Hybrid double-inlet valve for pulse tube cryocooler

A Gifford-McMahon (GM) type double-inlet pulse tube cryocooler system for providing cooling at cryogenic temperatures, comprising;

• a compressor supplying gas at a supply pressure through a supply line and receiving gas at a return pressure through a return line;
• a valve assembly connected to the supply and return lines;
• and
• a pulse tube cold head connected to the valve assembly, wherein the valve assembly cycles gas between the supply pressure and the return pressure to the pulse tube cold head through a connecting line, the pulse tube cold head comprising:
• at least one regenerator having a warm end and a cold end;
• at least one pulse tube having a warm end and a cold end;
• at least one double-inlet valve comprising:
• a fixed restrictor having a hole with a constant cross-sectional area or a tapered hole;
• and
• a needle valve coupled to the fixed restrictor in parallel, wherein the needle valve comprises a needle end port and a stem port, and wherein the needle valve is configured to allow and adjust flow from both directions between the needle end port and the stem port and to provide a flow resistance in one direction different from a flow resistance in the opposite direction;
• a buffer volume connected to the warm end of the pulse tube;
• a first line extending from the connecting line to the warm end of the regenerator, wherein one end of the fixed restrictor and one of the needle end port and the stem port are connected to the first line;
• a second line connecting the cold end of the regenerator to the cold end of the pulse tube;
• and
• a third line extending from the warm end of the pulse tube to the buffer volume through a single-inlet valve, wherein another end of the fixed restrictor and the other of the needle end port and the stem port are both connected to the third line at positions between the warm end of the pulse tube and the single-inlet valve.