Modelling and simulation of axial-virtual cathode oscillator using matlab simulink

Abstract

This thesis presents the modelling and simulation of an Axial-Virtual Cathode Oscillator (Axial-VIRCATOR), using the MATLAB Simulink software package. One dimensional model of VIRCATOR has been implemented by using mathematical model based on Child-Langmuir Law that describes the charge, charge density, current, voltage, power and efficiency of the VIRCATOR as a function of its mechanical parameters. Hence, the Axial-VIRCATOR model was chosen where its mechanical parameters such as cathode radius, anode-cathode (A/K) gap and tube diameter were evaluated. In order to adjust the tuning characteristics of the VIRCATOR tube which need to achieve the optimal output microwave power, energy and efficiency, the operation's frequencies were chosen carefully to be 4.0, 6.0, 6.3 and 8.0 GHz. Thus are the most crucial of factors to be investigated in this work. Other quantities such as the beam current, beam radius, cathode radius and transparency were derived in the analytical model and found to be in agreement with the simulation results which influencing the power efficiency, such as the anodetransparency factor Ta and the dispersion factor. Analysis results showed significant improvement of the efficiency, output power and the radiated energy of microwave output which are 43.94%, 11.64 GW and 2.4 Joules (1.5x10 13 MeV) respectively. This was achieved by carefully choosing the resonance characteristics of the VIRCATOR tube especially the influence of the relativistic component in the charge density solution, which shows a close approximation to the input current closest to the relativistic beam. The results showed by the simulation were compared to an up to date experimental publications and found to be compatible. An error calculation criterion has been implemented which shows minimum error values of -0.01 dB for the input voltage of 600 kV and this was agreed with the relativistic solution considered in this work.