In JFT-2M, the applicability of reduced activation ferritic steel to a fusion demonstration reactor has been demonstrated mainly concerning the ferromagnetic effect on plasma production, control, stability and confinement. The compatibility of the close ferritic wall with high-normalized beta plasmas has been investigated mainly because the demonstration reactor will utilize the wall stabilization effect. Due to improvements in the operation scenario and the modification of the guard limiter configuration, the region showing good compatibility was extended to the closer wall position (the wall position was normalized to the plasma minor radius; rwall/a∼ 1.25) and the higher normalized beta (βN ∼ 3.5), compared with the previous works with the relatively far wall position and stronger magnetic field (Tsuzuki K. et al2003 Nucl. Fusion. 43 1288). A reduction in the growth rate of the instability was also observed in the close wall case, which presumably corresponds to the wall stabilization effect, similar to a resistive wall without ferromagnetism.
Overview of JT-60U results towards the establishment of advanced tokamak operation