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Using numerical simulation, the operating mode of a relativistic Cherenkov microwave generator of the twistronic type has been demonstrated. The generator includes an electrodynamic system based on a backward-wave oscillator and modulating reflector with nonmonotonous, highly nonuniform energy exchange along the length of the system. The efficiency of power conversion from the electron beam to electromagnetic radiation is 56%, and the electronic efficiency is 66%. For an accelerating voltage of 340 kV and an electron beam current of 3.3 kA, the simulated generation power is 630 MW at a frequency of 9.7 GHz and a guiding magnetic field of 2.2 T.

The competition of oscillations in a relativistic backward wave oscillator (RBWO) based on a coaxial waveguide has been studied by theoretical and experimental methods. It is established that the starting current for asymmetric magnetic TEm1 type waves is lower than that for the TEM wave. Predominant excita� tion of the former waves is confirmed by numerical simulations using the PICcode KARAT. In an experi� mental RBWO prototype, the excitation of asymmetric oscillations was suppressed by longitudinal cuts in the central conductor of the coaxial waveguide. As a result, stable generation of the TEM wave has been achieved at a frequency of 1.23 GHz, a peak power of 260 MW, and a 28% efficiency of electronbeampower conver� sion into radiation power for a microwavepulse duration of 33 ns.

An elementary theory of an annular high-current electron beam in a uniform transport channel and a coaxial magnetically insulated diode is generalized to the case of counterpropagating electron beams with a spread over kinetic energies. Expressions for the sum of the absolute values of the forward and backward currents in a uniform transport channel and for the flux of the longitudinal component of the generalized momentum in a coaxial magnetically insulated diode as functions of the maximum electron kinetic energy are derived for different values of the relative width of the energy distribution function. It is shown that, in a diode with an expanding transport channel and a virtual cathode limiting the extracted current, counterpropagating particle flows are established between the cathode and the virtual cathode within a certain time interval after the beginning of electron emission. The accumulation of electrons in these flows is accompanied by an increase in their spread over kinetic energies and the simultaneous decrease in the maximum kinetic energy. The developed model agrees with the results of particle-in-cell simulations performed using the KARAT and OOPIC-Pro codes.

The article presents a review of works (mainly, of experimental ones) on production of subgigawatt and gigawatt microwave pulses of extremely short duration (5–7 RF periods) using backward-wave systems fed with nanosecond and subnanosecond high-current electron beams produced by compact accelerators. Theoretical approaches to the generation process (which is essentially non-steady-state) are briefly summarized. Using the effect of spatial accumulation of energy in a short running microwave pulse allows production of pulses with peak power notably higher then the driving electron beam power. Compact microwave sources developed for operation in the Ka-band and X-band are described. Special attention is given to the issue of high pulse repetition frequency operation of the sources.

The results of theoretical and experimental studies allowing the use of Cherenkov superradiance for the generation of electromagnetic pulses with a peak power higher than electron flow power are reported. For an injection current of 2.6 kA and a particle energy of 330 keV, the power of a microwave pulse with a carrier frequency of 9.3 GHz and a duration of 0.5 ns attained 1.2 GW.

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.

The dependence of the current on emitter size is obtained for a high-current planar diode with a discrete emitting surface. It is shown that if the distance between the emitters appreciably exceeds their size, the dependence of the current on the ratio of the emitter size to the diode gap is a power dependence with an exponent of 3/2. The voltage dependence of the current obeys the “three-halves” law up to higher voltages than that for a planar diode with a homogeneous emitting surface.

It is shown that reduction in the pulse length in a relativistic BWT, is accompanied by the appearance of explosive-emission plasma on the surface of the ripples of the slow-wave system. Generation stops because electrons emitted by the plasma absorb the electromagnetic wave. This absorption is sharply enhanced by the presence of ions emitted from the plasma.

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.

An experimental S-band vircator with premodulated electron beam based on a compact generator with inductive energy storage is described. The vircator radiation power was 300 MW at a power efficiency of about 5% and a pulse duration of 50 ns. The oscillation frequency, determined by the electrodynamic system parameters, remained unchanged during the pulse.

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.

The conditions required to achieve a constant current from an explosive cathode during the pulse in a high-current planar diode are calculated.