Design of the 3.7 GHz, 1 kW CW solid state driver for LHCD system of the SST-1 tokamak

Advances in solid state device technologies have seen its use foray into areas such as microwave heating and powering the RF cavities of an accelerator. This paper explores the possibility of use of a solid state source/driver for current drive systems of tokamaks. The design of a modular solid state source to be used as a driver for klystrons in the LHCD system of SST-1 tokamak is presented. It comprises of solid state power amplifier (SSPA) units, driven by voltage controlled oscillator (VCO) and pre-driver (gain) amplifier. The paper discusses about the design methodology and simulation of these individual components. The component and system level computer simulation based on behavioural and file based model was performed using AWR Microwave Office (MWO) software. The linear and non-linear EM analysis of individual components have been carried out to ascertain its performance. The designed VCO delivers an output power of 20.2 dBm and phase noise of -91.64 dB/Hz (100 KHz offset) at 3.7 GHz. The pre-driver stage (gain amplifier) provides a large signal gain of 15.7 dB and return loss of -14 dB at 3.7 GHz. The individual power amplifier draws a continuous wave (CW) output power of 45.2 dBm for an input power of 35 dBm and efficiency of 56.68%. The system simulation results exhibit around 1 kW of output power in ideal conditions.