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Results, obtained during the last decade on linear traps in Novosibirsk, verified the original concepts and led to discovery of new ways of plasma confinement in linear traps. It turns out that the multiple-mirror confinement, once thought to be suitable for pulsed fusion only, can work in tandem with gas-dynamic traps. Its helical-mirror variant can provide additional advantages for confinement of rotating plasmas such as radial and axial plasma pinch fluxes. The specially designed gas-dynamic mirrors can be run in the high-β “diamagnetic” regime, closely resembling the field-reversed configurations both in shape and in the quality of axial confinement. These new ideas form the groundwork of the possible road for linear traps to fusion.

Novel concept of the longitudinal plasma flow suppression by active plasma pumping in helicoidal magnetic field in mirror traps was proposed recently. Concept exploration device SMOLA is now being constructed to prove the possibility of the suppression and determine basic scalings of ist effectiveness. Technical solutions of the SMOLA device are described in the article. Vacuum system, magnetic system, plasma source and the source of the radial electric field are discussed. Estimations of the biasing required for optimal confinement are given. Physical program fort he first experiments is also proposed.

The review presents experimental studies of plasma-surface interaction and materials behavior under plasma loads done in the multiple-mirror trap of the GOL-3 facility. In the experiments for the PSI, the energy density in the extracted plasma stream varies from 0.5 to 30 MJ/m2. Parameters of near-surface plasma measured by a set of diagnostics are reviewed. Surface patterns of targets exposed to the plasma are analyzed. The erosion depth depends on the energy loads—it rises from 0 to 600 μm at 0.5 and 30 MJ/m2, correspondingly. Cracking and evolution of graphite and tungsten surface morphology are discussed. The enthalpy of brittle destruction of graphite (10 kJ/g), which determines the threshold of bulk damage of targets irradiated with a charged-particle flux with large penetration depth, was determined. Comparison of different facilities for PSI studies are presented. Heat flux play a key role to the target surface erosion.

The study is devoted to tungsten surface modification after irradiation at the GOL-3 facility with plasma loads corresponding to the ITER type I ELMs. In order to emulate heating with a steady plasma flux in the ITER divertor, some of the tungsten samples were preheated up to 500 °C. It was found out that the behavior of the surface modification (the crack pattern and the number of bubbles) depends on the initial temperature of the targets. While the orientation of major crack networks correlates with the direction of machining of the samples. Afterwards we have observed the process of craters’ formation caused by dust particle impacts.

A novel concept of helical mirror confinement with active axial and radial plasma flow control is discussed. The idea relies on the retarding force that appears when biased plasma experiences rotation in crossed electrical and helical mirror magnetic fields. Preparations for its experimental study started in Budker Institute of Nuclear Physics, Novosibirsk. Possible parameter space for a concept-exploration-class device SMOLA is identified. Details of numerical optimization of the magnetic structure of the device are presented. The main physical task for the SMOLA experiment will be direct demonstration of the helical mirror performance in simple experimental conditions at reasonably low plasma parameters.

A mathematical model of surface cracking under pulsed heat load was developed. The model correctly describes a smooth brittle–ductile transition. The elastic deformation is described in a thin-heated-layer approximation. The plastic deformation is described with the Hollomon equation. The time dependence of the deformation and stresses is described for one heating–cooling cycle for a material without initial plastic deformation. The model can be applied to tungsten manufactured according to ITER specifications. The model shows that the stability of stress-relieved tungsten deteriorates when the base temperature increases. This proved to be a result of the close ultimate tensile and yield strengths. For a heat load of arbitrary magnitude a stability criterion was obtained in the form of condition on the relation of the ultimate tensile and yield strengths.

New plans for next-step experiments on a multiple-mirror confinement in GOL-3 are discussed. The proposed changes in the hardware configuration include separation of the existing GOL-3 device into two independent plasma facilities. The first device will continue research on physics of highly turbulent electron-beam-heated plasma. It will use the existing generator of the electron beam and a shortened part of the existing solenoid. The second device will be devoted to a new experimental program on studies of efficiency of multiple-mirror end sections that should decrease power and particle losses from the trap. Details of the physics and upgrade plans for the new device, tentatively named GOL-NB, are discussed.

The first plasma campaign was completed in a start configuration of the GOL-NB multiple-mirror trap. The device included a 4-m-long high-field section, two end sections of magnetic flux expanders and a short temporary section for commissioning of two 25 keV, 0.75 MW neutral beams. Low-temperature start plasma was created by a coaxial arc plasma gun. The main objective of the first experiments is to develop and characterize the low-temperature plasma stream that will be used later for filling the central trap of GOL-NB with the start plasma. Plasma parameters and operation regimes are reported.

The paper presents experimental investigations of tungsten surface modification after plasma loads at the multimirror trap GOL-3. Energy loads on tungsten surface varied from 2 up to 4 MJ/m2 per shot with sets from 1 to 9 repetitive irradiations that corresponds to loads higher than tungsten melting threshold and is close to ITER giant ELM loads. Targets surface modification and transverse microsections after irradiation was studied by optical microscopy, SEM and hardness tester. Formation on tungsten surface of three different crack networks with typical cell sizes of 1000, 10 and 0.3 μm and bubbles are identified. The network of large cracks extend perpendicularly to the irradiated sample surface to a depth of 50–350 μm. Erosion depth depends on energy loads – rises from 20 to 200 μm at 2 and 4 MJ/m2 correspondingly. Cracking, development of tungsten surface morphology and droplets splashing are discussed.

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...

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...

The paper presents experimental investigations of plasma-surface interaction and materials behavior under plasma loads relevant to type I ITER ELMs. The experiments were performed with quasi-statio...

Investigation results for electromagnetic radiation emission induced by strong Langmuir turbulence driven by a microsecond relativistic electron beam are presented. The radiation is associated with...

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...

The paper reviews recent experimental results from GOL-3. Currently efforts are focused on further development of a physical database for multiple-mirror confinement systems and also on an upgrade of plasma heating systems of GOL-3 device. In general, current GOL-3 parameters demonstrate good prospects of a multiple-mirror trap as a fusion reactor.

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.

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.

Magnetic activity of plasma during the injection of 2-8 MW non-relativistic electron beam of sub-millisecond duration in GOL-3 is studied.The main parameters of fluctuations of the magnetic field a...

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...

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.

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.

Transient MHD activity in the multiple-mirror trap GOL-3 at the stage of plasma cooling after decay of the net current was studied. Such events are diagnosed as short bursts (generally shorter than...

Thomson scattering diagnostics has been updated to allow measurements at two instants of time for either of two spatial points in plasma during a single plasma discharge. Laser produces now two 15J...

The series of experiments on plasma heating by the electron beam of reduced diameter was carried out at the GOL-3 facility. To define the size of a high-temperature plasma region the imaging VUV sp...

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...

This paper presents prospect of now developed new 2 MW neutral beam injection system on GOL-3 facility. It discusses results of numerical simulation based on data from experiments on GOL-3. Vacuum ...

Boreskov Institute of Catalysis, 5 Lavrentjev Avenue, Novosibirsk, 630090, Russia e-mail: A.A.Shoshin@inp.nsk.su The studies of exposing of targets by hot-electron plasma exhaust from the multi-mirror trap GOL-3 are carried out. The results of Raman and SEM studies of surface modification of carbon materials with different ordering range of sp2 fraction (different graphite and glassy carbon) exposed by pulsed hot hydrogen plasma with energy density up to 8 MJ/m

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.

This contribution presents recent results of pellet technologies development for plasma fuelling in magnetic confinement machines with open or closed magnetic configuration. The current status of ITV7 pellet injector for GOL3 multimirror linear machine, PGS2.2 pellet guide system of ITV4 in-situ pellet injector for TUMAN-3M tokamak and ITV5 centrifuge pellet injector for Globus-M spherical tokamak is reported. New results on modeling of tangential pellet injection into TUMAN-3M tokamak are discussed as well.

Recently GOL-3 has been reconfigured to a multimirror trap with improved confinement and high ion temperature. A dense plasma is created with a life time in the millisecond range. BTI neutron bubbl...

On the basis of the modeling experiments of hot plasma influence on the graphite and tungsten materials performed on the GOL-3 device, an analysis was made of a possibility for explosive erosion to occur under ITER disruption conditions. In this analysis, the threshold value for explosive erosion obtained in the GOL-3 experiments was taken into account. Then the volumetric energy release was calculated for a hot plasma (T = 1–20 keV) reaching the target at the limit of irradiating flux close to the conditions of ITER disruption (an energy flux of up to 140 MJ/m2). It is shown that under such conditions, erosion can reach values much higher than those in the case of erosion under the effect of a plasma with lower temperature but with the same energy density.

The GOL-3 facility was used for exploratory plasma stream target experiments under conditions rather typical for the thermal quench phase of ITER tokamak plasma disruptions. The experiments allowed study of the properties of target plasmas formed from vaporized target materials in front of the target and determination of the target material erosion. Within 2 ps after the onset of the plasma stream a cloud of evaporated material is formed. The cloud expands along magnetic force lines with velocities around lo6 cm/s. Line radiation is observed from the target plasma corona, continuum radiation from the bulk of the cloud. The temperature in the plasma corona is about 1 eV. The black body temperature of the bulk cloud is below 0.5 eV. The erosion for graphite increases sharply upon reaching a threshold value of 1 MJ/m’ for the energy density of the hot plasma stream and achieves very high values.

New results are presented on studying the beam-plasma interaction and plasma heating dynamics at the INAR device. The specific features of the generation of 'hot' (E>approximately 1keV) plasma electrons containing the main part of the plasma energy are studied. In the case of a beam with a small initial angular spread, the 'hot' electrons are mainly generated near the point where the beam is injected into the plasma. Also reported are the results of the experiments in which the magnetic field in the beam-plasma interaction region was increased up to 70 kOe. In this case, at the plasma length of 75 cm, the total beam energy losses exceed 40%. The growth of the plasma energy content at higher magnetic field is observed. The first stage of the GOL-3 experiment is described which is aimed at the study of the plasma heating of a solenoid by a 100 kJ microsecond electron beam. This experimental device is ready for operation.

A set of diagnostics for plasma spectroscopy was developed for multimiror trap GOL-3. It includes survey spectrometer with spatial resolution and the high spectral resolution complex for line shape analysis. The systems allow recording waveforms of plasma radiation with spectral resolution of 0.01 nm and measure spatial distribution of line radiation intensity (simultaneously in π and a components). Analysis of radiation spectra was used for investigation of impurities structure and dynamics. Precise measurements of spectral line shape were used for finding the electron density and ion temperature from a line broadening. Description of the equipment and experimental technique as well the recent results are presented in the paper.

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...

Dynamics of light impurities at multimirror trap GOL-3 was studied using imaging spectroscopy diagnostics in VUV and visible spectral range. The results of impurity balance and transport simulation as well as comparison with measurements are presented in this paper. Concentration of impurities in plasma and diffusion coefficient are found out from the measurements. Suitability using VUV and XUV spectroscopy for measuring main plasma parameters is considered.

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.

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.