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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.

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.

Development of a new linear device for confinement of fusion plasmas is under way in the Budker Institute of Nuclear Physics, Novosibirsk. The new device combines features of existing GOL-3 and GDT...

Sub-THz radiation can be generated by conversion of plasma waves into electromagnetic (EM) radiation in a plasma with strong Langmuir (LT) turbulence produced via a two-stream instability of a high current relativistic electron beam (REB). Nonlinear plasmon-plasmon merging results in the generation of photons nearby the 2nd harmonic of the plasma frequency 2ω p (“2ω p -process”). For plasma densities of 1014 − 1015 cm−3, these frequencies are in the range of sub-THz waves at 370–570 GHz. The specific power density of sub-THz-wave emission from plasmas in the multi-mirror magnetic trap GOL-3 (at BINP) during injection of a 10-μs-REB with a current density of about 1 kA/cm2 at plasma densities n e ≈ 5∙1014 cm−3, electron temperatures T e ≈ 1.5 keV and magnetic induction B ≈ 4 T was measured to be approx. 1 kW/cm3 in the frequency band around 300 GHz. In the case of a weakly relativistic 100-μs-electron beam (90 keV) with 250 A/cm2 the corresponding results are 700 W/cm3 around 90 GHz with an efficiency of 1–2 % at n e ≈ 3∙1013 cm−3 (total power ≈ 30 kW). Theoretical investigations show that at a density of n e ≈ 3∙1015 cm−3 and a turbulence level of 5 % the generated sub-THz power can reach ≈ 1 MW/cm3.

The paper summarizes recent advances in physics of multiple-mirror confinement. GOL-3 in Novosibirsk is the only existing large-scale device of this type. Achieved plasma parameters are: n ~ 1021 m...

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.

New operation regime with a high-mirror-ratio corrugation at first 2 meters of GOL-3 plasma was studied. Five corrugation periods of 44 cm length were created with mirror ratio R ≈ 2.7 by means of special configuration of a power feed of existing solenoid coils. First data on the plasma heating, confinement and features of neutron emission from the strongly corrugated plasma in the above conditions are presented.

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.

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.

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.

Main results of researches on plasma heating and confinement of dense plasma in the multimirror trap GOL-3 are presented.Recently magnetic system of the facility was converted into completely multimirror one. This results in further improvement of energy confinement time of plasma with ion temperature {approx}1 keV. Collective plasma heating by {approx}120 kJ ({approx}8 {omega}s) relativistic electron beam results in T{sub e} {approx} 2 keV at {approx}10{sup 21} m{sup -3} density. High T{sub e} exists for {approx}10 {mu}s. To this time T{sub i} reaches {approx}2 keV. Ion temperature keeps at the high level during {approx}1 ms. The energy confinement time sufficiently increases and a value of n{tau}{sub E} = (1.5-3).10{sup 18} m{sup -3}s.

Study of a dense ({approx}10{sup 21} m{sup -3}) plasma heating by a relativistic electron beam and confinement of the plasma in multimirror magnetic field is carried out at the GOL-3 facility. The high-resolution spectral system in the visible region is used for investigation of plasma parameters.The analysis of the shape of D{sub {alpha}} spectral line shows that wings of this line are determined by the Doppler broadening from atoms being in the hot plasma core at high-temperature operation regime. A survey spectrometer with spatial and time resolution was used in addition to high-resolution spectrometer for detail study of this regime. Results of radial distribution measurements of D{sub {alpha}} line radiation show the presence of neutral deuterium in the hot plasma core. Ion temperature of the hot plasma achieves 2 keV.The evolution of radial distribution of D{sub {alpha}} line radiation, diagnostics features and results on ion temperature dynamics in the hot plasma core are presented in the paper.

Dense plasma heating by a relativistic electron beam and its confinement are studied in the multiple mirror trap GOL-3. Axial currents, which exist in the system, cause helical structure of the magnetic field. The safety factor q is shown to be below unity on the axis. Experimental data on the distribution and evolution of currents, structure of the magnetic field, and their influence on confinement and on MHD activity are discussed.

Results are presented from experiments on the injection of solid pellets into a plasma heated by an electron beam in the GOL-3 device. For this purpose, two pellet injectors were installed in the device. The target plasma with a density of ∼1015 cm−3 was produced in a solenoid with a field of 4.8 T and was heated by a highpower electron beam with an electron energy of ∼1 MeV, a duration of ∼7 s, and a total energy of 120–150 kJ. Before heating, the pellet was injected into the center of the plasma column transversely to the magnetic field. The injection point was located at a distance of 6.5 or 2 m from the input magnetic mirror. Polyethylene pellets with a mass of 0.1–1 mg and lithium-deuteride pellets with a mass of 0.02–0.5 mg were used. A few microseconds after the electron beam starts to be injected into the plasma, a dense plasma bunch is formed. In the initial stage of expansion, the plasma bunch remains spherically symmetric. The plasma at the periphery of the bunch is then heated and becomes magnetized. Next, the dense plasma expands along the magnetic field with a velocity on the order of 300 km/s. A comparison of the measured parameters with calculations by a hydrodynamic model shows that, in order to provide such a high expansion velocity, the total energy density deposited in the pellet must be ∼1 kJ/cm2. This value substantially exceeds the energy density yielded by the target plasma; i.e., the energy is concentrated across the magnetic field onto a dense plasma bunch produced from the evaporated particle.

Theoretical and experimental problems in the realization of a concept of a multi-beam generator are studied for the case of a four-channel planar FEM oscillator at 75 GHz. Computer simulations and “cold” and “hot” experiments have demonstrated clear possibility for construction of this oscillator based on the ELMI-device.

The experimental results on a multiple-mirror trap GOL-3 with a short section of reduced magnetic field (“magnetic pit”) are presented. The reduced specific energy release from a relativistic electron beam in the pit brings about a region with a temperature several times lower than in the surrounding plasma. The existence of the low-temperature region directly demonstrates that the longitudinal electron heat conductivity is suppressed in the collective electron-beam interaction with plasma.

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.

The problem of interaction of a plasma flow with an inhomogeneous magnetic field is considered. The field is generated by magnetic coils. Field lines along the coil axis form a channel which is use...

A numerical simulation of decelerating, scattering, and trapping fast electrons by plasma in a magnetic trap is reported. Fast non-thermal electrons are generated via the interaction of the relativistic electron beam with the plasma. Their energy significantly exceeds the thermal energy of plasma particles. For real experimental conditions where the mean free path of electrons is larger than the length of a local magnetic pit, the kinetic equation for distribution function of electrons is numerically solved. The effect of electron scattering and trapping into the pit is calculated.

This paper presents the results of experiments on two-stage heating of a dense plasma by a relativistic electron beam in the GOL-3 facility. A dense plasma with a length of about a meter and a hydrogen density up to 1017 cm−3 was created in the main plasma, whose density was 1015 cm−3. In the process of interacting with the plasma, the electron beam (1 MeV, 40 kA, 4 μs) imparts its energy to the electrons of the main plasma through collective effects. The heated electrons, as they disperse along the magnetic field lines, in turn reach the region of dense plasma and impart their energy to it by pairwise collisions. Estimates based on experimental data are given for the parameters of the flux of hot plasma electrons, the energy released in the dense plasma, and the energy balance of the beam-plasma system. The paper discusses the dynamics of the plasma, which is inhomogeneous in density and temperature, including the appearance of pressure waves.

Investigation of mechanism of plasma ions heating in a multimirror magnetic trap became actual due to the essential progress in experiments on GOL-3 facility at Budker Institute of Nuclear Physics. The mechanism of fast (in comparison with the Coulomb one) acceleration and heating of ions in a multimirror trap with injection of a powerful relativistic electron beam is discussed.

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 the first experiments on generation of 4-mm radiation in two-channel planar FEM with combined electrodynamic system carried out at the ELMI-device. The results of spectral and calorimetric measurements are presented and discussed.

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.

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.

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.

Review of the experimental results for the last two years on study of dense plasma heating and confinement in a long multimirror trap GOL-3 is presented. This facility is an open trap for confineme...

A short review of recent results obtained at the GOL-3-II facility is presented. This facility is an open trap with 12 m long plasma column with a longitudinal magnetic field of 4.5 T in the unifor...