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—A multi-chord beam diagnostic system for an open multiple-mirror trap GOL-NB is described. The system is based on a 10 keV ribbon beam of fast neutral hydrogen atoms generated by a wide-aperture ion injector with an arc plasma source. The plasma linear density profile is calculated from the attenuation of the beam after passing through the plasma. This paper discusses the design of the diagnostics and its capabilities, and also presents the measured profiles of the linear plasma density in the experiment on filling the trap with the starting plasma. The modernized version of diagnostics and the expected increase in its resolution are described. The prospects of using the Charge eXchange Recombination Spectroscopy (CXRS) method on the existing element base are evaluated.

The system is described for the formation of the low-temperature starting plasma flow in the GOL-NB trap. The starting plasma is a target for capturing heating neutral beams. The plasma flow is formed in the arc plasma gun installed in a relatively weak magnetic field. Next, it is compressed in the increasing magnetic field and then transported to a distance of approximately 4 m. The design of the plasma gun is described. Optimization of the operating regimes and scenarios of the system for creating the starting plasma made it possible to reduce the gas load onto the vacuum system of the facility, which resulted in reducing the losses associated with the presence of gas dragged along together with the plasma. The plasma flow at the outlet from the high magnetic field section is increased approximately four times, as compared to the results of the first plasma campaign. It is discussed how the limiters and other intrachamber electrodes affect the plasma flow formation. The achieved plasma flow parameters will be sufficient to start the experiments on plasma heating with the help of neutral beams at the GOL-NB multi-mirror trap in its full-design configuration.

A system of four-electrode Langmuir probes developed for the GOL-NB multiple-mirror trap is discussed. The system is used for studies of a low-temperature start plasma (1019–1020 m-3, 5 eV) that fills the device during the initial phase of the experiment. The probe allows simultaneous measurements of plasma density, electron temperature and radial electric field. The accuracy of the probe measurements is also discussed.

The program of the deep upgrade of the GOL-3 multiple-mirror trap is presented. The upgrade is aimed at creating a new GOL-NB open trap located at the GOL-3 site and intended to directly demonstrate the efficiency of using multiple-mirror magnetic cells to improve longitudinal plasma confinement in a gasdynamic open trap. The GOL-NB device will consist of a new central trap, adjoint cells with a multiple-mirror magnetic field, and end tanks (magnetic flux expanders). Plasma in the central trap will be heated by neutral beam injection with a power of up to 1.5 MW and duration of 1 ms. At present, physical experiments directed at developing plasma technologies that are novel for this facility are being carried out using the 6-m-long autonomous part of the GOL-3 solenoid. The aim of this work was to develop a method for filling the central trap with a low-temperature start plasma. Transportation of a plasma stream from an arc source over a distance of 3 m in a uniform magnetic field with an induction of 0.5–4.5 T is demonstrated. In these experiments, the axial plasma density was (1–4) × 1020 m–3 and the mirror ratio varied from 5 to 60. In general, the experiments confirmed the correctness of the adopted decisions for the start plasma source of the GOL-NB device.

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.

The formation of positive singly charged molecular ions with the relative molecular weight 254 ± 3 on the surface of a tantalum band was studied. The ions were fixed by recording their emission at temperatures from 320 to 450°C when the band was rapidly heated. Measurements were largely performed in a vacuum, although the formation of molecular ions was also observed at atmospheric pressure in nitrogen.

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.

An electric discharge with a current of about 1 pA that appears at an air humidity >60% in an electric field >10 kV/cm is described. The experimental data demonstrate the presence of a discharge induced by ion emission from a wet surface rather than of a corona discharge. Emission decreases the potential of the insulated electrode according to the law U(t) ∼ e−k√t. The static electric field is measured with a fixed collector and a vibrating screening grid.

An overview of the newly built neutral beam injection system is presented. This system is intended for creating a population of warm ions in the central cell of the recently developed GOL-NB facility. The system includes two neutral beam injectors and appropriate power supply and control means. Beam parameters are: energy 25 keV, total power 1.5 MW, pulse duration 5 ms.

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.

Helicons (circularly-polarized electromagnetic waves) propagate in a plasma with density exceeded cut-off for its frequency, and provide effective energy delivery to plasma. Accordingly, helicon discharge is one of the most suitable way for production of high-density low-temperature plasma. Helicon plasma sources, operating in the MHz frequency range and respectively low magnetic fields (0.01-0.1 T), capable to create plasma with density up to 1013 cm−3. At the same time, next generation of linear plasma facilities for both for PMI studies and fusion applications requires production of plasma with density above this limit. Theoretical studies predict that such increasing of density can be achieved by application of powerful microwave sources of GHz range frequency. The aim of the presented experiments is experimental verification of theoretical predictions and search of conditions for effective delivery of electromagnetic power to plasma towards development of stationary source of dense plasma for linear ...

The kinetics of alkali metal ion emission from metal surfaces heated to temperatures of 800–2500 K is studied. The ion current relaxation is described by the relationship \(I = Ae^{ - B\sqrt t } + {C \mathord{\left/ {\vphantom {C {\sqrt t }}} \right. \kern-\nulldelimiterspace} {\sqrt t }} + I_0 \). After the relaxation, the ion emission is recovered when the surface is exposed to H2O at room temperature. The nature of the phenomenon is discussed.

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 ...

The possibility of recording a chemical reaction occurring on the surface of a metal target in a collisionless plasma jet by analyzing the longitudinal-velocity spectra of jet-plasma ions scattered by the target is shown. The target is a Ta strip with a 3×0.1 mm cross section. The ion energy is 30 eV. It is found that, after rapid heating of the target to 1000 K, the current produced by scattered ions decreases and is then restored in a time of 40 s for nitrogen ions and 60 s for hydrogen ions. The relaxation of the current correlates with the accumulation of an intermediate reagent (probably, TaO2Na+ ions) on the target surface; the reagent participates further in the formation of experimentally observed ions with a mass of 245±1 (probably, TaO2Na+ · H2O).

The experience gained in using an array of cylindrical Langmuir probes as a perturbing body for plasma-jet diagnostics is described. The plasma potential on a part of the probe is determined from the ion-scattering minimum at that part. The potential values thus obtained are compared with the results of an analysis of the probe characteristics. The conditions for applicability of the method are discussed. A density marker is created by applying a voltage pulse with a duration of 30 ns to the probes, and time-of-flight probing of the plasma jet is performed.

Experimental data on the relaxation of currents due to ion emission, charge leak from a dielectric surface, and polarization of electrodes in various electrolytes are reported. It is shown that the same nonexponential law of the current relaxation, I(t) ∼ exp( $$ - \alpha \sqrt t $$ ) is applicable in all these cases. A common mechanism of these phenomena is discussed.

Ion emitters formed from a diverging plasma jet make it possible to obtain high-precision beams [1-3]. A feature of ion sources with such emitters is their high sensitivity to a weak magnetic field. In [4] a longitudinal magnetic field of 60e increased ion current by 50%. In [5] afield of i-i00 Oe was used in order to control the beam current. It was shown by experiment in [6] that an increase in beam current by a factor of 3.7 under the action of a longitudinal magnetic field of 40 Oe arose for two reasons: by a relatively weak (7%) increase in the escape of plasma caused by an anodic opening connected with magnetic isolation of the anode [7], and focusing of the ion flux by a magnetic field outside the anode opening. In contrast to typical plasma optic devices [8-10] which focus ion beams with energy ~i keV in a strongly magnetized plasma, in the devices in question the natural plasma lens operates on a highly balanced ion flux with energy %30 eV [2, ii] with a weak magnetic field. The considerable effect of action of a weak magnetic field on the posibility to retain the small phase volume of the beam makes it desirable to use this phenomenon for controlling ion sources and to study it further. The present work is an account of this study.

An arc proton source [i-3], used as a unit in a plasma diagnostics system [4] or as a unit in high-voltage injectors of precision proton beams [5, 6], is affected by external magnetic fields. Moreover, a magnetic field can be used to control the plasma flow [5, 7, 8]. In view of this, the effect of a longitudinal magnetic field was studied in [8, 9] in the range from 1 to i00 G on a plasma jet. In [8] we determined that the fourfold increase in current under the effect of a 40-G; magnetic field is due mainly to the focusing of the plasma jet; the reported data indicate that the focusing action is localized in a region 1 cm from the plasma generator anode. We also found that the focusing is associated with the existence of an electron current in the jet. In our study we generated a pulsed electron current, whose duration was much shorter than the time of flight of protons in the action region of the magnetic field; this enabled us to use the time-of-flight method to determine the distinctive features of the effect of the magnetic field on different parts of the jet.

Scattering of plasma-jet protons by a strip formed by long parallel metal filaments was investigated. The strip is located perpendicularly to the jet at a distance of70 mm from an ion extractor. Results of the experiment are adequately described by a model of a beam of noninteracting particles.

The linear charge density on arc segments of a lentil cavity in a two-dimensional homogeneous conductor in a uniform external electric field is determined analytically. A singularity of the current density on the edges of the segments makes the resultant relations a helpful test for numerical computational algorithms.

We describe the diagnostics of a plasma jet ejected from the anode hole of a pulsed arc hydrogen plasma source [1-3]. The front part of this source and the grid electrodes are shown in Fig. i. Grid 1 is at the potential of the plasma, and grid 2 is grounded. Therefore, for a positive plasma potential such a grid diode forms a proton beam [4]. If the diameter of the grids is much larger than the distance between them, the effect of space charge between the grids on the divergence of the beam can be neglected. In a number of cases the effect of the space charge field after the grids can also be neglected if a charge-exchange cell (CC), into which gas is admitted to neutralize the space charge of the beam, is located right after the grids [2, 5]. Therefore, such parallel wire grid electrodes, when combined with a charge-exchange cell, form a beam whose divergence along the wires is determined mainly by the velocity distribution of the protons in the plasma jet [i, 2]. From the phase characteristic of this proton beam it is possible to recover the velocity distribution of protons in the plasma in the direction of the grid wires. It is particularly simple to recover this distribution by analyzing the fast hydrogen atoms formed from these protons in the charge-exchange cell rather than the protons. In this case the particle motion can be considered as free streaming, since the effect of space charge has been eliminated over the whole beam path.

Overview of the activity on the development of the new multiple-mirror trap GOL-NB to be built in Budker Institute will be presented. This device to be build in BINP in several years as a deep conversion of the existing GOL-3 facility. The device will consist of a central trap with two 0.75 MW neutral beams, two multiple-mirror solenoids, two expander tanks and a plasma gun that creates start plasma. Plasma will be NBI-heated and confined in the central trap that is essentially a compact version of the GDT device with the well-known physics. The multiple-mirror sections should decrease the power and particle losses along the magnetic field. The main physical task of GOL-NB is the direct performance demonstration of the multiple-mirror sections that will change the escaping plasma flow and equilibrium plasma parameters in the central trap depending on the magnetic configuration chosen. In this paper, we will discuss new results in scenario modeling and progress in the hardware, including neutral beam injec...

This paper presents a new method of determining the longitudinal energy from the rotation of a plasma jet in a transverse magnetic field. The authors consider the motion of a plasma jet with total current and ion current in a transverse magnetic field. The mass per unit length is related to the ion current and the longitudinal proton velocity by the expression M approx. = m /sub p/ I /sub p/ /eV. The paper shows two profiles of a jet with proton current of 0.6 A and total current of -1A, deviated by magnetic fields of +38 and -38 G.