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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.

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 ...

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.

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.

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.

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...