Tokamak Energy runs superconducting fusion magnets at 13.7 tesla

What happened

Tokamak Energy is a fusion developer based near Oxford in England. Its Demo4 system is a full magnet set arranged as it would be in a spherical tokamak, a type of fusion machine shaped more like a cored apple than a doughnut. The company presented the test results at the Applied Superconductivity Conference in Pittsburgh, in the United States, in the same week as its announcement. The campaign tested the whole assembly together, not single coils on their own, so the coils, joints, cooling and current supply all had to work as one system.

The company reports these results. The main coils carried 5,600 amps. The system was cycled between 77 kelvin and 17 kelvin, which is between about minus 196 and minus 256 degrees Celsius. The coils resisted sideways mechanical stress of 150 megapascals, which the company compares to almost 1,500 times atmospheric pressure. More than 90 superconducting joints worked reliably over the campaign.

This was a step up from an earlier test. In November 2025, Nuclear Engineering International reported that Demo4 had reached 11.8 tesla at minus 243 degrees Celsius. The new peak of 13.7 tesla is about 1.9 tesla higher. For comparison, a strong fridge magnet is far below 1 tesla, so fields of this size need special materials and very careful mechanical design.

The results feed into Tokamak Energy's work on STEP, a planned fusion plant at West Burton in England. The company is the magnet systems partner for the project under a £70 million contract with UK Fusion Energy that runs to March 2029. Tokamak Energy also has a separate business, TE Magnetics, which aims to sell superconducting magnets for uses outside fusion.

The engineering behind it

A superconductor is a material that carries electric current with no resistance once it is cold enough. Older superconductors need cooling with liquid helium to about 4 kelvin. High-temperature superconductors, or HTS, work at much warmer temperatures, though still far below freezing. Nuclear Engineering International notes that HTS can carry roughly 200 times the current density of copper. That is what allows small, very strong magnets.

Demo4 has 44 coils. Fourteen vertical limbs each hold two coils that make the main ring-shaped, or toroidal, field. Two more coil sets, each built from eight coils, make the poloidal field that shapes and holds the plasma. A pressurised helium system at up to 20 bar keeps everything cold. More than 600 sensors measure voltage, field, temperature and stress, so engineers can see exactly how each part behaves.

Strong magnets push hard on their own wires. Current flowing in a magnetic field feels a force, and at 13.7 tesla those forces become very large. This is why the 150 megapascal stress test matters. If the coils move or crack under that load, the superconducting tape can be damaged. Thermal cycling adds more stress, because materials shrink and grow by different amounts each time the system is cooled and warmed.

The forced discharge tests were about safety. A large magnet stores a lot of energy in its field. If part of a superconductor suddenly becomes normal and resistive, an event called a quench, that energy can heat one small spot and destroy it. Engineers must detect the problem quickly and remove the energy safely. Tokamak Energy says it forced several discharges at up to 12.5 tesla and found no hot spots or damage.

What it means in Nepal

Fusion power is still a research goal, and no source here connects this work to Nepal. The useful lesson for a student is in the methods. Demo4 combines four kinds of engineering in one system: electromagnetics to design the coils, mechanics to hold them together, cryogenics to keep them cold, and electronics to measure and protect them. Most large electrical systems need the same mix, even when they are not superconducting.

Protection and measurement are good examples. Every power transformer, generator and long cable must be able to fail safely. Engineers design sensors to detect faults, circuits to disconnect power quickly and paths to remove stored energy. Demo4's 600 sensors and its forced discharge tests are an extreme case of the same idea. The principle, that a system must be tested in fault conditions and not only in normal use, applies to any electrical installation.

The story also shows the value of long, patient testing. Tokamak Energy ran Demo4 for 14 months and about 10,000 hours, and New Civil Engineer reports that the work improved its manufacturing and jointing methods and its computer models. Careful record keeping, data analysis and step-by-step testing are skills that any engineer can practise, on a lab bench or on a final-year project, long before working on a large machine.