Research on high-beta plasmas based on two-fluid relaxation theory

Relaxation phenomena have been observed in many plasma experiments, and some theoretical explanation have been presented. Recently Mahajan-Yoshida has discovered a new relaxation state based on two-fluid plasma theory, and proposed a possibility for confining high-beta plasmas. In this theory two fluids (electron and ion) should relax to the conditions; V - ∇ x B αB, B + ∇ x V = βV, resulting in a relation given by β + (V/VA)2 = constant. This is called Beltrami/(generalized) Bernoulli condition. To explore this new relaxation state experimentally, a toroidal device with an internal coil is suitable, where strong plasma flow in the toroidal direction is induced by E x B drift by introducing a radial electric field. Since the E x B flow velocity increases as the minor radius is increased, a high-beta plasma could be confined in the core region. A torus device called S-RT is planned with a floating superconductor coil. This paper describes its engineering design and discusses expected plasma parameters. At present, a device with a normal conductor, called Proto-RT, has been constructed, and experiments of electron injection have been carried out. In addition, a small-scale torus device with a superconductor coil, called Mini-RT, are under construction, where a high-temperature superconductor (HTS) made of Bi-2223 tape is employed as a floating coil. This is the first challenge to explore the feasibility of HTS coils for fusion plasma devices. (author)