TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes

ACQUISITION PROGRAM: PMS 502, CG(X) Program Office, ACAT 1

OBJECTIVE: Develop a rugged, low maintenance cryocooler to provide cost effective cryogenic cooling for distributed High Temperature Superconducting Degaussing Systems (HTSDG) onboard Navy ships.

DESCRIPTION: The HTS degaussing systems will operate in a temperature range of 30-60K, but require discrete cooling for each loop as degaussing coils are located throughout the ship. To counteract efficiency losses of junction boxes, helium circulation, current feed-through etc�, HTSDG systems require approximately 200 watts of heat lift at 50K per cable for lengths up to 100 meters Depending on ship class, up to 40 of these cryocooler are required to be installed in a distributive manner. The current commercially available cooling solution is a cryocooler which meets this performance requirement at 50K while drawing about 7.5 kilowatts of electric power. The cryocooler has a maintenance cycle of 10,000 hours. Because this cryocooler incorporates an oil based compressor, during each maintenance cycle, the oil absorbers need to be changed and at every other maintenance cycle, the seals on the cold head need replacement.

The Navy desires a cryocooler that, for equivalent cooling, has a lower acquisition cost, has reduced maintenance requirements, is more rugged than land based systems, and can provide improved efficiency. Aspects such as smaller physical size and lower weight would receive positive favor.

PHASE I: Demonstrate the feasibility of a low cost, innovative, cryocooler concept(s) to achieve 200 W of heat lift at 50K, while optimizing the requirement for low maintenance. Identify any scalability limitations for a novel cryocooler concept. Perform bench top experimentation where applicable to demonstrate concepts. Complete preliminary design for a cryocooler that addresses the needs as identified above.

PHASE II: Develop, demonstrate and fabricate a prototype as identified in Phase I. In a laboratory environment, demonstrate that the prototype meets the performance goals established in Phase I. Verify final prototype operation in a representative laboratory environment and provide results. Develop a cost benefit analysis and a Phase III installation, testing, and validation plan.

PHASE III: Working with government and industry, construct a full-scale prototype and install onboard a selected Navy ship. Conduct extended shipboard testing.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: A low cost cryocooler has commercial application beyond the Navy. This cryocooler could be used in HTS power cables, the required capacity range will be appropriate for liquid nitrogen cooled cables and commercial motors and generators. Incorporation of this cryocooler, liquefaction systems at a lower cost, would make it possible for more academic institutions to afford such a system.

REFERENCES:
1. Fitzpatrick, B. "High Temperature Superconducting Degaussing Demonstration and Development," to be published in the proceedings of ASNE Day 2007, June 2007.

2. Snitchler G., Gamble B., Kalsi S.S., "The performance of a 5 MW high temperature superconductor ship propulsion motor" Applied Superconductivity, IEEE Transactions on Volume 15, Issue 2, Part 2, June 2005 Page(s):2206 � 2209.

3. Radebaugh, R. "Refrigeration for Superconductors" Proceedings of the IEEE Volume 92, Issue 10, Oct. 2004 Page(s):1719 � 1734.

4. Curcic, T.; Wolf, S.A. "Superconducting hybrid power electronics for military systems" Applied Superconductivity, IEEE Transactions on Volume 15, Issue 2, Part 2, June 2005 Page(s):2364 � 2369.

KEYWORDS: Cryogenic; Superconductor; HTS; Cryocooler; Refrigeration; Degaussing; Motors; Generators

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