Study of high-performance plasmas in the Large Helical Device

Recent results from LHD experiments are presented together with the progress of the related fusion technology supporting the experiment. An ultra-long pulse discharge with central electron and ion temperatures of 2 keV and electron density of 1.2 x 1019m−3 was successfully maintained for 48 minutes. Such a high performance plasma was heated and sustained by electron cyclotron resonance heating (ECH) with newly developed gyrotrons and ion cyclotron range of frequency (ICRF). Due to the continuous heating with the relatively high power of 1.2 MW, the total heating energy during the long pulse discharge reached 3.36 GJ, which is the world's record. The highest central ion temperature of 8.1 keV was also recorded in the last experimental campaign. In these experiments, it is essential to reduce the edge electron density, i.e., edge neutrals. Dedicated wall conditioning was performed to evacuate neutrals in the vessel wall before the main discharge with the high heating power. This process realizes the quite low recycling for particles, which results in the reduction of the edge plasma density.