N. G. Kolganov

An X-band gigawatt amplifier

In an X-band Cerenkov amplifier driven by a 0.8-MeV 6-kA electron beam, a gigawatt-level of power radiated in a Gaussian pattern in a 70-ns pulse duration has been demonstrated. The coherence of the output radiation is provided by dividing the oversized interaction space into separate sections with different azimuthal symmetry that couples only with the electron beam. A large gain of 47 dB and an efficiency of 23% are obtained using a regenerative amplification of a backward-wave amplifier (BWA) that produce a modulation of the electron beam. The efficiency of this device is 27% when the BWA-modulator operates in the regime of auto oscillations.

Sources of Coherent Terahertz Radiation

New results in the field of high‐frequency gyrotrons, gyro‐multipliers and orotrons allow one to consider these electron devices as promising candidates for the realization of powerful and available sources in Terahertz range. Electron beams with a very high compression of up to a factor of 4,400 have been obtained and selective generation at the 1st–5th cyclotron harmonics have been demonstrated in Large Orbit Gyrotrons (LOGs) at millimeter and submillimeter wavelengths at operating voltages from 50 to 250 kV. When operating at the third cyclotron harmonic (TE3,8 and TE3,9 modes in the first oscillator; TE3,5 mode in the second oscillator) output power levels of 10–20 kW have been obtained in the frequency range of 0.37–0.41 THz. Gyro‐multipliers with self‐exciting low‐frequency sections are proposed and studied theoretically. Low‐voltage orotrons have been demonstrated in the frequency range of 0.1–0.4 THz with output powers of 1.0–0.1 W and typical electrical‐mechanical frequency tunability within an o...

Microwave source of multigigawatt peak power based on a relativistic backward-wave oscillator and a compressor

The effect of passive compression of frequency-modulated pulses in dispersive media is used to raise the microwave radiation peak power to a multigigawatt level. A waveguide with a helically corrugated surface is applied as a dispersive medium, and a relativistic 3-cm backward-wave oscillator with an accelerating voltage decaying within the pulse duration serves as a source of frequency-modulated pulses. The compression of pulses to an FWHM of 2.2 ns attended by a rise in the peak power by a factor of 4.5 (to 3.2 GW) is demonstrated with a SINUS-6 accelerator.

Experimental Study of a Relativistic Resonant Traveling-Wave Tube With Selective Feedback Provided by Bragg Reflectors

The realization of single-mode generation in a microwave oscillator is considered for a relativistic resonant traveling-wave tube (RTWT) with spiral Bragg reflectors at the ends of a multimode electrodynamic system. An oversized azimuthally symmetric slow-wave structure was chosen so that only two field structures are synchronous with a 1-MeV electron beam. Experiments using different means that allow us to separate these field structures are described. As a result, two radiation patterns were observed separately, which are a narrow Gaussian-like wave beam with a power of up to 1.5 GW and an efficiency of about 20% in 40-ns pulses and radiation corresponding to the E01 mode with four times weaker power. The dependences of RTWT operation on the parameters of the electron beam, the length of interaction space, reflection coefficients, and the amplitude of guide axial magnetic field are investigated in detail.

Voltage-tuned relativistic backward wave oscillator

A relativistic backward wave oscillator for the 10-GHz range with the oscillation frequency tuned within about 5% by changing the accelerating voltage from 600 to 350 kV has been developed. Discrete variations in the voltage and the corresponding frequency tuning from pulse to pulse is rapidly performed by changing the anode-cathode distance in the vacuum diode without breaking vacuum in the working volume. During this, the electron beam power remains almost constant, while the output microwave power varies within 0.4–0.8 GW. The introduction of a dielectric cylinder into the accelerating gap provides a smooth voltage drop from 600 to 350 kV with the corresponding frequency tuning during a 20-ns pulse.

Measurement of high-power microwave pulses by resistive hot-electron sensors

Use of hot-electron semiconductor detectors for the measurement of high-power microwave pulses may lead to anomalously large errors. Methods of separation of the error signal and determination of the measurement error are considered.

X-band amplifier of gigawatt pulse power

In X-band Cherenkov amplifier driven by 0.8 MeV 6 kA electron beam, the gigawatt power in pulses with duration 70 ns is achieved. The coherence of output radiation is provided by division of the oversized interaction space on separate sections coupled with the electron beam only. The high gain of 47 dB (and accordingly narrow 1% bandwidth) are obtained with the regenerative regime of operation of BWA-modulator used as a pre-amplifier.

Low-impedance relativistic backward wave oscillator

It is shown that the limiting electron-beam current in a relativistic backward wave oscillator (BWO) can be increased using a slow-wave system (SWS) in the form of a circular waveguide with shallow rectangular corrugation. This idea was checked both experimentally and numerically for a 3-cm BWO with a short homogeneously corrugated SWS and a resonance reflector-modulator. The experiments showed that the proposed BWO with an explosion-emission electron gun and said SWS can effectively operate on 60-Ohm electron beams at a gigawatt output power.

A high-power relativistic backward wave oscillator with a longitudinal slot slow-wave system

It is established that longitudinal slots in the slow-wave system of a high-current relativistic backward wave oscillator (BWO) can be used as additional means of mode selection and effective absorption of near-wall plasma. Using these properties, it is possible to increase the limiting pulse duration and repetition rate of BWO output radiation pulses.

Cooperation of traveling and quasi-cutoff waves in a cyclotron-resonance maser

A new version of a cyclotron-resonance maser is studied theoretically and experimentally. Here, a spatially periodic helical electron beam couples traveling (autoresonance) and quasi-cutoff (gyrotron) waves of the same frequency, interacting with them at different cyclotron harmonics. The theory and early experimental results show that this maser can effectively generate a traveling wave with low quasi-cutoff wave excitation losses using a very simple feedback system.