Fusion Science and Technology / Volume 43 / Number 1T / January 2003 / Pages 203-207
Stability / dx.doi.org/10.13182/FST03-A11963594
A plasma relaxation under the condition of a strong plasma flow has been studied by Mahajan-Yoshida, and the possibility for confining high beta plasmas has been discovered. In this self-organized state, two fluids (electron and ion) would relax to the condition given by the relation β + (V/VA)2 = const. To study a self-organized structure with strong plasma flow, we have introduced an internal coil device, by inducing an ExB toroidal flow with an appropriate radial electric field. We have constructed an internal coil device Proto-RT with a normal conductor, and have successfully produced an electron plasma by injecting electron beam through chaotic orbits across the magnetic separatrix. The radial electric field of a few kV/m has been confirmed, and the built-up potential is sufficient to drive an Alfvenic flow velocity. Now we are constructing a Mini-RT device, which is equipping a levitated ring with a high temperature superconductor (HTS) coil. The magnetic field strength near the floating coil is around 0.1 T, and the plasma production with 2.45 GHz Electron Cyclotron Heating is planned. In addition to the electron injection demonstrated in the Proto-RT device, we are preparing several techniques to build up the radial electric field in the plasma. For example, the utilization of direct orbit loss of high energy electrons produced by ECH might be feasible. The orbit calculation results show that the electrons with the energy of more than 10 keV would escape at the outer region of the plasma column, yielding the build-up of the radial electric field. The HTS coil system with the PCS coil has been fabricated and the excitation test has been carried out. We have succeeded in achieving a persistent current, and it is found that the decay constant of the coil current is evaluated to be around 40 hours and 6.5 hours at 20 K and 40 K, respectively. To study a position control of a floating HTS coil, we have fabricated a small HTS coil (R=0.04 m and Ic= 2.6 kAturns), and succeeded in levitating it during a few minutes with an accuracy of ~ 30 micrometers.