Recent results from the Large Helical Device

Abstract

The most important finding in the Large Helical Device (LHD) experiments so far is that an inward-shifted configuration exhibits good plasma performance with a scaling similar to that of ELMy H-mode tokamaks. The inward-shifted configuration has been predicted to have unfavourable magnetohydrodynamic (MHD) properties, even though it has significantly better particle-orbit properties. However, no serious confinement degradation due to the MHD activities was observed, resolving favourably the potential conflict between stability and confinement. Neoclassical transport loss can be suppressed even in a low-collisionality regime, and in this way the inward-shifted configuration was shown to make the LHD plasma properties favourable. Then, it is very important to realize more improved plasma performance and higher temperature plasmas for extending the plasma-parameter regime in order to obtain data that can be extrapolated to a reactor. In the fifth campaign in 2001–2002, an increase in the heating power achieved an electron temperature Te of over 10 keV and an ion temperature Ti of 5 keV. A Te profile, which is characteristic of internal transport barriers, was also observed when the electron cyclotron resonance heating power was highly focused on the centre of the plasma sustained by neutral beam injection.