Speaker
Mr
Haruhiko Saitoh
(Japan)
Description
The Ring Trap 1 (RT-1) device is a magnetospheric levitated dipole field configuration constructed for the study of high-beta plasma suitable for burning advanced fuels. As observed in planetary magnetospheres, dipole plasmas can be stable against MHD interchange and ballooning instabilities even in bad curvature regions, due to the effects of field lines compressibility. In the first series of experiments in RT-1, plasma is generated and maintained by using electron cyclotron resonance heating (ECH) at 2.45 and 8.2GHz, and high-beta (local beta~70%) hot-electron plasma that sustained for more than 1s has been realized. In the presence of intense energetic charged particles in plasmas, emergence of several kinds of fluctuations and instabilities are widely known. Understanding of the stability limit and fluctuation properties is very important for the stable operation of high-beta fusion plasma in the magnetospheric configuration. In this study, we report the emergence of magnetic fluctuations and disruptive rapid loss of RT-1 plasma observed in the presence of intense hot electrons. At low neutral gas pressure operation, very intense hot electrons are generated by ECH in the plasma. In such cases, the plasma sometimes becomes unstable and the excitation of MHz-range magnetic fluctuations was observed. Magnetic fluctuations were measured with pickup coils located at different toroidal and poloidal positions. The fluctuations rotate in the electron curvature drift direction and have no clear phase difference along field lines, and disruptive loss of plasma was simultaneously observed. The onset of instability has a strong correlation with the ratio of hot electron component in the plasma. The destructive magnetic fluctuations were observed when the hot electron ratio was above ~40%. Kinetic effects due to the intense hot electrons may provide an energy source to induce the disruption, restricting the stability conditions of magnetospheric plasmas. Stabilization of the fluctuations is realized by reducing the ratio of hot electron component with optimized formation conditions, realizing the formation of stable high-beta plasma.
Country or International Organization of Primary Author
Japan
Primary author
Mr
Haruhiko Saitoh
(Japan)
Co-authors
Mr
Hidenori Mikami
(University of Tokyo)
Mr
Junji Morikawa
(University of Tokyo)
Prof.
Masaru Furukawa
(University of Tokyo)
Mr
Norikazu Kasaoka
(University of Tokyo)
Mr
Shingo Emoto
(University of Tokyo)
Mr
Shota Iizuka
(University of Tokyo)
Mr
Takeaki Harima
(University of Tokyo)
Mr
Wataru Sakamoto
(University of Tokyo)
Mr
Yohei Kawazura
(University of Tokyo)
Dr
Yoshihisa Yano
(University of Tokyo)
Mr
Yoshiya Goto
(University of Tokyo)
Mr
Yuta Kaneko
(University of Tokyo)
Prof.
Zensho Yoshida
(University of Tokyo)
