Comprehensive Analysis of a Slow Wave Structure for an X-band MILO

Magnetically Insulated transmission Line Oscillator (MILO) is a relatively new High Power Microwave (HPM) device that has recently received increasing attention because it does not require an external magnetic field and can generate gigawatt (GW) of power from L to Ku bands. Furthermore, it is a compact and lightweight tube and can operate at low impedance
$(\sim 10\ \Omega)$
. The most significant element in a magnetically insulated transmission line oscillator (MILO) is a slow wave structure (SWS) in which the interaction between the RF field and particles occurs. This study aimed to design an SWS for an X-band MILO using a High-Frequency Structure Simulator (HFSS) and Particle in Cell (PIC) Simulator (CST-PS). HFSS was used to obtain the structure's dispersion relation and investigate the resonant mode frequencies through EigenmodeSolver. Previous investigations demonstrate that a MILO oscillates in the
$\pi$
-mode, which is the spatial harmonic associated with the SWS with the highest
$Q$
. The field distribution associated with this mode produces the strongest coupling to the electron flow. In our studies, parameter optimization was investigated, and particular attention was focused on the phenomenon of mode competition observed during different simulations. The simulations displayed remarkable performance in sizes and weight terms and the potential to produce very high output power. Dispersion diagrams will be shown, highlighting the interaction between modes propagating in the structure and beamline as the input voltage varies. An X-band MILO with the simulated SWS was designed, and a PIC simulation was done to confirm our proper design. A pulse signal of 500 kV and 100 ns pulse length in PIC simulations generate the relativistic beam. TEM mode and high-order modes are evaluated. A peak power of 450MW and frequency of 9.4 GHz is observed. Conclusions and possible future developments will be discussed.