Recent progress and future prospects of the JT-60 program

Recent results from JT-60U on high performance and steady-state experiments are presented. High fusion performance of n_D(0)τ_ET_i(0)=1.1×10²¹ m^-3·s·keV, Q_DT~0.6, S_n =5.6×10¹⁶ s^-1 has been obtained in the regime named “High-β_p H-mode”. A total plasma pressure has achieved ~0.12 MPa and a bootstrap current has reached ~1 MA in these high fusion performance plasmas. Optimization of current profile and heat deposition profile has substantially extended attainable β_N and β_p values, reaching 4.0 and 4.3, respectively. In a quasi steady state of ELMy H-mode, β_N~3, β_p~3 and H-factor~2.2 was sustained under the full current drive condition (bootstrap current ~50%, beam driven current ~50% at Ip=0.5 MA). In addition, driven current of 3.6 MA has been obtained by lower hybrid wave, and the capability of LH and NB as active current driver was demonstrated. Experiments show high safety factor is attractive to obtain high plasma performance. Also described are the future plan of a new 500 keV negative ion beam system and a proposal of further modification of JT-60U named “JT-60 Super Upgrade”. JT-60 Super Upgrade aims to establish an integrated basis of physics and technology for steady-state tokamak reactors like SSTR