Study of poloidal magnetic fields in the Tuman-3 tokamak

Results are reported from measurements of the poloidal magnetic fields in the Tuman-3 tokamak. The iron core of the magnetic conductor inside the plasma-filled region (aspect ratio R/a = 2.3) greatly influences the conditions needed to sustain an equilibrium plasma column. The experimental data are compared with calculations obtained by solving a magnetostatic problem in the axisymmetric approximation. The calculated results for the model magnetic conductor agree with the experimental data to within approx.5%. For the configuration studied, the poloidal field sustained a stable equilibrium plasma column of large radius with small vertical instability; the cross section of the plasma column was nearly circular. Under the experimental conditions, the parameters of the poloidal magnetic field depend only weakly on the degree of saturation of the iron core. The measurements are used to design a system for controlling the position of the plasma column.