Author/Authors :
Matsuoka، نويسنده , , K. and Okamura، نويسنده , , S. and Nishimura، نويسنده , , K. and Tsumori، نويسنده , , K. and Akiyama، نويسنده , , R. and Yamada، نويسنده , , H. and Sakakibara، نويسنده , , S. and Lazaros، نويسنده , , A. and Xu، نويسنده , , Francisco J. and Ida، نويسنده , , K. and Tanaka، نويسنده , , K. and Morisaki، نويسنده , , T. and Morita، نويسنده , , S. and Arimoto، نويسنده , , H. and Ejiri، نويسنده , , A. and Fujiwara، نويسنده , , M. and Idei، نويسنده , , H. and Iguchi، نويسنده , , H. and Kaneko، نويسنده , , O. and Kawamoto، نويسنده , , T. and Kubo، نويسنده , , S. and Kuroda، نويسنده , , T. and Motojima، نويسنده , , O. and Ozaki، نويسنده , , T. and Pustovitov، نويسنده , , V.D. and Sagara، نويسنده , , A. and Takahashi، نويسنده , , C. and Toi، نويسنده , , K. and Watari، نويسنده , , T. and Yamada، نويسنده , , I.، نويسنده ,
Abstract :
A volume-averaged equilibrium β value 〈βeq〉 of 2.14% is achieved in a compact helical system using two neutral beam lines with balanced injection and intense wall conditioning with Ti gettering. This value is the highest β value realized so far in helical systems. Reheat mode, where the stored energy increases after turn-off of a strong gas puff, is employed in the experiment. Discharge conditions are as follows: Bt = 0.61 T; beam power through the port, 1.1 MW (coinjection) and 0.8 MW (counterinjection); line-averaged electron density ne = 6.5 × 1013cm−3. Amplitudes of magnetic fluctuations integrated over the frequency range from 3 kHz to 100 kHz become saturated at 〈βeq〉 higher than 1%. Dominant coherent modes are mn = 21 and 11 when 〈βeq〉 is lower and higher respectively than 1%. Dependence of the energy confinement time τE on ne (up to 8 × 1013 cm−3) and Bt (from 0.6 to 1.8T) is also studied in this high β experiment. When the density increases τE degrades compared with the LHD scaling; the density dependence exhibits Bohm-like behaviour. On the contrary, τE scales as Bt≈0.75, which is rather close to the LHD scaling (gyro-Bohm-like behaviour).
