|
|
One important key technology towards a steady-state tokamak reactor
is a divertor, an exhaust control system of extra-heat and impurity
particles from the core plasma. The divertor is composed of a
specially-shaped magnetic field at the outer edge of the plasma,
divertor plates and a vacuum pumping system and works to exhaust
fusion-produced extra-heat and particles ("helium ash") from the
core plasma and also to prevent an influx of impurities into the
plasma. Since the divertor plates serve as dumps for energetic
impurity particles and high extra-heat flux from the plasma, they
should have sufficient endurance for such severe engineering conditions
and an intensive research and development of their materials and
mechanical structures are required. It is also necessary to decrease
or dissipate the heavy heat load to the divertor plates on the
basis of some appropriate physical mechanisms. One most promising
concept to do this is to create high density and low temperature
plasma around the divertor plates and dissipate the influx of
heat energy as radiation of light through various physical processes
occurring in such high density and low temperature plasmas (the
radiative cooling divertor), thus reducing the heat flux to the
divertor plates, where the plasma around the divertor plates is
working like a "cushion" for their protection. This concept is
now actively studied experimentally (see Fig. 2-5). In JT-60, we have demonstrated this mechanism operates quite well to dissipate up to 70% of the energy influx to the divertor as light radiation and to reduce remarkably the heat influx to the divertor plates (see Fig. 2-6). The radiative divertor plasma was produced using neon gas puffing, a pulsed introduction of a certain amount of the gas to the divertor region of JT-60 where a rarefied plasma exists before the introduction of the neon gas. Neon gas is used because it radiates well in the plasma. We have also observed that an undesirable influence on the confinement of the main plasma can be minimized by carefully optimizing the neon gas puffing. As a result we have provided an important data base for the design of the divertor of a fusion reactor such as ITER. |
Reference
K. Itami et al., Improved Confinement of JT-60U Plasmas, Plasma Phys. Control. Fusion, 37, A255 (1995). |
Select a topic in left column |
Persistent Quest-Research Activities 1996 Copyright(c)Japan Atomic Energy Research Institute |