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A diagnostic has been developed to study the focusing dynamics of a high-power electron beam on a target. The diagnostic uses a pinhole camera to observe bremsstrahlung from the converter target. A data acquisition system yields images of the beam focal spot with a frame duration of 20 ns and an almost unlimited recording duration. The focal spot dynamics of a linear induction accelerator with an energy of 1.5 MeV, a current of 1.2 kA and a pulse duration of 350 ns were studied. The focal spot was found to be disrupted within the first 100 ns of the pulse. Defocusing has a complex 3-D character. The feasibility of additional cleaning of the target using an accelerator pre-pulse was shown. Stable beam focusing for up to 200 ns was demonstrated.

Numerical simulation of physical processes in the electron-optical system of a DUET accelerator was carried out using the ERA-DD code. The calculations were made on adaptive quasi-structured grids developed by the authors. A mathematical model for the emission plasma surface deformable when solving the problem is proposed. In this model, the problem is considered in a two-dimensional axisymmetric approximation and the front of the electron entrance to the computational domain is represented as a set of circular arcs connected by necks. In order to increase the accuracy of the calculations, it is proposed to divide the multi-scale extended domain into two subdomains and alternately solve self-consistent problems in the subdomains using the Schwarz alternating method. The beams are simulated by the method of current tubes, and the electric field potential is calculated by the finite volume method. The obtained characteristics of the beam are compared with experimental data. It is shown that for the operating parameters of the beam source, its losses on the accelerator components are minimal and can be caused primarily by the imperfect alignment of the holes in the mask and the support grid, as well as by deviations of electron beams generated by the structures located on the periphery of the emission electrode.

Influence of backstreaming ions from the target on spot size of focused 2 MeV electron beam was considered. The 2D version of the particle-in-cell code KARAT was used to study the formation of the ions stream and dynamics of the electron beam. It was shown that light species emitted from the target can disrupt the beam. The emission of low-ionized states of tantalum cannot disrupt the beam during about 30 ns or longer. A few non-invasive techniques of mitigation of the beam disruption were considered. Final magnetic lens with fast variation of magnetic field of several hundred Ampere-turns per nanosecond is capable to stabilize initial spot size of the compressed beam at the target.

Experimental and theoretical investigations on simultaneous generation and transport of two microsecond E-beams with an electron energy of 0.8 MeV and beam currents of up to 3 kA at a high current density of ~1-1.5 kA/cm2 are described in this paper. Peculiarities of using such beams for a generation of millimeter and submillimeter radiation in a free-electron maser are discussed. Parameters of the beams that are suitable for these applications are experimentally demonstrated.

The geometry of the ribbon diode of the U-2 accelerator is optimized to increase both the current density and the total current of the relativistic electron beam for its subsequent injection into the plasma of a multimirror GOL-3 trap. Beam simulation in the diode was performed using the POISSON-2 applied software modified on the basis of the results obtained using the theory of a planar diode in an inclined magnetic field. As a result of the optimization, the diode geometry and the magnetic field configuration were found that should provide a factor of 1.5–2 increase in the current density in experiments with a small angular divergence of electron velocities.

Performance of flash radiography units implies a high spatial resolution. Thus, focused electron beams are utilized to produce bremsstrahlung x-ray at the solid target. Strong heating of the target up to 1-10 eV temperature and formation of dense plasma can lead to beam disruption. In case of multi-pulse operation mode of radiography unit the plasma produced by the first pulse can strongly affect subsequent pulses. In present work we utilize the model of Zeldovich and Raizer to estimate the electron density in the target plasma. The typical parameters of radiography units based on linear induction accelerators is considered. It is shown that electron density in plasma expanding after first pulse is high enough to affect subsequent electron beams.

The results of experiments and numerical simulation of compression of an intense electron beam in increasing field of magnetic mirror and its transmission through a linear magnetic system are presented. This system is used as a test module for a section of the GOL-3 magnetic trap. The study was carried out for the beam with a spread in initial electron pitch angles and a non-uniform radial current distribution. An analytical estimate of the vacuum beam-current limit was obtained taking into account the initial pitch angles of electrons and the beam compression in the magnetic field. The simulation results are compared with the results of experiments; in both cases similar phenomena of beam reflection and diode breakdown are observed.

A model of dynamics and heating of a plasma cloud in a magnetic field is considered in a two-temperature approximation. Based on a predictor-corrector-type implicit difference scheme, spreading of a plasma cloud in an external magnetic field is numerically simulated, and the influence of this field on spread dynamics is evaluated.

An efficient algorithm is proposed enabling numerical simulations of plasma dynamics in a nonuniform magnetic field. The present numerical data are in good agreement with experimental data obtained in a GOL-3 setup and with previous simulations. The experimentally observed effect of fast transfer of energy to ions is confirmed.

The problem of energy recuperator for a high current sheet electron beam used to drive a millimeter-waves generator is considered. There are two main obstacles to solving the problem. The first one is the presence of a magnetic field guiding beam electrons. The second obstacle is significant energy and angular spreads of the electrons in the waste beam. To overcome these obstacles, we suggest a novel scheme of a recuperator. The main idea of the proposed scheme is the use of a decelerating electrical field together with a guiding magnetic field that has longitudinal and spatial periodic transverse components. Resonance of a bounce electron motion with the cyclotron motion in this field gives a strong increase in the Larmour radius of electrons with the energy in a narrow interval. The decelerated electrons with the resonance energy fall away from the beam and are absorbed by a collector at a proper potential. It is shown that efficiency of this novel scheme can reach about 80% even if the sheet beam has a broad energy spectrum.

A new method of intense relativistic electron beam modulation at frequencies up to ∼1 GHz is suggested. Current modulation is provided by using the azimuthal magnetic field of the beam to control the beam reflection from the magnetic mirror. The results of computer simulations for a 2-MeV, 20–50-kA beam are presented.

Paper describes main features of a project of an experiment at ELMI-device on two-stage generation of submillimeter radiation pulses. In this experiment two parallel high current sheet beams will be used. Submillimeter waves generation is based on stimulated scattering of mm-waves accumulated in the resonator of a planar FEM-oscillator driven by one of these beams.

In calculating high-current relativistic beams of charged particles moving in electromagnetic fields, it is necessary to take account of the effect of the electric and magnetic self-fields products by the beams themselves. This effect has been modeled on a computer [1, 2]. The present paper describes numerical algorithms contained in the KSI-BESM compiling system [3] which permit the inclusion of a broad class of relativistic problems, taking account of the magnetic field of currents flowing in the metal parts of the device being calculated, and also problems with virtual cathodes.

Strong relativistic electron beams in the microsecond range, with a current density of 1-10 kA/cm/sup 2/, and a stored energy of tens of hundreds of kilojoules can be used effectively for plasma heating in open traps. The authors given the results of numerical calculations of the parameters of beams obtained in diodes with quasiplane and annular cathodes in an external magnetic field. The results of the calculations are compared with the experimental data. The comparison is made for initial times (t less than or equal to 0.4 ..mu..sec), when the change in the accelerating gap due to filling of the diode with plasma is still insignificant. The question of the influence of nonuniformity of emission from the cathode on the amount of current of a plane diode is also analyzed by numerical modeling.

The article is devoted to a verification of the law of similarity in the flow of a rarefied magnetized plasma around a body under conditions which simulate the conditions of flow around artificial earth satellites in the ionosphere. The law of similarity for flow around plates and cylinders of different sizes (R0/ϱi≈0.5–1, V0/Vi≈1.5–2) is confirmed experimentally. It is shown that the patterns of flow around a plate and a cylinder coincide at small values of the parameter δ(δ=R0/zH). The effect of the potential of the bodies on their flow patterns is studied.