H. Idei

H. Igami

H. Takahashi

H. Zushi

K. Hanada

K. Nagasaki

K. Nakazawa

R. Kawarazaki

R. Minami

S. Kubo

T. Eguchi

T. Imai

T. Kariya

T. Numakura

T. Saito

T. Shimozuma

Y. Tatematsu

Y. Yamaguchi

Y. Yoshimura

National Institute for Fusion Science (NIFS-Repository)

        We have proposed a digital based millimeter wave interferometer for precise density profile measurement1.Figure 1 shows a block diagram of this interferometer. This system will be installed in the central cell of GAMMA10. The image non-radiative dielectric guide (INRDG) antenna is utilized for a transmitter. The interferometer electronics provides signal with multiple frequency component to the antenna. The INRDG antenna transmits multiple probe beams which are spatially distributed according to that frequency. Transmitted beams are collected by the receiver antenna. The phase differences due to plasma are analyzed numerically in a PC. Fig. 1 Block diagram of interferometer for validity confirmation experiment  In the previous fiscal year, we have confirmed that shape of a Teflon plate is clearly observed by means of experimental system without the mirrors. In this year, we have been designing and fabricating those quasi-optical mirrors. Figure 2 shows the illustration of ray tracing performed by CODE V (Synopsys Inc.). A cylinder shown in the center is GAMMA10 plasma. Two offset parabolic mirrors are located besides the plasma. A transmitting antenna and a receiving antenna are installed at each focal point of the reflectors. The red, green, and blue colored rays correspond to the probe beams with three different frequencies. The probe beams propagate upper side of the plasma with this quasi-optical system. These parabolic mirrors have been fabricated in the machine center of Fukuoka Institute of Technology. Fig. 2 Ray tracing result of the quasi-optical system for GAMMA10 plasma. We have now installed these parabolic mirrors in the interferometer system, as shown in picture.1. The INRDG antenna, and the receive antenna are installed at the focal point of each reflectors. Picture 1 Experimental setup of the new interferometer system performed in our experimental room (FIT). The preliminary experiment is being performed, and shows distributed optical path shown in Fig.2. It seems that the shape of a formed styrol inserted between two mirrors is observed, however, is still bluer image. We need a proper analysis method for this data to make the image clear. Development of the software will be discussed in the next time. 1) Kogi, Y. et al.: Review of Scientific Instruments 83(2012) 10E347.  A 28 GHz 1 MW 1 s gyrotron with TE8,3 cavity has been developed to upgrade the ECH systems of GAMMA 10/PDX. In the short pulse, the maximum power of 1.25 MW was obtained at the beam voltage Vk = 80 kV and the beam current Ik = 50 A. The stable operation of 0.6 MW 2 s was obtained at Vk = 70 kV, Ik = 23.9 A. The output power and pulse width were limited by the power supply and the water dummy load. In the recent studies for the advanced heating, 28 GHz range gyrotrons are required in various plasma experimental devices like QUEST of Kyushu University, Heliotron J of Kyoto University and so forth.  The final purpose of this NIFS collaborative program is the progress of the electron heating study such as the electron Bernstein wave (EBW) heating in super dense core (SDC) plasma. For the first step of this study, the Tsukuba 28 GHz 1 MW gyrotron is adapted to QUEST ECH system and the plasma heating effect in QUEST is demonstrated. In 2013 studies, the super conducting magnet (SCM) and Tsukuba 28 GHz gyrotron were installed first in the QUEST ECH system that was remodeled for triode-gyrotron operation in 2012. The SCM was installed on the oil tank and cooled down. The setting position of SCM was adjusted so that the magnetic axis of SCM accorded with gyrotron axis. The gyrotron and matching optics unit (MOU) were installed. The plumbing of the coolant were attached. The high power test of gyrotron was carried out, while the malfunctions of the combination drives of the power supply and the gyrotron were settled. The RF power was measured by a water dummy load at the MOU output and the coupling waveguide output attached at MOU. The gyrotron output power was confirmed until 370 kW. The output RF beam profile and phase form the gyrotron are adjusted by Matching Optics Unit (MOU), and the RF beam is coupled to a corrugated waveguide with its diameter of 63.5 mm as HE11 mode. The RF power coupled to the waveguide mode transmits 0.85 m to the vertical direction. And it transmits about 10 m to the horizontal direction after being bent 90 degrees by the miter bend. RF transmission line is evacuated in a vacuum. A picture of gyrotron and transmission wave guide installed at QUEST is shown in Fig.1. Adjustment of the gyrotron operating parameter and the pulse width extension were carried out, while RF power was injected to QUEST plasma. The successful results were obtained that the over dense plasma production more than 1×1018 m-3 which was higher than cut-off density at 8.2 GHz and EC-driven plasma current of 60 kA in QUEST plasma experiment. The electron temperature was 80 eV. On the other hand, the design study of a dual-frequency gyrotron which can operate with oscillation power of 1.5～2 MW at 28 GHz and 35 GHz was progressed for GAMMA10/PDX, QUEST, NSTX in Princeton Plasma Physics Laboratory (PPPL) and Heliotron J. The beam current Ik dependences of cavity oscillation powers Po obtained by calculation are shown in Fig.2. For both 28 GHz TE8,5 mode and 34.8 GHz TE10,8 mode, over 2 MW can oscillate with same cavity resonator.     In addition, the design study of 14 GHz gyrotron for GAMMA10/PDX and QUEST has been started. The cavity oscillation mode was decided to TE4,2 mode, based on the design results of cavity resonator, magnetron injection gun (MIG), radiator and electron beam trajectory. Beam current dependences of cavity oscillation powers obtained by calculation are shown in Fig.3. For 14 GHz TE4,2 mode, oscillate power of over 1 MW was obtained.   Fig.1  Picture of the gyrotron and transmission wave guide installed at QUEST               (a)                         (b) Fig.2 Beam current dependences of cavity oscillation power of dual-frequency gyrotron with each  electron beam pitch factor α (a) 28 GHz TE8,5 mode (b) 34.8 GHz TE10,8 mode.   Fig.3 Beam current dependences of cavity oscillation power of 14 GHz gyrotron. 511§12. Cooperative 28 GHz ECH Study for High Density Plasma Heating and Development of 14 GHz and 28 GHz/35 GHz GyrotronKariya, T., Imai, T., Minami, R., Numakura, T., Eguchi, T.,  Nakazawa, K., Kawarazaki, R. (Univ. Tsukuba),  Zushi, H., Hanada, K., Idei, H. (Kyushu Univ.),  Nagasaki, K. (Kyoto Univ.),  Saito, T., Tatematsu, Y., Yamaguchi, Y. (FIR, Univ. Fukui),  Kubo, S., Shimozuma, T., Yoshimura, Y., Igami, H., Takahashi, H.

Cooperative 28 GHz ECH Study for High Density Plasma Heating and Development of 14 GHz and 28 GHz/35 GHz Gyrotron

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Cooperative 28 GHz ECH Study for High Density Plasma Heating and Development of 14 GHz and 28 GHz/35 GHz Gyrotron

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