Modelling and Optimisation of Relativistic Magnetron with Transparent Cathode : Applications for High-Power Microwaves

Sammanfattning: This thesis aimed to investigate the relativistic magnetron (RM), which is a high-power microwave (HPM) source. Since the RM can generate high-intensity microwave radiation, it can be used as a pulsed electromagnetic weapon to target electronic systems in different objects, such as drones, missiles, or vehicles. Other applications include electromagnetic compatibility (EMC) testing. In this thesis, a novel design of an RM with a transparent cathode configuration was investigated. This RM, referred to as the FOI-magnetron, was developed with the goal of generating the more advantageous TE11 mode of microwaves. This thesis starts with an in-depth theoretical exploration of the physics surrounding the RM, followed by a proof-of-concept study, where we compare our simulation results against published data. We then investigate the FOI-magnetron to determine if the transparent cathode configuration is more favourable than a solid cathode configuration. Particle-in-cell (PIC) simulations in MAGIC3D were used to study the RM, and extensive parameter studies were conducted for the FOI-magnetron to optimise its performance. The simulations revealed that the FOI-magnetron suffered from leakage currents. Moreover, parameter studies of the FOI-magnetron with transparent cathode demonstrated favourable TE11-mode emission of microwaves with a peak output power reaching 590 MW after 15 ns, having a frequency of 2.56 GHz, and an efficiency of 37%. Comparisons between thetransparent and solid cathode for the FOI-magnetron showed a slightly lower output power and efficiency for the transparent cathode, with minimal difference in the rise time of microwaves. Additionally, the transparent cathode exhibits a higher overall impedance and leakage currents. On the other hand, a lower back-current density on the transparent cathode and emitter was shown, resulting in less damage to the material. In this study, we found that we could reduce leakage currents by extending the interaction region without impacting the performance of the FOI-magnetron. Also, the frequency was shown to change with either a shorter emitter or a longer interaction region, allowing for frequency control. Lastly, a modified design of an RM with a semitransparent cathode showed a promisingly high efficiency of 46% with an output power of 600 MW. This design utilised endcaps, which are useful for significantly reducing leakage currents