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Experiments at the multimirror open trap as plasma emitter of THz radiation (GOL-PET) facility have shown that the injection of a relativistic electron beam (REB) with a kiloampere current into a magnetized plasma column is accompanied by the generation of a THz radiation flux. Our experiments have revealed three-generation mechanisms. The first mechanism is the scattering of upper hybrid waves on plasma density gradients, the second is the direct pumping of electromagnetic waves by an electron beam, and the last one is the merging of two upper hybrid waves into an electromagnetic one. Both theoretical and experimental studies have shown the possibility to achieve a megawatt power of the flux at the upper hybrid frequency in the presence of significant plasma density gradients. Resent experiments have shown that a strong density decrease at the end of the plasma column is necessary for high-efficiency emission of the generated flux along its axis. This THz radiation flux is emitted from the column into a vacuum chamber and then through an output window to the atmosphere. The measurement results of the spatial and angular properties of such a megawatt flux are described in our article.

The SMOLA open magnetic trap was created at the Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences (BINP SB RAS) for studying the physics of suppression of plasma longitudinal losses from the system in which rotating plasma is confined in a magnetic field with helicoidal symmetry. The possibility of controlling the plasma rotation velocity is crucial in this concept. Methods of spectroscopic and magnetic diagnostics that allowed obtaining parameters of plasma rotation in the experiments are described. The angular plasma rotation velocity was found to be (0.5–1) × 106 s–1 in different regimes of system operation. The dependences of angular plasma rotation velocity on various parameters of the experiment are discussed.

For plasma heating and stabilization in open magnetic traps, the high-power neutral beam injector with tunable beam energy was developed at Budker Institute of Nuclear Physics. The initial energy of the beam particles is 15 keV, and it can be subsequently increased to 40 keV. In this case, the neutral beam power increases from 1.7 to 3.5 MW. A distinctive feature of this injector is the fact that, as the accelerating voltage considerably changes, the ion beam current remains constant. The injectors based on the ion sources with tunable energy are used in experiments at the C-2W open trap (USA).

A plasma gun for forming a plasma stream in the open magnetic mirror trap with additional helicoidal field SMOLA is described. The plasma gun is an axisymmetric system with a planar circular hot cathode based on lanthanum hexaboride and a hollow copper anode. The two planar coils are located around the plasma source and create a magnetic field of up to 200 mT. The magnetic field forms the magnetron configuration of the discharge and provides a radial electric insulation. The source typically operates with a discharge current of up to 350 A in hydrogen. Plasma parameters in the SMOLA device are Ti ~ 5 eV, Te ~ 5–40 eV and ni ~ (0.1–1) × 1019 m−3. Helium plasma can also be created. The plasma properties depend on the whole group of initial technical parameters: the cathode temperature, the feeding gas flow, the anode-cathode supply voltage and the magnitude of the cathode magnetic insulation.

Results of spectral and magnetic diagnostics of plasma differential rotation in the GOL-3 multiplemirror trap are presented. It is shown that the maximum frequency of plasma rotation about the longitudinal axis reaches 0.5 MHz during the injection of a relativistic electron beam into the plasma. The data of two diagnostics agree if there is a region with a higher rotation frequency near the boundary of the electron beam. Plasma differential rotation can be an additional factor stabilizing interchange modes in the GOL-3 facility.

Project of powerful submillimeter wave generator based on intense interaction of a relativistic electron beam with a magnetized plasma is developed at BINP RAS in collaboration with NSU. In presented experiments, the beam with parameters 0.8 MeV/15 kA/6 μs is injected into a plasma column with the density ∼ 1015 cm-3. Spectral composition of the emission from the plasma column is studied in the frequency band 0.1 – 1 THz. In the analysis of the results of our studies we focus on the role of strong plasma density gradients in generation of sub-mm waves.

This paper describes results of GOL-PET experiments on subterahertz (0.1–0.5 THz) emission from a magnetized plasma column during passing of a high-current $(\sim \hbox{10 kA})$ relativistic $(\sim \hbox{0.6 MeV})$ electron beam. The subterahertz radiation is generated in the plasma due to high-level turbulence induced by two-stream instability of the electron beam. These experiments are carried out at the specialized GOL-3T device. For the plasma density range 10 $^{14}\hbox{–10}^{15}~\hbox{cm}^{-3}$ , we have studied emission dynamics from the plasma column in its transverse and longitudinal directions. The spectral composition and polarization of the radiation was also investigated.

Generation of terahertz radiation in the magnetized plasma column due to the two-stream instability developing in the relativistic electron beam (REB) with a current of 10 kA is studied at the GOL-PET facility. In the first series of the experiments, at the regular transverse plasma density gradients, power of the generated terahertz radiation increased thirty times. At a frequency of the upper-hybrid oscillations (0.2–0.3 THz) and pulse duration of few microseconds, it reached 4 MWs. In the next experiments, when the additional longitudinal density gradients were created in plasma, the radiation power exceeded 10 MWs. These results are described in this paper.

Heating and confinement of plasma in a multimirror magnetic configuration have been studied at the GOL-3 facility (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk). The experiments are aimed at estimating the densities and charge states of the main impurities in the GOL-3 plasma and determining their contribution to the effective plasma charge. Plasma with a density of ∼1015 cm−3 was heated by a relativistic electron beam (1 MeV, 8 μs, ⩽200 kJ). At the end of electron beam injection, the plasma temperature reached 1 keV. The densities of impurities were determined using VUV and visible spectroscopy, as well as mass spectrometry of the residual vacuum. To determine the effective plasma charge, the experimental data were compared with the results of numerical simulations of the ionization balance of impurities. It is shown that the effective plasma charge calculated with allowance for the contributions from the main impurities does not exceed Zeff = 1.8, which cannot explain the experimentally observed improved confinement of low-density plasma.

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.

Results from different facilities for plasma-surface interaction (PSI) studies are compared and their relevance to each other and conditions of ITER transient events are discussed. For PSI studies different types of devices were used including open traps, tokamaks, linear plasma machines including quasi-stationary plasma accelerators, electron beams and lasers. The same damage thresholds were demonstrated with different techniques. At energy loads corresponding to ITER transient events (edge localized modes (ELMs), disruptions, etc.) only macroscopic erosion mechanisms are important. They are cracking, droplet formation and macroscopic mass losses of the target. Cracking occurs during cooling stage after irradiations. Details of plasma stream parameters are of secondary importance for cracks formation; only target temperature plays a role. Macroscopic mass losses strongly correspond with melting of a thin surface layer and heat loads play a key role for melting. Heat flux defines the targets surface erosion.

In the paper, last experiment’s results on sub-THz wave emission from the area of relativistic electron beam-plasma interaction in the GOL-PET device are described. A plasma column with the diameter of 6 cm, length of 2.5 m and electron density (0.2-2)×1015 cm−3 is confined by multiple-mirror magnetic field with mean value of 4 T. The relativistic electron beam injected into the column, has the following parameters: energy Eb ∼ 0.8 MeV, current Ib ∼ 30 kA, current density Jb ∼ 2 kA/cm2 in the mean magnetic field. Previous studies have shown that the beam pumps the plasma electron oscillations in a vicinity of the upper hybrid wave branch. These plasma oscillations can be converted in electromagnetic waves on regular or artificial plasma density gradients in a vicinity of upper hybrid frequency. The electromagnetic waves with the double upper hybrid frequency are also generated in the beam-plasma system due to coalescence of the plasma oscillations in case of high level of the oscillation energy density. T...

New experimental results on magnetic compression and transport of low-temperature arc plasma at ∼3 m distance are presented. The magnetic compression ratio of the plasma stream varied from 5 to 60 at the initial plasma diameter about 5 cm. Theory predicts that the multiple-mirror magnetic field should not significantly decelerate and weaken the collisional low-temperature arc plasma. In the experiments, the transport efficiency of the plasma stream in the multiple-mirror configuration of the solenoid was compared with the same in a uniform solenoidal field. As the result, the plasma with (1–4)×1020 m−3 density at the axis was obtained at ∼3 m distance from the arc plasma source. The experiments simulated the baseline scenario of GOL-NB filling by the start plasma. Finally, the experiments described in the paper validated the decisions made for the GOL-NB start plasma source.

The latest experimental campaign at the GOL-3 multiple-mirror trap was mainly aimed at features of heating and stability of the electron-beam-heated turbulent plasma. The discussed experiments feat...

Multimirror approach to plasma confinement for fusion is studied at GOL-3 facility in the Budker Institute of Nuclear Physics (Novosibirsk, Russia). The presented work is devoted to diagnostics of heavy impurities in plasma of this facility. The main purpose is quantitative measurement of density, degree of ionization of the main heavy impurities in plasma and their contribution to an effective charge of plasma at the GOL-3 facility. Density of interested elements was measured by optical spectroscopy and mass-spectroscopy of residual vacuum. A number of spectroscopic diagnostics has been developed for this purpose. Experimental data were compared with results of numerical calculations of impurities dynamics. As a result it is revealed that the contribution of heavy impurities to effective charge of plasma does not exceed 20%; thus the presence of impurities in plasma of the GOL-3 facility does not influence essentially the plasma confinement at the multimirror trap.

Results of experiments on injection of a sequence of several electron beam pulses (80–90 keV, 20–75 A, ∼30 μs) into 1019–1021 m−3 deuterium plasma are presented. The first beam pulse was injected into deuterium gas, the following pulses propagated through residual plasma that survived the inter-pulse periods. A typical pulse duration was of the order of 106 ω p − 1 that is much longer than most of the interaction-related processes. However, we noticed significant differences in plasma processes between the first pulse and the rest ones. A suggested physical factor behind those differences is longitudinal plasma current that develops during the first beam pulse.

For studying entries of impurities into thermonuclear plasma, when injecting heated neutral beams, the spectroscopic diagnostics intended for promptly monitoring the plasma composition of the radiofrequency (RF) emitter of the powerful fast neutral beam injector is designed. The analysis of plasma radiation spectra allowed us to determine the rotational temperature of the neutral hydrogen and estimate the oxygen-to-carbon impurity ratio in the RF emitter. In this work, the long-term dynamics of the neutral oxygen line brightness is studied, and the influence of the discharge chamber ageing and warming-up on the impurity content is determined.

New experimental results on magnetic compression and transport of low-temperature arc plasma are presented. In the experiments, the transport efficiency of the plasma stream in a multiple-mirror configuration was compared with the same in a uniform solenoidal field. The magnetic compression ratio of the plasma stream varied from 5 to 60 at the initial diameter of 5 cm. As the result, the plasma with (1 – 4)×1020 m-3 density at the axis was obtained at ∼3 m distance from the plasma source. Theory predicted that a multiple-mirror magnetic field should not significantly decelerate and weaken collisional plasma. The experiment confirmed this prediction. In the presented work, we simulated the baseline scenario of GOL-NB filling by cold start plasma.

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.

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.

Experiments involving irradiation of carbon targets with a hot electron plasma stream performed on the GOL-3 facility were aimed at the simulation of the effect of hot plasma of a thermonuclear reactor on plasma collectors in regimes close to those expected in the ITER. In these experiments, the emphasis was on the study of the surface-erosion processes exposed to the plasma stream. The graphite evaporation and chemical-erosion processes were studied with absolutely calibrated spectroscopic systems of the visible region. Spectroscopic experiments yielded data on the flow of carbon atoms from the surface of a plasma collector and on the contribution of chemical erosion to the surface-damage process. The obtained values are compared with the results of direct measurements of the erosion depth and the results of numerical calculations.

Electromagnetic emission from plasma in the vicinity of the fundamental plasma frequency and at its double value during a relativistic electron beam (REB) relaxation is studied at the GOL-3 facility [1]. In our paper we will present results of experiments carried out on the specialized GOL-PET device for the emission of terahertz radiation from plasma at its density ∼ 1015 cm−3 and the magnetic field strength 2–4 T. The plasma column created by a high-voltage discharge in the GOL-PET device has its diameter 6 cm and the length about of 250 cm. The injected electron beam has the following parameters: ∼0.8 MeV, ∼20 kA, ∼10 μs. The beam current density in the plasma is up to 3kA/cm2. The radiation in the frequency interval from 0.1 up to 0.8 THz is analyzed by fast eight-channel polychromator and polarimeter based on frequency selection quasioptical elements.

Experiments on the formation of a high-pressure pulse in a solid under the action of a high-power (up to 3 TW/m2) pulsed (8 μs) flow of 0.8-MeV relativistic electrons and hot plasma have been performed. A technique for measuring a high pulsed pressure from the shift of the R1 (694.23-nm) and R2 (692.8-nm) ruby fluorescence lines has been developed. The minimum pressure that can be measured by the developed instrument is 0.1 kbar. The pressure measured in experiments on the interaction of an electron beam and hot plasma with a surface reached 1.1 kbar, which is in good agreement with the calculation results. It is revealed that the X rays induced by the electron beam are quite intense enough to excite ruby fluorescence, which allows measurements to be performed without pumping the R1 and R2 lines by external radiation.

In experiments on the plasma heating and confinement in the GOL-3 multimirror trap, a deuterium plasma with a density of ∼1015 cm−3 and an ion temperature of 1–2 keV is confined for more than 1 ms. The plasma is heated by a relativistic electron beam. The ion temperature, which was measured by independent methods, reached 1.5–2 keV after the beginning of the beam injection. Since such a fast ion heating cannot be explained by the classical energy transfer from electrons to ions through binary collisions, a theoretical model of collective energy transfer was proposed. In order to verify this model, a new diagnostics was designed to study the dynamics of neutron emission from an individual mirror cell of the multimirror trap during electron beam injection. Intense neutron bursts predicted by this model were detected experimentally. Periodic neutron flux modulation caused by the macroscopic plasma flow along the solenoid was observed. The revealed mechanism of fast ion heating can be used to achieve fusion temperatures in the multimirror trap.

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.

First experimental results on microwave radiation at double plasma frequency from plasma heated by ~100 keV, 2-10 MW electron beam of ~100 μs duration in GOL-3 are presented. Measurements were done...

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.

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.

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 paper presents new experimental results from the GOL-3 facility on stabilization of some beam instability modes by controlled conditions at an exit beam receiver. In the experiments the space n...

Transverse losses from hot dense plasma were studied on the GOL-3 facility. Concentration of impurities, effective charge of ions in plasma, line radiation power and charge exchange loses were found from spectroscopic measurements in VUV and visible spectral regions. Estimation of effective charge of ion required for comparison of measurements and predictions of global confinement time was derived from the measurements of impurities concentration.

Summary form only given. Fast plasma heating in a multi-mirror magnetic trap by a high-current beam of relativistic electrons is a promising way to achieve fusion-grade plasma parameters. A high-level Langmuir turbulence develops during the beam-plasma interaction. These high-energy-density plasma oscillations can generate electromagnetic (EM) radiation in a wide frequency range extending from the plasma frequency to its 2nd harmonic. Thus the spectrum of EM emission can achieve 1 THz at 3·1015 cm−3 plasma density. The first experiments on the generation of sub-mm waves by a beam-heated plasma carried out at the GOL-3 facility were presented in [1]. Here we present results on sub-mm wave generation for plasma densities 1014–1015 cm−3 during injection of a relativistic electron beam (≤ 0.8 MeV, 30 kA, ∼10 ms).

There are described electromagnetic spectra of radiation emitted by magnetized plasma during sub-relativistic electron beam in a double plasma frequency band. Experimental studies were performed at the multiple-mirror trap GOL-3. The electron beam had the following parameters: 70–110 keV for the electron energy, 1–10 MW for the beam power and 30–300 μs for its duration. The spectrum was measured in 75–230 GHz frequency band. The frequency of the emission follows variations in electron plasma density and magnetic field strength. The specific emission power on the length of the plasma column is estimated on the level 0.75 kW/cm.

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.

Status of dc H− ion source development for tandem accelerator of boron capture neutron therapy is described. Upgrade and study of the Penning surface‐plasma source with hollow cathodes was continued. Results of source optimization, of ion optic computer simulation, and of emittance measurement are presented. The upgraded source delivers dc H− beam with energy 25 kV, current 8 mA, 1rms emittance ЄX ∼ 0.2 π mm⋅mrad, ЄY ∼ 0.3 π mm⋅mrad at discharge power ⩽ 0.5 kW.

The paper presents results of measurements of sub-terahertz electromagnetic emission from magnetized plasma during injection of a powerful relativistic electron beam of microsecond duration in plasma with the density of 3 × 1014 cm−3. It was found that the spectrum of the radiation concentrated in three distinct regions with high level of spectral power density. The first region is located near f1 = 100 GHz; the second one is in the vicinity of 190 GHz, and the third region is in the frequency interval f3 = 280–340 GHz. Polarization vectors of the emission in the first and third regions (f1 and f3) are directed mainly perpendicular to the magnetic field in the plasma. At the same time, the polarization of the radiation in the vicinity of f2 = 190 GHz is parallel to the magnetic field. The most likely mechanism of electromagnetic wave generation in the frequency regions f1 and f2 is the linear conversion of the plasma oscillations into the electromagnetic waves on strong gradients of the plasma density. Th...

The paper reviews the results of development of steady-state arc-discharge plasma generator with directly heated LaB6 cathode. This arc-discharge plasma generator produces a plasma jet which is to be converted into an atomic one after recombination on a metallic plate. The plate is electrically biased relative to the plasma in order to control the atom energies. Such an intensive jet of hydrogen atoms can be used in negative ion sources for effective production of negative ions on a cesiated surface of plasma grid. All elements of the plasma generator have an augmented water cooling to operate in long pulse mode or in steady state. The thermo-mechanical stresses and deformations of the most critical elements of the plasma generator were determined by simulations. Magnetic field inside the discharge chamber was optimized to reduce the local power loads. The first tests of the steady-state arc plasma generator prototype have performed in long-pulse mode.

Summary form only given, as follows. Varying the pulse duration and amplitude of a pressure wave in solids can provide a unique possibility to control solid-state transformations and composition of new products. Realization of such a control by varying temperature pulses is already well known. As to the influence of the pressure variation, the importance of the duration of pressure pulses was claimed in a number of publications in the field of mechanochemistry, but real experiments are hard to come by. The aim of our work is to find a way for the control of the time profile of the pressure wave in solids by using a high-power microsecond REB for surface irradiation of a solid target. Generally speaking, high-power particle beams with short pulse duration are widely used as one of methods to generate high pressure pulses in solids, for example, for nuclear fusion application. Our presentation deals with the results of experimental and theoretical studies of application of microsecond REB to induce solid-state transformations under special conditions. Several typical examples belonging to different classes of pressure-induced solid-state transformations are considered, including structural transformations with and without significant contribution of an electronic component, with model systems ranging from simple inorganic salts and oxides to complex oxides and organic molecular solids. The evolution of pressure inside a solid target induced by the irradiation of its surface by microsecond REB with variable current density (equal to the one generated by U-2 accelerator) is simulated. The results of the simulations are used to optimize the geometry and the material of the target comprising the sample, in which a solid-state transformation is to be induced. The experimental diagnostics is discussed, which can be used to measure the conditions of the experiment (in particular, pressure dynamics), to follow the transformation and to characterize its product.

Phenomenon of fast heating of plasma ions in the multimirror trap GOL-3 is discovered and explained. An essence of effect is that ion component of the plasma is heated during electron beam injection much faster (at 100 - 1000 times) than due to binary electron-ion collisions. An analysis of experimental results is presented and discussed. A model of fast non-Coulomb ion heating is suggested.

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...

Two separate topics on a pellet injection activity at the multimirror trap GOL-3 are presented. The first topic is connected with studies of influence of a high-energy-density plasma on solids. A carbon pellet of 2-mm diameter was injected into the plasma for this purpose. The second discussed topic is a status of works on a cryogenic pellet injector for plasma fueling at GOL-3.

Recent results of the experiments at GOL-3 facility are presented. In present configuration of the device, plasma with a density of 10 14 ÷10 16 cm -3 is confined in a 12-meter-long solenoid, which comprises 55 corrugation cells with mirror ratio B max /B min =4.8/3.2 T. The plasma in the solenoid is heated up to 2-4 keV temperature by a high power relativistic electron beam (∼1 MeV, ∼30 kA, ∼8 μs, ∼120 kJ) injected through one of the ends. Mechanism of experimentally observed fast ion heating, issues of plasma stability and confinement are discussed.