The ASDEX Upgrade tokamak in Germany has recently successfully demonstrated a new technique for enhancing the functioning of the divertor plasma exhaust system. This was achieved using a fast feedback control system to inject small amounts of argon into the main space and of nitrogen directly in front of the divertor plates, thereby actively cooling the plasma edge.

The injected gas particles are excited to luminescence on contact with the hot plasma. The energy is thus gently removed from the plasma as ultraviolet or x-ray light. Unlike in the hot core, where this cooling effect of impurities has to be avoided, it is very useful at the edge of the plasma: Before the fast plasma particles impinge on the divertor plates, they have already lost their energy to the nitrogen and argon atoms.

For more information on this technique, visit: http://www.ipp.mpg.de/ippcms/eng/presse/pi/12_12_pi.html