Abstract-Analytical investigation of self-oscillating condition for resonant terahertz extended interaction oscillators

Physics of Plasmas

Hooman Bahman Soltani,  Habibollah Abiri, 

Critical oscillating condition for the EIO with N = 10: (a) SWS and the excited RF field, (b) the formed electron bunches, (c) RF voltage at the voltage monitor, and (d) the spectrum of the RF voltage.

https://aip.scitation.org/doi/10.1063/1.5091480

Extended Interaction Oscillators (EIOs) are high-frequency sources of millimeter wave and terahertz radiations. The dimensions of the EIO resonant structure should be smaller to generate higher frequency signals. However, due to the skin effect and decreasing the available beam surface area, the maximum obtainable oscillating frequency of any RF geometry of EIO is limited. Analytical relations for maximum attainable frequencies of resonant EIO geometries in the sense of beam-wave coupling are derived and presented in this paper. They are directly expressed in terms of the standing-wave profile of the RF resonant circuit in this work. The maximum frequencies are expressed in terms of a defined two-variable analytical function U for single-section resonant EIOs. Besides, an algebraic formula is derived for a critical unloaded frequency of an EIO geometry (fcr) in terms of the resonant circuit field distribution. A 4/5 power-law dependency is derived for a maximum oscillating frequency vs a number of periods of the RF circuit. For two completely different EIO geometries, the results of the obtained relations are compared with the outcomes of a particle-in-cell solver, showing acceptable agreement for both the structures. In addition to computational rapidity, the obtained relations present an analytical viewpoint to estimate and improve the high-frequency generation capability of terahertz extended interaction oscillators.

Abstract- Criteria for Determining Maximum Theoretical Oscillating Frequency of Extended Interaction Oscillators for Terahertz Applications

 Hooman Bahman Soltani, Habibollah Abiri

http://ieeexplore.ieee.org/document/8307245/

Extended interaction oscillators (EIOs) are high-frequency vacuum-electronic sources, capable to generate millimeter-wave to terahertz (THz) radiations. They are considered to be potential sources of high-power submillimeter wavelengths. Different slow-wave structures and beam geometries are used for EIOs. This paper presents a quantitative figure of merit, the critical unloaded oscillating frequency ( fcr ) for any specific geometry of EIO. This figure is calculated and tested for 2π standing-wave modes (a common mode for EIOs) of two different slow-wave structures (SWSs), one double-ridge SWS driven by a sheet electron beam and one ring-loaded waveguide driven by a cylindrical beam. The calculated fcrsare compared with particle-in-cell (PIC) results, showing an acceptable agreement. The derived fcr is calculated three to four orders of magnitude faster than the PIC solver. Generality of the method, its clear physical interpretation and computational rapidity, makes it a convenient approach to evaluate the high-frequency behavior of any specified EIO geometry. This allows to investigate the changes in geometry to attain higher frequencies at THz spectrum.