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We propose and study a scheme of a microwave pulse generator operating in the frequency ranges near 37 and 73 GHz, in which the electron interaction with both the (−1)st harmonic of the counterpropagating TM02 mode and the synchronous slowed-down TM01 mode is combined in a sectionalized slow-wave system with an average diameter of 2.5λ. An efficient current modulation at the input of the slow-wave system is ensured in the region of the cathode–anode gap and the matching section, which reduces the diffraction loss of the energy flow directed towards the cathode. Numerical modeling shows that the efficiency of converting the electron-beam power to microwave radiation is up to 50%. Experiments demonstrate a stable regime of generation of subgigawatt pulses at an efficiency of more than 40% in the upper part of the millimeterwavelength range, which have a reproducible spatial wave structure corresponding predominantly to the TM01 mode at the input of the emitting horn.

—A complex of equipment for diagnosing the parameters of laser radiation of semiconductor targets, which are excited by high-frequency-modulated electron-beam pulses, is described. The ability to control the shape and duration of laser radiation in the picosecond range via high-frequency modulation of an accelerating-voltage pulse was demonstrated experimentally. A train of laser-radiation pulses with a maximum intensity of up to 2 × 107 W/cm2 was obtained on a cadmium sulfide target (λ = 525 nm).

Ferrite spiral delay lines intended for synchronization of high-voltage generators. The results of output pulses’ time stability are presented. All testes were carried out in both single- and two-channel systems. Adjustable precise synchronization of two nanosecond high-voltage generators (−150-kV, 5-ns full-width at half-maximum) are analyzed in this paper. The trigger high-voltage pulse was split into two channels to switch on identical double forming lines of each generator through controlled high-pressure spark gaps (nitrogen 60 atm). Designed coaxial ferrite spiral lines with an external bias field were installed in both synchronized channels. Adjustment of the bias field not only sharpens the trigger pulse but also varies its front delay and, respectively, the start of the driven generators. The maximum delay of one channel relative to the other was 1.5 ns. The minimum standard time deviation (relative jitter) of two nanosecond high-voltage generators was determined at the level of 55 ps.

Properties of the runaway electron flow (REF) generated in an air-filled high-voltage interelectrode gap with a drastically inhomogeneous electric field distribution are presented. We have shown that REF initiated near the tip of a conical cathode involves high-energy electron fraction with ultrashort length of about 10 ps. Analytical and numerical considerations show that the REF generation and cessation is determined by a combination of ionization processes in the gas in the vicinity of the cathode, resulting in multiplication of free electrons and expansion of the cathode plasma layer, and dynamic processes that switch on/off a threshold electric field at the anode side plasma border which is sufficiently high for electrons to become runaway. The characteristic time of REF generation and termination can be estimated from the rate of ionization at a near-threshold field as ~2 ps. This elementary time determines the pulse length for the runaway electron current that was calculated to be ~6 ps, which is close to its experimental value.

This paper describes two approaches which have been developed in the past few years for the creation of electronically controlled steering of the microwave beam formed by multichannel auto-oscillators. The first one is based on two- and four-channel gyromagnetic nonlinear transmission lines operating in the generation mode at subgigawatts power level and decimeter wavelengths. The second approach uses Cherenkov superradiance in two and four parallel backward-wave oscillators with centimeter wavelengths. We present the results of several recent experiments and analyze the physical and technical limitations to arrange new radiating arrays.

The paper presents research results on enhancing the peak power of microwave pulses with sub- and nanosecond length using a backward-wave oscillator (BWO) operating at 29 GHz frequency and possessing a reproducible phase structure. Experiments are conducted in two modes on a high-current electron accelerator with the required electron beam power. In the first (superradiation) mode, which utilizes the elongated slow-wave structure, the BWO peak power is 3 GW at 180 ns pulse duration (full width at halfmaximum, FWHM). In the second (quasi-stationary) mode, the BWO peak power reaches 600 MW at ~2 ns pulse duration (FWHM). The phase spread from pulse to pulse can vary from units to several tens of percent in a nanosecond pulse mode. The experiments do not show any influence of microwave breakdown on the BWO power generation and radiation pulse duration.

Fast processes associated with emission, acceleration, and drift motion of a high current, moderately magnetized electron beam (particles energy ~300 keV; current ~3 kA) were studied experimentally when tubular explosive-emission cathode was supplied by subnanosecond rise time voltage pulse. Kinematic effect causes the sharpening of the observed beam front which was proven by particle-in-cell numerical modeling. The angular structure of tubular beam was studied through the current waveform records from collector probe after beam propagation through a radial-slit collimator. Current waveforms had time resolution no worse than 10 ps and provided the analysis of the beam temporal structure after its acceleration as well as in the process of further electrons drift motion in a finite guiding magnetic field.

Test results of high-voltage one- and four-channel radio-frequency (RF) generators based on the coaxial gyromagnetic ferrite-filled nonlinear transmission lines (NLTL) with external magnetic bias and RF-modulation frequency of a high-voltage pulse envelope of ∼8 GHz are presented. Electrical strength of oil-isolated NLTLs was tested in a compact version of one-channel generator based on the RADAN driver at a repetition rate of 100 pps. In case of a stationary setup, 5-ns pulse with -500 kV amplitude was split into 4 channels with individual NLTLs. Gyromagnetic line output pulses had fast damped RF-modulation with a maximum modulation depth more than 50% and the peak amplitude of -200 kV. Independent control of a delay time in each channel was realized by the coaxial spiral lines with a central biased ferrite core. The coherent summation possibility of RF fields in the free space radiated by a 4-channel system of conical dielectric antennas was demonstrated.

Experiments on summation of linearly polarized Gaussian wave beams in free space from two and four synchronous nanosecond Ka-band relativistic backward wave oscillators (BWOs), each having an output power of about 200 MW with controllably shifted oscillator frequencies have been carried out. An about 0.5% frequency shift in one of the channels was equivalent to a one-period phase delay of the carrier frequency. In a two-channel version of the device, a full beat cycle was obtained for a pulse with quadratic (with respect to the number of sources) enhancement of the power flux density at the interference maximum of the integral directional pattern (DP). In the case of a four-channel device, a diagonal displacement of the DP lobes has been demonstrated.

Variations in the transient time and in the microwave pulse duration and peak power have been demonstrated for a relativistic subgigawatt $Ka$ -band backward-wave oscillator (BWO) with the slow-wave structure geometry, the accelerating voltage, and the electron beam current remained unchanged. This was done taking into account that the BWO operation mode depends on the starting-current-to-beam-current ratio. Efficient variation of the starting current was attained by changing the beam path in view of a significant difference between the times of the guide pulsed magnetic field diffusion into the electron injection region and beam-wave interaction space.

The synchronized operation of four gyromagnetic nonlinear transmission lines (NLTLs) was tested with a pulse repetition frequency up to 1 kHz during 1 s bursts. High voltage pulses with a duration of ∼5 ns from the solid state driver S-500 were split into four 48 Ω channels reaching about -200 kV in each channel with ∼10% variation in the amplitude. The maximum peak voltage at the NLTL output was within 220-235 kV with the maximum modulation depth of decaying oscillations up to 90% at the center frequency near 2.1 GHz. The relative delay between channels reached the half-period of the center frequency of oscillations. The associated beam steering by four element array of conical helical antennas was demonstrated in a horizontal plane at 17°. The effective potential of radiation reached 360 kV at the radiation axis. The effect of ferrite temperature on the shock wave velocity in gyromagnetic NLTL is observed.

Test results of high-voltage subnanosecond pulse generator with a hybrid, two-stage energy compression scheme are presented. After the first compression section with a gas discharger, a ferrite-filled gyromagnetic nonlinear transmitting line is used. The offered technical solution makes it possible to increase the voltage pulse amplitude from −185 kV to −325 kV, with a 2-ns pulse rise time minimized down to ∼180 ps. For the small output voltage amplitude of −240 kV, the shortest pulse front of ∼85 ps was obtained. The generator with maximum amplitude was utilized to form an ultra-short flow of runaway electrons in air-filled discharge gap with particles’ energy approaching to 700 keV.

For the first time, we demonstrate experimentally the possibility of Cherenkov superradiant generation with a phase imposed by an ultrashort seed microwave pulse. The phases of seed and initiated Ka-band microwave pulses were correlated with the accuracy of 0.5-0.7 rad for the power ratio down to -35 dB. Characteristics of such a process were determined in the frame of a basic theoretical model that describes both spontaneous and stimulated emission of an electron beam moving in corrugated waveguides. The obtained results open up opportunities of reaching extremely high radiation power density in phased arrays of short-pulse coherently operating microwave generators.

We present and analyze characteristics of the runaway electron flow in a high-voltage (the voltage rise rate of up to 1.5 MV/ns) air-filled electrode gap with a strongly nonuniform electric field. It is demonstrated that such a flow contains a high-energy electron component of duration not more than 10 ps. According to numerical simulations, runaway electron generation/termination is governed by impact ionization of the gas near the cathode and switching on/off a critical (sufficient for electrons to run away) electric field at the boundary of the expanding cathode plasma. The corresponding characteristic time estimated to be 2–3 ps is defined by the ionization rate at a critical field.

This paper presents new experimental data that enable the observed processes in nonlinear ferrite lines to be related with the theoretical positions of the spin waves of the magnetization precession under the conditions of a high-power microwave. Such an approach has not been considered in earlier discussions on the subject and can contribute to the theory of the generation of oscillations in a gyromagnetic ferrite medium. These new aspects were used to design a new type of generator. The specific feature is the presence of regularity in the ferrite lines in the generation mode of microwave oscillations. The repeating regularity enabled the implementation of multistage pulse shape converters capable of operating in two modes and providing extreme parameters of the output pulses. Two variants of multistage converters of nanosecond high-voltage pulse shapes with a duration of ∼4 ns at a half-height and with an amplitude of −500 kV were designed and tested. The assembly of the converters and the driving generator are described in the stationary setup. In the first case, the rise time shortened to ∼45 ps, and the amplitude increased to −850 kV due to the sharpening of a pulse and the formation of a shock wave by the cascade of three nonlinear transmission lines. A record rate for the increase of the leading peak voltage of ∼15.5 MV/ns was reached. In the second case, the new approach for the generation of a sequence of subnanosecond pulses was presented and tested, and each pulse of the previous stage was modulated by the next stage doubling the number of pulses while conserving a deeper modulation. As a result, at the top of the incident pulse, a sequence of subnanosecond peaks with a large modulation depth (∼70%) was formed when the maximum voltage amplitude reached −700 kV. The results of the emission of such pulses are also presented.

We review the studies of phase stabilization of a pulsed relativistic backward-wave oscillator (BWO) excited by the feed voltage with a steep front. Results of radiation phase stabilization are compared with the results of in-phase excitation of two independent nanosecond relativistic microwave backward-wave oscillators of the 8-mm wavelength range. Stable and controlled (by correcting the voltage front) synchronization of two channels with identical high-current electron beams is demonstrated for the case of generation power of up to 230 MW and a pulse duration of up to 100 oscillation periods in each beam.

The theoretical premises and experimental results of phase control in high-power microwave oscillators with nanosecond pulse duration are presented. In experiments, two-channel backward wave oscillators (BWOs) for both steady state (100-150 cycles) and super-radiance (SR) mode operation (10-20 cycles) are discussed. For the phase control, the shift of the moment with fastest current rise is provided in the sections of nonlinear transmission lines with axially biased ferrites. The voltage pulse sharpening and shift of group velocity depend on the dc axial magnetic field. In SR mode, two-channel source is capable of producing 2 × 0.3 GW pulses with duration of 2 ns and the center frequency of 10 GHz. The source operates at the repetition rate up to 100 pps with electronic control of the phase in one channel relative to another. The last experiment is carried out using two synchronized compact RADAN-type drivers with two parallel Ka-band BWOs (100 MW, 2 ns, 37 GHz). The controllable shift of interference picture is a proof of the coherency in the aggregated radiation. At the maximum of the pattern in the far zone, the detector indicateds fourfold increase in power density over that measured from single channel.

The coherent composition of the wave beams of two relativistic nanosecond backward-wave tubes (BWTs) with an 8-mm range and peak power in each channel of up to 230 MW is implemented. A specific feature of this experiment was power supply of explosive-emission cathodes by split pulses supplied by a completely solid-phase SOS modulator with reduced amplitude scatter. The voltage growth rate was increased compared to previous experiments, which made it possible to transition to the region of weaker magnetic fields ∼2 T, which was less than cyclotron resonance field, while retaining stable emission of the electron beams. As a result, a standard deviation of phase scatter between the channels of 0.5 ps was found on the time scale.

The possibility of in-phase excitation of two independent nanosecond-pulsed relativistic 37-GHz backward-wave oscillators (BWOs) with high-current electron beams has been studied. This regime can be achieved using BWO switching with a picosecond precision. It is shown that long-term (up to 100–200 periods of the field) phase locking in each channel is stably reproduced from pulse to pulse, which ensures coherent summation of the output wave beams at a megawatt power.

Two modifications of the compact subnanosecond high-voltage bipolar pulse generator with an active unit based on a high-impedance charging line, forming line, and two uncontrolled nitrogen spark gaps without gas purging are studied. In both cases, the forming lines are charged with compression of the energies of incident pulses with a ∼160-kV amplitude, a ∼4-ns duration, and a ∼1.5-ns leading edge. The difference of operation modes of the circuits and their efficiency are specified by a point of connecting the load. In conditions of nanosecond prebreakdown overvoltage at a 100-Hz repetition rate, the spark gaps were energized with a relative scatter of ±(100–170) ps, thus specifying the stability of the shape of output bipolar pulses with a voltage difference up to 250 kV.

An effect of the nonlinear compression of ultrashort microwave pulses has been observed in the process of the amplification of quasistationary electron beams. The Cherenkov mechanism of the interaction of a rectangular electron beam with a decelerated wave in a waveguide partially filled with an insulator is used. The experiment has been conducted on a setup consisting of two synchronized RADAN high-current accelerators. The first accelerator supplied a generator of 37-GHz superradiance pulses with a duration of about 300 ps. The second accelerator with a beam current of up to 1.2 kA and an electron energy of about 300 keV was used in an amplifying section. The theoretical analysis shows that the amplification of the electromagnetic pulses (at least by a factor of 4 in the power) is accompanied by a strong decrease in their duration (down to 100 ps).

Designs of compact converters intended for compression of high-voltage pulses with durations of a few nanoseconds and operating in a traveling wave mode were examined. The energy compression unit contained two lines-high-impedance and forming-with a high -pressure gas spark discharger used as a switch. A traditional serial connection of lines was replaced by a parallel connection to increase the energy compression efficiency. The power of the initial pulse (amplitude, 145 kV; half-height duration, 4 ns; and rise time, 1.5 ns) at a load of 45 Ω was increased by a factor of 1.8, while the calculated value was 2.5. The amplitude was as great as -195 kV, and the power was 17% higher relative to the circuit with a serial connection of lines. When shaped, the pulse was compressed in time to 0.8 ns. Two modifications of devices converting the initial pulse with an amplitude of -160 kV and a rise time of 0.3 ns into pulses with amplitudes of -210 and -250 kV and durations of 0.80 and 0.45 ns, respectively, were tested. Waveguide components of the converters were developed, with which it was possible to minimize the dimensions of the device in order to avoid excitation of higher harmonics while maintaining the electric strength.

The stability of operation of parallel explosive-emission cathodes driven by a split high-voltage pulse with a subnanosecond leading front has been studied. It is established that, upon the training of graphite cathodes in vacuum with up to ∼104 pulses, the current pulse fronts of injected high-current electron beams exhibit a mutual temporal dispersion not exceeding ten picoseconds. The dynamics of this parameter during the training stage, the variation of the absolute spread, and the growth of a relative delay of the moments of beam injection have been investigated.

A compact repetitive superradiative Ka-band BWO is described, and the results of a study of its characteristics are presented. For an electron beam transported in a magnetic field of 2 T, which is less than the value corresponding to a cyclotron resonance, the efficiency of the conversion of electron beam power to pulsed electromagnetic radiation is close to unity. The peak power of an electromagnetic superradiative pulse of 250-ps duration is ~ 500 MW.

The results of investigations of converters ensuring correction of the shape and energy compression of high-voltage (∼200 kV) pulses with durations of several nanoseconds and the formation of pulses with subnanosecond rise times across a load of ∼50 Ω are described. The converters are assembled on the basis of forming and transmitting coaxial lines and a high-pressure nitrogen spark gap. Correcting devices are open-circuit strip-line stubs connected to different points of the transmitting or forming line. Depending on the stub connection point, a series or parallel discharge of the forming line and stub to the load is initiated after switching of the spark gap. As a result, the pulse may become either longer or shorter; in the latter case, its amplitude increases. The design of the stubs built into the insulating gap of the coaxial line does not increase the size of the device at all.

We demonstrate both theoretically and experimentally the possibility of correlating the phase of a Cherenkov superradiance (SR) pulse to the sharp edge of a current pulse, when spontaneous emission of the electron bunch edge serves as the seed for SR processes. By division of the driving voltage pulse across several parallel channels equipped with independent cathodes we can synchronize several SR sources to arrange a two-dimensional array. In the experiments carried out, coherent summation of radiation from four independent 8-mm wavelength band SR generators with peak power 600 MW results in the interference maximum of the directional diagram with an intensity that is equivalent to radiation from a single source with a power of 10 GW.

Technical parameters of a CLAVI pulsed cathodoluminescence spectroscope are presented. The device is used for the nondestructive spectral luminescence analysis of defects in solid optical and laser materials (crystals, glasses, and ceramic materials). Illustrating examples are presented.

The generation of ultrashort superradiant pulses in the stimulated scattering of an intense microwave (38 GHz) pump wave by a counterpropagating high-current relativistic electron bunch has been observed. Scattered radiation is a single ∼200-ps pulse with a peak power of about 1 MW. Owing to the Doppler shift of the radiation frequency, frequencies up to 150 GHz are present in the spectrum of the scattered pulse.

Results of tests of a fast-repetitive nanosecond modulator with a peak output power of 3 GW are presented. It comprises of a type S-5N charging driver, a power compressor based on a pulsed forming line, and a gas spark gap. The modulator has been designed for the formation of high-current electron beams and high-power microwave generation in a pulsed-repetitive regime. Excitation of 10-GHz microwave pulses /spl sim/1 ns long in a relativistic backward-wave oscillator with an elongated periodic slow-wave system has been studied. Optimization of the regime of interaction between electromagnetic fields and particles provided an average power of microwave radiation in the burst-repetitive mode (1 s; /spl sim/700 Hz) of up to 2.5 kW at a focusing magnetic field (/spl sim/0.6 T) below the cyclotron resonance region. The peak output power of the oscillator exceeded 2 GW.

The regime of excitation of microwave pulses in a 10-GHz range at a pulse duration of 0.8 ns and a peak power of ∼2 GW has been studied in a relativistic backward wave oscillator with an extended periodic slow-wave system. A pulsed electron accelerator generating high-current electron beams (3 GW, ∼600 keV, ∼5 kA, 7 ns) at a repetition rate of 700 Hz and a pulse train width of 1 s has been developed based on a high-voltage generator with inductive energy storage, a semiconductor current interrupter, and a pulse-sharpening hydrogen-filled discharge gap. Optimization of the regime of the field-particle interaction allowed an average microwave power of 2.5 kW to be obtained at a transport magnetic field strength reduced below the cyclotron resonance value.

An original relativistic backward tube (BWT) for a 38 GHz range is developed and tested. The BWT is capable of generating stable pulses of ∼250 ps duration and a peak power of ∼250 MW in trains with a length of up to 1 s at a repetition rate of 1–3.5 kHz. The BWT design implements an inhomogeneous slow-wave structure of increased cross section with a band reflector. A pulsed electron beam (∼270 keV, ∼2 kA, 0.9 ns) was injected by a high-current accelerator based on a high-voltage generator with an inductive energy store, a semiconductor current interrupter, and a pulse-shaping hydrogen-filled discharge gap. A focusing magnetic field of 2 T was generated by a cooled pulsed solenoid power-supplied from a special stabilized current source.

This paper presents the results of investigations of the mode of nonsteady-state oscillations with a short-time power burst which is characteristic of the initial stage of the transient process in a backward wave oscillator when the beam operating current is far in excess of the starting current. Numerical simulations have yielded the conditions under which the efficiency of the power transfer from an electron beam with a particle energy of 300 keV, a current of 2 kA, and a duration of 1 ns into a microwave pulse containing 8-10 high-frequency field periods approaches 90%. Experimentally, it has been demonstrated that the production of pulses like these with a duration of 200-250 ps, a power of up to /spl sim/400 MW, and a central frequency of about 38 GHz is feasible.

The regime of nonstationary oscillations with a short-time power burst, which is typical of the initial stage of a transient process developed when a beam current significantly exceeds the starting level, is studied in a relativistic backward wave tube (BWT) operating in the millimeter wavelength range. The results of numerical calculations allowed conditions to be established that provide for a nearly 90% efficiency of the power transfer from an electron beam with the parameters 300 keV, 2 kA, 1 ns to the microwave pulse with a duration of 8–10 periods of the microwave field oscillations. The experiments showed the possibility of generating such pulses with a width of 200–250 ps and a power of up to ∼400 MW at a central frequency of about 38 GHz.

Cherenkov superradiance observed when an electron bunch rectilinearly moves through a slow-wave periodic system is studied theoretically and experimentally. The simulation based on averaged equations and the direct numerical simulation using the PIC-code KARAT show that the peak power of the microwave pulses varies as the total number of the particles in a bunch squared. This finding is confirmed experimentally. Ultrashort (300 ps wide) high-power (up to 140 MW) pulses are generated at a frequency of 39 GHz. As an electron source, the high-current subnanosecond RADAN-303 accelerator is used. It injects 0.5-to 1.5-ns-wide electron bunches of current up to 2 kA and energy 200–300 keV. The simulation suggests that the power of the electromagnetic pulses can be increased further (up to 300 or 400 MW) by optimizing the accelerating voltage pulse shape.

Experimental results of the observation of superradiation from intense, subnanosecond electron bunches moving through a periodic waveguide and interacting with a backward propagating TM01 wave are presented. The ultra-short microwave pulses in Ka, W, and G band were generated with repetition frequencies of up to 25 Hz. Observation of RF breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, leads to an estimate of the peak power as high as 60–120 MW for the 300–400 ps pulses at 38 GHz. The initial observation of 75 GHz 10–15 MW radiation pulses with duration less than 150 ps, and of 150 GHz microwave spikes with a risetime of 75ps are also reported. Comparison with simulations is discussed as well.

We report on the results of testing a hybrid subnanosecond modulator with an input resistance of 50 Ω based on an all-solid-state high-voltage nanosecond-pulse charging source with an inductive energy accumulator, a semiconductor current switch, and a pulse shaper with gas-discharge gaps. Use of the sharpening and cutting discharge gaps filled with hydrogen at a pressure of 100 atm ensured the stable formation of pulses with a peak amplitude of up to 140 kV and a pulse width of ∼500 ps at a repetition rate of up to 2 kHz.

Test results of a combined subnanosecond modulator with an output impedance of 45 Ω, which incorporates an all-solid-state high-voltage nanosecond charging device (with an inductive energy storage and a semiconductor opening switch) and a pulse sharpener with gas-filled gaps, are presented. The sharpening and cutting spark gaps filled with hydrogen at a pressure of 100 atm ensured the formation of stable pulses with amplitudes of –(180–200) kV and durations of ∼ (400–700) ps at a repetition frequency of up to 3.5 kHz. An average output power of 1.4 kW was achieved for the modulator's burst-mode operation with a number of pulses in a packet of 104at a maximum pulse repetition rate.

Experimental results are presented of the observation of stimulated Cherenkov radiation when intense subnanosecond electron bunches were moving through a dielectric-loaded waveguide. The ultrashort duration microwave pulses (up to 400 ps which is equivalent to ∼10 periods of the radiation) in combination with specific dependencies of peak microwave power on interaction length demonstrate that this emission can be interpreted as coherent superradiant (SR) emission. The peak power associated with the SR emission was ∼1–2 MW. The spectrum of radiation belongs to the frequency range 38–48 GHz. The experimental results are compared with theoretical analyses.

Experimental results of the observation of coherent stimulated radiation from subnanosecond electron bunches moving through a periodic waveguide and interacting with a backward propagating wave are presented. The subnanosecond microwave pulses in Ka and W bands were generated with repetition frequencies of up to 25 Hz. The mechanism of microwave pulse generation was associated with self-bunching, and the mutual influence of different parts of the electron pulse due to slippage of the wave with respect to the electrons; this can be interpreted as superradiance. The illumination of a panel of neon bulbs resulted in a finely structured pattern corresponding to the excitation of the TM01 mode. Observation of rf breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, leads to an estimate of the absolute peak power as high as 60 MW for the 300-ps pulses at 38 GHz. These results are compared with numerical simulations. The initial observation of 75-GHz, 10-15-MW radiation pulses with a duration of less than 150 ps is also reported.

The first results of the observation of superradiance from a single, subnanosecond, high current, electron bunch passing through a wiggler immersed in a guide magnetic field are presented. The 300–500 ps microwave pulses were generated in the high gain regime for both the conventional and reverse directions of the guide magnetic field. The dependence of the radiation power on the interaction length as well as the absolute value of the power, 100–200 kW, were related with the development of self-bunching and consequently with coherent emission.

The generation of microwave pulses in a 10-GHz range has been studied in a nonstationary relativistic backward wave oscillator (BWO) operating at a pulse train repetition rate of up to 300 Hz. Regimes with a stabilized phase of the high-frequency filling of pulses with respect to the accelerating voltage pulse front have been observed at a BWO peak output power of ∼1 and 3 GW. In pulse trains with a length of 10–100 s, the average output microwave power reached ∼1 kW.

Intense microwave pulses (several hundreds of kilowatts) of ultrashort duration (less than 0.5 ns) were obtained from an ensemble of electrons rotating in a uniform magnetic field. The comparison with theoretical simulations proves that this emission can be interpreted as cyclotron superradiance. The maximum radiation power was achieved under group synchronism conditions, when the electron bunch translational velocity coincides with the group velocity of the wave propagating in the waveguide.

We have experimentally studied the possibility of increasing the working life of explosive-emission cathodes operating at high repetition frequencies (several kilohertz) of nanosecond accelerating voltage pulses. Micrographs of the cathode surface upon training, photographs of the operating cathode, and analyses of the material carried away from the cathode showed that a substantial role in the cathode degradation is played by heating of some regions of the emissive edge up to a temperature of graphite melting.

We have theoretically and experimentally investigated the process of induced coherent emission (superradiance) in an electron bunch rotating in a homogeneous magnetic field. We have shown that this process makes it possible to generate ultrashort microwave pulses. In this case, the optimum conditions are found under group synchronism conditions, when the translational velocity of the bunch matches the group velocity of the radiation propagating in the waveguide circuit. For experimental investigation of the superradiance, we used a RADAN accelerator with subnanosecond electron pulse sharpener. In the 35 GHz range, we obtained microwave pulses with record short duration, down to 0.4 nsec for a peak power level up to 200 kW.

The excitation of superbroad-band TEM antennas with a high-voltage subnanosecond modulator permitting a pulse-repetition frequency of up to 100 Hz is experimentally investigated. The modulator consists of a RADAN-303B nanosecond driver and a pulse amplifier based on gas discharges. The instrument generates unipolar and bipolar pulses of tunable length and amplitude. The amplitude and power of the pulses sent to the antenna reach 100 kV and 200 MW. Data are obtained on the stability of the parameters of the subnanosecond modulator pulses. Information is given on the electrical strength of the air insulation in the matching interval between the modulator and the antenna. The superbroad-band pulses emitted are recorded at distances of up to 25 m. The characteristics of the instrument permit the spatial resolution of reflections from conducting objects with a shape-inhomogeneity scale of no more than 25 cm. Emitters with increased directionality in the E or H (E and H) planes based on two (four) TEM antenna supplied with split modulator pulses are investigated. In-phase and antiphase antenna configurations are considered.

Specific features of superradiance in waveguide under group synchronism conditions are studied theoretically. Progress in experimental observation of cyclotron superradiance based on using a subnanosecond pulse generator with explosive electron emission is discussed.

Intense (several hundreds of kilowatts) subnanosecond coherent microwave radiation — cyclotron superradiance of an electron swarm moving in a uniform magnetic field — was recorded. The maximum power of the radiation was observed under group synchronization conditions, when the translational velocity of the swarm is equal to the group velocity of the waves in the waveguide channel.

The regime of excitation of subnanosecond high-power microwave pulses has been studied in a Cherenkov device with an extended periodic slow-wave structure, using an electron beam from a compact pulsed high-current electron accelerator (290 keV, 2.3 kA, 1 ns). Conditions are established for which the power conversion coefficient can reach up to 1.5 at an output pulse power of 1.2 GW and a pulse duration of 200 ps.