|Acquisition Program: ||Silk Tread EC and SSEE|| Objective: ||The objective of this work is to demonstrate that the functions of cryo-cooling and the production of electricity at low temperatures can be combined into a single system. This would strongly enable the utilization of cryogenic electronics by removing a dominant source of heat load on the cooler, the parasitic heat load that flows down to the electronics along with the electrical power needed to operate it.
|| Description: ||Cryogenic electronics such as cryoCMOS and superconducting digital logic require both a low temperature environment and a supply of electricity of an AC or DC nature. The electrical leads bringing that current down from room temperature also transport both static and dynamically produced heat loads to the low temperature environment. Were the required electrical power produced at low temperature, this lead related heat load would be omitted, eliminating more than half the total load in a digital superconducting system. So long as this electrical production is a byproduct of the cooling, and thus does not add a new inefficiency heat load, the system energy performance will clearly benefit. When packaging such systems for military applications, there is a further requirement that the system operate in a moving environment which may include significant g forces at arbitrary angles, shock, and continual vibration. This unpredictability of the net mechanical acceleration appears to favor thermodynamic cycles with strongly forced flows. The shock and imported vibration aspects require extra care be given to details such as insuring that moving parts do not drag on their enclosure’s walls and suggest the use of gas bearings rather than wearing ones. Because of the low temperatures desired (4-40K) and the resultant low Carnot efficiency, the thermodynamic cycle selected must have an expectation of delivering high energy efficiency (percentage of Carnot limit) after engineering optimization. In addition, magnetic fields originating from the cooler’s operation and straying into the sample space must be controllable down into the micro-Gauss range. The complete cooler is very likely to be of a multi-stage design and the provision of ways to change the relative magnitude of the heat lift on each stage is desirable, thereby making some stages available as heat sinks for heat loads that are independent of the operation of lower temperature stages. A design that can be scaled to different cooling and electrical loads is particularly desirable. The first design should be notionally for 1.5 W of lift at around 4K while providing 10A DC current at 2 mV bias at 30K or 300W of lift and 60 Hz AC current at 1.5V bias and 20A, both at 30K .
|| ||PHASE I: The goal of phase 1 is to complete a detailed engineering design for the combined cooling stage and electrical generator to be realized in phase 2. The most desired temperature for this stage would be 30K, tho both higher (to 70K) and lower (to 3K) temperature designs will be considered. Estimates of the ratio of cooling power and electrical power produced, the volume added by the addition of the generation function, and the percent of Carnot efficiency that might be achieved should be made during this phase and discussed in any phase 2 proposal written. The phase 1 proposal should carefully explain why the specific thermodynamic cycle proposed is well suited for the entire imagined 4K, multistage cooler and notionally how each of the performance/reliability issues mentioned in the description section could be addressed during later phases.
|| ||PHASE II: During phase 2, the vendor will realize, test, and iterate the design formulated during phase 1. In addition, the design of a complete 4K tactical cooler able to generate/deliver electrical power at about 30K will be formulated and modeled, even if funding prevents its complete realization.
|| ||PHASE III: During phase 3, the vendor will realize, test, and iterate the complete design formulated during phase 2. Then the resulting product will be combined with low temperature electronics and used to demonstrate system functionality in field tests of the combined technologies.
PRIVATE SECTOR COMMERCIAL POTENTIAL/|| ||DUAL-USE APPLICATIONS: The primary commercial application is likely to be cryoCMOS server farms. This is because room temperature silicon based computers have run into fundamental physics related issues (intense (100’s of W/cm2) waste heat) that will prevent their further increases in speed. Increasing the number of cores adds substantially to the difficulty of programming and thus its typical computational inefficiency. By using cryogenic temperatures in the 30-100K range, the speed of CMOS can be doubled at the same time as the energy dissipation per flop can be reduced. CryoCMOS will win out in contexts where latency matters, especially if the multiplier that describes the wall plug power required to lift a W from the cold stage can be minimized by eliminating the heat load associated with delivering the computer’s power. Applications in research laboratory instrumentation and automated test equipment are also likely to develop
|| References: ||
1. M. Rabinowitz, "Cryogenic Power Generation," Cryogenics Vol. 17, 319-330 (1977).
2. M. Rabinowitz, "Superconducting Power Generation," IEEE Power Engineering Review 20 No.5 (2000) pp.8 – 11
3. Fevrier, A; Laumond, Y, “Prospective Uses of Superconductors for 50/60 Hertz Applications,” Proceedings of the Eleventh International Cryogenic Engineering Conference--ICEC 11; Berlin; FRG; 22-25 Apr. 1986. pp. 139-152. 1986
4. Istvan Vajda, "Conceptual Design of an All Superconducting Mini Power Plant Model," delta, pp.267, The First IEEE International Workshop on Electronic Design, Test and Applications (DELTA '02), 2002|
|Keywords: ||Cryocoolers; electrical generation; cryopackaging; tactical cryocoolers; Carnot efficiency; parasitic heat loads|