DYNAMIC IMPEDENCE MATCHING AND PULSE SHAPING OF HIGH VOLTAGE HIGH PULSE POWER SUPPLY

Abstract

High Voltage High Pulse Power Supply plays a vital role in the generation and amplification of high power RF and Microwave. High power RF and Microwave has various commercial and industrial applications in the field of fundamental research in physics, advanced applications in medical science, quality inspection in aerospace industry etc. Klystron is used as the microwave power generator which uses transmission line based Pulse Forming Network to generate required high voltage to the cathode of Klystron. These high voltage high pulse power are extensively used in rugged environment eventually leading to unavoidable technical issues frequently. This thesis discuss about the problems related to these High Voltage High Pulse Power Supply, their diagnosis techniques using various output parameter observations. The performance of pulse power systems were observed continuously on daily basis throughout the years and a considerably rich database of various parameters like signals, waveforms and trends have been analysed to predict the behavioural performance within the module. The analysis will be a key feedback factor for quick diagnosis, rectification and design modifications. The performance of High Voltage High Pulse Power Supply (HVHPPS) changes with the change in the load parameters i.e. dynamic impedance, cable length, temperature variation, cavity dimension change, applied cathode voltage, magnetic strength etc. The High Voltage High Pulse Power Supply (HVHPPS) for RF and Microwave types of load requires always a very good impedance matching, to achieve maximum power transmission and minimum reflection. The mathematical modelling and analysis of High Voltage High Pulse Power Supply (HVHPPS) performance on various type of load like magnetron, klystron, particle accelerator etc. In this thesis the mathematical modelling of subsystem of High Voltage High Pulse Power Supply (HVHPPS) and load are generated. Accordingly the load behaviour changes incorporated and analysed the effect at the source side based on hardware results. The mathematical modelling analysis result is validated through the experimental hardware model. In the present scenario of pulse power applications, transmission of high voltage pulses varies as per load condition. In the early days of its application, High Voltage High Pulse Power Supply (HVHPPS) designs were only for a short distance between the load and the source, where the effect of cable length was not taken into account for design. i The load under observation is Klystron based high energy particle accelerator system. The performance of pulse power systems were observed continuously on a daily basis throughout the year and detailed analysis was carried out. The model of pulse forming system provides details of pattern distortion of the pulse shape due to various dynamic parameter changes i.e. impedance, Load Voltage, Load Current, Cavity Dimensional Changes (Microwave components), temperature variations etc. High Voltage High Pulse Power Supply (HVHPPS) systems are designed with the goal to match fixed load, so that precise pulse output can be achieved. The HVHPPS output pulse shape changes with load impedance variation due to various reasons. Due to changes in impedance, the performance of Pulse Power Supply degrades and reflects the power to the source end which causes component failure and system shut down. To overcome such problems, a scale down High Voltage High Pulse Power is designed and developed to match the dynamic impedance variations. In earlier days, all HVHPPS were designed using microcontroller where the problem of pulse to pulse monitoring and computational speed were compromised. The availability of variable and self-defined field programmable gate array (FPGA) controller, ensures flexibility to design pulse to pulse shaping and various vital parameter monitoring. This thesis presents the design and implementation of High Voltage High Pulse Power Supply over an FPGA platform to meet the fast response requirement. An experimental test hardware is designed and developed for HVHPPS to implement novel techniques of dynamic impedance matching and pulse shaping on klystron and results are validated experimentally.