Elimination of the asymmetric modes in a Ka-band super overmoded coaxial Cerenkov oscillator

Abstract

The issue of asymmetric modes output of a Ka-band super overmoded coaxial Cerenkov oscillator is analyzed in this paper. Due to serious passband overlapping in a super overmoded coaxial slow wave structure (SWS), the asymmetric competition mode EH11 can hardly be suppressed thoroughly by the methods adopted in moderately overmoded devices, especially in the startup of oscillation. If the output structures reflect the asymmetric modes, the asymmetric mode competition in SWS will be aggravated and the normal operation state will be destroyed. In order to solve this problem, a taper waveguide is inserted at a specific position to achieve the destructive interference of the reflected TM11, and a special support structure is designed to avoid reflection of TE11. With these methods, asymmetric mode competition can be successfully eliminated, and the oscillator is capable of achieving a steady fundamental mode operation performance.

Investigation and suppression of asymmetric modes competition in Cerenkov device by conductivity anisotropic material loading

“…Recently, considerable attention has been paid to improve the operational stability of Cerenkov devices; however, one major issue that limits the operational stability * Author to whom any correspondence should be addressed. is mode competition [10][11][12][13][14][15][16][17]. Many technical methods have been proposed for suppressing symmetric mode competition [18,19], but discussions on asymmetric mode competition are scant.…”

“…Many technical methods have been proposed for suppressing symmetric mode competition [18,19], but discussions on asymmetric mode competition are scant. To date, the main methods for suppressing asymmetric modes are improving the uniformity of the electron beam and optimising the output structures [12,15,[20][21][22]. It is difficult to improve the uniformity of the electron beam in an explosive emission cathode, which is widely used in HPM sources.…”

Experimental study on the influence of grain boundary on breakdown in relativistic backward wave oscillator

“…The phenomenon of pulse shortening is a critical bottleneck that prevents the achievement of higher output power and longer pulse width by RBWOs [13][14][15]. Many factors can cause pulse shortening, including poor electron beam quality, dielectric window breakdown and mode competition [16][17][18]. Among these factors, radio frequency (RF) breakdown in slow-wave structures (SWSs) is considered as the best-known factor.…”

A novel self-injection relativistic backward wave oscillator

“…Moreover, the electron beam interacts with not only the designed operating mode, unexpected beam-wave interaction will decrease the conversion efficiency of the generator [14,[26][27][28][29]. Generally, through designing appropriate beam parameters and dispersion characteristics, the coupling impedance and temporal growth rate of the operating mode are much larger than that of the other modes, which verify the dominant role of the desired mode [30,31]. But, with the increasing of the pulse duration time, the self-excitation risk of parasitic modes is growing, which may seriously degrade the performance of the RBWO and cause pulse shortening [32,33].…”