Surface Of Slow-wave Structure Research Articles

Investigation of damage traces on the SWS of the RBWO with a low guiding magnetic field

For the high power microwave (HPM) generator, damage on an RF structure surface is harmful for a long time operation. In this paper, we investigate damage traces on slow-wave structure (SWS) of the relativistic backward-wave oscillator (RBWO) with a low guiding magnetic field. By theoretical and experimental analysis, we find that damage traces on SWS surface are mainly caused by the bombardment of beam electrons pulled back. Moreover, it is suggested that damage traces are not caused by RF breakdown, the bombardment of secondary electrons, and the bombardment of particles from collector plasma. Importantly, to decrease damages and prolong the working life of the RBWO with a low guiding magnetic field, the electric field which pulls electrons to the RF structure surface (saying Ez and −Er) should be decreased by special design for the RF structure, such as blending and parameters adjustment. Those results may offer benefit guides for study of the RBWO with a low guiding magnetic field.

Research on effects of space charge field in relativistic backward wave oscillator

The breakdown problem in the relativistic backward wave oscillator (RBWO) limits the microwave pulse energy and should be solved. The slow wave structure (SWS) is the most key component of the RBWO. The breakdown of SWS may be triggered by field-induced electron emission and electron bombardment on the wall. This paper demonstrates that the space charge field of the relativistic electron beam (REB) can enhance the electric field forbidding field-induced electron emission and decrease the electric field igniting the RF breakdown, and therefore, the RF breakdown can be significantly suppressed. However, the enhanced electric field will enlarge the radial displacements of electrons, especially the high-energy electrons. When the RBWO operates with a low guiding magnetic field or a long-pulse REB, this situation will worsen and some electrons may possess large enough radial displacements and bombard on the SWS surface with the help of radial oscillation of REB and radial expansion of cathode plasmas. This may aggravate the breakdown of SWS.

Помножувач частоти у субміліметровому діапазоні хвиль. Частина 2. Обґрунтування моделі компактних електронних ущільнень, які існують тривалий час

Subject and Purpose. Part 1 of the present paper presents a feasibility study of a submillimeter frequency multiplier based on a clinotron with a single slow-wave structure. The aim of Part 2 is to gain a better insight into the electron bunching mechanism, seeking for efficient energy exchange between the electron bunches and the RF field in the multiplier of the sort. Methods and Methodology. The research method is a theoretical analysis given to the electron bunching process in a BWO-type oscillator with rigorous numerical models involved. The bunch longitudinal size is calculated in steady state regime with regard to the space charge influence. The necessary conditions for compact electron bunching are sought via numerical integration of the motion equations of electrons subject to the interaction with the RF field of the slow-wave structure. Results. A mechanism of compact electron bunching has been revealed by numerical modeling and described. The pattern of long-lived compact electron bunches continuously moving along the surface of the clinotron comb-type slow-wave structure holds owing to the continuous deposition of compact electron bunches on the comb surface. The compact bunches are formed in electron beam layers farthest from the comb surface but moving to it in consequence of the electron beam inclination under magnetic field action (the clinotron effect). The bunch size and its dependence on the problem parameters have been specified. The research results find use in analysis of operational regimes of conventional clinotrons. Clinotron designers are provided with relevant recommendations. Conclusion. A model of electron bunching in clinotron-type oscillators has been developed with regard to the process of deposition of electron beam layers on the comb-type slow-wave structure surface. It is the existence of a system of compact electron bunches continuously moving along the comb surface that makes possible efficient electron beam interaction with the high-frequency electromagnetic field of multiplied-mode oscillations. We justifiably claim that multipliers of the kind can be advanced to the short-wave end of the submillimeter band.

Design and numerical simulation of a high power capacity relativistic backward wave oscillator with an electron collection cavity

A high power capacity relativistic backward wave oscillator with an electron collection cavity (ECC) placed at the downstream of the slow wave structure (SWS) is presented. The breakdown threshold is increased, and the density of seed electron is suppressed by preventing the secondary electron, plasma, and powder generated from the bombardment of spent electron beam on the surface of the collector drifting to the extractor and beam-wave interaction region. The maximum longitudinal electric field in the device is reduced through extension of the span between electron beam and slow wave structure and weakening the Cerenkov radiation. The conversion efficiency reaches up to 52% owing to enhanced transit time radiation taking place at the entrance of the ECC. The maximum longitudinal electric field is 1.1 MV/cm on the surface of SWSs when the output power is 7.3 GW and the power capacity improves significantly.

Relativistic Gigawatt BWT microwave pulse duration increased upon treating the slow-wave structure surface with a low-energy high-current electron beam

A new method of insulator surface treatment, which allows the electric strength of the material to be increased, is proposed and verified. Using this method for treating the slow-wave structure of a relativistic backward wave tube (BWT), the microwave pulse duration was increased from ∼6 to ∼30 ns at an output BWT radiation power of 3 GW.

Pulsewidth limitation in the relativistic backward wave oscillator

Spontaneous pulse shortening occurring in a relativistic backward wave oscillator (BWO) at gigawatt power levels is studied in experiment and theory. It is experimentally demonstrated that this phenomenon is accompanied by formation of an explosive-emission plasma at the surface of the corrugated slow-wave structure (SWS). Termination of microwave emission is explained by the increase of the BWO starting current from the absorption of the operating electromagnetic wave by electrons emitted from the plasma, whereas the intensity of the absorption radically increases offing to the presence of positive ions emitted from the plasma. Application of oil-free vacuum and electrochemical polishing of the SWS surface in an X-band BWO allowed generation of 3-GW, 26-ns microwave pulses with an energy of /spl sim/80 J, thereby demonstrating pulse lengthening by a factor of four.

Relativistic carcinotron with a thermionic injector of electrons

An experimental study directed to the determination of a mechanism for microwave breakdown in a relativistic X-band carcinatron is presented. An electron beam was generated using a thermionic cathode, which provided a stable beam geometry. The use of this cathode decreased the probability of breakdown caused by electron bombardment of the slow-wave structure. An important part played in microwave breakdown are molecules absorbed on the slow-wave structure surface. It is shown that the presence of these molecules, an implementation of conditions for secondary-electron resonant discharge (SERD), can result in a very fast (during 10-20 ns) limitation of the radiation pulsewidth. To remove the adsorbed molecules, heat degassing of the slow-wave structure and a collector of electrons was applied, going on continuously, during a working day of the device. By degassing and choice of slow-wave structure material, output radiation power of the device was increased by a factor of ten (up to 5 MW at the pulsewidth of 10 /spl mu/s).