Present Status of Systems and their Prospects

Recent research has made significant progress for the plasma confinement in helical systems. Experiments have been carried out in W7AS, CHS, ATF, H-E and others. The plasmas, whose electron temperature is around 2–3keV, ion temperature is 1 keV and density is 2–3×10²⁰ m^-3, are well confined with the energy confinement time τ E =10–40ms and the stable beta value reaches at < β >> 2% (β (0)=7%)[1]. The obtained scalings for the global energy confinement time such as LHD, GRB(Gyro-Reduced Bohm), L-G(Lackner-Gottardi) scalings are comparable with the tokamak L-mode scaling in the above parameters' range. The improved confinement modes are also explored in helical systems as H mode or the control of plasma profile.

In this paper, firstly present experimental results are reviewed on the confinement, MHD equilibrium/stability beta limit, and secondly the outline of LHD and W7X program is described.

Finally, is discussed the feasibility of helical systems as a fusion reactor, based on the present experimental results.