Speaker
Mr
Junpei Itagaki
(Plasma Research Center, University of Tsukuba)
Description
Heterodyne reflectometers are used for fluctuation measurements of a high-performance mirror plasma on GAMMA 10. It is important that the offset in IQ signals is minimized to evaluate density fluctuations quantitatively when the phase and amplitude modulation components are separated. A horn antenna pair for transmitting and receiving microwaves is installed inside the vacuum chamber in the anchor cell. When the microwave power reflected from the cutoff layer inside the plasma directly is low, the finite level of the offset will become a big issue. The offset will arise from unintended reflections inside the vacuum chamber. If such reflections have variable path length in relation to the displacement of the plasma column and the change in diffraction, the offset will be varied in time. In addition to efforts to minimize unintended reflections, we use an RF power detector (PD) to check such a time-dependent offset component. By dividing the received microwave, two amplitude components are obtained; one is from PD, which is the actual reflected power received with the antenna, and the other from calculation of IQ outputs. The offset can be evaluated by comparing these two amplitudes and then eliminated even if unintended reflections change in time. The amplitude component that was calculated with the offset eliminated by this method nicely recreated the PD signal. The phase component with the offset correction showed clear peaks of fluctuations.
Financial support was received in part from Grants-in-Aid for Young Scientists (B) (Grant No. 15K17797) and from Bidirectional Collaborative Research Program of NIFS (Grant No. NIFS17KUGM132).
Primary author
Mr
Junpei Itagaki
(Plasma Research Center, University of Tsukuba)
Co-authors
Mr
Atsuto Tanaka
(Plasma Research Center, University of Tsukuba)
Dr
Junko Kohagura
(Plasma Research Center, University of Tsukuba)
Mr
Koki Izumi
(Plasma Research Center, University of Tsukuba)
Dr
Mafumi HIRATA
(Plasma Research Center, University of Tsukuba)
Dr
Makoto Ichimura
(Plasma Research Center, University of Tsukuba)
Dr
Masayuki Yoshikawa
(Plasma Research Center, University of Tsukuba)
Prof.
Mizuki Sakamoto
(Plasma Research Center, University of Tsukuba)
Mr
Ryo Sekine
(Plasma Research Center, University of Tsukuba)
Dr
Ryuya Ikezoe
(Plasma Research Center, University of Tsukuba)
Mr
Seowon JANG
(Plasma Research Center, University of Tsukuba)
Mr
Shuhei Sumida
(Plasma Research Center, University of Tsukuba)
Mrs
Yoriko Shima
(Plasma Research Center, University of Tsukuba)
Prof.
Yousuke Nakashima
(Plasma Research Center, University of Tsukuba)
Mr
Yushi Kubota
(Plasma Research Center, University of Tsukuba)
