Magnetics Business & Technology - July/August 2020 - 16

RESEARCH & DEVELOPMENT

Development of a High-Field, Non-Insulated, High Temperature
Superconducting Magnet for Fusion Research and Other Applications
By Dr. Zbigniew Piec and Thomas W. Overton, General Atomics
Recent advances in superconductor technology, especially hightemperature superconductors (HTS), have revolutionized industries from defense and transportation to energy, medicine, and
basic science. Magnets employing superconducting (SC) material in their windings can achieve significantly higher magnetic
fields at much greater efficiencies than those relying on non-SC
materials. Superconducting magnets are unique enablers for
industrial and science applications such as medical diagnostics,
nuclear fusion, and particle accelerators. HTS magnets in particular offer considerable promise for these applications.
Modern SC materials provide high current densities in a wide
range of magnetic fields and temperatures. These features are
used in SC magnets to produce high fields, reduce magnet size,
and lower power consumption. The development of rare-earth
barium copper oxide (REBCO) conductor tape, which is an HTS
material, offers intriguing possibilities for such magnets with their
benefits over low-temperature superconductors (LTS). HTS conductors can either be operated at higher temperature with less
current carrying capability, or they can be operated at low temperatures (4-10K) at higher fields than LTS. Though prototype
REBCO magnets have been demonstrated, these typically use
immersion cooling (placing the coil in a cryogenic bath), which is
impractical for many applications.
Research into fusion energy has long been a driver of innovation
in magnet technology. General Atomics (GA) has been developing HTS magnets based on REBCO conductor to advance the
magnetic fusion energy development program in conjunction with
operating the DIII-D National Fusion Facility in San Diego for the
U.S. Department of Energy. Magnetic fusion devices require high
magnetic fields, and it is believed by the fusion community that
HTS magnets could significantly enhance performance characteristics while reducing both the size and cost of fusion devices,
potentially including future fusion power plants.

Figure 1. The GA HTS magnet. Conductive cooling is provided by
the cryocoolers mounted on top. No cryogens are used inside the
housing.
This HTS magnet was wound from 500 meters of 12-mm REBCO tape procured from SuperPower, a New York-based supplier
of superconducting tape and wire. At the start of the project, the
maximum production length of REBCO conductor tapes with
consistent Ic (critical current) was limited. To reduce the cost, SuperPower provided a 500-meter length of conductor composed
of three sections with lengths that ranged from 150 meters to 180
meters. Thus, the delivered tape contained two resistive splices
(~20 nΩ) made by SuperPower.
The completed magnet has a 10-cm inner diameter, 20-cm outer
diameter, and was wound with a conductor tension of ~50 N,
using winding equipment and technician support from Energy to
Power (E2P) Solutions of Tallahassee, FL, as shown in Figure
2.

Development
GA's HTS magnet development takes place at its Magnet
Technologies Center (MTC) in San Diego, California. The MTC
is a state-of-the-art facility that builds on GA's 50-year history of
developing large and innovative magnets for fusion energy, defense, medical, and other applications. The MTC can perform all
stages of LTS magnet design and fabrication for the largest and
most powerful SC electromagnets. Over the past several years,
the MTC has also successfully expanded their core capabilities
in development of HTS magnet technology.
As part of its research into fusion applications, GA engineers
have developed a design for a 6 Tesla non-insulated (NI) HTS
REBCO-based magnet that uses conductive cooling, rather than
immersive cooling methods (i.e., no active cryogens are inside
the magnet housing).
The first example was completed in 2019 (Figure 1).
Figure 2. E2P HTS REBCO tape winding system with the pneumatically controlled tension.

Magnetics Business & Technology * July/August 2020

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