Control of Toroidal Expansion of a High Beta Plasma Column in a Pinch Tokamak by Programmed Pulsed Vertical Field

Abstract

Dynamics of high beta toroidal pinch plasmas in the major radius plane are calculated after a simple model and compared with experimental results of STP-2 screw pinch 1) which is operated under the condition of T e ≃20 eV and n e ≃1.2×10 15 /cm 3 . It is demonstrated that the calculation agrees with the experimental results in the early phase of the discharge where the plasma keeps a high beta value (poloidal β p ≃3) while the discrepancy between them begins to grow after 8 µs from the start of the main discharge because the β p value decreases considerably. In order not to deviate the plasma column from the center of the discharge tube a concept of the effective dissipative force generated by a proper programming of the pulsed vertical field is introduced. It is demonstrated that this concept is useful to keep the shock-heated high beta plasma in the center of the discharge tube since unfavorable toroidal expansion disappears completely in a few microseconds by a proper programming of the pulsed vertical field.