High-Frequency Low-Temperature Regenerative Heat Exchangers

Even with multi-layer insulation blankets, cryogenic thermal switches, thermal distribution systems (such as cryogenic heat pipes), and advanced thermal/structural isolation systems, the mission capability of a fully-passive, stored cryogen system is compromised by the lack of an active cooler to recharge the system. This shortcoming is particularly acute at very low temperatures (<15 K) because there are no proven, long-life space cryocooler technologies for that operational temperature range. The primary technological barrier to extending proven Stirling and pulse tube technologies down to liquid helium temperatures is the absence of a regenerator design that will function at the high frequencies (> 30 Hz) required to enable small, compact designs typical of existing flexure-bearing, space-qualified cryocoolers. Irvine Sensors Corporation proposes to develop an advanced regenerator, based upon the use of novel rare earth metal matrix designs to enable very-low-temperature Stirling and pulse tube cryocoolers for both ground and space applications. The matrix will offer the combined benefits of low porosity and an extremely high surface-area-to-volume ratio, both of which are essential for very low temperature operation. Our goal is to achieve a 50 percent improvement in efficiency for high-frequency regenerators operating around a cold head temperature of 5 K.