Abstract
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.
Highlights
In designing a commercial fusion reactor, steady-state operation is important to decrease the cost of electricity and to increase the lifetime of the fusion plant
In order to understand the mechanism of the penetration and production for impurities, toroidal phasing experiments for ion cyclotron heating (ICH) have been conducted to decrease the impurity production associated with RF sheath potential and energetic particles at the plasma edge with a dipole phase in the Large HelicalDevice (LHD)
Antenna was broader and located around the region geometrically closest to the minimum of DLCFS, and this region for the handshake shape (HAS) antenna was not strongly related to direct energetic particle losses during ICH. These results suggest that the local heat load using the HAS antenna is decreased with the improvement of heat conductivity using the carbon-fibercomposite and the reduction of parasitic losses associated with the energetic particles in front of the ion cyclotron range of frequencies (ICRF) antenna
Summary
In designing a commercial fusion reactor, steady-state operation is important to decrease the cost of electricity and to increase the lifetime of the fusion plant. A long-pulse discharge with the plasma duration time (sd) of 54 min was demonstrated with the line-averaged electron density (ne) of 0.4 1019 m3, the central electron temperature (Te0) of 1 keV, and the radio-frequency (RF) heating power (PRF) of 0.5 MW (electron cyclotron heating (ECH): 0.1 MW, ion cyclotron heating (ICH): 0.4 MW) in a hydrogen-minority heating regime with helium plasmas.. As plasma duration time and RF heating power increase, hot spots and sparks appear at various places inside of the vacuum vessel. With the persistence of strong hot spots and increasing frequencies of flashes, long-pulse discharges are usually terminated by an unpredicted radiation collapse within a time scale of 0.2 s.3. 19 min in steady-state operation with a helium plasma and the improvements of ICH using the HAS antenna
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