Amir E. Jahromi

Modeling and development of a superfluid magnetic pump with no moving parts

Current state of the art sub Kelvin Superfluid Stirling Refrigerators and Pulse tube Superfluid Refrigerators use multiple bellows pistons to execute the cycle. These types of displacers can be replaced by a newly introduced pump, a Superfluid Magnetic Pump, with no moving parts. Integration of this pump in the Pulse tube Superfluid Refrigeration system will make it a sub Kelvin Stirling refrigeration system free of any moving parts that is suitable for use in space cooling applications. The Superfluid Magnetic Pump consists of a canister that contains Gadolinium Gallium Garnet particles that is surrounded by a superconducting magnetic coil. The driving mechanism of this pump is the fountain effect in He II. A qualitative description of one cycle operation of the Superfluid Magnetic Pump is presented followed by a numerical model for each process of the cycle.

Development of a Numerical Model of a Superfluid Magnetic Pump for Space Science Applications

A superfluid magnetic helium pump that requires no moving parts is described. The pump consists of a canister filled with Gadolinium Gallium Garnet particles surrounded by a superconducting magnetic coil. This pump is capable of driving thermodynamic refrigeration cycles that provide cooling for space science detectors at temperatures below 100mK. A numerical model that predicts pump performance is presented. This model has been used to design a prototype superfluid magnetic pump.

Novel 4He Circulator for Cooling of Large Space Superconducting Magnets

Large superconducting magnets are used in various space science applications (that is, particle detectors designed to search for antimatter, dark matter, and the origin of cosmic rays in space). To prevent or recover from a potential magnet quench, it is extremely important to control the operating temperature of superconducting magnets. One effective method for maintaining superconducting coils at sufficiently low temperatures while in application is to exchange heat with He-II, which exhibits an abnormally high, effective thermal conductivity (≥80,000  W/m·K) under certain conditions. In this work, a novel superfluid magnetic pump with no moving parts is discussed as a new method for maintaining magnet coils below their superconducting transition temperature Tc. Unlike traditionally used thermomechanical pumps, the superfluid magnetic pump will have minimal superfluid helium depletion and will be able to provide flow rates that enable maintaining of the superconducting magnet coils at low temperatures.

Development of a Space-Flight ADR Providing Continuous Cooling at 50 Mk with Heat Rejection at 10 K

Future astronomical instruments will require sub-Kelvin detector temperatures to obtain high sensitivity. In many cases large arrays of detectors will be used, and the associated cooling systems will need performance surpassing the limits of present technologies. NASA is developing a compact cooling system that will lift heat continuously at temperatures below 50 mK and reject it at over 10 K. Based on adiabatic demagnetization refrigerators (ADRs), it will have high thermodynamic efficiency and vibration-free operation with no moving parts. It will provide more than 10 times the current flight ADR cooling power at 50 mK and will also continuously cool a 4 K stage for instruments and optics. In addition, it will include an advanced magnetic shield resulting in external field variations below 5 μT. We describe the cooling system here and report on the progress in its development.

Construction and experimental validation of a simple, compact, resealable, and reliable Vycor® superleak assembly for use at low temperatures

A new method of constructing a superleak assembly for use in experiments involving (4)He or (3)He-(4)He mixtures at very low temperatures is described. Superleaks are made of a porous medium with very small pores and channels. Superleaks are often incorporated in thermomechanical pumps, superfluid magnetic pumps, dilution refrigerators, and superfluid helium transfer systems. We used several cylindrical pieces of Vycor, a permeable glass with average pore diameter of 40 Å and porosity of 28%, as a candidate to be used in our superleak assembly. Our design is simple and compact. Our superleak assembly can be disassembled and easily reassembled for reuse. We successfully tested and validated this device at temperatures between 1.4 K and 2.7 K. We experienced no superfluid leaks into the surrounding vacuum. We also report that thermal cycling caused no performance degradation. It is our goal to share the design and construction techniques of this new superleak assembly.