HTS Magnets vs. LTS Magnets

Until relatively recently, the only means of achieving magnetic fields high enough to meet the levels needed in certain applications was to base machines on LTS (low temperature superconductor) wires. Although these systems represented an improvement over devices relying on conventional copper wire coils, their size, cooling demands and operational requirements made them expensive and technically challenging alternatives.

Magnets that incorporate HTS wires offer a significant set of benefits over older LTS devices. In a number of applications, HTS-based machines have demonstrated their reliability in uses such as magnetic separation, minesweeping, ion sources, beam switching magnet, vibrating sample magnetometry and high field insert coils.

Advantages of HTS magnets stem from:

Simpler Cooling Systems Most HTS coils operate at 20-40 Kelvin (K) compared to LTS coils that generally operate at less than 10 K. Higher operating temperatures mean that, unlike LTS coils and magnets, many HTS applications do not require actively-cooled shields. Their temperature can be controlled by simpler, standard industrial refrigeration systems. It is also easier to design cryogen-free HTS magnets, an important consideration in underdeveloped countries where the liquid helium mandated for cooling LTS magnets is not available. Simpler, more standardized cooling systems means HTS coils and magnets offer more design flexibility, simpler manufacturing processes, fewer moving parts and compact packaging than their LTS counterparts. These factors also deliver savings on transportation and installation.

Thermal Stability Coils and magnets operating at extremely low temperatures, such as those of LTS applications, are more vulnerable to quenching (sudden loss of superconducting properties) than HTS coils and magnets (which can operate at much higher temperatures). In addition, most LTS coils operate much closer to their critical temperature than their HTS counterparts. This means HTS coils and magnets can withstand greater temperature change without losing their superconducting properties.

Lower Cooling Costs Since LTS coils operate below 10 K, cooling costs are extremely high for any application that generates significant heat. Raising operating temperatures from the 4.2 K required by many LTS coils and magnets to the 20 K used for HTS coils and magnets cuts refrigeration costs by a factor of 10.

Higher Magnetic Fields The high upper critical fields of HTS wire can produce magnetic fields stronger than those possible with LTS wire alone. HTS inserts produce fields up to 25 Tesla when used in LTS generated background fields.

HTS magnets are commercially available today. Experience with the initial applications, which were in the military and scientific domains, are expected to give rise to expanded applications addressing other markets. Companies that supply HTS magnets are summarized in the “Component Supplier” section.