Experimental studies of ITER demonstration discharges

ITERデモンストレーション放電の実験研究

Sips, A. C. C.*; Casper, T.*; Doyle, E. J.*; Giruzzi, G.*; Gribov, Y.*; Hobirk, J.*; Hogeweij, G. M. D.*; Horton, L. D.*; Hubbard, A. E.*; Hutchinson, I.*; 井手 俊介; 諫山 明彦; Imbeaux, F.*; Jackson, G. L.*; 鎌田 裕; Kessel, C.*; Kochl, F.*; Lomas, P.*; Litaudon, X.*; Luce, T. C.*; Marmar, E.*; Mattei, M.*; Nunes, I.*; 大山 直幸; Parail, V.*; Portone, A.*; Saibene, G.*; Sartori, R.*; Stober, J. K.*; 鈴木 隆博; Wolfe, S. M.*; C-Mod Team*; ASDEX Upgradeチーム; DIII-D Team*; JET-EFDA Contributors*

Sips, A. C. C.*; Casper, T.*; Doyle, E. J.*; Giruzzi, G.*; Gribov, Y.*; Hobirk, J.*; Hogeweij, G. M. D.*; Horton, L. D.*; Hubbard, A. E.*; Hutchinson, I.*; Ide, Shunsuke; Isayama, Akihiko; Imbeaux, F.*; Jackson, G. L.*; Kamada, Yutaka; Kessel, C.*; Kochl, F.*; Lomas, P.*; Litaudon, X.*; Luce, T. C.*; Marmar, E.*; Mattei, M.*; Nunes, I.*; Oyama, Naoyuki; Parail, V.*; Portone, A.*; Saibene, G.*; Sartori, R.*; Stober, J. K.*; Suzuki, Takahiro; Wolfe, S. M.*; C-Mod Team*; ASDEX Upgrade Team; DIII-D Team*; JET-EFDA Contributors*

ITERにおける放電の時間発展に関して、実験的に検証した。すなわち、着火から電流立ち上げ,電流フラットトップ,電流立ち下げである。着火に関しては、JETのような大型トカマクではECRFによる補助なしで、またECRFによる補助が有る場合にはすべての装置でITERの要求である一周電界0.35V/mでの着火を確認できた。立ち上げ時には、早期にダイバータ移行し大きなプラズマ断面を早くに形成することによりインダクタンスをよく制御できることがわかった。フラットトップでの種々の特性、特にH-mode遷移後と逆遷移後のインダクタンスの変化についてデータが得られた。

Key parts of the ITER scenarios are determined by the capability of the proposed poloidal field (PF) coil set. They include the plasma breakdown at low loop voltage, the current rise phase, the performance during the flat top (FT) phase and a ramp down of the plasma. The ITER discharge evolution has been verified in dedicated experiments. New data are obtained from C-Mod, ASDEX Upgrade, DIII-D, JT-60U and JET. Results show that breakdown for 0.23-0.33 V m is possible unassisted (ohmic) for large devices like JET and attainable in devices with a capability of using ECRH assist. For the current ramp up, good control of the plasma inductance is obtained using a full bore plasma shape with early X-point formation. This allows optimization of the flux usage from the PF set. Additional heating keeps (3) 0.85 during the ramp up to = 3. A rise phase with an H-mode transition is capable of achieving (3) 0.7 at the start of the FT. Operation of the H-mode reference scenario at 3 and the hybrid scenario at = 4-4.5 during the FT phase is documented, providing data for the (3) evolution after the H-mode transition and the (3) evolution after a back-transition to L-mode. During the ITER ramp down it is important to remain diverted and to reduce the elongation. The inductance could be kept 1.2 during the first half of the current decay, using a slow ramp down, but still consuming flux from the transformer. Alternatively, the discharges can be kept in H-mode during most of the ramp down, requiring significant amounts of additional heating.