NBI-assisted plasma heating with one or two injectors of fast neutral atoms was studied at the Globus-M2 spherical tokamak at the toroidal magnetic fields of 0.8–0.9 T and plasma currents of 0.35–0.4 ...MA. Measurements of the spatial temperature and electron density distributions, performed using the Thomson scattering diagnostics, showed a twofold increase in heating of plasma electrons during the injection of neutral particles with energies of up to 45 keV at the beam power of 0.75 MW, as compared to the ohmic heating regime. Switching on the second additional beam with the particle energy of up to 30 keV and power of up to 0.5 MW resulted in obtaining the hot ion mode in the range of mean plasma densities of (1.6–10) × 10
19
m
−3
. According to the data of active spectroscopy and neutral particle analyzer diagnostics, in the hot zone, the ion temperature reached 4 keV at the plasma density of 8 × 10
19
m
−3
, which is more than 2.5 times higher than the electron temperature.
The results of measuring the electron temperature and density spatial distributions in plasma of the Globus-M2 tokamak using the Thomson scattering diagnostics are presented. The diagnostics provides ...measurements throughout the entire tokamak discharge, starting from time of gas breakdown. The Thomson scattering data were analyzed in order to determine the positions of the last closed flux surface, the plasma magnetic axis, and the radius of inversion during the saw-tooth oscillations. The results of measurements performed during the internal reconnection of magnetic field lines are presents, as well as the dynamics of spatial distributions of electron temperature, density and pressure during the plasma transition to the H-mode. The results of measuring the electron temperature distribution in the scrape-off layer using the Thomson scattering diagnostics are also presented for distances up to 4 cm outside the last closed flux surface.
The Globus-M2 spherical tokamak is the considerably upgraded Globus-M facility. Its technical parameters were increased as much as possible to achieve the promising range of physical parameters ...(sub-fusion temperatures and collisionality of much less than unity). These parameters will be achieved in a compact magnetic configuration similar to that of the Globus-M tokamak, the plasma current and toroidal magnetic field amounting to 0.5 MA and 1 T, respectively. The demand to increase the magnetic field and plasma current in the Globus-M2 resulted in the need for a complete redesign of the electromagnetic system because the plasma equilibrium requirements have changed and the mechanical and thermal loads have considerably increased as compared to the Globus-M. The vacuum vessel and the in-vessel components of the new Globus-M2 tokamak remain the same. Power supplies were upgraded to provide the required currents in the toroidal field coil and the central solenoid. The Globus-M2 tokamak was build up and preliminary tests were carried out. New auxiliary heating systems and diagnostics were developed and installed to be used in future experiments. Fist plasma was achieved at the Globus-M2 in April 2018.
The results of reconstruction of equilibrium magnetic configurations in the Globus-M spherical tokamak by means of the EFIT code and by the method of movable filaments with the use of the data from ...magnetic measurements are compared. The EFIT code allows one to completely reconstruct the magnetic configuration by solving the Grad−Shafranov equation. In the method of movable filaments, the distribution of the toroidal current flowing through the plasma is described by a set of infinitely thin current-carrying rings. In this method, the last closed magnetic surface (LCMS) and the open surfaces lying beyond the LCMS are calculated. Using both methods, the coordinates of the regions where the separatrix strikes the divertor plates were determined. The results obtained agree well with the distributions of the temperature over the tungsten divertor tiles measured using an IR camera.
Research data for drag currents in the Globus-M spherical tokamak are presented. The currents are generated by injecting atomic beams of hydrogen and deuterium. Experiments were carried out in the ...hydrogen and deuterium plasma of the tokamak. It has a divertor configuration with a lower
X
-point, a displacement along the larger radius from–1.0 to–2.5 cm, and a toroidal field of 0.4 T at a plasma current of 0.17–0.23 MA. The beam is injected into the tokamak in the equatorial plane tangentially to the magnetic axis of the plasma filament with an impact diameter of 32 cm. To provide a 28-keV 0.5-MW atomic beam with geometrical sizes of 4 × 20 cm (at a power level of 1/
e
), an IPM-2 ion source is used. The generation of noninductive currents is detected from a rise in the loop current and a simultaneous dip of the loop voltage. The injection of the hydrogen and deuterium atomic beams into the deuterium plasma results in a noticeable and reproducible dip of the loop voltage (up to 0.5 V). Using the ASTRA transport code, a model is constructed that allows rapid calculation of noninductive currents. Calculations performed for a specific discharge confirm that the model adequately describes the effect of drag current generation.
We report on a measurement of thermal neutrons, generated by the hadronic component of extensive air showers (EAS), by means of a small array of EN-detectors developed for the PRISMA project (PRImary ...Spectrum Measurement Array), novel devices based on a compound alloy of ZnS(Ag) and 6LiF. This array has been operated within the ARGO-YBJ experiment at the high altitude Cosmic Ray Observatory in Yangbajing (Tibet, 4300 m a.s.l.). Due to the tight correlation between the air shower hadrons and thermal neutrons, this technique can be envisaged as a simple way to estimate the number of high energy hadrons in EAS. Coincident events generated by primary cosmic rays of energies greater than 100 TeV have been selected and analyzed. The EN-detectors have been used to record simultaneously thermal neutrons and the air shower electromagnetic component. The density distributions of both components and the total number of thermal neutrons have been measured. The correlation of these data with the measurements carried out by ARGO-YBJ confirms the excellent performance of the EN-detector.
Plasma parameters in the Globus-M spherical tokamak have been measured upon injection of a deuteron beam with energy about 30 keV and a power of up to 700 kW. Dependences of the ion temperature and ...neutron yield on the plasma current and density and the gap width between the wall and plasma are considered. Possible characteristics of fast-ion confinement in the modified Globus-M2 tokamak are discussed.
Neutral beam injection into the Globus-M spherical tokamak at the early stage of discharge leads to the development of instabilities in a frequency range of 50–200 kHz, which have been identified as ...toroidal Alfvén eigenmodes (TAEs) 1. The influence of these modes on the confinement of fast particles has been studied with the aid of a neutral particle analyzer (NPA) and a neutron detector. The isotope effect was studied using hydrogen and deuterium both in the injected beam and in the target plasma. A correlation analysis of signals from magnetic probes showed that the observed modes in most cases contain a single harmonic with toroidal number
n
= 1. Upon the injection of deuterium into deuterium plasma, the development of TAEs led to a decrease in the neutron flux by 25%, whereas the fluxes of high-energy recharge atoms decreased by 75%. After the injection of hydrogen, a decrease in the flux measured by NPA did not exceed 25%.
The effects of exposure to two different stress factors—a weak static magnetic field (WSMF) with a magnetic induction of 200 μT and oligopeptide epigenetic regulators—were studied. The results of ...explant exposure to tissue-specific oligopeptides and to WSMF were comparable. Experiments on cognitive behavior suggested that oligopeptides Ala–Glu–Asp–Pro and Lys–Glu–Asp–Ala had a beneficial effect on medium-term memory formation. It is noted that external WSMFs efficiently affect biological objects due to their high penetrating capacity in biological media.
It is known that neutron background is a major problem for low-background experiments carrying out underground, such as dark matter search, double-beta decay searches and other experiments known as ...Underground Physics. We present here some results obtained with the en-detector of 0.75 m
2
, which is running for more than 4 years underground at a depth of 25 m water equivalent in Skobeltsyn Institute of Nuclear Physics, Moscow State University. Some spontaneous increases in thermal neutron flux up to a factor of 3 were observed in delayed anti-correlation with barometric pressure. The phenomenon can be explained by the radon barometric pumping effect resulting in similar effect in neutron flux being produced in (α,
n
)-reactions by alpha-decays of radon and its daughters in surrounding rock. This is the first demonstration of the barometric pumping effect observed in thermal neutron flux underground.
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