Abstract
This study analyzes the dependences of the size of the luminous region of hydrocarbon pellet cloud on the ablation rate, as well as on the ambient plasma electron density and temperature. ...The data were obtained in a series of experiments where spherical solid polystyrene pellets with a diameter of ≈900
μ
m at a speed of ≈450 m s
−1
were injected into hydrogen plasma of the large helical device. The ambient plasma with an electron temperature of 0.5–1.5 keV and a density of (1–7) × 10
19
m
−3
was maintained by injection of neutral atom beams with total the heating power of 3–14 MW. A scaling law was derived for determining the transverse size of the cloud’s luminous region from the known values of the pellet’s current radius as well as the values of the density and temperature of the ambient plasma at the place of image acquisition. The interdependencies between various dimensions of the luminous region obtained in the line spectrum are established. The presence of such dependences makes it possible to describe the dimensions of the luminous region comprehensively by means of the scaling law for its transverse size.
Abstract
The current work reports on the significant rise of the fusion triple product in experiments carried out on the compact spherical tokamak (ST) Globus-M2 with a twofold increase in the ...toroidal magnetic field. A tenfold rise in the
n
.
T
.
τ
E
product was recorded during an increase in the magnetic field from 0.4 to 0.8 T and the plasma current from 0.25 to 0.4 MA at an unchanged auxiliary heating power value. Limited reasons may affect this positive trend, among which are energy confinement improvement and an increase in the efficiency of neutral beam heating. Despite the increase in the magnetic field, the neutral beam injection (NBI) led to clear and reproducible transition to the H-mode accompanied by a decrease in the turbulence level at the plasma edge. It was experimentally confirmed that strong dependence of the energy confinement time on the magnetic field value is conserved at a higher magnetic field approaching 0.8 T. Enhancement of energy confinement is connected to a collisionality (
ν
*
) decrease. While for conventional tokamaks the confinement dependence on collisionality becomes weaker with decreasing
ν
*
dependence, in the ST, in contrast, we observe its strengthening.
The Globus-M spherical tokamak has demonstrated practically all of the project objectives during the 15-year period of operation. The main factor limiting further progress in plasma performance is a ...relatively low toroidal magnetic field. The maximum toroidal magnetic field achieved on Globus-M was 0.4 T with the exception of a limited number of shots with 0.55 T, which led to damage of the toroidal field coil in 2002. The increase of the magnetic field up to 1.0 T together with the plasma current up to 0.5 MA will result in the significant enhancement of the operating parameters in the upgraded Globus-M2 machine. The experimental program will be focused on plasma heating and non-inductive current drive and will contribute to the creation of a physical and technological base for the compact fusion neutron source development. In the article a brief overview of the physical background for the machine upgrade is outlined. The current status of the project implementation is described. First experimental results on moderate magnetic field increase from 0.4 T up to 0.5 T in the existing Globus-M machine are discussed. The improvement of plasma confinement as well as enhancement of efficiency of the beam driven current is observed.
The diagnostic of the peripheral plasma parameters in terms of the relation of lines of neutral helium is included in the diagnostic complex of the tokamak Globus-M2. The first measurements of the ...peripheral plasma parameters are performed near the lower X point. The measured spatial distributions of the electron temperature and density are in satisfactory agreement with the simulation with the SOLPS-ITER code.
The concept of next-generation spherical tokamak is being considered: the Globus-3 project, which, in its characteristics, is compatible with the infrastructure existing at the Ioffe Institute, but ...differs from the currently operating Globus-M2 tokamak in the stronger toroidal magnetic field (1.5–3.0 T) and increased duration of plasma discharge. The parametric analysis data are presented that determined the preliminary selection of the facility parameters. Three options for the electromagnetic system were considered: with the warm copper coils, with the pre-cooled copper coils and with the coils made of high-temperature superconductors. For the first option, the concept for designing the electromagnetic system and vacuum vessel of the facility has been developed. The basic shot scenario with duration of up to 3 s at the field of 1.5 T and plasma current of 0.8 MA is presented.
Birds have evolved in direct contact with natural nanoparticles (NPs) that are identical to artificial trace-element NPs. This relationship, the high action potential and their ability to reduce ...environmental pollution make NPs a promising component of bird diets. However, from available published studies there is no unity in justifying the applied dosages of NPs and their calculations. NPs are used in the studies in various doses, for example: Cu 0.5-50 mg/kg, Ag 10-1000 mg/kg, Se 0.2-5 mg/kg, Cr 500-1500 ppb. Therefore, universal approaches and criteria of NP investigations are necessary for the establishment of their use in feed. The mechanisms of action of the trace elements in artificial NPs in birds vary from the those of ionic forms of trace elements, which determine the differences in the productive effect. According to data from different authors, chickens receiving NPs in feed have higher chickens body weight by 13-24%. Such benefits have increased interest in sources of trace-element NPs significantly over the past two decades. The design of trace-element NPs has led to promising developments in the safe use of NPs for poultry nutrition, such as coating NPs with inert substances and adjusting their size. However, constraining circumstances determined by the difficulty of predicting the toxic properties of nanostructures exist, even though artificial trace-element NPs are a relatively safe class of nanostructures due to their production requirements, and metal NPs are already used in human food and medicine. The following review discusses the benefits and potential hazardous effects of NPs and the possibility of using them as feed supplements for poultry.
Boundaries of densely populated areas can approach with time to old subsurface repositories of radioactive waste due to growth of settlement territories. Protective isolation of the repositories was ...sometimes insufficient. Penetration of groundwater into the repository and discharge of the polluted water into neighboring rivers can lead to radioactive pollution of water resources of the region. Special rehabilitation measures at the repository sites are required to prevent this. Their efficiency is considered on example of former repositories of an atomic research center in Moscow (Russia). Radioactive materials were extracted from the subsurface burials for consequent disposal in a safer repository. A limited volume of polluted enclosing sedimentary rocks was also extracted and placed back after flushing with water. Analysis of rock pollution shows that these rehabilitation measures cannot enhance substantially a forecast of radioactive pollution. Moreover, loosening of the sedimentary rocks at the site of the earthwork leads to focusing of meteoric water from the surface in the domain of the most severe pollution of the underground medium. Elevated concentration of humic and fulvic acids in the surface water could intensify highly mobile colloidal form of actinide migration after the rehabilitation procedure. Place of polluted water discharge at a river bank and time of colloid-facilitated migration of radionuclides from the repository to the discharge place were estimated by computer simulation. Sampling of river sediments after approximately this time showed that concentration of uranium in the sediments at the calculated point exceeded about twice its values at neighboring sampling points up- and downstream (bottom sediments, which were polluted before remediation, were eliminated by a foregoing channel-cleaning of the river). Distributions of uranium in the sampled columns of the bottom sediments evidence that pollution of the sediments is caused by groundwater discharge. A comparison with the results of the mathematical modeling shows that this is in good agreement with the assumption of fast colloid-facilitated migration of uranium from the repository site. Along with the analysis of limited conditioning of the polluted rocks, these results indicate that the considered remediation method is less effective than hydraulic isolation of waste disposal area like it was performed at Oak Ridge National Laboratory.
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.
