Products and Capabilities

Wire

Coils

Superconducting FCL Elements

Wire

Definition

Superconductors are well known to carry high current with near zero ohmic loss. In coil form, such as in an electromagnet, a charged and closed loop can carry current, and hence magnetic field, for long periods of time (of the order of months to years depending on the detail design). This makes a superconductor ideal for high field magnets, and consequently, it is commonly used in MRI and nuclear magnetic resonance (NMR) systems throughout the world. Hyper Tech is well equipped to produce two wire formed superconductors: MgB₂ and Nb₃Sn.

MgB₂ Wire

Nb₃Sn Wire

MgB₂ Wire

History of MgB₂

In January 2001, Japanese University professor Dr. Akimitsu announced that MgB₂ was superconducting up to 39 Kelvin. Since that discovery, Hyper Tech has been working on making the compound into a high performing, low cost superconductor wire.

Shortly after its creation, Hyper Tech developed and patented the continuous tube forming and filling (CTFF) process to make a powder metallurgy based wire of the MgB₂ superconductor. To manufacture a multifilament wire, numerous monofilaments containing the superconducting powder must be stacked within a tube and then drawn down to the required wire diameter and length. Hyper Tech’s patented process involves manufacturing wire starting with a metal ribbon that is continuously filled and formed into a tube. Traditionally, manufacturers must fill a tube of fixed length before drawing the wire. This method results in two problems: 1) the tube filling process results in an uneven density of material within the tube and 2) larger and larger diameter tubes are necessary to obtain longer lengths of wire.

In just more than five years, Hyper Tech has consistently manufactured monofilamentary and multifilamentary wires of up to 4 kilometers in length, which is necessary to be commercially viable. In order to evaluate the MgB₂ wire performance, 740 meters were wound into coils and tested. This enabled evaluation of superconductivity over the wire length and provided a preview of potential magnet applications. In November 2005, Hyper Tech fabricated a solenoid coil producing 2.4 Tesla at 20 Kelvin, 1.8 Tesla at 25 Kelvin, and 0.9 Tesla at 30 Kelvin. This coil met the magnetic field strength requirements to be viable in many applications, such as MRI systems currently using permanent magnets (up to 0.35 Tesla).

In August 2006, this milestone was exceeded when a 53-centimeter diameter test coil, also aimed at the MRI industry, was fabricated using a react-and-wind process. It too performed at the expected field strength and current.

Once the technical hurdles are cleared, the single most important criterion for the acceptance of MgB₂ based magnets in the market place is that they provide a performance and reliability comparable to or exceeding that of existing magnets but at a lower life-cycle cost.

When compared with permanent magnets, there are two potential advantages of MgB₂. The first is the possibility of achieving the typical magnetic field strengths of considerably more than 0.4 Tesla (up to 1.5-2.0 Tesla) with a lower initial capital equipment cost and lower life-cycle cost. Second, higher field strengths and larger zones of homogeneous magnetic field can be achieved with MgB₂ superconductor than with permanent magnets. Compared with low-temperature superconductors, the life-cycle costs of MgB₂ coils are lower due to the higher operating temperature and associated refrigeration cost. In the on-going effort to eliminate liquid cryogen, the temperature tolerance of MgB₂ better suits it for dry operation using only a cryocooler and conduction cooling.

MgB₂ conductors can operate at temperatures of 20 to 30 Kelvin. They can be supplied in round or rectangular cross sections giving them advantages in manufacturing and handling as well as a higher coil current density. MgB₂ is lighter weight and can be produced at a lower cost than the high temperature ceramic superconducting tape conductors BSCCO or YBCO-coated when operated in the 20 Kelvin range. MgB₂ wire is versatile in that it can be sized (amperage and J_c) for the appropriate coil size and performance. MgB₂ wire behaves more like a metal superconductor with regard to persistent current type coils than the superconducting tapes.

Potential applications include MRI systems, superconducting FCLs, transformers, inductors, reactors, motors, and generators. Of these, the most promising applications are projected to be MRI systems and superconducting FCLs.

Typical MgB₂ Wire Specifications

Hyper Tech can manufacture wires that are 1 to 4 kilometers in length with 7 and 19 filaments.

Specification	Value
Diameter	0.7 mm to 0.9 mm (others available)
Number of Filaments	7 and 19 (higher available experimentally)
Condition	Reacted and un-reacted and insulated with S-glass
Heat Treatment Temperature/Time	700 degrees C/20 minutes (Nominal)
Jc @ 20 K – 2T	175,000 A/cm2 (Nominal)
Maximum Allowable Axial Strain	0.35%
Continuous Piece Length	1-4 km
Superconductor fraction	13 – 18% (Under development - increase to 30%)

Multifilament Wire with Solid Cu Core	Monofilament Wire

Nb₃Sn Wire

Hyper Tech has developed high performance Nb₃Sn wire suitable for applications in high energy physics (e.g., accelerators), research magnets and commercial applications (e.g., high field MRI systems). The core of this work is on various types of internal-tin Nb₃Sn superconductors.

Conventional rod-in-tube (RIT) Nb3Sn conductor	RIT Nb3Sn conductor constructed with splits to lower the effective diameter (deff) of the superconductor

“Tube type” Nb3Sn conductor: sub-elements are fabricated with Nb integral tubes as compared with Nb filaments (rods) in RIT construction	Low AC-loss Nb3Sn conductor designed for fusion energy applications

Coils

The development of long length multifilamentary wire production has enabled Hyper Tech to design and fabricate a series of MgB₂ wound solenoid and racetrack coils. Establishing excellent properties over length in these early demonstrations has led to producing more realistic coils with MgB₂ superconductor wire relevant to specific applications. Long length characterization in coil form is equally important for the advancement of the MgB₂ superconductor because most commercial applications will require several multikilometer lengths of wire.

Wind-and-react solenoid coils

Hyper Tech has fabricated several solenoid coils wound with long lengths of Nb/Cu/Monel^TM -type multifilament wire employing a wind-and-react approach. That is, the MgB₂ wire is wound onto the finished bobbin and reacted at 650 to 700 degrees C for 20 minutes and subsequently vacuum impregnated with epoxy.

Hyper Tech wound one such coil fabricated by the wind-and-react process with 740 meters of 0.83 mm diameter strand totaling 3,463 turns around a 3.8 cm bore. This coil attained a field of 3.9 T at 4 K, 3.0 T at 15 K, 2.4 T at 20 K, 1.8 T at 25 K, and 0.9 T at 30 K.

Wind-and-react solenoid coil: 740 meters

Ic, Jc and Je as a function of temperature for 740 meter wind-and-react solenoid coil

React-and-wind solenoid coils

Hyper Tech fabricated a demonstration solenoid coil using a react-and-wind approach; the bore size in this coil was 53 cm which is relevant to many applications including specialty MRI systems. The coil generated a field on axial of 0.12 T at 20 K, which corresponded to predictions based on short sample wire results.

React-and-wind solenoid coil: 53 cm bore wound with 820 meters of MgB2 wire

Wind-and-react racetrack coils

Hyper Tech has fabricated more than 10 single-layer racetrack coils for a cryogenic rotor in a liquid helium-cooled superconducting generator demonstration. The racetrack coils were made using the wind-and-react approach. One coil reached 400 A at 4 K.

Wind-and-react racetrack "rotor" coil

Hyper Tech fabricated four complete rotor coil packs for delivery to NASA. Each pack contained 580 meters of MgB₂ superconducting wire. The wire was wound in a racetrack form around a copper former and Inconel center core. It was subsequently enclosed within an aluminum housing and potted to fill all voids.

These rotor coil packs are for a liquid hydrogen cooled 2 MW alternating current generator intended for hypersonic aircraft. Four coil packs make up the rotor. The rotational speed of the generator is to be 20,000 rpm.

Demonstration rotor coil pack

Superconducting FCL Elements

A superconducting FCL is a device that uses superconductors to instantly limit electrical surges before they reach a circuit breaker. Conventional utility equipment that currently mitigates this problem consists of large copper coils called line reactors. These are bulky devices that continuously consume power. Superconductors alone possess the unique physical properties that allow them to react instantly to current changes. In their superconducting state, they pass electricity continuously without power losses at normal levels while limiting current surges. The main advantages of superconducting FCLs are their negligible influence on an electrical network under normal operating conditions, fast response to over-current conditions, and response without an external trigger.

Schematic of MgB2-based superconducting FCL and superconducting FCL element

There are several types of superconducting FCLs but they fall into two basic categories: resistive and inductive. A resistive superconducting FCL operates as described above and is generally configured as shown in the schematic. They are intended to be passive and have a recovery time dependent entirely on the selected method of cooling. If the fault energy is stored inertially in a heat sink, the recovery time will be long, on the order of minutes, as determined by the mass of the components. An inductive superconducting FCL is designed to remain superconducting and stores the fault energy within the coils of the superconductor while providing the necessary impedance to limit the fault current. The inductive superconducting FCL is not usually preferred because of its greater size and cost, which are driven by the large volume of superconductor required.