Vladimir P. Tarakanov

Pulsewidth limitation in the relativistic backward wave oscillator

Spontaneous pulse shortening occurring in a relativistic backward wave oscillator (BWO) at gigawatt power levels is studied in experiment and theory. It is experimentally demonstrated that this phenomenon is accompanied by formation of an explosive-emission plasma at the surface of the corrugated slow-wave structure (SWS). Termination of microwave emission is explained by the increase of the BWO starting current from the absorption of the operating electromagnetic wave by electrons emitted from the plasma, whereas the intensity of the absorption radically increases offing to the presence of positive ions emitted from the plasma. Application of oil-free vacuum and electrochemical polishing of the SWS surface in an X-band BWO allowed generation of 3-GW, 26-ns microwave pulses with an energy of /spl sim/80 J, thereby demonstrating pulse lengthening by a factor of four.

Generation of ultrashort microwave pulses based on cyclotron superradiance

We have theoretically and experimentally investigated the superradiance from a bunch of electrons rotating in a homogeneous magnetic field. A RADAN-303B modulator equipped with a subnanosecond pulse slicer has been used to generate high current subnanosecond electron bunches (250 kV, 0.1-1 kA, 0.3-0.5 ns). Transverse momentum was imparted to the electrons by a kicker. It is shown that for the experimental observation of cyclotron superradiance from high current electron bunches the optimum conditions are the conditions of group synchronism, when the translational velocity of the bunch coincides with the group velocity of the radiation propagating in the waveguide. In the 35 GHz range microwave pulses with record short duration, down to 0.4 ns, with a peak power level up to 200 kW, have been obtained.

Undulator superradiance effect and its applicability for the generation of multimegawatt terahertz pulses

The generation of multimegawatt terahertz pulses based on the superradiance of picosecond electron bunches moving in a periodic magnetic (undulator) field is shown to be possible. The theoretical study of superradiance processes is based both on the method of an averaged ponderomotive force and on direct numerical PIC (particle in cell) simulations. The analysis is performed in the K′ reference frame comoving with the electrons followed by the recalculation of radiation characteristics to the laboratory frame using the Lorentz transformations. Within the framework of the averaged approach, the electron bunch is represented as an ensemble of macroelectrons interacting between themselves through the radiation fields and Coulomb forces. The superradiance effect includes particle bunching followed by coherent emission of a single intense pulse from the entire volume of an electron bunch whose length exceeds considerably the wavelength. PIC simulations of this process based on the KARAT code have been performed for a more detailed analysis including the transverse inhomogeneity of the undulator field, the relativistic pattern of electron motion in this field, etc. A considerable simplification of the calculation procedure when passing to the comoving reference frame due to the commensurability of all spatial scales, including the radiation wavelength, the bunch length, and the length of the train of the pump wave into which the undulator field is transformed, is shown to be possible.

PIC Simulation of the Dynamics of Electrons in a Conical Vircator

We presented a vircator with conical ballistic focusing and carried out the PIC simulation of the dynamics of electrons in it. It is shown that the virtual cathode has the shape of a curvilinear figure of rotation. It was found that the oscillations in the vircator are resonant at a single frequency. The dependence of the vircator oscillation frequency of the current beam was calculated. The oscillation frequency monotonically increases from 2 to 6 GHz with the increase in the current beam from 10 to 50 kA, but the average power of microwave radiation grows nonmonotonically.

Generation of subnanosecond microwave pulses by intense electron bunches moving in a periodic backward wave structure in the superradiative regime

In this paper results of the experimental investigation of superradiance of intense subnanosecond electron bunches moving through a periodic waveguide structure and interacting with a backward propagating wave are presented.

Novel source of powerful subnanosecond microwave pulses based on superradiance

Describes a novel source of powerful subnanosecond microwave pulses based on superradiance. This source exploits coherent stimulated emission of intense subnanosecond electron bunches moving through a periodic waveguide and interacting with backward propagating wave. The 300 ps /60 MW microwave Ka band pulses were generated with repetition frequencies of up to 25pps. Observation of RF breakdown of ambient air as well as the illumination of a panel of neon bulbs with a finely structured pattern corresponding to the excitation of the TM/sub 01/ mode confirms the high level of the absolute power. The experimental results are compare with results of the numerical simulation based on the particle-in-cell (PIC) code KARAT. The simulations show that mechanism of microwave pulse generation is associated with self-bunching and the mutual influence of a different part of the electron pulse due to slippage of the wave with respect to the electrons and thus can be interpreted as superradiance.