Wire

technology

 

What is superconducting wire

Superconductivity allows the transmission of electricity with low or no resistance or electrical loss.  High temperature superconductors using the ceramic YBCO become superconducting at the temperature of liquid nitrogen.  These superconducting wires transmit enormous amounts of electricity in small cross sections without electrical loss and by definition without generating heat.  No loss or heat means that extremely powerful magnets can be designed and built using superconducting wire, allowing designers to create smaller, more powerful and efficient electrical devices.

Where copper can transmit 500 amps per sq-cm, MetOx superconducting material can transmit more than 2,000,000 amps per sq-cm.  

The MetOx 2G HTS wire architecture is unique among wire systems utilizing YBCO as the current carrying layer.  MetOx utilizes a modified Metal Organic Chemical Vapor Deposition system developed by the University of Houston.  While conventional MOCVD is a known method of thin film deposition utilizing a gas filled reactor chamber which ultimately results in the precursor being deposited on a substrate, it is very slow.  Based on research at the UH and MetOx, the MetOx modified MOCVD process results in 5-10 times faster deposition than conventional MOCVD while producing perfectly atomically ordered films that requires the deposition of thousands of atomic layers to reach a thickness of 1 micron or more.

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A photograph of the MetOx HTS wire layers is shown below.

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The three types of superconducting wire

1. High Temperature Superconducting (HTS) Wire – 2nd Generation (2G)

The discovery of yttrium barium copper oxide, or YBCO, by Dr. Paul Chu at the Texas Center for Superconductivity in 1987 made the creation of superconducting material at high temperatures possible.  Relative to copper and other lower temperature superconductors, YBCO is considerably more effective at carrying current per unit of volume and requires a considerably different cooling system to achieve its superconducting properties. This second generation superconducting material provided the potential to reduce manufacturing complexity, while retaining the advantages of HTS Gen 1 performance.  

Nonetheless, to date, reasonable manufacturing costs for existing manufacturers of Gen 2 materials with YBCO have been elusive, and neither government nor industry has been able to economically produce wire at a price point that would drive rapid adoption for mainstream applications.  Except for MetOx, all existing processes are complex and require substantial capital and production costs. 

As compared with first generation HTS wire, second generation HTS wire:

  • Utilizes YBCO as its superconductivity component
  • Is more energy efficient – stemming from loss-free electrical  transmission process
  • Produces less energy loss converted to heat which equates to the elimination of toxic and flammable heat transfer oils currently used for cooling high power copper devices
  • Produces larger amounts of energy per unit volume
  • Has the potential to be less expensive
  • Has the ability to produce stronger magnetic fields which result in higher energy applications from HTS wires
  • Is less effected in the presence of a magnetic field

2. High Temperature Superconducting (HTS) Wire - 1st Generation (1G)

 

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BSCCO Wire

The first generation of HTS wire, termed HTS Gen 1 was based on bismuth, strontium, calcium, copper oxide, or BSCCO, a relatively high-price, low-efficiency material that relies on a powder in tube manufacturing method utilizing an expensive silver matrix.  These first generation wires relied on manufacturing techniques which are quite similar to LTS wire.  In addition to suffering from high production costs due to the complex stranded architecture and high silver content, BSCCO is commercially produced for some products but will not enjoy widespread application.

First generation HTS wire:

  • Utilizes BSCCO, powder in a silver tube technology
  • Operates in cold conditions between LTS and copper
  • Is inefficient and expensive
  • Services limited (but real) markets due to high cost and low performance

3. Low Temperature Superconducting (LTS) Wire

wire4The first superconducting wire was developed nearly fifty years ago.  To be effective, it has to be cooled with liquid helium to near absolute zero (-452F).  It was (and is) extraordinarily expensive to own and operate. Nearly all LTS applications utilize wound and stranded multifilament wires and cables based on NbTi, Nb3Sn or other A15 compounds.  Nonetheless, its novel performance seeded the market for a new generation of applications, most notably, magnetic resonance imaging (MRI) machines and high energy physics such as linear accelerators.  The extraordinarily high operating costs of LTS have forestalled market adoption, limiting applications to only high value, niche markets and research and development.

LTS Wire limitations are:

  • Operates with no electrical loss but near absolute zero
  • Is extremely difficult and expensive to keep to cool
  • Because of its high cost to own and operate, current LTS wire applications are limited to high cost imaging (MRI, NMR.. etc) and high-energy physics.

Superconducting Wire Comparison

Feature

LTS

HTS Gen 1

MetOx HTS Gen 2

Operating Temperature

-452oF

-323oF

-323oF

Performance

300,000 A/sq-cm

30,000 kA/sq-cm

2,000,000 A/sq-cm

Coolant

Liquid Helium

Liquid Nitrogen

Liquid Nitrogen

Carrier/Substrate

Copper matrix

Silver matrix

Alloy

Active Layer

NbTi

BSCCO

YBCO

Own operate cost

Extremely high

Moderate

Approaching copper

 

 

 

MetOx HTS wire production technology

Metal Oxide Technologies, in collaboration with the Texas Center for Superconductivity (TcSUH) and the Space Vacuum Epitaxy Center (now the Center for Advanced Materials a NASA commercialization center), both at the University of Houston, has developed a revolutionary YBCO coated conductor high temperature superconducting wire production system.
wire5This system represents the only truly continuous coated conductor processing capability know to us in the world. The MetOx system produces fully operational HTS wire air to air, reel to reel, starting from textured annealed metallic substrate produced at our commercial rolling mill partner. The primary elements are shown in the isometric drawing. Stabilization and insulation are the final steps to make a complete wire product.
wire6The MetOx air-to-air, reel-to-reel system reduces handling and improves process cycle time resulting in very low down time. In addition, the simple variable speed motor control system allows high speed operation with immediate scaling to over 1 Km tape length dependent only on reel diameter.

The MetOx 100% low vacuum process eliminates the requirement for high vacuum equipment and a clean room environment. The MetOx modular system design provides for ease of process modification and line expansion. Substrate pretreatment and texture annealing are in line with the deposition process reducing the potential for handling damage. Post- deposition tetragonal-orthorhombic phase anneal and silver stabilizer anneal are also in line.

 The MetOx modified metal organic chemical vapor deposition of buffer and YBCO film provides a proven high rate (>1mm/min) and high performance (>2MA/cm2) and thick (5mm) films. MetOx precursor technology ensures stoichiometry and uniformity, optimizes material utilization and enables easy scale up. In addition, the process benefits from a wide deposition area (2cm prototype and 20cm production system) and ease of scale up through reactor addition.

The MetOx in-line process control, currently implemented for tape transport and precursor feed, ensures stable operation and uniform properties. Real time logging of all process and operating variables insures rapid understanding of how process changes affect system reliability and end product coated conductor quality.

MetOx believes that its system represents the lowest possible capital cost approach to YBCO coated conductor fabrication, affecting the largest cost drivers in projected complete wire costs. The system is furthermore very compact, allowing parallel systems to be installed and operated in a small manufacturing footprint. The capacity of the pictured, fully updated, prototype system is 150 km/yr, scalable to a production capacity of 2,000 km/yr for each full scale production module. The system and processes are the subject of 23 U.S. and foreign patents and applications, with additional intellectual property in progress.