Academician A. D. Sakharov’s idea concerning the emission of atomic flux from hot plasma (1951) inspired scientists of A. F. Ioffe Physico-Technical Institute to create the first in the world ...instrument called Neutral Atom Analyzer in 1960 and then in 1961 to use it successfully on the Alpha device (USSR, 1958–1963). Now the analysis of fluxes of fast atoms referred to as Neutral Particle Analysis (NPA) is one of the main diagnostic methods for the ion component of plasma in tokamaks, stellarators, and other devices. NPA provides a unique opportunity for studying the ion distribution functions, ion temperatures and hydrogen isotope ratio in hot plasma. Neutral particle analyzers developed at the Ioffe Institute were widely used in the USSR until the late 1970s, and afterwards began to be employed worldwide. Since then, most of the information on the ion distribution functions and the behavior of fast ions in fusion plasma is obtained from NPA measurements on all leading magnetic confinement fusion systems worldwide. The specialized complex of atom analyzers currently being created at the Ioffe Institute is included in the primary list of ITER diagnostics. The integration of this complex on ITER is expected to begin in 2025.
First Globus-M2 Results Bakharev, N. N.; Balachenkov, I. M.; Chernyshev, F. V. ...
Plasma physics reports,
07/2020, Volume:
46, Issue:
7
Journal Article
Peer reviewed
Globus-M2—a new 1-Tesla spherical tokamak—was recently launched. The main features and research directions of this machine in scope of fusion–fission reactor development are described. Main results ...of the first experimental campaign with toroidal magnetic field up to 0.73 T and plasma current up to 0.33 MA are discussed. Significant improvement of the discharge parameters as compared to Globus-M was achieved. Plasma total stored energy higher than 7 kJ was obtained. Energy confinement time increase was consistent with predictions by spherical tokamak scalings. Toroidal Alfvén eigenmode-induced losses decrease with increase of plasma current and toroidal magnetic field. For the first time, LHCD with the toroidal wave slowing-down was successfully used at a spherical tokamak.
The statistics of the pressure and velocity-field fluctuations in a subsonic turbulent jet is investigated. The data obtained previously in the numerical calculation by the LES method for a round jet ...with the Mach number M = 0.8 and the Reynolds number Re ~ 750 000 are analyzed. Pulsations are considered both in the potential core of the jet and in the mixing layer. For studying the statistics and identifying the intermittency (the property of statistics to differ from normal), the probability-density function and the flat factor (the ratio of the fourth moment to the square of the second moment) are used. It is shown that, in contrast to the homogeneous isotropic turbulence, where the velocity fluctuations have Gaussian statistics, for a turbulent jet, the velocity field statistics turns out to be intermittent at the boundary of the potential core and at the outer boundary of the mixing layer. An explanation that this difference is related to the contribution of large-scale fluctuations of the mean flow (instability waves), is proposed. It is also shown that the intermittency of the pressure field in the region of the outer boundary of a turbulent jet cannot be associated with large-scale oscillations but is a characteristic of small-scale turbulence, as well as in the case of homogeneous isotropic turbulence.
The stability of a cylinder in circulation flow of an inviscid incompressible fluid is considered. The investigation of stability in the simple two-dimensional system is of considerable interest ...since in this problem the analytical solution can be obtained in both spectral and initial problems. The investigation of the critical layer region in which the phase perturbation velocity coincides with the velocity of mean flow is of particular interest since just in this region the perturbations are concentrated and grow indefinitely.
The plasmaphysical code is presented that makes it possible to simulate the energy distributions of atoms escaping from plasma of the toroidal facilities. The code includes calculations of the ...particle spatial distributions in the charge-exchange plasma target consisting of atoms and hydrogen-like impurity ions. The calculations of the charge-exchange target are performed in two ways: using the Monte Carlo method and solving the ionization balance equation in the coronal approximation. The code can be used to interpret the neutral particle analyzers (NPAs) data. In particular, with its help, the ion temperatures determined using the NPAs can be corrected. The code can be also used to estimate the atomic fluxes from plasma onto the first wall expected at the currently designed fusion facilities.
The results of a detailed study of the structure of the sound field of a subsonic turbulent jet are presented. The experimental data obtained by the azimuthal decomposition technique and numerical ...data obtained by large eddy simulation are used for the analysis. Two approaches for modeling the noise sources are compared: the “small-scale” turbulence model and the instability-wave model. It is shown that the model of “small-scale” turbulence makes it possible to reproduce the nontrivial radiation directivity characteristics of azimuthal modes in a wide range of parameters and, apparently, is more appropriate for the physics of noise-generation processes in subsonic jets.
It is well known that a sound source related to nonstationary motion of vortices at small Mach numbers can be obtained in the incompressible inviscid fluid approximation. In this study, it is ...proposed to describe the perturbation dynamics of an incompressible ideal fluid using the Lagrangian and Hamiltonian formalism with the displacement field and momentum density perturbation as canonical variables. Based on Noether’s theorem, the conditions of quadrupole moment conservation in the evolution of small perturbations of stationary flows have been formulated. It has been shown that these conditions are always satisfied for perturbations of uniform jet flows. The obtained results not only yield a solution to the general mechanics problem on motion integrals; they are also significant in aeroacoustics because the quadrupole moment of a vortex flow is the principal term of sound source expansion in the Mach number.
The possibility of controlling instability waves in the mixing layer of a subsonic unexcited jet is studied. These waves can be noise sources in both free jets and jets as parts of configurations. In ...the study the method of experimental diagnostics of the instability waves in the near field of a jet using an azimuthal multimicrophone array is realized. The data on the near field fluctuations are used for testing the control strategy proposed by the authors. The strategy consists in narrowband sliding filtration of the original signal and the formation of a narrowband controlling action on the basis of the linear principle of signal superposition. The results of the study represent the next step toward the realization of an active control system suppressing natural instability waves in turbulent jets.
Neutral particle analysis on ITER: present status and prospects Afanasyev, V.I.; Chernyshev, F.V.; Kislyakov, A.I. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2010, Volume:
621, Issue:
1
Journal Article
Peer reviewed
This paper presents the physical basis for measuring the neutral particle fluxes emitted by ITER plasma and describes the instrumentation for that developed in Ioffe Institute (St. Petersburg, ...Russia). Possible mechanisms of the neutralization of the hydrogen and helium ions in the thermal and supra-thermal energy ranges are considered. Numerical simulation results of the neutral fluxes produced by the neutralization processes of the bulk thermal deuterium and tritium ions, the knock-on deuterium and tritium ions and the confined alpha particles are presented.
Presented ITER NPA system consists of low energy neutral particle analyzer (LENPA) and high energy neutral particle analyzer (HENPA). The analyzers provide the measurements in the thermal (10–200
keV) and supra-thermal (0.1–4
MeV) ranges .
Calculation of the counting rates in the analyzer energy channels shows that NPA system will be able to measure D/T ratio both in ITER plasma core (
r<0.4
a) by measuring the neutralized knock-on deuterons and tritons and in plasma medium region (
r>0.4
a) by measuring of the neutralized thermal deuterons and tritons. The possibility of measuring a flux of the neutralized confined alphas is also discussed in the paper.
In the framework of the isotope effect studies at the FT-2 tokamak, the efficiencies were compared of the lower hybrid wave heating of the ion components of the hydrogen and deuterium plasmas with ...high densities (close to the Greenwald limit, 〈
n
e
〉 ≤ 10
20
m
–3
). It was experimentally ascertained that, in accordance with the theoretical concepts, the efficient axial heating of the deuterium plasma ions occurs, as opposed to the peripheral heating of the hydrogen plasma ions. Such an isotope effect occurs due to the different localization of the plasma-RF wave interaction regions. The distinctive feature of these experiments is the fact that, in deuterium plasma, during the preliminary ohmic heating, the dependence of the energy lifetime on density τ
Е
(
n
) is linear (LOC dependence), and, with increasing density, the transition to the improved ohmic confinement mode occurs. In hydrogen plasma, on the contrary, the transition to the saturation mode is observed. In this study, the considerable decrease in τ
Е
was revealed, observed during the additional lower hybrid wave heating in both hydrogen and deuterium plasmas.
