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High Temperature superconductor wire
Superconductivity
One area of expertise of AMPeers is superconducting materials. Superconductors are materials that exhibit zero resistance to the flow of electricity. As such, they can be very impactful in applications which can greatly benefit from high electric power density, high magnetic fields, power delivery in an ultra-compact volume, better power quality and high energy efficiency.
High Temperature Superconductors (HTS) are materials that exhibit zero resistance at temperatures above the boiling point of liquid nitrogen, which is abundant and inexpensive. HTS wires can carry 300 – 600 times the current carrying capacity of copper wires of the same size.
Applications
High Temperature superconductor wire can carry the same amount of current that the copper wires adjacent to it.
Applications of Superconductors
HTS have the potential to provide multiple commercial solutions to a broad spectrum of sectors of the US economy such as energy, defense, industrial applications, communications, and medicine. In the energy sector, for example, HTS devices have the potential to benefit both renewable and non-renewable energy industries, accelerate introduction of smart grid hardware applications and improve sustainability through enhanced energy efficiency, high power density, less CO2 emission, better power quality and improved resiliency and security of the power grid.
Superconductor cables can be used to efficiently transmit power over long distances from remote sources of wind, solar and nuclear power plants, as well as deliver 5 to 10 times more power to congested metropolitan areas and vastly improve production of unconventional petroleum reserves along with substantial reduction in water consumption and carbon dioxide emissions. The feasibility of offshore wind turbines, operating at 10 MW and higher, improves because of the reduction in size and weight by 50% when using HTS generators. Superconducting Magnetic Energy Storage (SMES) devices have the very real opportunity to enable grid-scale energy storage for effective deployment of intermittent renewable energy sources since they provide the benefits of rapid charging and discharging large amounts of power at higher efficiency and with much longer lifetimes compared to conventional grid-located batteries.
A unique feature of superconductors, namely, zero resistance below a critical current value and a rapid rise in resistance above this value can be deployed as fault current limiters, where they would interrupt power surges in millisecond response times while hardening the Nation’s electric power grid to natural disasters and terrorist attacks.
Superconductors enable achievement of ultra-high magnetic fields, even at the levels of tens of Tesla. Such high magnetic fields can enable realization of compact fusion reactors that can provide a clean source of electricity without the need for energy storage. Ultra-high-field superconductors enable Magnetic Resonance Imaging (MRI) and are now being developed for Proton Beam Therapy. The high magnetic fields enabled by superconductors have led to Nuclear Magnetic Resonance (NMR) equipment used for identifying the chemical signatures of complex molecules and is widely employed in drug discoveries. Superconducting magnets are also widely used in High Energy Physics in Accelerators such as the Large Hadron Collider at CERN, Geneva, Switzerland.
STAR® Round Superconducting Wires
STAR® – Symmetric Tape Round – superconductor wires offer unparalleled electromechanical performance for many high magnetic field and high power applications. STAR® wires are the only superconductor wires available today with a diameter of just 1 – 2 mm, bend radius capability of 15 mm, and high critical currents over a wide range of temperatures from 4.2 K to 77 K. Other round superconductor wires cannot be bent to such small diameters or cannot be used at temperatures much higher than 4.2 K.
The enabling technology of STAR® wires is a novel symmetric superconductor tape technology developed by AMPeers and its partner, University of Houston. In a symmetric tape architecture, the RE-Ba-Cu-O (REBCO, RE = rare earth) superconductor film is positioned near the neutral plane by an optimum combination of substrate and copper stabilizer thickness. Additionally, the substrate – typically a high-strength alloy such as Hastelloy – is only 18 – 20 µm thick which provides excellent flexibility. Symmetric REBCO tapes can be bent to 0.8 mm in diameter with greater than 95% critical current retention, whereas standard REBCO tapes degrade even below 6 mm bend diameter.
STAR® wires exhibit excellent performance in high magnetic fields even when bent to a radius of 15 mm. STAR® wires of 1.3 to 2 mm in diameter have been fabricated by winding multiple symmetric REBCO tapes helically on 0.51-1.02 mm diameter copper former. An 1.3 mm diameter STAR® wire exhibited an engineering current density (Je) of 586 A/mm2 at 20 T. Another STAR® wire of 2.04 mm diameter made with 12 strands of symmetric tape exhibited a critical current (Ic) of 1396 A at 4.2 K, 24 T. Based on its alpha value of 0.77, a Ic of 1615 A is projected at 4.2K at 20 T.
AMPeers has demonstrated STAR wires with record-high Je of ~ 600 A/mm2 at 4.2 K, 30 T corresponding to Je of > 1,000 A/mm2 at 4.2 K, 20 T using high current REBCO tape strands made using Advanced Metal Organic Chemical Vapor Deposition (MOCVD). Advanced MOCVD tapes exhibit more than 3x the critical current of commercial-grade REBCO tapes.
AMPeers has scaled up symmetric REBCO tapes with 18 – 20 µm thick substrate to 100 meters and STAR® wires to over 60 meters. An 1.84 mm diameter, 61.5 meter STAR® wire has been demonstrated with a Ic of 370A at 77 K. A 23 m long, 1.95 mm diameter STAR® wire has been produced with a Ic of 482 A at 77 K.
STAR® wires are now being tested for use in ultra-high field accelerator magnets for High Energy Physics and other applications that require magnetic fields beyond 20 Tesla or temperatures above 4.2 K. Such high magnetic fields or higher temperatures are outside the realm of capability of present superconductor wire technology based on Nb-Ti and Nb3Sn. Because of their isotropic mechanical properties and capability to be bent to 15 mm radius, STAR® wires can enable complex magnet geometries such as canted cosine theta (CCT). A CCT magnet made with STAR® wires with a bend radius of 15 mm at the pole region showed no wire degradation after winding, confirming the robustness of STAR® wires. The magnet reached 78% of the short-sample prediction at 4.2 K at a peak current of 8.9 kA.Since STAR® wires are comprised of transposed tapes, they are also beneficial for applications requiring low AC losses.
Multi-strand, compact transposed STAR® cables have been demonstrated with 6 STAR® wires wound around a copper core. AMPeers and Lawrence Berkeley National Laboratory (LBNL) successfully demonstrated a 6-around-1 cable made of six STAR® wires and one Cu core with a twist pitch of 52 mm. The nominal cable diameter is 5.8 mm. STAR cables have been bent to a radius of 45 mm with less than 5% change in critical current. STAR® cables have been wound on to CCT dipole magnets with no degradation in critical current (1,462 A @ 77 K, self-field) and n value after winding.
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