Speaker
Dr
Ryuya Ikezoe
(Plasma Research Center, University of Tsukuba)
Description
Control of waves in ion cyclotron range of frequencies (ICRF) is crucial for better performance of the GAMMA 10 plasma, which utilizes ICRF heating as the main heating scheme and is susceptible to an unstable ICRF wave named as Alfvén-ion-cyclotron (AIC) wave. Traditional beach heating using a slow wave has been used in GAMMA 10, and is very effective for realizing high ion-temperature plasma of the order of kilo-electron volts near the midplane of the central mirror field. However, there remains much to be cleared in association with ICRF heating in a mirror configuration; e.g. saturation of confined energy against ICRF heating power, transient-like variation of heating efficiency observed in the ramp-up phase of the GAMMA 10 plasma, significant sensitivity of heating efficiency to the magnetic field strength, and so on. In order to clarify these fundamental things, experimental assessment of internal wave-field structure has been desired.
We have been developing one of such measurement systems by using microwave reflectometry. Recent development of our reflectometer system enabled clear separation of phase modulation component from amplitude modulation component included in the reflected microwave and gave good coherent signals associated with the global structure of the ICRF waves. Interestingly, the amplitude modulations at the wave frequencies suddenly lost coherency with increasing distance between measurement points, contrary to what observed for the phase modulations. The long correlation beyond the half plasma radius, which is confirmed for the phase modulation signals, indicate that they nicely reflect radially expanded eigenmode structures, which are theoretically predicted characteristic of ICRF waves for a low-density small-sized plasma column like the GAMMA 10 plasma.
We successfully obtained precise radial profiles of the density fluctuations associated with the externally applied ICRF waves and spontaneously excited AIC waves by using the developed reflectometer system, which could give us insights into ICRF wave physics related to above mentioned unclear issues. Damping picture of slow wave near its ion-cyclotron resonance layer was already observed, which will be a first step towards the clarification and improved control of the GAMMA 10 plasma.
Primary author
Dr
Ryuya Ikezoe
(Plasma Research Center, University of Tsukuba)
Co-authors
Dr
Junko Kohagura
(Plasma Research Center, University of Tsukuba)
Mr
Junpei Itagaki
(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
(University of Tsukuba)
Prof.
Mizuki Sakamoto
(Plasma Research Center, University of Tsukuba)
Mr
Seowon Jang
(Plasma Research Center, University of Tsukuba)
Mr
Shuhei Sumida
(Plasma Research Center, University of Tsukuba)
Prof.
Yousuke Nakashima
(Plasma Research Center, University of Tsukuba)
