Improved Particle Control for High Integrated Plasma Performance in JT-60U
HIDENOBU TAKENAGA*
Japan Atomic Energy Research Institute, Naka-machi, Naka-gun, Ibaraki-ken, 311-0193, Japan
Abstract.
The JT-60U high performance plasmas characterized by the internal and/or edge transport barriers (ITB and/or ETB) have been optimized for integration of high confinement, high bN, high bootstrap current fraction. In order to extend the integration to other elements of 1) high density, 2) high efficient helium ash exhaust, 3) high edge radiation and 4) high plasma purity, improvement of particle control such as fuelling, transport and exhaust is crucial. In this paper, particle control related to 1) - 4) is highlighted. 1) For the extension to high density regime, the multiple pellet injector has been installed for injection from low field side midplane : LFS(mid) or high field side top : HFS(top). The plasma density reached up to Greenwald density in the OH plasma using the LFS(mid) pellets (2.1 mm cube, 10 Hz and 690 m/s) at Ip=0.8 MA. In the high power NBI heated plasma, the LFS(mid) pellet was less effective due to deteriorated fuelling efficiency and short density decay time. For the HFS(top) pellet injection, fuelling efficiency seems to be independent of the NBI power. 2) The effective He exhaust of t*He/tE=3 was achieved in the ELMy H-mode plasma. In the reversed shear (RS) plasma, t*He/tE=11 was obtained inside the ITB. 3) For simultaneous sustainment of high confinement and high radiation, Ar seeding was applied. The radiaton loss power was enhanced up to 80% of the heating power with H89L=1.5 in the ELMy H-mode plasma. In the RS plasma, H89L 2 was achieved with a high radiation power fraction of 70%. 4) For understanding of impurity transport at the ITB in the RS plasma, He, C and Ne transport was investigated. Particle diffusivity was significantly reduced at the ITB and almost the same for all species. The inward pinch velocity was larger for higher Z impurity at the ITB.
* On behalf of the JT-60 Team.