We present the design and experimental results of a novel overmoded slow-wave high-power microwave (HPM) generator that is featured by its compactness, low-operation magnetic field, and potentially high power and high efficiency. The device includes two slow-wave structure (SWS) sections, a resonant cavity, and a tapered waveguide. The resonant cavity was well designed and was used to achieve the axial mode selection and to decrease the length of the SWS sections. The radial mode selection is achieved using the property of "surface wave" of the device to excite the TM/sub 01/ mode while making the higher TM/sub 0n/ modes unexcited. The physical mechanisms of axial and radial mode selections ensure that the microwave is produced with a single mode and a narrow band. The feasibility of low magnetic field operation is also investigated based on the characteristics of the overmoded slow-wave devices. Experiments were carried out at the Spark-2 accelerator. At diode voltage of 474 kV, beam current of 5.2 kA, and guiding magnetic field strength of 0.6 T, a microwave was generated with power of 510 MW, mode of TM/sub 01/, and frequency of 9.54 GHz. The relative half width of the frequency spectrum is /spl Delta/f/f= 0.6%, and the beam-to-microwave efficiency is about 21% in our experiment.

A novel overmoded slow-wave high-power microwave (HPM) Generator

An oversized rectangular corrugated backward wave oscillator is designed and theoretically analyzed to produce TM01 high power microwave radiation in the frequency of 868GHz without mode competition The device includes a slow wave structures, a resonant reflector, and an output waveguide The slow wave structure and the reflector are matched to achieve mode selection and enhance interaction efficiency Feedback processes from the reflector are introduced to explore mode selection in the configuration In particle in cell simulation, high power microwaves of TM01 mode are generated with peak power of 20GW, frequency of 868GHz, and conversion efficiency is 286% when beam voltage is 500kV and current 14kA

Investigation of an oversized backward wave oscillator as a high power microwave generator

Within the framework of a quasi-optical approach, the nonlinear theory of relativistic surface-wave oscillators is developed. By presenting the radiation field as a sum of two counter-propagating wave-beams which are coupled on a shallow corrugated surface, we describe formation of an evanescent slow wave. Taking into account the excitation of a slow wave by a sheet electron beam, we simulate linear and nonlinear stages of interaction that allows us to define the threshold conditions, the electron efficiency, and the output coupling. It is shown that the considered type of an oscillator can be used for generation of powerful sub-THz radiation.

Quasi-optical theory of relativistic submillimeter surface-wave oscillators

This paper describes a new design of a relativistic Cherenkov oscillator with strong modulation of the e-beam current at the input of two-sectioned slow-wave structure, as well as numerical and experimental results on generation of few gigawatt-level $X$ -band pulses with pulse duration of up to 35 ns. Due to special phase shift between two sections and electrodynamic coupling between $E_{01}$ surface wave and $E_{02}$ volume mode, the first one is locked at the upper boundary of the passband and the second one gains more transparency. An electron beam can interact simultaneously with two waves with higher power conversion efficiencies, which in simulations amount up to 47% and 30% for high (~4 T) and low (~1 T) guiding magnetic fields, correspondingly. The tests of the geometry optimized in simulations were performed on the base of SINUS-7 high-current electron accelerator in the diode voltage range of 400–850 kV and current from 7 to 16 kA. The repeated and full-pulsewidth generation of about 1.5-GW microwave power is achieved only in the low magnetic field. The pulse shortening and the mode competition took place in the strong magnetic field. The results are considered as preliminary for creation of the efficient relativistic millimeter-wave oscillators at magnetic fields below the cyclotron resonance.

Two-Wave Cherenkov Oscillator With Moderately Oversized Slow-Wave Structure

High power vacuum electronic devices of millimeter wave to terahertz regime are attracting extensive interests due to their potential applications in science and technologies. In this paper, the design and experimental results of a powerful compact oversized surface wave oscillator (SWO) in Y-band are presented. The cylindrical slow wave structure (SWS) with rectangular corrugations and large diameter about 6.8 times the radiation wavelength is proposed to support the surface wave interacting with annular relativistic electron beam. By choosing appropriate beam parameters, the beam-wave interaction takes place near the π-point of TM01 mode dispersion curve, giving high coupling impedance and temporal growth rate compared with higher TM0n modes. The fundamental mode operation of the device is verified by the particle-in-cell (PIC) simulation results, which also indicate its capability of tens of megawatts power output in the Y-band. Finally, a compact experimental setup is completed to validate our design. Measurement results show that a terahertz pulse with frequency in the range of 0.319–0.349 THz, duration of about 2 ns and radiation power of about 2.1 MW has been generated.

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A megawatt-level surface wave oscillator in Y-band with large oversized structure driven by annular relativistic electron beam.

Results of theoretical and experimental studies of a GW-class, large diameter microwave oscillator are presented The device consists of a large cross-section (overmoded), slow-wave structure with a unique profile of wall radius specifically designed to support surface waves and to provide a strong beam-wave coupling at moderate voltage (500 kV), an internal adjustable microwave reflector, a coaxial microwave extraction section, and a coaxial magnetically insulated field emission electron gun In preliminary experiments carried out at 83 GHz, the power level exceeding 05 GW and efficiency of 15% have been measured calorimetrically

Overmoded GW-class surface-wave microwave oscillator

Summary form only given. Results of theoretical and experimental studies of a GW class, large diameter microwave oscillator are presented. The device consists of a large cross-section (overmoded) slow-wave structure with a unique profile of wall radius specifically designed to support surface waves and to provide a strong beam-wave coupling at moderate voltage (500 kV), an internal adjustable microwave reflector, a coaxial microwave extraction section and a coaxial magnetically insulated field emission electron gun. In preliminary experiments carried out at 8.3 GHz the power level exceeding 0.5 GW and efficiency of 15% have been measured calorimetrically.

/pdf/overmoded-gw-class-surface-wave-microwave-oscillator-404oi70y6i.pdf

D. Lingze

Papers

Overmoded GW-class surface-wave microwave oscillator

Overmoded GW-class surface wave microwave oscillator