Physics of Fusion Plasmas and Experiments in the TST-2 Spherical Tokamak

AKIRA EJIRI^1*

¹Grad. School Frontier Sciences, The University of Tokyo, Chiba, Japan

* Presenter:AKIRA EJIRI, email:ejiri@k.u-tokyo.ac.jp

Plasma physics is one of critical fields to realize nuclear fusion energy. Understanding the behaviors of plasma, and generating or controlling plasma is quite important. In this talk, I would like to explain the academic appeal of the physics of fusion plasmas.

Since very high　temperature plasma　should　be　confined in a device which is made of solid material, various physics in various temperature ranges appears. Due to the low dissipation, turbulence and waves play important roles. In addition, fluid-like behavior, particle orbit effect and wave-particle interactions in a complex magnetic configuration must be considered. The strong electromagnetic interaction induces nonlinear phenomena and often self-organization. The above various keywords indicate the diversity of physics.

When we consider the realization of fusion power energy, efficiencies should be high. Then we need to heat the plasma efficiently, and to reduce the turbulent transport which cools down the plasma. For the technical integrity of the device, we need to consider plasma-material interaction, and material science.

While a large size machine is necessary to generate fusion relevant high temperature (e.g., > 1 keV) and high density (e.g. , 1E20/m3) plasmas, small machines can be used flexibly. TST-2 is a small spherical tokamak device (with major radius of about 0.36 m) in the University of Tokyo. The main research topic is wave physics aiming at an efficient current drive by lower hybrid waves. The efficiency was much lower than the ideal case, and we found there are three possible mechanisms deteriorating the efficiency, that is, (i) RF induced transport, where accelerated electrons show gradual spatial diffusion, (ii) parametric decay instabilities, where ions are heated, (iii) power deposition at the open field line regions and at the sheath region, where electrons and ions are lost at the solid walls.

Keywords: Nuclear Fusion, High Temperature Plasma, Spherical Tokamak, Lower Hybrid Wave