S. A. Kitsanov

A vircator with electron beam premodulation based on high-current repetitively pulsed accelerator

The paper describes theoretical, numerical, and experimental studies of a decimeter wavelength vircator with electron beam premodulation. Possible mechanisms for the excitation of electromagnetic oscillations in virtual cathode systems are analyzed (modulation of current, reflex klystron effect, and inertial bunching of reflected particles). It is demonstrated that the microwave efficiency in a double-gap virtual-cathode system may be substantially higher than that in a single-gap one. Based on one- and three-dimensional numerical simulations, an experimental mockup of double-gap vircator without external magnetic field has been developed. In experiments employing the SINUS-7 high-current repetitively-pulsed electron accelerator, single-mode microwave generation in the S-band was obtained with /spl sim/1 GW peak power and /spl sim/25 ns pulse width at about 5% efficiency. The generator showed frequency stability from pulse to pulse and throughout each pulse, which proves the dominant role of the electrodynamic system used in the vircator construction. Varying the cavity parameters allowed continuous frequency tuning within about 15% at half power. Sample batch operation of the system at 20 and 50 p.p.s. was demonstrated.

Repetitively Pulsed Relativistic Cherenkov Microwave Oscillator Without a Guiding Magnetic Field

Repetitively pulsed modes of operation of a Cherenkov microwave oscillator without an external magnetic field for the electron energies of 0.5 and 1.2 MeV were realized in the experiment. In a batch mode with a 1-Hz repetition frequency, the oscillator efficiencies (taking into account the total diode current) were 8% ±2% and 16% ±3 %, respectively (at 0.2 ±0.04-GW and 2.5 ±0.5-GW peak generation power, respectively). For a batch mode with a 10-Hz repetition frequency, the corresponding efficiencies were 7% ±1% and 15% ±3%, respectively (at 0.17 ±0.03-GW and 2.0 ±0.4-GW peak generation power, respectively). Investigations of the lifetime of velvet-covered cathodes and anode grids of oscillators were carried out in repetitively pulsed modes. The lifetime of the anode grid and velvet-covered cathode for the electron energy of 1.2 MeV was about 3000 pulses, and for the electron energy of 0.5 MeV, it can exceed 11 000 pulses.

Relativistic BWO with enhanced frequency tunability

The paper presents experimental studies of broad-band frequency tuning in a relativistic backward-wave oscillator (BWO) with an electrodynamic system of increased cross section and a resonant wave reflector. Frequency tuning within 12% was realized by mechanically shifting the reflector about the slow wave structure (SWS). The parameters of the driving electron beam were fixed. With a magnetic field of 4.6 kOe, the maximum microwave power was 4/spl plusmn/1 GW at 3.6 GHz.

S-band vircator with electron beam premodulation based on compact pulse driver with inductive energy storage

This paper describes an S-band vircator system with electron beam premodulation, built on the base of the MARINA compact high-voltage pulser with inductive energy storage. The peak microwave output was /spl sim/1 GW with /spl sim/5% power efficiency and 50-ns full-width at half-maximum. The microwave frequency was constant during the pulse as determined by the resonator. Substantial spontaneous shortening of the microwave pulse was observed. Possible mechanisms for this phenomenon are discussed and supported by three-dimensional KARAT simulations.

Vircator with electron beam premodulation built around a high-current pulsed-periodic accelerator

Theoretical, numerical, and experimental studies of a vircator with the premodulation of a dm-wave electron beam are performed. Possible oscillation mechanisms in virtual-cathode systems (modulation of passing current, effect of reflex klystron, and inertial bunching of particles reflected) are analyzed. The microwave efficiency of the vircator using a two-gap electrodynamic system is shown to be significantly higher than that of the vircator with a one-gap system. Based on the results of the numerical experiment, a prototype of a two-stage vircator in the absence of an external magnetic field is designed. In experiments using a high-current pulsed-periodic accelerator, single-mode oscillations with a power of up to 1 GW, a duration of ≈25 ns, and an efficiency of ≈5% are generated in the dm-wave range. The oscillation frequency is demonstrated to be stable during a pulse and from pulse to pulse, which suggests the decisive effect of the electrodynamic system. It is shown that the oscillation frequency can continuously be tuned in a half-power bandwidth of ≈15% by varying the parameters of the resonator.

Relativistic backward-wave tube with mechanically tunable generation frequency over a 14% range

A tunable-frequency low-magnetic-field relativistic microwave oscillator is realized experimentally based on a relativistic backward-wave tube with a modulating resonance reflector. The generated frequency is tuned mechanically by moving the oscillator slow-wave structure relative to the reflector. At fixed parameters of the corrugations and of the electron bunch, a frequency tuning range of about 14% measured between −3-dB (relative to the maximum peak generated microwave power) points is realized. The maximum pulse power of 3.4 ± 0.7 GW was obtained at a carrier frequency of 3.65 GHz in a magnetic field of 0.44 T.

Pulsed 5-GW Resonance Relativistic BWT for a Decimeter Wavelength Range

The results of numerical modeling and experimental investigation of a high-power, resonance relativistic backward wave tube are presented. By using the working TM01 mode reflections from the ends of the electrodynamic system, optimum conditions for the electron beam interaction with both the (−1)st harmonic of the backward electromagnetic wave and the main harmonic of the concurrent wave are achieved. A single mode generation with 5 GW output power and a 30% efficiency was obtained in experiments at a frequency of 3.6 GHz. The working frequency can be controlled within 15% (at the half maximum power level) by changing the slow-wave structure period at the constant electron beam parameters.

Experimental investigation of electron beam in the squeezed state

The electron beam transported in a two-section drift tube of a SINUS-7 setup has been studied. A high-density electron beam in the “squeezed” state has been obtained with a relativistic factor γb below that corresponding to the limiting current (γ > Γ1/3).

Measuring the virtual cathode velocity

An electron beam with a virtual cathode (VC) transported in a two-section drift tube of a SINUS-7 high-current electron accelerator has been studied. The dependence of the VC velocity on the injected current has been experimentally determined for the first time. It is established that the VC motion in the drift tube is accompanied by microwave oscillations, which are caused by transient processes involved in the formation of a compressed electron beam.

Tunable vircators with e-beam premodulation

The paper describes theoretical, numerical, and experimental studies of a decimeter wavelength vircator with electron beam premodulation. Possible mechanisms for the excitation of electromagnetic oscillations in virtual cathode systems are analyzed. In experiments employing the SINUS-7 high-current repetitively-pulsed electron accelerator, single-mode microwave generation in the S-band was obtained with /spl sim/1 GW peak power and /spl sim/25 ns pulse width at about 5% efficiency. Frequency tuning and repetitive batch operation were demonstrated.