[en] The results of studies on relativistic SHF-generators - orotron and gyrotron for obtaining data on the quality of a high-current electron beam shaped in the section of a linear induction accelerator are given. Axisymmetric resonators as sections of weak-irregular waveguides were used in both generators. Stable generation of short-wave radiation of 15-20 MW at the efficiency of 5-7% SHF pulse duration of 50 ns was obtained in the orotron at the wave length of 8.5 mm and current of 600 A. Stable generation of 7-10 MW SHF-radiation at the efficiency of 3-5% and pulse duration of 150 ns was observed in the gyrotron at the wave length of 12 mm. Under further acceleration in the following sections of the accelerator the electron beam may be used for obtaining radiation of shorter waves

[en] Induced radiation of electron fluxes at gyrofrequency harmonics is investigated using the simplest maser model with an electrodynamic system representing a two-mirror quasioptical resonator. The induced cyclotron radiation at gyrofrequency harmonics is characterized by high electron efficiency slowly decreasing with growth of harmonics number under close-to-autoresonance conditions which are realized for wave propagation at a small angle to the direction of a homogeneous magnetostatic field. However, due to a rapid drop of the electron coupling coefficient with the wave the operating current grows rapidly, and generation is practically possible at harmonics with small numbers. The induced synchrotron radiation on an isolated high harmonics realized at the wave propagation at an angle close to the electron pitch-angle has, on the contrary, a comparatively low efficiency but the operating current irows very weakly with increase of the harmonics number

[en] For a Cyclotron Resonance Maser (CRM) with a helical axis-encircling electron beam, the possibility of a strong interaction between cutoff (gyrotron) and traveling Doppler-up-shifted Cyclotron Autoresonance Maser (CARM) modes, which are in resonance with the electrons at the same frequency, is demonstrated. This effect can be used in a CRM-oscillator of a new type, where the feedback and the mode selectivity for the operating traveling mode are provided due to the excitation of the cutoff mode. According to both the theory and experiment, such a scheme can provide an effective excitation of the traveling mode with negligibly low losses associated with the cutoff mode

[en] A system of nonlinear self-consistent equations, describing the development of one-dimensional field fluctuations of a space charge of a plane thin (with a thickness of the Larmor diameter) relativistic electron flux moving in a homogeneous magnetic field in a free space is determined. The proper field of a perturbed flux along with a Coulomb one also contains eddy components. At low flux concentration the corrections for the cyclotron frequency harmonics of its free oscillations. The instability increment, caused by the negative mass effect, decreases with the growth of the translational electron velocity. At relativistic particle velocities the eddy fields play a great role. Taking into account the effects related to these fields, in particular, radiation, carrying energy away from the flux, the increment dependence on the particle energy and cyclotron harmonics number is qualitatively changed

No abstract available

[en] The Cyclotron Autoresonance Maser (CARM) is a well-known variety of FEMs. Unlike the ubitron in which electrons move in a periodical undulator field, in the CARM the particles move along helical trajectories in a uniform magnetic field. Since it is much simpler to generate strong homogeneous magnetic fields than periodical ones for a relatively low electron energy (Brit-pounds ≤1-3 MeV) the period of particles' trajectories in the CARM can be sufficiently smaller than in the undulator in which, moreover, the field decreases rapidly in the transverse direction. In spite of this evident advantage, the number of papers on CARM is an order less than on ubitron, which is apparently caused by the low (not more than 10 %) CARM efficiency in experiments. At the same time, ubitrons operating in two rather complicated regimes-trapping and adiabatic deceleration of particles and combined undulator and reversed guiding fields - yielded efficiencies of 34 % and 27 %, respectively. The aim of this work is to demonstrate that high efficiency can be reached even for a simplest version of the CARM. In order to reduce sensitivity to an axial velocity spread of particles, a short interaction length where electrons underwent only 4-5 cyclotron oscillations was used in this work. Like experiments, a narrow anode outlet of a field-emission electron gun cut out the open-quotes most rectilinearclose quotes near-axis part of the electron beam. Additionally, magnetic field of a small correcting coil compensated spurious electron oscillations pumped by the anode aperture. A kicker in the form of a sloping to the axis frame with current provided a control value of rotary velocity at a small additional velocity spread. A simple cavity consisting of a cylindrical waveguide section restricted by a cut-off waveguide on the cathode side and by a Bragg reflector on the collector side was used as the CARM-oscillator microwave system

[en] The cyclotron autoresonance maser (CARM) is one of the promising modifications of free-electron masers (FEM) operated at the millimeter and submillimeter waves. In this range CARM requires particle energies significantly lower than for the ubitron, and magnetic fields smaller than those for the gyrotron. The CARM is considered as a possible source of coherent millimeter wavelength radiation with large average (continuous) power for plasma heating in controlled fusion devices

[en] One of the main features of FELs and FEMs is the possibility of fast and wideband tuning of the resonant frequency of active media, which can be provided by changing the particle energy. For a frequency adjustable FEM-oscillator, a broadband microwave system, which is simply combined with an electron-optical FEM system and consists of an oversized waveguide and reflectors based on the microwave beams multiplication effect has been proposed and studied successfully in open-quotes coldclose quotes measurements. Here, the operating ability of a cavity, that includes some key elements of the broadband microwave system, was tested in the presence of an electron beam. To provide large particle oscillation velocities in a moderate undulator field and the presence of a guide magnetic field, the FEM operating regime of double resonance was chosen. In this regime the cyclotron as well as undulator resonance conditions were satisfied. The FEM-oscillator was investigated experimentally on a high-current accelerator open-quotes Sinus-6close quotes that forms an electron beam with particle energy 500keV and pulse duration 25ns. The aperture with a diameter 2.5mm at the center of the anode allows to pass through only the central fraction of the electron beam with a current about 100A and a small spread of longitudinal velocities of the particles. Operating transverse velocity was pumped into the electron beam in the pulse plane undulator of a 2.4cm period. The cavity with a frequency near 45GHz consists of a square waveguide and two reflectors. The broadband up-stream reflector based on the multiplication effect had the power reflectivity coefficient more than 90% in the frequency band 10% for the H¹⁰ wave of the square waveguide with the maximum about 100% at a frequency 45GHz. The down-stream narrow-band Bragg reflector had the power reflection coefficient approximately 80% in the frequency band of 4% near 45GHz for the operating mode

[en] A method for the generation of quasi-unipolar pulses based on coherent synchrotron radiation from a quasi-planar electron bunch moving along a curved trajectory is proposed and theoretically studied. It is demonstrated that the experimental realization of this method at an existing installation (Terahertz to Optical Pulse Source) can result in generation of picosecond pulses with a peak power of up to 200 MW

[en] A large number of electron microwave devices require initially rectilinear high-quality electron beams for effective operation. In FEMS such beams are pumped up to sufficiently high operating-oscillation velocity and small initial particle oscillations (cyclotron oscillations if the beam is focused by an axial magnetic field) can lead to a rather large transverse velocity spread and, correspondingly, axial velocity spread. Thus, an acute problem for these devices (essentially more important than for Cherenkov-type devices) is the formation of a beam in which electrons initially move along the axis with minimum oscillations. A new method to form such a beam by a two-electrode axially-symmetrical gun of simple configuration immersed in a uniform axial magnetic field is discussed in this paper. This method allows to improve the quality of an electron beam passing through a narrow anode outlet. It is well-known that the anode aperture acts as an electrostatic lens and disperses the electron beam. In the presence of an axial magnetic field this unwanted dispersing action can be compensated simultaneously for all electrons of the paraxial electron beam by means of a magnetic field generated by a small additional coil placed down-stream from the anode aperture. If the coil length is equal to half the electron Larmor step, then the action of the border cod fields comes to two kicks which, being correctly phased, compensate the spurious rotary electron velocities. Computer simulations using the EPOSR-code intended for the calculation of electron guns both for the temperature- and space-charge-limited regimes prove the effectiveness of this method. In particular, for a version of field-emission gun the correcting coil reduces about five times the maximum transverse velocity in the beam. Positive effect from applying this method was proved at a realization of a high-efficiency CARM-oscillator