Fizika plazmy
ISSN(Print): 0367-2921
Media registration certificate: No. 0110354 dated 03/02/1993
Founder: Federal Research Center "Institute of General Physics named after A.M. Prokhorov RAS", National Research Center "Kurchatov Institute", Russian Academy of Sciences
Editor-in-Chief: Smirnov Valentin Panteleimonovich
Number of issues per year: 12
Indexation: White List (level 3), Higher Attestation Commission List, RISC
Current Issue
Vol 49, No 12 (2023)
ТОКАМАКИ
Diagnostic Complex of the Globus-M2 Spherical Tokamak
Abstract
The diagnostic complex of the Globus-M2 spherical tokamak (R = 36 cm, a = 24 cm), the only
operating tokamak in Russia with a divertor plasma configuration, which operates in the range of subthermonuclear
temperatures (Te to 1.6 keV, Ti to 4.5 keV) and densities (ne to 2 × 1020 m–3), is described. The Globus-
M2 tokamak is the unique scientific facility, which is a part of the Federal Center for Collective Use of
the Ioffe Institute, Russian Academy of Sciences “Materials Science and Diagnostics in Advanced Technologies.”
This allows third parties to perform their research using it. The work contains a list of all diagnostics
currently available on the tokamak. The description of the diagnostics is structured in such a way that the
reader gets an idea of their capabilities for measuring plasma parameters with an emphasis on the limits and
accuracy of the measured values, and also spatial and time resolution. At the same time, many technical
details are omitted in order to save space; references are given to papers with a more detailed description of
individual diagnostics.
Divertor Thomson Scattering on Globus-M2
Abstract
We present the first Thomson scattering (TS) measurements of electron temperature and density
in the lower divertor of the Globus-M2 tokamak. The divertor TS diagnostics is designed for local measurements
of the Te(z, t) in the range of 1–100 eV and ne(z, t) in the range of m–3. Parameters of the
probing Nd:YAG laser are as follows 1064 nm/2 J/100 Hz/3 ns. The probing chord is launched vertically at
R = 24 cm and covers areas of the inner leg, vicinity of separatrix and private flux region. Along probing chord
of 110 mm, 9 spatial points were realized. Advanced filter polychromators were used to analyze Thomson
scattering spectra.
Synthetic Diagnostic of Spectra of Charge-Exchange Atoms for Analysis of Influence of the MHD Instability on Fast-Particle Confinement in Spherical Tokamaks Globus-M/M2
Abstract
Absorbed power of the neutral-injection beam in spherical tokamaks Globus-M/M2 is estimated
numerically. Deceleration of fast particles is simulated by means of the NUBEAM code. The signal of analyzer
of charge-exchange atoms is simulated by means of the FIDASIM code using the distribution function
of fast ions calculated by means of the NUBEAM code. Comparison of calculated and experimental signals
allowed determining the degree of influence of instabilities on confinement of fast particles along with
absorbed beam power.
Neutral Injection Complex for Globus-M2 Spherical Tokamak
Abstract
The injection complex that heats plasma of Globus-M2 spherical tokamak consists of two injectors
which supply high-energy beams of hydrogen (deuterium) atoms into the device’s plasma. Injectors are
autonomous and allow for preparing and setting up the device and measuring the parameters of the atomic
beam independently of the other injector and of the tokamak. The authors provide detailed analysis of each
injector’s configuration, substantiate their selection of the experiment layout for introducing beams into the
tokamak plasma, set forth characteristics of both injectors’ atomic beams injected into the tokamak plasma,
and discuss the results of experiments on additional heating of Globus-M2 tokamak plasma obtained by
injecting two atomic beams.
Plasma Stored Energy Analysis during Neutral Beam Injection in the Globus-M2 Tokamak Using the Pet Equilibrium Code and Diamagnetic Measurements
Abstract
The thermal energy stored in plasma Wp, normalized internal plasma inductance li and current
beta bi are calculated via the free-boundary equilibrium PET code. The equilibrium reconstruction algorithm
is iterative method of minimizing two parameters, the distance between the reconstructed plasma
boundary and that simulated by the PET code, as well as the difference between the plasma diamagnetic flux
from PET and the experimental one. The discharges from the Globus-M2 tokamak with a toroidal magnetic
field up to 0.9 T and a plasma current of 0.3–0.4 MA in a mode with auxiliary heating by two atomic injectors
are analyzed. The possibility of using approximate formulas for estimating and is considered. The measured
diamagnetic flux is used to determine bdia and then to calculate Wdia . The normalized internal plasma
inductance is additionally determined from the measured vertical magnetic field under the assumption that bp=bdia.
Heat Load onto the Globus-M2 Tokamak Wall due to Fast Ion Loss during Development of Toroidal Alfvén Eigenmodes
Abstract
The results of experiments are described, which were performed at the Globus-M2 tokamak and
aimed at studying the fast ion loss at the outer tokamak wall due to fast ions interaction with the toroidal
Alfvén eigenmodes. The local heating of carbon tiles was experimentally measured, and the corresponding
heat flux was calculated. It was shown how simulations of the lost particle orbits can explain the characteristic
features of the spatial map of wall heating. The flux of lost fast particles onto the wall was studied as a function
of the instability amplitude. It has been demonstrated that the simulations predict similar dependence of the
fast ion flux on the instability amplitude and also correlate its nature to the peculiarities of fast ions spatial
distribution.
First Experiments on Reduction the Heat Load on the Divertor Plates of the Globus-M2 Tokamak Using Nitrogen Seeding and Their Comparison with Simulation Results
Abstract
At the compact spherical Globus-M2 tokamak, a series of experiments was conducted to study the
effect of the injection of nitrogen on the discharge parameters. The experiments were carried out in discharges
in deuterium in the divertor configuration, and the auxiliary heating was performed by deuterium
neutral beam injection. During the nitrogen seeding, a substantial decrease in electron temperature near the
divertor was recorded as well as a sharp decrease of the heat flux onto the divertor plate, while the density and
temperature of the main plasma changed insignificantly. Simulations by the SOLPS-ITER showed a satisfactory
agreement with the experiment.
Features of Plasma Disruption in the Globus-M2 Spherical Tokamak
Abstract
Data on plasma disruption processes in the modernized Globus-M2 spherical tokamak are presented.
Electron temperature and density profiles before the disruption, immediately after thermal quench
and in the stage of plasma current quench are measured using the diagnostics of Thomson scattering of laser
radiation. The dependence of the plasma current decay time during disruption on the pre-disruption current
value is determined. The distribution of the toroidal current, which is induced during disruption, in the shell
of the vessel is determined on the basis of magnetic measurements. Electromagnetic loads on the vessel are
calculated.
Real-Time Plasma Magnetic Control System with Equilibrium Reconstruction Algorithm in the Feedback for the Globus-M2 Tokamak
Abstract
To control the plasma shape during a tokamak discharge, it is necessary to calculate the plasma
shape in real-time. The rate requirements for the shape calculations are especially high for tokamaks with a
small radius, such as Globus-M2 (St. Petersburg, Russia). A real-time magnetic plasma control system for
the Globus-M2 tokamak with flux and current distribution identification (FCDI) algorithm for the plasma
equilibrium reconstruction in feedback is presented. The control system contains discrete one-dimensional
and matrix proportional-integral-derivative controllers synthesized by the matrix inequality method using
the plasma LPV model calculated on experimental data, and carries out the coordinated control of the plasma
position and shape as well as the compensation for the scattered field of the central solenoid. The FCDI algorithm
is improved for the operation in the real-time mode, and makes it possible to reconstruct the plasma
shape in 20 μs. The digital control system with a feedback algorithm was simulated on a real-time test bench,
consisting of two Speedgoat Performance Real-Time Target Machines (RTTM), and demonstrated the average
Task Execution Time (TET) value in 67 μs.
Free-Boundary Plasma Equilibrium Computation in Spherical Globus-M2 Tokamak by Means of the pyGSS Code
Abstract
The pyGSS code constructed for computation of free-boundary plasma equilibrium in spherical
Globus-M2 tokamak is described. Currents in the coils of the electromagnetic system, their coordinates,
plasma current, positions of the limiter and current-conducting wall, etc., are used as the input parameters.
Free parameters determining spatial distribution of equilibrium pressure and current density are selected in
the course of code execution in such a way that the results of reconstruction would agree with the experimental
measurements of the poloidal magnetic flux by means of toroidally closed loops. The results of computation
of equilibrium are compared with those obtained by means of other codes and experimentally measured
thermal plasma energy, position of the separatrix outer leg, the diamagnetic-loop signal, etc.
Development of Next-Generation Spherical Tokamak Concept. The Globus-3 Tokamak
Abstract
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.