A Tokamak Device Using Force-Balanced Coils and Plasma Behavior.

Abstract

When a high magnetic field tokamak reactor is designed with reasonable sizes, the force-reduction technique is necessary. We have proposed Force-Balanced Coils (FBCs) for the purpose of vanishing of Lorentz forces exerted on the conductors and simplifying the construction of coil systems. The force-balanced winding provides not only the toroidal magnetic fields but also the poloidal magnetic flux to induce the plasma current. The net radial force is reduced by a factor of 10 from that exerted on the toroidal magnetic field coils. We have manufactured a small tokamak device with FBCs (RX(X=major)/aX(X=minor) 0.3/0.1 m) to demonstrate plasma production and confinement. The toroidal magnetic field of 0.9 T at the vessel center and the plasma current up to 10 kA were achieved by two-step FBC excitation. The plasma column with Te of 50 eV and ne of 2×1019 m-3 was well centered in the vacuum vessel.