High performance and prospects for steady state operation on JT-60U

Recent experimental results for steady state high performance plasma on JT-60U are described, emphasizing plasma control, especially active control of profiles. In reversed shear (RS) plasma, a DT equivalent fusion gain of 0.5 was sustained for 0.8 s ( ~ the energy confinement time) by controlling plasma b with a newly developed stored energy feedback control technique. An internal transport barrier (ITB) with an RS configuration was successfully maintained by means of LHCD in full current drive quasi-steady state for 4.7 s. The viability of a steady state RS configuration sustained by a large bootstrap current fraction has been demonstrated in ELMy H mode edge RS plasmas for the first time. In high-bp ELMy H mode plasmas, an integrated core plasma performance with H factor of 2.56, bN = 2.4, and bootstrap current fraction and noninductively driven current fraction close to the ITER requirements was achieved at Ip = 1.5 MA in a near full current drive state by negative ion based NB (N-NB) injection. A rudimentary simulation of a reactor operation with simultaneous feedback control of both the core and divertor plasmas has been demonstrated in ELMy H mode plasma. Aiming at active control of the pressure gradient at the ITB in RS plasmas, a feedback control system of the electron temperature gradient has been developed and optimization of the discharge scenario using this system has recently started.