Technology Developments for ECRH System

Full text: The gyrotron based electron cyclotron resonance heating (ECRH) system is used on tokamaks ADITYA-U and SST-1. The ECRH system consists of a high power gyrotron, corrugated waveguide based transmission line and a quasi-optical launcher. The 42 GHz gyrotron delivers 500 kW power for 500 ms duration. This gyrotron operates at ∼ -48 kV beam voltage and ±18 kV anode voltage. This system draws around 20 A beam current. This is a critical systems associated with high voltage power supply systems. A dedicated protection system is used to protect the gyrotron in an event of fault. An ignitron based crowbar system removes the voltage within 10 μs and ensures the safe operation of the gyrotron. In order to operate the system with more reliability, power supplies and protection system are being upgraded indigenously. An advance thyristor-based solid-state crowbar is under development which will replace the ignitron crowbar system. A 20 kV solid-state crowbar has been developed and tested successfully, and subsequently integrated with the existing anode power supply. The prototype crowbar at 30 kV has also been tested successfully. A 50 kV solid-state crowbar has been designed and is under development. An IGBT based solid-state switch has been developed successfully which has been tested up to 18 kV. This can replace the existing anode power supply which has slow rise time. This IGBT based switch facilitates the system for modulation. An advance launcher has been designed and is currently under procurement. This launcher consists of two mirrors (one focussing and other plane) mounted on a SS flange. The focussing mirror is fixed, however, the plane mirror can be steered in ultrahigh vacuum (UHV) environment. The plane mirror is connected with two mechanisms for necessary movement in two directions. The system is designed to minimize backlash and give precession movement with position indication. This prototype launcher can be used as a real-time feedback launcher with some additional modifications. The paper discusses the technologies developed indigenously for the safe, reliable and accurate operation of ECRH system on tokamaks. (author)