Article
Where superconductors are used, and what keeps them cold
Uses of superconductors include MRI and NMR magnets, particle accelerators, fusion magnets, power cables, fault-current limiters, maglev, quantum circuits, magnetic sensors, motors, and generators. Their roles range from established instruments to experimental machines and field demonstrations, and all require cooling suited to the material and operating conditions [1][2][3][4][5][6][7][8][9].
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MRI and NMR: strong, stable magnetic fields
MRI uses a stable background magnetic field to support medical imaging, while NMR spectroscopy uses magnetic resonance to investigate samples. Niobium titanium, or NbTi, is an established magnet conductor; niobium tin, or Nb3Sn, and cuprate conductors extend the choices for higher-field research instruments. The iScience review by Yao and Ma describes NbTi magnets generating fields up to 9 tesla at 4.2 kelvin, a conductor capability rather than a typical clinical scanner specification [1].
NMR also places demanding requirements on field stability and uniformity. The iScience review describes a Bi-2212 superconducting insert used in a 950 megahertz NMR system [1]. That example concerns a high-field instrument, not a claim that every spectrometer uses the same conductor. The dedicated MRI and NMR application guides explain how the winding, joints, cryostat, and field quality fit together [1].
Particle accelerators and fusion: guiding charged particles
Accelerator magnets bend and focus particle beams. CERN reports that the Large Hadron Collider's NbTi main magnets operate at 1.9 kelvin and produce an 8.33 tesla bending field [2]. Superfluid helium circulates through the cooling system, illustrating how a conductor's useful operating point depends on both field and temperature. This is an operating accelerator application, not a hypothetical replacement for conventional wiring [2].
Fusion magnets instead confine plasma, with conductor choices including Nb3Sn and rare-earth barium copper oxide, or REBCO [1][3]. MIT News reports a large-scale REBCO magnet demonstration at approximately 20 tesla and describes the approach operating at 20 kelvin [3]. The result establishes magnet engineering evidence; it does not establish a completed fusion plant delivering net electricity. The accelerator and fusion guides separate these magnetic duties and their protection requirements [2][3].
Power cables and fault-current limiters: different electrical duties
Superconducting power cables carry high current through compact conductors, while resistive fault-current limiters deliberately develop resistance during a fault. Bi-2223 and REBCO have been used in demonstrations of both applications, as described in iScience [1]. The iScience review identifies the liquid-nitrogen temperature region at approximately 77 kelvin, but actual devices choose operating conditions for current capacity, heat load, and protection [1].
Karlsruhe Institute of Technology reports that AmpaCity connected substations in Essen with approximately 1 kilometer of superconducting cable designed for 10,000 volts and 40 megawatts [4]. KIT describes a ceramic conductor cooled to approximately 73 kelvin, expressed in its release as about minus 200 degrees Celsius, and reports a superconducting short-circuit limiter supplied for test operation [4]. Those are project-specific engineering figures. Refrigeration, AC losses, joints, fault behavior, and recovery still belong in any whole-system comparison [1][4].
Maglev: onboard magnets and guideway coils
Superconducting maglev uses onboard magnets interacting with guideway coils for levitation, guidance, and propulsion. JR Central describes NbTi onboard coils cooled in liquid helium to approximately 4 kelvin, giving the brochure's temperature as about minus 269 degrees Celsius [5]. The train body is not cooled to that temperature; the superconducting windings sit inside an insulated magnet assembly.
JR Central describes a levitation gap of approximately 10 centimeters for its SCMAGLEV system [5]. This engineered interaction with a guideway is different from a small demonstration in which a superconducting specimen floats near a permanent magnet. The maglev application guide follows the transport system, including cryogenic equipment and the infrastructure needed beyond the onboard superconducting coil [5].
Quantum computing and SQUIDs: controlling and measuring quantum circuits
Superconducting quantum processors use electrical circuits with Josephson junctions to create and control qubits. The Sycamore paper in Nature describes aluminum metallization and Josephson junctions, with the chip cooled below 0.02 kelvin in a dilution refrigerator [6]. Nature reports operation with 53 qubits in that experiment [6]. This is a cryogenic processor demonstration, not evidence that superconducting circuits replace ordinary computers for every task.
SQUIDs, or superconducting quantum interference devices, use superconducting loops and Josephson junctions to sense magnetic flux. They can detect the weak magnetic fields associated with brain activity rather than compute with qubits. The review in Sensors describes niobium thin-film magnetometers and reports typical SQUID cryogenic operation at 4.2 kelvin [7]. The processor needs control and readout circuitry, while biomagnetic sensing requires shielding and careful signal measurement [6][7].
Motors and generators: cold field windings in rotating machines
Superconducting motors convert electrical power into shaft power, while generators perform the reverse conversion. The iScience review describes Bi-2223 and REBCO demonstrations in rotating machines [1]. NASA's partially superconducting HEMM motor has a design rating of 1.4 megawatts and rotor coils intended to remain near 50 kelvin, stated by NASA as minus 223 degrees Celsius [8]. NASA describes component testing before a full-scale machine test, so its rating must not be presented as measured aircraft service performance [8].
The EcoSwing consortium's presentation at the Magnet Technology conference describes a REBCO wind-generator rotor with an operating temperature below 30 kelvin and reports a 3 megawatt test run on a wind turbine [9]. The EcoSwing consortium distinguishes that result from the intended 3.6 megawatt output, which a converter-system fault prevented it from reaching [9]. Cooling, rotating interfaces, fault protection, and repair access are part of the machine. The wind-generator and electric-aircraft guides explore these integration constraints [8][9].
Data-center power: a demonstrated link, not universal adoption
Data-center power delivery is another studied use of superconducting cables. Sakura Internet and the Ishikari project consortium reported a 500 meter superconducting DC transmission test before supplying a data center [10]. Sakura Internet's joint release describes high-temperature superconducting material and circulating liquid nitrogen, giving liquid nitrogen's reference temperature as about minus 196 degrees Celsius, or approximately 77 kelvin [10]. That reference temperature should not be mistaken for a measured temperature profile along the cable, and the release does not identify a specific superconducting compound.
In its subsequent release, Sakura Internet reports beginning superconducting DC supply from a solar installation rated at 200 kilowatts to the Ishikari data center [11]. That is evidence of a field demonstration supplying computing equipment, distinct from a proposed internal busbar layout or widespread sector adoption. The cooling plant, terminals, protection, and power-conversion equipment remain part of the electrical system; a superconducting conductor alone does not establish a facility-wide energy saving. The transmission-cable guide covers the shared engineering questions [10][11].
Sources
- Superconducting materials: Challenges and opportunities for large-scale applicationsiScience, 2021
- Cryogenics: Low temperatures, high performanceCERN
- Tests show high-temperature superconducting magnets are ready for fusionMIT News, 2024
- Operation of Longest Superconducting Cable Worldwide StartedKarlsruhe Institute of Technology, 2014
- SUPERCONDUCTING MAGLEV (SCMAGLEV)JR Central
- Quantum supremacy using a programmable superconducting processorNature, 2019
- Superconducting Quantum Magnetometers for Brain InvestigationsSensors, 2025
- High-Efficiency Megawatt Motor (HEMM)NASA, 2025
- Development, test, installation, and commissioning of the 3 MW superconducting EcoSwing wind power generatorEcoSwing consortium, Magnet Technology conference, 2019
- 500mの直流超電導送電に成功!Sakura Internet and Ishikari project consortium, 2015
- データセンターへの超電導送電を開始Sakura Internet and Ishikari project consortium, 2015
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