POTENTIAL FUTURE USES

This section discusses potentially important applications that could rely on the availability of helium at a low price: magnetic levitation, superconducting magnetic energy storage, energy conversion systems, cryogenic wind tunnels, and superconducting electronics.

Magnetic Levitation

Superconducting magnets could be a central feature of a transport technology involving magnetic levitation (MAGLEV). In this technology, trains are levitated above their tracks, eliminating wheels and permitting very high-speed operation without frictional losses. The Japanese version of MAGLEV is based on the magnetic repulsion between a conducting track and high-power, helium-cooled, superconducting magnets on the vehicle. The highest speed achieved by a full-size test vehicle was 250 mph. A scaled-down, non-passenger-carrying vehicle attained 321 mph (517 kph) in 1979. Although superconducting MAGLEV technology was pioneered in the United States, there has been almost no domestic effort to develop it over the past 30 years.

Superconducting Magnetic Energy Storage

Superconducting magnetic energy storage (SMES) devices store energy in magnetic fields. These systems are highly efficient and could be used for equalizing energy distribution in power systems on small scales, e.g., to keep high-security computer systems running. The devices consist of closed coils of superconducting wires. The coils can be fed and discharged by means of a switch that connects the winding with the power grid. Superconductors are the only appropriate materials for SMES devices because they have no electrical resistance and thus can be operated in a persistent current mode without being connected to a power supply. A SMES device is the only method of storing electrical energy without first converting it to mechanical or chemical energy. The energy density in superconducting coils is comparable with that in flywheels (i.e., higher than that for capacitor banks, but less than that for batteries). Their short cycle times make them competitive with batteries, however. SMES units can be large scale (i.e., 1 MWh to more than 1 GWh) or small-to-medium scale (i.e., a few watt-hours to 1 MWh).

Energy Conversion Systems

Superconducting technology is considered to be an important secondary technology for plasma confinement fusion. Helium would play a critical role in cooling the superconducting magnets that would provide the magnetic containment environment. This kind of fusion technology would become widespread only in the very distant future, if ever. Nevertheless, it is essential to mention it as a potential user of helium as a refrigerant for superconducting magnets, which would probably require liquid-helium temperature refrigeration even if they were made from high-temperature superconducting wire.



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