Design, fabrication and testing of 7 kV, 6 A series connected IGBTs switch for triode based 20 kW stage ICRF amplifier

Abstract

Many high power RF amplifiers, working at various frequencies are being used in ICRH group. High power RF output is obtained by amplification in stages i.e. 50 W, 2 kW, 20 kW, 200 kW. These stages are connected as chain and act as driver for the final stage amplifier of ∼1.5 MW. The high power tubes used in these amplifiers (e.g. Triodes, Tetrodes), need DC power sources up to few mega-watt working at ∼30 kV.The Triodes and Tetrodes that are in use are vulnerable to internal arc faults. To protect them from permanent damage, DC Voltages need to be removed within few tens of microseconds. The conventional power supplies that are being used are short circuited with a very fast switch known as crowbar switch. Ignitron based crowbar switches are widely in use but are being replaced because of the presence of large quantities of toxic Mercury. Further, above crowbar methods cause enormous stress (during the short circuit) of the power supply and can cause considerable disturbance in the power lines.With the development of solid state series switch such short circuits of conventional supplies can be avoided. It is envisaged that a series IGBT switch rated at 7 kV, 6 A would be suitable for HVDC power supply of 20 kW stage.This development involves complete switch design, selection of IGBTs, static and dynamic voltage balancing circuit design. Further, isolation level requirements of various circuits and components are analyzed and adequate isolation is provided. The 7 kV, 6 A series switch is fabricated and successfully tested.