Development and Fabrication Of Multi-Channel Trigger Modules For Ignitrons Used In Capacitor Bank Power-Supply Of Aditya-U Tokamak

Abstract

The project describes a low cost, an easy to implement circuit for triggering ignitrons in Aditya-U tokamak. A multistage capacitor bank is described which is used to switch the power to the electromagnetic coils, used in tokamak with major radius of 0.75 m, a minor radius of 0.25 m, and a toroidal field of 1.5 T at the plasma center. A combination of capacitors charged to a different voltage is switched in at appropriate times. In tokamak, plasma is being confined, the plasma shot requires the multistage capacitor bank which will get charged as soon as the ignitrons are triggered. The triggering of ignitron can be done using a SCR or a driver circuit. Three capacitor banks, the fast bank is charged around 6 kV, the first slow bank is charged to about 4.5 kV, and a second slow bank is charged to a desirable voltage which is about 2.5 kV. The Ignitron switches are used to discharge the capacitor banks, since it has a short transient response, a fast voltage rise (3-10 kV/s) as well current rise compared to typical inductive system and have small spark duration. The triggering of ignitron circuit is pointed out in the project. The ignitron is endowed with a separate trigger using SCR 10RIA 100. The triggering circuit is designed with the help of a 555 timer, working in a monostable mode. As the ignitron requires high current, a darlington transistor is embowed before the ignitron since it allows heavy current to pass through it. Details of the circuit and practical considerations of working with SCRs are discussed and is presented in this report. The timer consists of a RC delay network which stretches the ignitor current pulse and is sustained till the load voltage favorably provide the conduction bias for the ignitron. The trigger delays to the various capacitor bank sections are parameter dependent. To avoid repetitive adjustments in the delays, a novel scheme for consistent triggering is also highlighted, effective operations of which is verified by experimental results.