Dr. Boaz Almog and Mishael Azoulay working in the group of Prof. Guy Deutscher at TAU’s Raymond and Beverly Sackler School of Physics and Astronomy have developed superconducting wires using fibers made of single crystals of sapphire to be used in high powered cables. Factoring in temperature requirements, each tiny wire can carry approximately 40 times more electricity than a copper wire of the same size. They have the potential to revolutionize energy transfer, says Dr. Almog.
A sapphire substrate carrying a superconductive layer of a compound of the formula YBa2Cu3O7-x (YBCO), the layer having surface area of at least 10 cm2, and critical current of at least 100 A/cm width at a temperature of 77K or higher. In one exemplary embodiment, the thickness of the superconductive layer is between 10 nm and 50 nm. In another exemplary embodiment, the thickness of the superconductive layer is more than 600 nm. In preferred embodiment, an YSZ layer and a non-superconductive YBCO layer separate between the superconductive layer and the substrate.
High temperature superconducting wire usually carries 4-10 times the power of copper SuperPower state-of-the-art second-generation high temperature superconductor (2G HTS) wire can carry up to one hundred times as much current as conventional copper wire.
Beating the heat
One of the things that make our copper wires inefficient is overheating, Dr. Almog explains. Due to electrical resistance found in the metal, some of the energy that flows through the cables is cast off and wasted, causing the wires to heat up. But with superconductors, there is no resistance. A self-contained cooling system, which requires a constant flow of liquid nitrogen, keeps the wire in its superconducting state. Readily available, non-toxic, and inexpensive — a gallon of the substance costs less than a gallon of milk — liquid nitrogen provides the perfect coolant.
Even with the benefit of liquid nitrogen, researchers were still hard pressed to find a material that would make the ideal superconductor. Superconductors coated on crystal wafers are effective but too brittle, says Dr. Almog, and although superconductors on metallic tapes had some success, the product is too expensive to manufacture in mass quantities.
To create their superconductors, the researchers turned to sapphire fibers, developed by Dr. Amit Goyal at the Oakridge National Lab in Tennessee and lent to the TAU team. Coated with a ceramic mixture using a special technique, these single-crystal fibers, slightly thicker than a human hair, have made innovative superconductors.
Dr. Almog is currently working to produce better superconductors that could transport even larger amounts of electric current.
One area where such superconductors could lend a hand is in collecting renewable energy sources. “Sources such as wind turbines or solar panels are usually located in remote places such as deserts or offshore lines, and you need an efficient way to deliver the current,” explains Dr. Almog. These superconductors can traverse the long distances without losing any of the energy to heat due to electrical resistance.
Superconducting cables could also be an efficient way to bring large amounts of power to big cities “If you want to supply current for a section of a city like New York, you will need electric cables with a total cross-section of more than one meter by one meter. Superconductors have larger current capacities using a fraction of the space,” says Dr. Almog. Different parts of a city could be cross-wired, he adds, so that in the event of a blackout, power can be easily rerouted.