ACT Team Wins Grant to Model Current Sharing in CORC Cables

Advanced Conductor Technologies, SuperPower Inc. and Lawrence Berkeley National Lab (LBNL) have been awarded a grant of almost $200,000 through the U.S. Department of Energy’s (USDOE) new Innovation Network for Fusion Energy (INFUSE) program for a project entitled “Development of a Modeling Toolbox for CORC Cable Performance Evaluation. The partners plan to develop a simulative toolset that would assist them in gaining a deeper understanding of current distribution between tapes in CORC cables in fusion magnets, taking into account the common performance variations within REBCO tapes when operating at high magnetic fields.

“We have been working on fusion related applications for CORC cables since 2012,” commented ACT President Danko van der Laan. “About 50% of our funding from USDOE comes from the Office of Fusion Energy Sciences.”

Project Addresses Uneven Current Distribution

Uneven current distribution in multi-tape cables is potentially a serious problem in most high-field magnets since it can lead to quenching. The cables, and especially the terminations, need to be developed so that the current distributes evenly between tapes.

“Current sharing between tapes could be seen as a benefit, because current could potentially bypass local defects without causing a hot spot in the magnet winding,” van der Laan said. “It is especially important for very large magnets, such as for compact fusion magnets, because a high level of current sharing eases the requirements of the tapes that go into the cable, making the magnet more cost effective and easier to construct.

“The toolbox at the end of the one-year program should be based on an accurate model that describes the CORC cable with its relevant properties as parameters. These will be adjustable in an effort to further optimize the CORC cable for certain magnet applications. The model should tell us what the impact of those changes would be on the overall performance of the conductor, allowing us to improve the CORC cable more effectively and more efficiently.”

Work Will Test for Variations in Chemistry and Processing Conditions

This simulation tool would allow for the design of CORC cables to be specifically tailored for fusion magnet applications based on actual REBCO tape performance variations. Such a capability would ensure optimal cable operation and prevent conductor burnout during a magnet quench. The work will emphasize the variations in high-field REBCO tape performance that are due to variations in chemistry and processing conditions, plus other key parameters such as contact resistance between REBCO tapes in CORC cables.

“We might consider the use of certain surface treatments on the superconducting tapes before cabling that may enhance the current sharing by reducing the contact resistance,” van der Laan said. “These could be softer metals instead of the relatively hard copper plating that is standard on tapes from SuperPower.”

The partners have a history of working together. SuperPower produces the HTS superconducting tapes for ACT’s CORC cables. LBNL is currently developing HTS magnets based on CORC cables.

CORC Cables Offer Unique Benefits for Magnet Applications

CORC cable technology was developed by van der Laan when he was a researcher with CU and the National Institute of Standards and Technology (NIST) (see Superconductor Week, Vol 25, No 11). A CORC® cable is thinner and more flexible than most contemporary HTS cables while carrying the same or more current.

The CORC approach involves winding layers of REBCO tapes in a helical fashion around a thin core. The REBCO tapes used in the cables have a high tolerance for strain compared to other HTS tapes, allowing for the use of an unusually slender copper former.

Van der Laan highlighted some of the benefits of CORC cables for fusion, as well as for other magnets: “Overall, CORC cables are round and isotropic with respect to bending direction and performance in magnetic field. Current sharing between tapes due to tapes being wound in opposite directions between layers allows some degree of dropouts to be present in the tapes, but also allows the tape performance to vary within a certain degree without causing performance issues.”

INFUSE to Accelerate Fusion Development

The ACT-SuperPowe-LBNL collaboration is one of twelve to be funded through the INFUSE program, which is sponsored by the Office of Fusion Energy Sciences (FES) within USDOE’s Office of Science. INFUSE seeks to accelerate fusion energy development through private-public research partnerships. The program links private sector companies with the USDOE’s national labs.

INFUSE solicited proposals from the U.S. fusion industry, and the selected projects were awarded between $50,000 and $200,000 each, with a 20% cost share by industry partners. The awards are subject to a successful negotiation of a Cooperative Research and Development Agreement (CRADA) between the companies and the partnering laboratories. Funding is not provided directly to the private companies but instead supports the partnering labs to enable them to collaborate with their industrial partners.

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