The compact toroids (CTs) include Field Reversed Configurations (FRCs) and Spheromaks. They are characterized by the simply-connected configuration that requires no external magnet linking with toroidal plasma. This paper presents an introductory review on CT researches and contains the following chapters ; 1. Magnetic configurations of CT plasmas, 2. Generations of CTs, 3. The tilt instabilities, 4. The equilibrium and beta values of CTs, 5. The MHD relaxation of spheromaks in connection with those of RFPs, and 6. Prospects of DTs to fusion reactors.
A variety of plasma processes are summarized from the point of view of discharge physics. Since low temperature plasmas are widely used, our attention is paid to glow discharge, especially high frequency glow discharge. The basic properties and internal structure are discussed.
Modelling of the reactive gas discharge plasma has been carried out. Numerical solutions of the relation between particle densities (various ions and radicals) and discharge conditions (gas pressure, gas mixture ratio and electron density) are presented and discussed. The results show that the radical particle densities are always more than one order of magnitude larger than the ion densities. There is an optimum value in gas pressure and gas mixture ratio for producing the free radicals.
The relaxation phenomena characterized by the OV line radiation and soft X-ray sawtooth was observed in the CTCC-I spheromak device. The temporal evolution of spheromak plasma in the resistive decay phase have been investigated experimentally. During the sawtooth rise time, the equilibrium configuration of spheromak is changed in time because of plasma resistivity inhomogeneities, resulting in the occurence of the MHD instability. During the sawtooth fall time, the redistribution of peaked current profile due to the instability returns the plasma to near the Taylor minimum energy state, being accompanied by flattenning of the soft X-ray flux profile with an associated decrease in the particle density of 50-60% near the magnetic axis.