Runaway beam regime in small tokamak TBR-1

The runaway-mode discharges have been obtained in the TBR-1 tokamak at low plasma density ne approx approx 1012 cm-3. Comparison with the existing theory of the runaway electrons phenomena shows that runaway electrons generate close to 100% of the total toroidal current at plasma electron temperature of 40-60 eV. Equilibrium of the plasma-beam system is characterized by high value of the Shafranov parameter A. Its value increase monotonically with time and reach 1.8 by the end of discharge. The measurements of the vertical equilibrium field and shift of the current center with respect to the plasma boundary allow estimating the minor radius orbit shift, internal inductance and beta poloidal of the runaway beam