Thyristor making switch system for plasma startup control in RFX

The necessity of better plasma current control during the startup phase asks for a toroidal loop voltage modulation obtained with the multi step reduction of the transfer energy resistor in the OH circuit. The paper begins by discussing the characteristics of such a modulation and then describes the modifications realized and tested on the power supply and magnet systems to prove the feasibility of such an operation; finally, on the basis of the results obtained, we describe the design of the making switch system, based on a 100 mm thyristor valve.