Frascati Tokamak Transformer Switching System

Abstract

Plasma ionization and heating, in the Frascati Tokamak, is obtained generating an emf along the plasma column, by switching the dc current flowing in the Tokamak transformer.30 kA flowing in the 60 mH transformer inductance must be commutated into a resistance to generate 40 kV across the transformer itself.

Studies and tests to solve this problem have been conducted, on different types of breakers, in cooperation between Tecnomasio Italiano Brown Boveri, Milan and Laboratori Gas Ionizzati, Frascati.

Satisfactory results have finally been obtained using a DLF commercial air blast breaker in a chopper type circuit.

A capacitor bank in parallel to the breaker is discharged immediately after the contacts separation and the arc in the switching element is estinguished at the first current zero. A saturable reactance in series with the breaker reduces the current decay rate to allow sufficient deionization time.