Group High-T

H. Nakano

H. Takahashi

I. Yamada

K. Nagaoka

R. Yasuhara

S. Murakami

National Institute for Fusion Science (NIFS-Repository)

  Enhancement of the output power per gyrotron has been planned in the Large Helical Device (LHD) and the replacement of the existing gyrotrons with higher-power tubes is in progress. An electron cycrotron resonance heating (ECRH) system with eight gyrotrons has been operated for preionization and plasma heating. Of these, high power 77-GHz gyrotrons with an output power of more than 1 MW each have been operated since the experimental campaign in 2007. At present, three 77-GHz gyrotrons are operational for plasma experiments. In addition, a high power gyrotron with the frequency of 154 GHz (1 MW/5 s, 0.5 MW/CW) was newly installed in 2012. Figure 1 shows the history of the ECRH power coupled to the transmission line PMOU and the port-through power of ECRH into the LHD PECRH_pt. The heating capability of ECRH on the LHD has been upgraded year by year. The LHD now has 4.6 MW of a simultaneous-injection-ECRH power available for experiments. In the research, we tried the expansion of the high electron temperature regime of the LHD plasmas using the high power ECRH system. In order to focus the high-power 77 GHz EC wave on the plasma center, the experiments were carried out under the magnetic configurations of Rax = 3.53 m/ Bt = 2.705 T and Rax = 3.60 m/ Bt = 2.705 T. Figure 2 shows the radial profiles of the electron temperature Te and the electron density ne in a typical high Te plasma with the moderate high line-averaged electron density ne_fir of 1x1019 m-3 produced using ECRH alone. Highly accurate Te profiles were obtained by the accumulation of data of Thomson scattered light during 6 fixed-condition discharges with the three YAG laser beams all injected together. A central electron temperature of 13.5 keV was successfully achieved using a center-focused ECRH of 4.4 MW. The values of Te0 significantly exceeded 8.7 keV, obtained in previous experiments at ne_fir of 1x1019 m-3. Higher-density operations with ne_fir of more than 3x1019 m-3 were also carried out using ECRH alone. The plasma stored energy of 530 kJ with the energy confinement time of 120 ms was realized in the discharge without a radiation collapse. The value is new record of Wp in ECRH plasma and is 1.66 times larger than the previous achievement. Figure 3 shows the map of simultaneously attained Te0 and ne_fir for ECRH discharges. The plasma parameter regime with regard to the electron temperature was successfully extended in high density conditions. 02462000 2005 2010PMOUPECRH_ptP MOU, PECRH_pt [MW]YearInstallation of1st 77 GHz gyrotron2nd 77 GHz3rd77 GHz154 GHz Figure 1. The history of PMOU and PECRH_pt. 05101502462.5 3 3.5 4 4.5T e [keV]n e [x1019 m-3]R [m]Tene#114707-712,t = 3.9 s,ne = 1.0x1019m-3,PECH = 4.4 MW Figure 2. The radial profiles of Te and ne in a typical high Te plasma with ne_fir of 1x1019 m-3 produced using ECRH alone.  Figure 3. The map of simultaneously attained Te0 and ne_fir for ECRH discharges. 58§6. Extention of High Te Regime in the Large Helical DeviceTakahashi, H., Nagaoka, K., Nakano, H., Yamada, I., Yasuhara, R., High-T Group,  Murakami, S. (Kyoto Univ.)

Extention of High Te Regime in the Large Helical Device

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