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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.

In the Institute of Nuclear Physics, SB RAS, experiments are carried out on injection of electron beam into open magnetic trap GDT. The trap is a mirror cell with a large mirror ratio filled with deuterium plasma with subthermonuclear parameters. Two expanders are attached to both sides of the trap. There are volumes with a diverging magnetic field, used to reduce longitudinal losses from the trap. The source of the electron beam is located in the expander, in the region of a weak magnetic field and is exposed to a supersonic plasma ion stream emerging from the trap. The source of a diode-type operates with a thermionic cathode and a hollow metal anode. The plasma from the trap enters the diode through the anode liner and stops by the potential of the cathode, forming an anode electrode. Its surface and the metal surfaces of the electrodes determine the electron-optical characteristics of the diode and the beam formed in it. The paper presents the results of two-dimensional numerical simulation of the beam source and calculated electron beam angular characteristics. The numerical model uses the plasma flow parameters measured in the experiment and results of solving the one-dimensional Poisson equation for the Debye layer on the surface of the anode plasma.

The paper reports on a comparative study of two different types of diode system for producing intense submillisecond electron beam in a source with low-pressure arc plasma emitter. The first is a planar multi-aperture diode comprising cathode and anode performed as molybdenum grids with 241 round openings of few millimeters in diameter. In the second system electrons are accelerated in a sheath between the grid-stabilized cathode plasma and the open boundary of beam-generated anode plasma. It was demonstrated in experiments that latter system should be advantageous in terms of maximally achievable beam current and total beam energy content, but there are drawbacks connected with slow anode plasma build-up that require further study.

Experiments on the detection of γ rays generated in the 13C(p, γ)14N reaction at the Novosibirsk vacuum-insulated tandem accelerator were carried out. Owing to the updated detection system, it was possible to measure the energy spread of beam protons and develop a method for long-term stabilization of the slow drift of the beam energy. The measured energy spread was 1.20 ± 0.15 keV, which was only 0.07% of the total beam energy. This makes the tandem accelerator developed by the vacuum-insulated Budker Institute of Nuclear Physics an attractive tool for solving various research and applied problems.

Emission of positively charged ions from a plasma emitter irradiated by a counterpropagating electron beam is studied theoretically. A bipolar diode with a plasma emitter in which the ion temperature is lower than the electron temperature and the counter electron flow is extracted from the ion collector is calculated in the one-dimensional model. An analog of Bohm’s criterion for ion emission in the presence of a counterpropagating electron beam is derived. The limiting density of the counterpropagating beam in a bipolar diode operating in the space-charge-limited-emission regime is calculated. The full set of boundary conditions on the plasma emitter surface that are required for operation of the high-current optics module in numerical codes used to simulate charged particle sources is formulated.

The generation of a 250-μs-wide electron beam in a plasma-emitter diode is studied experimentally. A plasma was produced by a pulsed arc discharge in hydrogen. The electron beam is extracted from a circular emission hole 3.8 mm in diameter under open plasma boundary conditions. The beam accelerated in the diode gap enters into a drift space in the absence of an external magnetic field through a hole 4.1 mm in diameter made in the anode. The influence of electron current deposition at the edge of the anode hole on the beam’s maximum attainable current, above which the diode gap breaks down, is studied for different accelerating voltages and diode gaps. The role of processes occurring on the surface of the electrodes is shown. For an accelerating voltage of 32 kV, a mean emission current density of 130 A/cm2 is achieved. The respective mean strength of the electric field in the acceleration gap is 140 kV/cm. Using the POISSON-2 software package, the numerical simulation of the diode performance is carried out and the shape of steady plasma emission boundaries in the cathode and anode holes is calculated. The influence of the density of the ion current from the anode plasma surface on the maximum attainable current of the electron beam is demonstrated.

A ribbon diode of a U-2 accelerator (800 kV, ∼30 kA) intended for generating a high-intensity electron beam for heating plasma in a GOL-3 multimirror magnetic trap (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences) is described. The parameters of the beam characterized by a high brightness (∼7 kA/(cm2 sr)) in a magnetic field of ∼5 T resulting from a numerical simulation of the beam formation process are presented. The results of simulation of the beam transport and transformation of the profile of its cross section during movement of electrons in a curvilinear guiding magnetic field are presented. The calculated cross section is compared to the beam imprint on a 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.

First stage of neutral beam heating system was developed at the GOL-3 facility. Configuration of magnetic field and initial gas distribution were adopted for operation with NBI system. As a result the neutral beam with 0.5 MW power and 0.8 ms pulse duration was achieved and stable regimes suitable for beam injection experiments were found. The neutral beam system was used in first experiment as diagnostic tool for measuring the plasma density. Dynamics of plasma density and its radial distribution were studied in experiments.

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.

Terahertz emission from plasma with strong Langmuir turbulence excited by high current relativistic electron beam (REB) is experimentally studied at the GOL-3 facility (BINP)1. The typical parameters of the beam used in the experiments, were the following: 0.6÷0.8 MeV/20 kA/10 μs. In recent experiments the beam current density was about 1÷2 kA/cm2 in a plasma column with the density ∼ 2·1014 cm−3 that allowed us to get sub THz-emission with a power of a few kW/cm3 in the frequency range 100÷400 GHz.

A novel high-power (10 MW) sub-millisecond electron beam is developed for injection into the open (linear) plasma devices. The beam is produced by extraction of electrons from a plasma of pulsed ar...

Experiments on plasma heating by a high power electron beam at the GOL-3 facility have shown, that ion temperature with a multiple mirror configuration of the magnetic field is much higher than for plasma heating in a simple solenoid. A new mechanism of fast collective heating of a plasma ions is suggested. The efficiency of the heating depends on local density of the beam electrons. In the corrugated magnetic field this creates a periodical longitudinal variation of plasma pressure during the beam injection. Then the pressure gradients result in plasma motion towards the midplane of each magnetic cell. Numerical simulations and special experiments demonstrate that fast thermalization of the energy of the directed plasma motion occurs. This mechanism requires about one ion-ion collision time that is much faster than usual electron-to-ion energy transfer time.

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.

Recently high plasma parameters were reached in experiments on plasma heating in the multi-mirror open trap GOL-3. In these experiments deuterium plasma with density 10-10 cm in the 12-m trap with corrugated magnetic field of 4.8T/3.2T was heated by a relativistic electron beam of eU ≤ 0.8 MeV, I ≤ 20 kA, j ~ 1-2 kA/cm, pulse duration ~ 9 μs and angular spread θ ≤ 0.2 rad. The electron temperature Te ~ 1-4 keV and ion one to Ti ~ 1-2 keV were reached. After the beam pulse the electron temperature of the plasma quickly (~ 20 μs) decreased to ~100 eV. In turn, this leads to an increase in the rate of cooling of ions through the ion-electron collisions, which, together with particle losses determines the energy confinement time of plasma as 0.5-1 ms. To increase the plasma parameters a prolonged heating of the plasma by the electron beam is proposed. The paper considers basic physical phenomena in the beamplasma interaction and required parameters of the longpulse beam. A choice of long pulse beam parameters is based on the obtained experimental results and scalings. Then estimates of the expected plasma parameters under the influence of the new beam have been done.

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.

In experiments at ELMI-device (BINP, Novosibirsk) the operation of 4-mm free electron maser (FEM) with two dimensional distributed feedback was demonstrated [1, 2]. These results gave a base for development multichannel planar FEM with 2-D distributed feedback [3]. In case of two channels jointed by special waveguide 2-D distributed feedback can be also used for two stage generation of submillimeter radiation exploiting an intercavity scattering scheme [3]. As the first step on studying of two stage generation we performed the experiments on simultaneous generation and transport of two intensive sheet electron beams. We modified the geometry of a ribbon accelerator diode at the ELMI-device and realized simultaneous generation of two sheet beams with the following parameters: the electron energy − 0.8 MeV, the total current of each beam - 3 kA, the cross section 0.4×7 cm and the pulse duration - 3 mcs. These sheet beams were transported on the length 1.3 m in slit vacuum channels with cross section 0.95×9 cm in the guiding magnetic field 1.7 T [4]. Next step of this series of experiments is devoted to realization of the two stage scheme. The paper presents results of the experiments and theoretical analysis of a prospect of the two stage scheme for THz pulses generation.

Essential progress was achieved in experiments on heating the dense plasma in the multimirror trap GOL-3 by high power relativistic electron beam in last few years. The beam parameters at the experiments were the following: electron energy ∼1 MeV, beam current ∼25 kA, beam current density in plasma ∼2 kA/cm2, pulse duration about 10 ms, total energy of the beam pulse ∼150 kJ [1]. Due to the high level of the current density and effect of a novel mechanism of ion heating the temperature of ions reached 2−3 keV at the electron temperature about 3 keV for the plasma density ∼1015 cm−3 [1]. Energy confinement time of the plasma in these experiments has reached the level of 1 ms. The basic condition of such parameters achievement is anomalously low electron thermal conductivity along the trap axis which is provided by small scale Longmuir turbulence developing as a result of two-stream instability [2]. In order to analyze a prospect of further increase of plasma parameters for reaching a fusion area, to elongate the beam pulse duration was decided. As the first step on solving this task we are performing the experiments at the accelerator U-2 on 1.5 fold increase of the E-beam duration. To investigate in more details the process beam-plasma interaction we carry out measurements on temporal dynamics of the plasma electron distribution function in the range of 0–5 keV and on evolution of energy distribution functions of the beam electrons as well. We also measure an electromagnetic radiation gone out from the plasma column as result of transformation of two Langmuir waves in electromagnetic one in strong turbulent plasma. This electromagnetic radiation is measured in the frequency band 210−550 GHz. Results of the pointed experiments and their discussion are presented in this paper.

Essential progress was achieved in experiments on heating the dense plasma in the multimirror trap GOL-3 by high-power relativistic electron beam in last few years. The beam parameters at the experiments were the following: electron energy ~1 MeV, beam current ~25 kA, beam current density in plasma ~2 kA/cm2, pulse duration 9 mus, total energy of the beam pulse ~150 kJ. Due to the high level of the current density and effect of a novel mechanism of ion heating the temperature of ions reached 2-3 keV at the electron temperature about 3 keV for the plasma density ~1015 cm-3. Energy confinement time of the plasma in these experiments has reached the level of 1 ms. The mechanism of fast ion heating is based on the collective ion acceleration along the magnetic field lines produced by high-gradients of the electron pressure in the plasma due to enhanced heating in the mirrors. The basic condition for such mechanism realization is anomalously low electron thermal conductivity along the trap axis which is provided by small scale Langmuir turbulence developing as result of two-stream instability. In order to analyze fusion prospects of such way of plasma heating in the long solenoid trap it is necessary to investigate experimentally the possibility of further increase of plasma parameters by the elongation of the beam pulse. As the first step on solving this task we have performed the experiments at the accelerator U-2 on 1.5 fold increase of the e-beam duration. Results of these experiments are presented in this paper. Conditions for durable generation in magnetically insulated diode, stable transportation and compression in the magnetic field of intense REB found in the experiments, permit us to increase the beam pulse duration from 9 mus to 14 mus with somewhat less energy of the electrons but with the same level of the energy content in the pulse. In the paper we describe the experiments on the diode voltage shaping for better matching of pulse generator with the accelerator diode as well as the results of measurements of the beam cross section by means of X-ray obscure and sectional calorimeter. Also we discuss the directions of future investigations aimed to the increase of the beam parameters in order to obtain (5-10) keV temperature of the plasma confined in multimirror trap.

This paper describes main features of a project on two- stage generation of submillimeter radiation pulses at ELMI-device. In this project one sheet beam will drive 2D Bragg planar FEM in which intensive 4-mm radiation accumulated in the FEM resonator, is used for stimulated scattering on the another sheet beam.

To provide basic operations of semiconductor and radiation materials technologies, a multipurpose implanter with intense ion beams was developed at the Institute of Nuclear Physics. The generated beamparameters are as follows: ions are H+, O+; C+; the ion energy is up to 200 keV; the beam current is up to 2 mA; and the implantation mode is continuous. The size of the target to be processed can reach 76 × 76 mm2. During the implanter operation, the target chamber vacuum reaches 10−4 Pa. The entire process of target irradiation is fully automated.

A method for determining the spatial structure of a high-power relativistic electron beam is described. Using an absolutely calibrated CCD collector, the thermal-radiation brightness distribution of the beam-collector surface is registered in the visible and near-IR spectral regions and then converted into a spatial distribution of the beam energy deposition in a target. This method is applied at a high specific beam-energy flux (∼1 kJ/cm2), one which causes noticeable erosion of the beam collector.

A description of the GOL-3-II facility and the first experimental results obtained on this new device are presented. This facility was constructed as part of the second stage of the GOL-3 programme for studying the interaction of microsecond electron beams with a plasma and its fast heating. The plasma column of the GOL-3-II facility is 12 m in length instead of 7 m for the first stage of GOL-3. The energy content of the capacitive storage for magnetic field supply has been increased from 10 MJ to 15 MJ. This allows us to have a magnetic field of up to 5 T in the homogeneous part of the solenoid and up to 10 T in its end mirrors. The expected key feature of the upgrading is an essential increase in the energy content of the electron beam injected into the plasma. The high-power electron beam generator U-2 is now used for the new beam - plasma interaction experiments with possible beam energy content of up to 0.3 MJ. It is shown experimentally that transportation of a 0.2 MJ electron beam through the 12 m plasma column is possible under conditions of almost full current neutralization. The collective beam - plasma interaction results in a plasma heating of up to 1 - 2 keV electron temperature at density.

Recent results of experiments on high-energy content E-beam application for plasma heating in a multimirror trap GOL-3 are presented. Conditions for optimal neutralization of injected beam and its stable transport through long plasma column are defined. Effective electron and ion heating of plasma is observed.