Plasma stabilization and diffusion in traps with spatial axes and with circular magnetic surfaces

Low pressure plasma stabilization and diffusion in traps with spatial axes are considered. The stabilization is based on magnetic axis displacement from the centre of curvature of the magnetic axis in toroidal or helical parts of the system. Such displacement produces a magnetic well in the trap and provides stabilization of a low pressure plasma. Magnetic axis displacement is produced in the part of the magnetic system which includes an inhomogeneous field and a transverse field with second and third harmonics. Calculations of conditions for obtaining a magnetic well are made for the Drakon trap. In the second part of the paper plasma diffusion in the Drakon trap is considered. It is shown that the diffusion coefficient in a hydrodynamic regime is close to the classical one determined by the magnetic field of a straight section. In the regime of rare collisions the diffusion coefficient has a strong dependence on the radial electric field and on the mirror ratio in the CRELs (curvilinear equilibrium elements). In the intermediate range of collision frequencies the diffusion coefficient is lower by about an order of magnitude than that in stellarators with equal aspect ratios in the tori and in the magnetic fields. (author). 6 refs, 3 figs