JT-60U latest results and future prospects

Experimental results achieved in the initial operation of JT-60U [Plasma Devices Operat. 1, 43 (1990)] are described in this paper. Experiments of JT-60U were initiated in March and deuterium experiments started in the middle of July. Multivariable noninteracting control was adopted to allow independent control despite the strong mutual coupling between the Ohmic heating coils and the vertical field coils. Well-controlled divertor discharges were successfully obtained using this method and discharges with plasma current up to 5 MA were achieved. In neutral beam heating experiments with PNBI≲22 MW, plasma stored energies Wdia of up to 4.8 MJ were obtained for 4 MA discharges. The high-βp regime with hot ions and enhanced confinement was investigated. The maximum βp reached 2.3, the maximum Ti of 20 keV was achieved and τE was improved to about 2.7 times as large as that of ITER89-P scaling [Nucl. Fusion 30, 1999 (1990)]. The maximum neutron rate of 1.3×1016 n/sec was also obtained in the highest-βp discharge. The corresponding QDD and the equivalent QDT were 8.9×10−4 and ∼0.20, respectively. Localized heat load in both toroidal and poloidal directions was clearly identified as ripple loss, and this was the first measurement of heat load mainly due to ripple trapped loss consistent with calculated results. Divertor plasma profiles measured with Langmuir probes show significant in–out asymmetry.