Development of steady-state operation using ion cyclotron heating in the Large Helical Device

Using a handshake shape (HAS) antenna phasing dipole for ion cyclotron heating (ICH), the heating efficiency was higher than that using a previous poloidal array antenna in the Large Helical Device. In order to sustain the dipole operation, real-time feedback for impedance matching and maintaining the same phase and power was adopted during long-pulse discharge. The HAS antenna was designed to reduce parasitic losses associated with energetic particle and radio-frequency (RF) sheath effects by field-aligned current concentration on the midplane. Local hot spots and the inhomogeneity of the diverter heat profile in the toroidal direction were reduced. The long-pulse discharge with an electron density (ne0) of 1 × 1019 m−3, center electron temperature (Te0) of 2.5 keV, a plasma duration time (td) of 19 min, and RF heating power (PRF) of 1 MW was achieved by ICH and electron cyclotron heating.