Speaker
Shinsuke Tokunaga
(Japan Atomic Energy Agency)
Description
Controllability of output power is one of the essential requirements for DEMO. Fuel control is expected as primary knob for the fusion power control. Pellet injection is considered as primary fueling technique in DEMO as with the ITER. Difference of requirement for fueling system in DEMO compared to ITER comes from demand of larger output. It consequences requirement of more fueling efficiency to obtain higher fuel density as well as sufficient purity under the conditions of density limit against to the larger He ash generation.
The fueling efficiency depends on pellet deposition profile. Because of high edge temperature, pellet ablation beyond the pedestal top is hopeless in DEMO. According to an output control simulation study with 1.5D transport code with pedestal suggests the fuel deposition profile peak preferably reaches at least r/a ~ 0.85. Thus, the plasmoid drift must be utilized to achieve the expected deposition depth. Because the pellet cloud drifts down the gradient of toroidal magnetic field in the positive R-direction, the Z-coordinate of injected point must locate in-between upper and lower edge of targeted flux tube.
In order to translate such requirements of the fuel deposition into engineering requirement specification of pellet injection system, we have investigated injection angle, speed and mass dependence of pellet deposition using a pellet ablation-drift code against to the profiles with pedestal. As the result of scan survey, pellet speed ~2000 m/s and poloidal angle >120 degrees at plasma surface are suggested as a rough estimation for DEMO R&D target. Since the pellet speed is limited by curvature of pellet guide tube (PGT), reconciliation among the PGT route with small curvature, location of coils and demand of neutron shielding arises as an engineering challenge. Optimization study of PGT route design and impact on neutron fluence on vacuum vessel will be presented.
Co-authors
Akinobu Matsuyama
(Japan Atomic Energy Agency, Rokkasho-mura, Japan)
Hiroyasu Utoh
(Japan Atomic Energy Agency, Rokkasho-mura, Japan)
Kenji Tobita
(Japan Atomic Energy Agency, Rokkasho-mura, Japan)
Nobuyuki Asakura
(Japan Atomic Energy Agency, Rokkasho-mura, Japan)
Shinsuke Tokunaga
(Japan Atomic Energy Agency, Rokkasho-mura, Japan)
Yoshiteru Sakamoto
(Japan Atomic Energy Agency, Rokkasho-mura, Japan)
Youji Someya
(Japan Atomic Energy Agency, Rokkasho-mura, Japan)
