Effect of non-uniform slow wave structure in a relativistic backward wave oscillator with a resonant reflector

Abstract

This paper provides a fresh insight into the effect of non-uniform slow wave structure (SWS) used in a relativistic backward wave oscillator (RBWO) with a resonant reflector. Compared with the uniform SWS, the reflection coefficient of the non-uniform SWS is higher, leading to a lower modulating electric field in the resonant reflector and a larger distance to maximize the modulation current. Moreover, for both types of RBWOs, stronger standing-wave field takes place at the rear part of the SWS. In addition, besides Cerenkov effects, the energy conversion process in the RBWO strongly depends on transit time effects. Thus, the matching condition between the distributions of harmonic current and standing wave field provides a profound influence on the beam-wave interaction. In the non-uniform RBWO, the region with a stronger standing wave field corresponds to a higher fundamental harmonic current distribution. Particle-in-cell simulations show that with a diode voltage of 1.02 MV and beam current of 13.2 kA, a microwave power of 4 GW has been obtained, compared to that of 3 GW in the uniform RBWO.

Optimization of relativistic backward wave oscillator with non-uniform slow wave structure and a resonant reflector

“…8 After adjusting the heights of the front-end 3-periods SWS and keeping the other 4-periods SWS unchanged, the output power increased to 4 GW from 3 GW of that with the uniform SWS, the microwave frequency is 9.7 GHz, and the corresponding beam-wave interaction efficiency of the device increased to 30% from 22%. For convenience of discussion, the device with non-uniform SWS, presented by Chen et al, is termed as "device A" here.…”

“…1(a) is the distribution of the electrons in real space of device B and shows the structure of the device, which differs significantly from that of device A. 8 Fig. 1(b) is the time history of the output power from device B, it can be seen that the average output power of this device is raised to about 5 GW from 4 GW of device A, and hence, the relative conversion coefficient increases 24% compared to the device A.…”

“…After optimization, the generation efficiency of microwave from the relativistic electron beam has increased 32% compared to that of the original device. 8 This optimization method is expected to be used to improve the performance of high power microwave sources with complicated structures.…”

“…For an example, Chen et al proposed a RBWO with non-uniform SWS and a resonant reflector, which has 18 structural parameters to be adjusted. 8 It is very difficult to adjust tens of the parameters of the structures experimentally and numerically.…”

“…The relativistic backward wave oscillator (RBWO) is one of the most promising high power microwave devices with the virtues of high power, high efficiency, and high repetition rate. [1][2][3] To increase the beam-wave interaction efficiency, some techniques are used, such as non-uniform slow wave structure (SWS), resonant reflector, and oversized structure, [4][5][6][7][8][9][10][11] etc. Compared to the conventional RBWOs, the structures of the improved devices are very complicated.…”