Experimental Divertor Physics

The working group Experimental Divertor Physics examines the plasma emission from the visible part of the spectrum up to the X-ray range.
 

The divertor is the dedicated area for the interaction of the plasma with the wall, leading to high power and particle fluxes. The plasma is guided along the magnetic field lines towards the cooled target plates. The material in this region must withstand the highest heat fluxes and the material of choice for this is tungsten.  The plasma particles (hydrogen, helium and other gaseous species) hit the wall as ions and recycle as neutral particles either into the plasma or are pumped away through slits between the tiles. Due to the high particle fluxes, tungsten is eroded from the wall and might also reach the plasma.

For the successful operation of a fusion reactor, the control of power and particle exhaust in the divertor is a very important element and the understanding of the underlying physics mechanisms is essential. The goal is a strong decrease of the plasma temperature up to the achievement of “detachment”, where ions recombine to neutrals before even hitting the target. The combination of plasma effects, atomic and molecular physics leads to a rather complex interaction, which is still an essential part of active fusion research.

In the “Experimental Divertor Physics” group, the focus is on experimental development of the most promising divertor scenarios and their investigation as well as on the exact measurement of the corresponding plasma parameters. These parameters are, among others, the total emitted radiation (measured by bolometry), the power flux density onto the divertor tiles (measured by infrared thermography) and the flux density of eroded tungsten atoms and other species (measured by spectroscopy). Spectroscopic measurements can also be used to determine the electron density, the temperature of electrons and ions and the concentration of impurities in the plasma.