Study of the Absorption of the Pulsed Microwave Radiation of a Gyrotron in an Al/Al2O3 Powder Mixture

We study the absorption of microwave gyrotron radiation by aluminum microparticles taking into account the Al₂O₃ nano-oxide film. The heating process of metal microparticles (linear size from 1 to 400 μm) in Al/Al₂O₃ powder fillings for a metal mass concentration of 10% has been experimentally explored. The increase in the field strength of electromagnetic waves upon diffraction on a double-layer structure consisting of a quartz plate and a thin layer of Al₂O₃ is considered. The calculation of the absorbed and reflected power of microwave radiation from a gyrotron at a frequency of 75 GHz using the Mie solution for a sphere and the effective medium approximation to calculate the optical properties of aluminum particles in a dielectric shell is presented. It is shown that for a microwave pulse power of more than 400 kW, local heating of aluminum in the region of the maximum electric field strength (7.5 kV/cm) to the melting temperature is observed within times not exceeding the gyrotron pulse duration (less than 8 ms).