Beyond the tokamak

TORPEX: plasma in a simple torus

TORPEX is a device for basic plasma physics, which appears on the SPC’s timeline in 2003. It is what physicists call a simple magnetised torus: a ring-shaped chamber with a major radius of 1 metre and a minor radius of 0.2 metres, surrounded by 28 toroidal coils and 4 vertical coils. The magnetic field lines wind around the ring in a helix, and the device is used to study the waves and turbulence that physicists call drift-interchange.

Its plasma is made by microwaves at 2.45 gigahertz, the frequency of a kitchen microwave oven, from hydrogen, helium, neon or argon. It is far cooler and thinner than in a tokamak: an electron temperature of about 5 to 10 electronvolts and a density of about 10¹⁶ to 10¹⁷ particles per cubic metre. That makes it possible to study turbulence and instabilities in detail. The SPC describes TORPEX as one of the few dedicated basic plasma physics devices in Europe, relevant to space and astrophysical plasmas as well as to magnetic fusion.

TORPEX can also be run in a configuration closer to a tokamak. A copper conductor carrying a current of up to about 1 kiloampere adds a further component to the magnetic field, and the device can also induce a plasma current of the same order.

Theory and simulation

A large part of plasma physics happens on computers. The SPC has its own research line in theory and numerical simulation, and already in 1995 it built its first massively parallel computing system for fusion research.

One example of its tools is GBS, a code hosted by EPFL that simulates turbulence at the edge of a tokamak plasma in three dimensions. It has been used for different magnetic geometries, including the snowflake divertor first made on TCV, and for simulations of TCV itself. Another example of how this work feeds into experiments: the artificial intelligence controller that steered TCV’s plasma in 2022 was trained on the SPC’s plasma simulator before it was used on the real machine (see The tokamak that changes shape).

Plasmas at low temperature

Not every plasma is for fusion. The SPC set up a group for industrial plasmas as early as 1989. Today its research line in low-temperature plasma physics and applications, LTP2A, studies how such plasmas behave and how they interact with materials and living systems.

On the industrial side, the group develops plasma technologies for more efficient manufacturing of microelectronics and advanced materials, in partnership with companies. On the biological side, a bio-plasma laboratory combines plasma physics, plasma chemistry and biology to study how cold plasmas can safely interact with living organisms, with possible uses in healthcare, agriculture and biotechnology. The work also loops back to fusion: on a device called RAID, the group is developing a new source of negative ions for neutral beam heating.

SULTAN: testing superconductors in Villigen

A fusion power plant would need huge superconducting magnets. Copper electromagnets would not meet the demands of the largest machines, so their coils are made of superconductors. In a tokamak such a magnet sits about one metre from a plasma at around 150 million degrees, while itself being cooled to 5 kelvin.

The SPC’s superconductivity group develops and tests conductors for such magnets. It is based not in Lausanne but at the Paul Scherrer Institute in Villigen, where the SULTAN facility has been operating since 1992. SULTAN can test conductors in a magnetic field of up to 11 tesla, produced by six superconducting solenoids, with a direct current of up to 100 kiloamperes, cooled by supercritical helium at 4.5 to 10 kelvin. Alternating and pulsed magnetic fields can be added on top of the steady field.

The SPC calls SULTAN the reference facility for ITER superconductors; it has also tested conductors for the magnets of the Wendelstein 7-X stellarator. The group also runs a facility called JORDI and lists a further one, EDIPO 2, as under construction (status as of 3 November 2026). More about the institute in Villigen is on Villigen.science.

How the pieces fit together

Each of these lines answers a different part of the same question. TORPEX and the theory group look at how turbulence carries heat out of a plasma; TCV tests whether a different plasma shape can tame it; SULTAN checks the conductors for the magnets of future machines; and the low-temperature work brings plasma physics into everyday technology. The basic principles behind all of them are on A magnetic bottle for a star.