K. Kodama,T. Sasajima, K. Masaki, N. Hosogane, S. Sakurai, M. Morimoto, Y. Miyo H. Hiratsuka, N. Akino, S. Takahashi, K. Kishiya, Y. Neyatani and M. Saidoh
Naka Fusion Research Establishment, Japan Atomic Energy Research Institute
In JT-60U, the modification from the open divertor to a W-shaped divertor with pumps was carried out between February and May of 1997, aiming to develop a new divertor which realizes good energy confinement and radiative divertor simultaneously. The W-shaped divertor is a type of inclined target divertor with a dome in the private flux region as well as inner and outer baffle plates. The divertor pumping will be done from the private flux region like ITER through three large pumping ports(560 mm in dia.). The designed maximum plasma current is 3 MA.
The W-shaped divertor were fabricated with small structural components sectioned in the toroidal directions(125 sections for divertor targets and a dome, 72 sections for baffle plates) . Toroidal and poloidal gaps between these structures were sealed with stainless thin plates(0.5 mm in thickness) insulated by ceramic plasma spray (about 0.3 mm in thickness) to reduce the back flow of neutral gas to the main plasma region. CFC tiles are used for divertor targets, baffle tiles at the divertor throat and the top of the dome where the high heat flux (10 MW/m2 x 4 s) is expected. Thermocouples were arranged to these tiles to measure the heat flux as well as an IRTV camera. Furthermore, to reduce the excessive heat flux at the tile edges, the surface level of tiles in the upstream side of the heat flux were manufactured so as to be 0.5 mm higher than the neighboring ones in the downstream side.
Eighteen Rogowski coils were installed to the baffle supports and basements of tiles to measure halo currents in disruptions. The influence of the halo currents on the divertor structures will be checked carefully before the plasma current level is raised.
Three cryopumps(1000 m3/s each) of the NBI ion source system were converted to the divertor pumps. The net pumping speed is 35-70 m3/s with an effect of Knudsen flow. To control the pumping speed during a shot, three fast shutter valves in the pumping ports, which were originally used for NBI heating, were modified so that their aperture could be changed to 0%, 25%, 50%, 75%, and 100%. The gas fueling locations were also rearranged for optimizing fueling methods, such as fueling to the main plasma, divertor fueling. etc..
The new divertor system will be operated from the beginning of June. This paper will present the installations of these systems.