Tokamak operation with a tungsten wall

In order to qualify tungsten as surface material for a future fusion reactor, the plasma facing carbon tiles of ASDEX Upgrade were coated with tungsten. The first experimental campaign – without wall conditioning by deposition of boron – demonstrated a favourable behaviour of tungsten with regard to hydrogen retention. After boronization, the reduced impurity content caused low intrinsic radiation. Injection of nitrogen re-established a radiative level required to protect the divertor from thermal overload, resulting also in an (unexpected) improvement of the energy confinement.