Transverse radiation input and output for planar relativistic surface-wave oscillators and amplifiers

Abstract

Planar surface-wave resonators are very attractive for development of relativistic high-current sources of high-power subterahertz radiation, due to their unique mode selective features. However, evanescent nature of the surface operating wave guided by periodic grating brings a number of difficulties such as wave scattering at the grating edges, power leakage to the cathode, and high ohmic losses. To overcome these problems, we propose using a bi-periodical gratings providing decoupling of the surface wave to the Gaussian microwave beam traveling in the transverse direction. Moreover, the same principle can be used for power input in the relativistic extended-interaction klystron with surface-wave resonators. An analytical quasi-optical theory based on coupled-wave equations are developed for surface-wave resonators with transverse power input-output, as well for planar beam devices based on these resonators. It is shown that the transverse energy extraction significantly reduces the Ohmic losses down to 10% of the radiated power which is essential for sub-THz range. The simulations based on both the quasi-optical model and PIC simulations show that surface-wave oscillator driven by 600 kV, 1 kA could produce 140 MW of output power at 150 GHz with 25% efficiency. For 150 GHz amplifier with the similar beam, simulations predict the 20–40 MW of output power and 20–30 dB linear gain in 1% bandwidth.