High-beta steady-state research and future directions on the Japan Atomic Energy Research Institute Tokamak-60 Upgrade and the Japan Atomic Energy Research Institute Fusion Torus-2 Modified

In the Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U), a high-βp ELMy H-mode (high-poloidal-beta high-confinement-mode with edge localized mode) plasma was sustained with βN∼2.7 for 7.4 s. Real-time neoclassical tearing mode (NTM) stabilization system was established and effective NTM suppression by early electron cyclotron (EC) wave injection was demonstrated. High fusion triple product of ni(0)τETi(0)=3.1×1020 keV⋅s⋅m−3 was achieved using the negative-ion based neutral beam current drive with βN∼2.5 and the bootstrap current fraction fBS∼50%. In a hot electron regime, a high electron cyclotron current drive efficiency of 4.2×1018 A/W/m2 was achieved at Te∼21 keV. Innovative current start-up scenario produced a current hole plasma with a very high fBS∼90%. No accumulation of helium and carbon impurities was observed for internal transport barrier (ITB) plasmas. While argon impurity was accumulated, EC injection effectively exhausted it across ITB. In a regime of ELM disappearance, a clear correlation between the ELM frequency and the toroidal velocity at pedestal was observed. In the Japan Atomic Energy Research Institute Fusion Torus-2 Modified (JFT-2M), high beta plasmas were produced with full ferritic inside wall up to βN=3.3, where high recycling steady H-mode discharges were developed up to βNH89P∼6 at ne/nGW∼0.7–1.0 with ITB. JT-60U started long pulse experiment in late 2003 and JFT-2M will conduct wall stabilization experiment in early 2004. The modification of JT-60 to a fully superconducting coil tokamak is regarded as the national centralized tokamak facility program to accomplish the high beta steady-state research in a collisionless regime.