Angular drift of the high current relativistic multi-beam in the hollow cylindrical waveguide

There are many kinds of high power microwave devices.According to the phase and frequency characteristics of the output microwave,they can be divided into the phase and frequency locking high power microwave (HPM) devices and HPM oscillator.Among them,the frequency and phase of HPM devices with locked frequency and phase can be adjusted by the injecting microwave,which has achieved great progress of the HPM research.In this paper,the latest progress of HPM devices with locked frequency and phase which have been developed by the Institute of Applied Electronics,China Academy of Engineering Physics in recent years are reviewed,covering relativistic klystron amplifier (RKA) and relativistic backward-wave oscillator (RBWO) with injection-locked.Aiming at the problems encountered in the research of high power and long pulse RKA,in this paper we briefly introduce the key technologies in design and experiment,including the beam-wave interaction merits,the suppression of multi-frequency oscillation,pulse shortening, high frequency and high power operation,high gain,etc.The performances of RKA,such as power,phase stability and gain,have been improved remarkably.High-power output with stable frequency and phase has been realized by single-annular beam RKA in S-band,whose output power reaches more than 1 GW with a pulse width of 165 ns and phase fluctuation of 18 at a repetitive pulse of 25 Hz/1 s.The high gain RKA also achieves a similar output power and phase stability under the condition of injected microwave power of several kW.In X-band RKA,a structure of coaxial multi-beam has been used to break through the limitations of high frequency and high power capacity,which generates more than 1 GW output power with an input power of 30 kW,the beam-wave conversion efficiency is 34% and the phase fluctuation is 15 with a pulse width of 140 ns.On the basis of an in-depth understanding of RBWO technology, and using the advantages of high efficiency and compact structure,the RBWO research of injection modulated electron beam is proposed and carried out.More than 1 GW output microwave with locked phase is realized by 100 kW seed microwave.These results not only extend scientific and technological research of a large family of HPM devices,but also make it possible for HPM devices to be used in power synthesis,particle acceleration,high-performance radar,etc.

Review on high power microwave device with locked frequency and phase

Huang¹,

Yang²,

Liu³

et al. 2018

Design and experiment of X-band high-repetition rate high-power multi-beam relativistic klystron amplifier

Liu¹,

Hua²,

Xiao³

et al. 2020

The relativistic klystron amplifier (RKA) is a very important kind of high power microwave device, which has the advantages of high power, high efficiency, stable output phase and amplitude. The development of multi-injection RKA toward engineering and practical application needs to further improve operating frequency and output power of klystron amplifier, while the RKA of conventional circular waveguide drift tubes is restricted by the physical factors such as geometric size, space charge force and high-voltage breakdown. The multi-beam RKA based on the technology of multiple electron beams can work at low voltage and guiding magnetic field, and can also possess high electron beam current and diversion coefficient. The physical limitation of conventional structure RKA is overcome, and the working frequency and the output power are improved. In the experiment, the X-band GW level power of microwave is obtained. The multi-beam RKA needs to further improve its working frequency and working life. In the experiment, the power conversion efficiency of multi-beam RKA is about 35%, and most of the remaining electron energy will accumulate on the collection pole at the end. If the heat dissipation of the collector is not designed appropriately, the collection will be seriously ablated when working at high heavy frequency. Thus a large quantity of plasma and secondary electrons are generated, which affects the stability of the device. To solve the problem of electron reflux bombarding the output cavity after electron beam exchanging energy in the gap of output cavity, the reflux process of relativistic electron beam in the device is analyzed in this paper. On this basis, a coaxial extraction structure with four-gap extension interaction is designed to avoid electron reflux and reduce the gap electric field, thus improving the working life of the device. At the same time, in order to solve the problem that the conventional water cooling channel can affect the output microwave mode in a high-frequency over-mode device, a mode transformation structure of coaxial TEM mode-fan-shaped TE<sub>10</sub> mode-coaxial TEM mode-circular waveguide TM<sub>01</sub> mode is designed. The mode conversion efficiency is greater than 99.9%, and the influence of collecting polar water cooling channel on the output microwave mode is avoided. The stable operation of multi-beam RKA in the X-band with a repetition rate of 45 Hz is realized experimentally, while the output power is over 1 GW and the microwave pulse width is over 100 ns. At present, the multi-beam RKA runs about 10000 times in total, and the output microwave parameters do not decrease significantly.

Optimal design and experimental research of several-gigawatt multiple electron beam diode

Liu¹,

Xiao²,

Hua³

et al. 2021

The relativistic klystron amplifier (RKA) is one of the most efficient sources to amplify a high-power microwave signal due to its intrinsic merit of high-power conversion efficiency, high gain and stable operating frequency. However, the transverse dimensions of the RKA dramatically decrease when the operating frequency increases to X band, and the power capacity of the RKA is limited by the transverse dimensions. An X-band multiple-beam relativistic klystron amplifier is proposed to overcome the radiation power limitation. Each electron beam propagates in separate drift tubes and shares the same coaxial interaction cavities in the multiple-beam relativistic klystron amplifier, and the transverse dimensions of the multiple-beam relativistic klystron amplifier are free from the operating frequency restriction and a microwave power of over 1 GW is generated in the experiment. For a high-power electron device, the transmission of electron beam is critical, and the power conversion efficiency of the device is affected. In this paper, we conduct an investigation into the transmission process of the intense relativistic multiple electron beams, and the number of the multiple electron beams is set to be 16. It is found that when the multiple electron beam is transmitted in the device, the electron beam rotates around the center of the whole device, causing the electron beam to deviate from the drift tube channel. At the same time, each electron beam rotates around itself, and the cross section of the electron beam is deformed and expanded. In the improper design of electron beam and drift tube parameters, two kinds of rotating motions cause beam to lose. A multiple-electron-beam diode structure is optimized by the particle-in-cell simulation to reduce beam loss, with the effects of the related factors taken into account. Each pole of the cathodes is made up of graphite and stainless steel. The cathode head is made up of graphite, for the graphite has a lower emission threshold. The cathode base and cathode pole are made up of stainless steel, for the stainless steel has a higher emission threshold. Also the shape and structure of cathode pole, cathode head and anode are optimized to reduce the electric field intensity on the cathode pole and enhance the electric field intensity on the end face of cathode head. At the same time, the electric field distribution of the cathode head is uniform to improve the electron beam emission uniformity. The simulation results demonstrate that the transmission efficiency of multiple electron beams can reach 99%. In the experiment, the transmission efficiency of multiple electron beams is 92% with a beam voltage and beam current of 801 kV and 9.3 kA, respectively.