Simons Foundation funds collaboration on stellarators

With permision from [Hudson et al, Phys Lett A, 382, 2018]

With permision from [Hudson et al, Phys Lett A, 382, 2018]

The Swiss Plasma Center participates in an international collaboration, funded by the Simons Foundation, to unveil the optimal magnetic configurations of stellarators so that their performances are similar to those of tokamaks - while retaining the advantage of being able to operate continuously. The optimization aims at exploiting the beneficial effect of some hidden symmetries that can be produced by specific arrangements of the magnetic coils.

The Simons Foundation, a private foundation created by billionaire mathematician and philanthropist Jim Simons, has awarded 2M$ per year over four years to an international collaboration, involving the physicist Joaquim Loizu of the Swiss Plasma Center, to develop a numerical model to optimize the configuration of stellarators by exploiting hidden symmetries.

A stellarator is a toroidal device that looks like a tokamak. However, it differs from the latter by the presence of non-planar magnetic coils, which makes the stellarators non-symmetric toroidally and therefore more complex. On the other hand, the particular structure of the coils prevents from generating a current in the plasma, thus making it more stable and easier to maintain over long periods of time. Historically, these advantages have generally been achieved at the expense of the performance of the machine, particularly in terms of quality of confinement. Indeed, by breaking the toroidal symmetry of the tokamaks, the stellarators do not confine the particles so well.

Recent discoveries have shown that some symmetries hidden in the magnetic field structure of stellarators can lead to confinement close to that of tokamaks. For example, if the magnetic field has no symmetry but its amplitude is constant along a special coordinate called Boozer, then the particles are confined as well as in a tokamak.

Simons Foundation funding supports an international and interdisciplinary team led by Princeton University, including several universities in the United States, UK, Germany, Switzerland, and Australia. The physicist Joaquim Loizu of the Swiss Plasma Center is part of the research team that will develop software to optimize the 3D configuration of stellarators by making the most of these hidden symmetries.