Forskningsprojekt ITER-experimentet

ITER, the next step on the road to provide fusion power as a virtually limitless energy source, is a tokamak experimental fusion reactor. Here, strong axisymmetric magnetic fields confine the hot plasma, with temperatures of about 150 million degrees or 10 times the temperature in the centre of the sun.

The tokamak configuration consists of strong poloidal and toroidal fields. External poloidal coils create the toroidal field while a toroidal current creates the poloidal field. In the basic configuration of the tokamak this current is inductively driven by a transformer which results in pulsed operation. A future fusion reactor will most like be operated in a steady-state configuration where the toroidal current will be sustained non-inductively. However, this so called advanced tokamak operation gives rise to a set of global mode instabilities which must be controlled.

One possible way of controlling these global modes is by adding a weak, non-symmetric 3D magnetic field through a set of external coils. ITER will be supplied with such coils but there is still a lot to be learned about these modes and how to control them best.

The EXTRAP-T2R, a medium-sized fusion experiment of the reversed-field pinch configuration and located at the Royal Institute of Technology, gives excellent opportunities to study global mode instabilities. The reversed-field pinch is inherently more unstable than the tokamak and hosts a range of so called resistive wall modes, a type of global modes. The experiment is equipped with 4 times 32 sensor and control coils in poloidal and toroidal direction, respectively, to give full coverage of the torus. EXTRAP-T2R was the first fusion experiment to show that global modes can be controlled by applying a weak 3D magnetic field.

The purpose of the project is to further study the physics of the resistive wall modes and to optimize the active control system. The work will be initiated at EXTRAP-T2R, utilizing the extensive coil coverage and feedback system, before tested at the ASDEX Upgrade fusion experiment, a tokamak designed to study and prepare for advanced operation scenarios at ITER.