Search

The electrostatic cumulation of current density in relativistic vacuum diodes with ring-type cathodes is described theoretically and confirmed experimentally. The distinctive feature of the suggested cumulation mechanism is a very low energy spread of electrons. As a result of electrostatic cumulation, a thin relativistic electron beam with a current density of 1 kA/mm2 can be formed.

Diverse approaches to helical flux compression generator’s (HFCG) inductance, resistance, and armature expansion calculations are evaluated. Comparison of simulated and experimentally obtained results is provided. Validity criteria for different simulation models are proposed. Consideration of armature acceleration under the pressure of detonation products and magnetic pressure is shown to be beneficial for accuracy of HFCG simulation. Control of HFCG temperature during simulation enables detecting the critical points of system operation.

High-power electron beam cumulation in a relativistic vacuum diode with a ring-type cathode is considered. The term “electron beam cumulation” here means electron beam self-focusing accompanied with multifold beam current density increase on the beam axis compared to the average current density in the cathode-anode gap. Space-charge repulsion of electrons emitted by the explosive-emission plasma on the inner edge of the cathode is shown to be the origin of this cumulation mechanism. Current density in the vicinity of beam axis is evaluated for different cathode inner diameter values both numerically and experimentally. Cathode with eccentric apertures of different diameters is studied experimentally.

Triode reflex geometry vircator operating within 3.0 - 4.2 GHz range with efficiency up to 6% is developed and experimentally investigated. Shiftable reflectors are shown to enable frequency tuning and output power control. Radiation frequency and power are analyzed for different cathode-anode gap values and varied reflector positions., Comment: 4 pages, 14 figures

The electrostatic cumulation of current density in relativistic vacuum diodes with ring-type cathodes is described theoretically and confirmed experimentally. The distinctive feature of the suggested cumulation mechanism is a very low energy spread of electrons. As a result of electrostatic cumulation, a thin relativistic electron beam with a current density of 1 kA/mm$^2$ can be formed. This quantity exceeds typical current density values in high-current Cherenkov sources by an order of magnitude. Such a beam can be used as an active medium in high-power terahertz sources., The 8th International Conference "Charged & Neutral Particles Channeling Phenomena Channeling 2018"

This paper reports the investigation of several types of large-area (20–40 cm2) explosive emission cathodes different in shape and emitting surface material. We concentrated on the cathodes with emitters made of dense fine-grained graphite and carbon-epoxy capillary arrays (multicapillary cathodes), but also considered a cathode with copper emitter. We experimented with planar and profiled (Ernst profile) emitters and a graphite ring-type cathode. The velocity of cathode plasma expansion, the stability of operation, and the homogeneity of generated beams are compared for different cathodes. The current density distribution over the beam cross section is examined using the beam imprint on the radiochromic film. The pepper pot method is used to find whether the beam is converging or diverging.

A novel explosive-emission cathode capable to produce high-current nanosecond electron bunches and enable tuning in terms of size is proposed and demonstrated to performance fit the particular problem. The record parameters, average diode current 6.5 kA and voltage 410 kV, are achieved by covering a conventional, planar copper cathode with a carbon film being composed of graphitic pyrolytic carbon (GrPyC). The demonstrated plasma expansion velocity and current density are comparable with those obtained with conventional graphitic cathodes. However, in contrast to purely graphite cathodes, the shape, size and surface profile of the proposed hybrid GrPyC/Cu cathodes can be readily adjusted allowing adjustments to fit requirements of a variety of high-current electronic applications.

This paper considers how the finite dimensions of a photonic crystal placed inside a resonator or waveguide affect the law of electron beam instability. The dispersion equations describing e-beam instability in the finite photonic crystal placed inside the resonator or waveguide (a bounded photonic crystal) are obtained. Two cases are considered: the conventionally considered case, when diffraction is suppressed, and the case of direct and diffracted waves having almost equal amplitudes. The instability law is shown to be responsible for increase of increment of instability and decrease of length, at which instability develops, for the case when amplitude of diffracted wave is comparable with that of direct one, that happens in the vicinity of $\pi$-point of dispersion curve. Application of photonic crystals for development of THz sources at electron beam current densities available at modern accelerators is discussed., Comment: 14 pages, 2 eps figures, presented at Channeling 2018, submitted to Physical Review Accelerators and Beams

Multicavity resonators for an axial vircator are developed and experimentally investigated. The frequency and radiation power are analyzed for different cathodes and anode meshes and varied cathode–anode gaps.

Design and experimental study of a detonator using a lengthy exploding wire fuse are proposed. A shock-wave unit using electrically exploding wire for initiating high-explosive charges to create axially symmetric detonation front is developed. The detonators are made and tested in two designs. The design details and the results of experiments are reported.

The expressions for spectral-angular distribution of quasi-Cherenkov radiation emitted by a relativistic particle traversing a photonic crystal are derived. The intensity of quasi-Cherenkov radiation in terahertz and optical ranges is shown to be high enough to allow the experimental study of quasi-Cherenkov radiation in these frequency ranges.

2-D simulation of the flux compression generator (FCG) operation enables the calculation of the local magnetic field outside the FCG stator. The magnetic field strength at a certain point outside the FCG stator is shown to be dependent on the stator geometry, the electric current in the FCG circuit, and the snapshot of the armature position with respect to the observation point. The measurements made by the dedicated probe placed on the stator support shell confirm the simulation results. The distinguished points of the time-dependent magnetic field strength make it possible to place the magnetic field probe on the stator support shell for noninvasive diagnostics of the FCG operation.

The time evolution of parametric X-ray radiation (PXR) produced by a relativistic charged particle passing through a crystal is studied. It is shown that the duration of PXR pulses can be much longer than the particle flight time through the crystal. This enables a thorough experimental investigation of the time structure of parametric X-ray pulses generated by electron bunches available with modern accelerators. The complicated time structure of parametric radiation can also be observed in artificial (electromagnetic, photonic) crystals in optical, terahertz, and microwave ranges of wavelengths.

Experimental observation of X-ray radiation from nonrelativistic (50–100 keV) electrons in crystals is reported and described as resulted from interference between parametric X-rays and coherent Bremsstrahlung . Possibility to tune X-rays frequency by crystal target rotation is demonstrated for the first time. Experiment details are discussed.

An experimental model of a tunable source of monochromatic x-rays was developed using nonrelativistic electrons passing through a single crystal silicon target. Theoretical predictions for x-ray output and characteristics were confirmed experimentally. The distinctive feature of the developed source is the possibility to tune x-ray frequency at fixed electron beam energy. In the present report, properties and potentialities of the developed source are considered. Copyright © 2007 John Wiley & Sons, Ltd.

Study of electron beam dynamics in a planar diode with explosive emission cathode is carried out both theoretically and experimentally.

We report on an experimental study of explosive electron emission properties of cathode made by nanometric thin pyrolytic carbon (PyC) films (2-150 nm) deposited on Cu substrate via methane-based chemical vapor deposition. High current density at level of 300 A/cm(2) in 5 . 10(-5) Pa vacuum has been observed together with very stable explosive emission from the planar cathode. The Raman spectroscopy investigation proves that the PyC films remain the same after seven shots. According to the optical image analysis of the cathode before and after one and seven shots, we conclude that the most unusual and interesting feature of using the PyC films/Cu cathode for explosive emission is that the PyC layer on the top of the copper target prevents its evaporation and oxidation, which leads to higher emission stability compared to conventional graphitic/Cu cathodes, and therefore results in longer working life. (C) 2014 Elsevier B.V. All rights reserved.

Feasibility of the conception of the volume free electron laser was verified by “OLSE-10” experimental prototype. Measurements of key parameters of the microwave radiation of the prototype have confirmed the features predicted theoretically. Possibility of smooth tuning of the radiation frequency and decrease of the threshold current density in a volume free electron laser are demonstrated. The set of VFEL characteristics showed that it might be the prospective source of tuneable polarized radiation in the microwave and Terahertz ranges [V.G. Baryshevsky, K.G. Batrakov, A.A. Gurinovich, et al., Nucl. Instr. and Meth. A 507 (2003) 137; V.G. Baryshevsky, A.A. Gurinovich, LANL e-print archive: physics/0409107 ; V.G. Baryshevsky et al., LANL e-print archive: physics/0409125 ]. Application of radiation of these wavelength ranges in science and engineering is highly challenging.

Spontaneous and induced parametric and Smith–Purcell radiation from electrons moving in periodic structures are considered. The electrodynamical properties of a crystal-like artificial periodic structure (a photonic crystal) formed by a periodic structure built from the metallic threads (“grid” volume resonator) is considered. The equation, which describes lasing of volume-free electron laser with a “grid” resonator (photonic crystal), are obtained.

Spectra-angular distribution of the orthopositronium 3γ-decay was investigated for the first time in an asymmetric geometry of annihilation, using multidetector spectrometer ARGUS. In order to analyse the experimental data, a method for selection of the three-photon annihilation events and background reduction, built on the well-known algorithm of Dalitz plane, was developed. The experimentally obtained distribution is found to be in a good agreement with prediction of quantum electrodynamics, calculated by the computer Monte-Carlo modelling. The technique realised in this experiment is going to be used for testing quantum electrodynamics of bound state.

Propagation of a nanosecond microwave pulse through a photonic crystal placed into an X-band waveguide is investigated. The nanosecond pulse is produced via shortening of the microsecond microwave pulse by the plasma electromagnetic band gap structure, which is formed in the waveguide by microwave breakdown ignited discharges inside three neon-filled glass tubes. Measured delay time for nanosecond microwave pulse propagation through the photonic crystal is about 23 ns that is in good agreement with the value obtained by numerical simulation. This time delay value corresponds to the group velocity of microwave pulses in the photonic crystal vgr ≈ 0.11c, where c is the speed of light in vacuum.

A compact high power microwave (HPM) source is reported. It generates short pulses by direct excitation of an antenna with a 300 kV Marx generator. Oil insulation is used to protect capacitor banks from breakdown, while discharge gaps are designed to work in air. The Marx generator risetime is less than 50 ns. The disk-cone antenna is also oil-insulated and operates in the self-breakdown regime. Radiated pulse has the duration about 2 ns and the spectrum from 800 MHz to 2 GHz. The HPM source is used for studying the vulnerability of computers and different electronic components. (4 pages)

First lasing of a volume free electron laser in the millimeter wavelength range is observed.

A Volume Free Electron Laser with a photonic crystal (crystal-like artificial periodic structure) formed by metallic threads (or foils) periodically strained inside a cylindrical waveguide is studied. Operation of Volume Free Electron Laser is discussed for different configurations of the photonic crystal.

Investigation of frequency tuning in volume free electron lasers with rectangular resonator is presented. Two experimental VFEL prototypes are considered. Several types of VFEL generators using different mechanisms of spontaneous radiation are analyzed. They are: undulator, Smith-Purcell and gyrotron. The optimal conditions for radiation tuning in each case are found. Comparison with experiment is given.

New possibilities of frequency tuning in vacuum electronic devices are considered by the example of volume free electron laser. Recent experimental results are presented along with some theoretical comments and technical proposals. Experimental study of dependence of radiation frequency and intensity on change of the angular orientation of grooves of diffraction gratings with respect to electron beam velocity due rotation of diffraction gratings is presented. Two geometries of diffraction are analyzed: those of Bragg and Laue. Change of lasing efficiency with grating rotation is considered. VFEL generator is proposed as a new type of tunable backward wave tube with variable period (due to gratings rotation) and VFEL amplifier is considered as a new type of tunable traveling wave tube.

Use of non one-dimensional distributed feedback in VFEL gives possibility of frequency tuning in wide range. In present work dependence of lasing process on the angle between resonant diffraction grating grooves and direction of electron beam velocity is discussed., LaTeX, 9 eps figures, to be presented at FEL2002 Conference

Based on a detailed analysis of explosive electron emission in high-current electronic devices, we formulate a system of equations that describes the expansion of cathode plasma and the generation of high-current electron beams. The system underlies the numerical algorithm for the hybrid code which enables the simulation of the charged particles' dynamics in high-current vircators with open resonators. Using the Gabor–Morlet transform, we perform a time-frequency analysis of vircator radiation.

Based on a detailed analysis of explosive electron emission in high-current electronic devices, we formulate a system of equations that describes the expansion of the cathode plasma and the generation of high-current electron beams. The system underlies the numerical algorithm for the hybrid code which enables simulating the charged particles' dynamics in high-current vircators with open resonators. Using the Gabor-Morlet transform, we perform the time-frequency analysis of vircator radiation.

Examining the temporal evolution of parametric quasi-Cherenkov terahertz radiation (PTR) produced by a relativistic charged particle passing through an electromagnetic crystal, we found that the duration of PTR pulses can be much longer than the particle flight time through the crystal. This enables a thorough experimental investigation of the time structure of parametric quasi-Cherenkov T-ray pulses generated by electron bunches available with modern accelerators. The complicated time structure of parametric radiation can also be observed in natural crystals in the x-ray range. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1 .JNP.6.061714)

Proc. FEL 2007, Novosibirsk, Russia. P.496-498