High-frequency Operation and Miniaturization aspects of Pulse-tube Cryocoolers

Cryocoolers are small refrigerators capable of achieving useful refrigeration below 120 K. Recent developments in the field of high Tc superconductors spawned a wide range of applications such as terahertz sensors, SQUIDS, low noise amplifiers, filters for microwave applications and many more. These devices are typically, nondissipating and require a cryocooler delivering refrigeration power of about 10 mW operating at 80 K. The existing commercial closed loop cryocoolers are huge, less reliable and expensive. Several research groups have been investigating development of cryocoolers using microsystems technologies for on-chip cryocooling. Gas cycles which, can be broadly divided into recuperative (steady flow) and regenerative (oscillating flow) cycles are the only current means of reaching cryogenic temperature in a single stage. The aim of this thesis is to investigate miniaturization of regenerative cycles. Pulse-tube cryocoolers, a variation of the Stirling cycle (regenerative type), are a fairly recent development in cryocooler technology. The principal advantage of a pulse-tube refrigerator is that it has no cold moving parts in the refrigerator