No abstract

This paper reviews the results of an experimental study undertaken in Heliotron J over the past few years to explore the physics design base for a new concept of a helical-axis heliotron. Measurements of electron cyclotron resonance (ECR)/neutral beam injection (NBI)/ion cyclotron range of frequencies (ICRF) heating plasmas have been made for understanding global energy confinement in connection with the international stellarator scaling law (ISS04), spontaneous confinement improvement (L-H transition), confinement improvement based on supersonic molecular beam injection (SMBI), magnetohydrodynamic (MHD) activity, edge plasma characteristics, including rotation of a filamentary turbulence structure, and plasma current control, including the electron cyclotron current drive (ECCD), the energetic-particle driven Alfvén eigenmodes, and related fast ion dynamics. The results are discussed in terms of the rotational transform ι/2π and the bumpiness ε b (or the effective helical ripple ε eff ). Control of these two parameters was experimentally demonstrated to be the key issue in determining the optimum performance of Heliotron J. The result confirms that the helical-axis heliotron provides a unique and high potential for exploiting an alternative and advanced path to future helical systems.