N121-077 TITLE: Modular Superconducting Cable Assembly

TECHNOLOGY AREAS: Ground/Sea Vehicles, Sensors

ACQUISITION PROGRAM: PMS 501, LCS Program, ACAT 1

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OBJECTIVE: Develop a modular, superconducting cable assembly that will allow for affordable, quick and reliable installation in naval shipboard applications.

DESCRIPTION: The Navy is developing several superconducting systems for use in future ships and submarines to reduce system weight, energy usage, and installed volume. These systems, such as degaussing and power distribution systems, rely on superconducting wires housed in a flexible cryostat to pass current and power from one source to another. The superconducting cable is the combination of the superconducting wire and the thermal insulation system (cryostat) necessary to keep it at cryogenic temperatures. The current state of the art in superconducting cable consists of an inner corrugated tube which contains both the superconducting tapes (conductor) and a cryogen (helium gas) for cooling for operation in the 40 to 80 K range at a working pressure up to 150 psig. This inner tube is encased in multi-layer insulation (MLI) radiation shielding as well as being supported with a thin twisted polymer to reduce contact with an outer corrugated tube. The outer corrugated tube contains a vacuum space maintained at 10-6 Torr, encapsulates the inner corrugated tube and has a thermal heat load of ~1 W/m. These cable assemblies are made in the factory at precise predetermined lengths, which can be a problem during shipyard installation if the cables need to be rerouted because the length is fixed and cannot be modified during installation. Should a problem arise, the cables would need to be uninstalled and the correct length made and re-installed at a later date. The current state of the art, fixed length cables, meets the requirements for system operation in terms of vacuum levels, helium containment, and a reasonable installation time (it takes approximately 20 man hours to install a 60 m cable length). Fixed lengths, however, create installation problems and cryostats cost more than $400/m, which are drawbacks and impediments to shipboard implementation.

The Navy seeks innovative approaches to the development of an improved, affordable, modular, superconducting cable assembly. Innovation needs to address numerous technical challenges, which include, but are not limited to installation in a high-humidity, unclean shipyard environment; 30 year service life without maintenance; obtaining and maintaining ultra-high vacuum levels of 10-6 Torr without active vacuum pumping; containment of pressurized cryogenic helium gas without leaks; thermal heat loads of less than 110W for a 100 meter cable including joints and terminations; weight requirement of less than 600 lbs for a 100 meter cable including joints and terminations; bend radius of less than 6 inches; and material cost(s) under $400/m. Given the nature of the application, concepts should consider the impact of a rugged shipboard environment.

PHASE I: Demonstrate the feasibility of a novel modular superconducting cable assembly concept able to operate with Navy cryogenic systems as defined above. Perform bench top experimentation, where applicable, as a means of demonstrating the identified concepts. Establish validation goals and metrics to analyze the feasibility of the proposed solution. Provide a Phase II development approach and schedule that contains discrete milestones for product development.

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: Upon successful Phase II completion, the company will support the Navy in transitioning the technology to military and commercial cryogenic or superconducting applications. Working with Navy and industry, as applicable, install onboard a selected Navy ship and conduct extended shipboard testing. The company will support the Navy for tests and validation to certify and qualify the technology for Navy use.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: A modular design may be of use in land-based High Temperature Superconducting (HTS) power cables and power delivery applications. Although land-based HTS power cables currently are small-scale R&D projects, as this technology matures it will transition into the commercial power delivery sector. A modular cryostat capability would be attractive commercially as it would allow a HTS-based power delivery solution to be modified in place when needed (e.g., routing around objects, expansion of line, allowance for construction), rather than requiring a replacement of the entire HTS cable.

REFERENCES:
1. B. Fitzpatrick, J. Kephart, E. M. Golda, "Characterization of Gaseous Helium Flow Cryogen in a Flexible Cryostat for Naval Applications of High Temperature Superconductors," IEEE Trans. App. Super., Vol. 17, No. 2, 2007.

2. American Superconductor, "High Temperature Superconductor Degaussing Coil System," www.amsc.com, 2010.

3. Victaulic Company, "IPS Carbon Steel Pipe � Pressfit System: Design Data Pressfit® Qualification Tests," www.victaulic.com, 1996.

KEYWORDS: cryogenics; superconductor; cryostat; degaussing; HTS; High Temperature Superconducting

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