigerator

A pulse tube refrigerator comprising:

• a pulse tube having a cold end and a hot end;
• a compressor in fluid communication with the cold end of the pulse tube;
• a first pressure buffer having a first pressure and in communication with the hot end of the pulse tube;
• and
• a second pressure buffer having a second pressure different from the first pressure and in communication with the hot end of the pulse tube;
• wherein
• a working fluid includes a first gas block flowing into and out from the compressor at the cold end of the pulse tube, a second gas block functioning as a gas piston and always present in the pulse tube, a third gas block flowing into and out from the first pressure buffer at the hot end of the pulse tube and a fourth gas block flowing into and out from the second pressure buffer at the hot end of the pulse tube, and wherein
• moving volume reduction means for reducing moving volumes of the first gas block, the third gas block and the fourth gas block by reducing a differential pressure at each stage in a refrigeration cycle.

A pulse tube refrigerator comprising:

• a refrigerating portion including a regenerator, a low temperature heat exchanger, a pulse tube and a high temperature heat exchanger connected in series;
• a pressure oscillator including a compressor, a high pressure valve and a low pressure valve for generating pressure oscillations of a working fluid in a pulse tube by connecting an outlet port and an inlet port of the compressor to the regenerator via the high pressure valve and the low pressure valve, respectively;
• means for selectively communicating plural different middle pressure levels with the high temperature heat exchanger, wherein each of said middle pressure levels being between an output pressure and an input pressure of the compressor;
• and
• a controller configured to arrange an opening condition of the high pressure valve, the low pressure valve and the buffer side valve so as not to overlap one another.