Pioneering experiments on atomic-beam-assisted generation of drag currents in the Globus-M spherical tokamak

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.     

Radial scanning diagnostics of bremsstrahlung and line emission in T-10 plasma

The paper describes the scanning spectroscopic diagnostics designed for measurement of line integrated plasma radiation in two visible spectral ranges. This diagnostic system is aimed at measuring the bremsstrahlung absolute values and profile with high spatial resolution. The bremsstrahlung absolute values are used to determine the value and radial distribution of effective plasma ion charge Z _eff(r) in T-10 discharges. The importance of Z _eff measurement is due to its strong influence on plasma heating, confinement, and stability. The spatial distribution of emission for one of the chosen spectral lines is measured simultaneously with bremsstrahlung. The spatial resolution of measurements is ~1 cm, and the temporal resolution is up to 10 ms. The spectral equipment and methods for its calibration are described. Examples of line integrated brightness distribution in a “continuum window” of 5236 ± 6 Å and brightness of the lines C⁵⁺ (5291 Å), He¹⁺ (4686 Å), and D_β (4861 Å) are given. Flattening of the bremsstrahlung brightness profile in the central region of the plasma column in some discharges with sawtooth oscillations in the T-10 is observed. The measured effective ion charge profiles in ohmic discharges with high plasma density and low discharge currents demonstrate accumulation of light impurities at the column axis; as a consequence, quenching of sawtooth oscillations in some discharges is observed. The developed diagnostics provides necessary data for investigation of heat, particle, and current transport in the plasma of the T-10. Successful application of the obtained data on Z _eff(r) for investigation of geodesic acoustic modes of plasma oscillations in the T-10 should be specially noted.     

On the Choice of Electron Cyclotron Heating Frequency for T-15MD Tokamak

Physics of Atomic Nuclei - Electron cyclotron heating is one of the methods of additional plasma heating and noninductive current drive in the T-15MD tokamak. One to eight gyrotrons with a total...     

EPR and photoluminescence spectra of smooth CD<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films from T-10 tokamak: The effect of iron impurity

The electron and spin structure of thick smooth hydrocarbon CD _x films (“flakes”) with a high relative deuterium concentration of x ~ 0.5, redeposited from deuterium plasma discharge onto the walls of the vacuum chamber of the T-10 tokamak and containing ~1 at % of 3d-metal impurities due to erosion of the chamber walls, are studied using electron paramagnetic resonance (EPR) and photoluminescence (PL). The resulting spectra are compared for the first time to the EPR and photoluminescence spectra of polymer (soft) a-C:H(D) films (H(D)/C ~ 0.5), which are considered model analogues of smooth CD _x films. A certain similarity of the CD _x films with a-C:H films was found in the electronic structure of the valence band. At the same time, the differences in the EPR and photoluminescence spectra were observed due to the presence of 3d-metal impurities in the CD _x samples, contributing to the conversion of sp ³ → sp ² in the formation of films in the tokamak and upon heating and thermal desorption. An impurity of, presumably, 3d metals was detected for the first time by EPR in the a-C:H films in an amount of approximately 0.2 ppm, related to the evaporation of graphite.     

COMPASS-D magnetic equilibria with lh and NBI current drive

Plasma equilibria are investigated numerically, using the ACCOME and ASTRA codes, on the COMPASS-D tokamak (R ₀ = 0:56 m, a = 0:17 m, B _T = 1:2 T, I _p = 200 kA, k = 1:7, δ_x = 0:4) for the planned Neutral Beam Injection (NBI) and Low Hybrid Current Drive (LHCD) systems. The LH system provides P _LH = 0:4 MW at n _∥ = 2:1 and f _LH = 1:3 GHz. The NBI system has two 40 keV deuterium beams in co-or counter-directions with a total power of 0.6 MW. The COMPASS-D tokamak can typically operate in two configurations-single null divertor (SND) and single null divertor with a higher triangularity (SNT). Higher triangularity provides access to higher confinement and improved stability, and leads to larger n _∥ up-shifts for better slow LH wave absorption.We investigate the range of densities n = 2 ÷ 6 × 10¹⁹ m^?3. Both the LH and NB driven currents decrease with density. The magnetic shear reverses with off-axis beam incidence. In the given plasma parameter range, typically up to 60 kA of bootstrap current is driven and with NB co-injection up to 80 kA of NB current is driven. LHCD is weak at f = 1:3 GHz and BT = 1:2 T, but at n = 3 × 10¹⁹ m^?3 the LH driven current is about 40 kA, so that the required plasma current of 200 kA is supported almost non-inductively.     

Cluster-Type Structure of Amorphous Smooth Hydrocarbon CD<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Films (<Emphasis Type="Italic">x</Emphasis> ~ 0.5) from T-10 Tokamak

Structure of smooth hydrocarbon CD _x films with a high deuterium ratio x ~ 0.5 redeposited from T-10 tokamak D-plasma discharges (NRC Kurchatov Institute, Moscow) has been studied. For the first time, small and wide angle X-ray scattering technique using synchrotron radiation and neutron diffraction have been employed. A fractal structure of CD _x films is found to consist of mass-fractals with rough border, surface fractals (with rough surface), plane scatterers and linear chains forming a branched and highly cross-linked 3D carbon network. The found fractals, including sp² clusters, are of typical size ~1.60 nm. They include a C₁₃ fragment consisting of three interconnected aromatic rings forming a minimal fractal sp² aggregate 9 × C₁₃. These graphene-like sp² clusters are interconnected and form a 3D lattice which can be alternatively interpreted as a highly defective graphene layer with a large concentration of vacancies. The unsaturated chemical bonds are filled with D, H atoms, linear sp² C=C, C=O, and sp³ structural elements like C-C, C-H(D), C-D_2,3, C-O, O-H, COOH, C _x D(H) _y found earlier from the infrared spectra of CD _x films, which are binding linear elements of a carbon network. The amorphous structure of CD _x films has been confirmed by the results of earlier fractal structure modeling, as well as by researches with X-ray photoelectron spectroscopy which allow finding a definite similarity with the electron structure of their model analogues — polymeric a-C:H and a-C:D films with a disordered carbon network consisting of atoms in sp³ + sp² states.     

Influence of Fuel Ratio in D–<Superscript>3</Superscript>He/ST Fusion Power Reactor

The effect of different fuel ratio f³ (the ratio between the ³He and D densities) on D–³He fusion reaction in spherical tokamak has been considered. By solving the zero dimensional particle and power equations numerically the temporal evolution plasma parameters such as the fusion power, synchrotron power and radiation power for different fuel ratios are calculated and compared to each others.     

Analysis of tokamak plasma confinement modes using the fast Fourier transformation

The Fourier analysis is a satisfactory technique for detecting plasma confinement modes in tokamaks. The confinement mode of tokamak plasma was analysed using the fast Fourier transformation (FFT). For this purpose, we used the data of Mirnov coils that is one of the identifying tools in the IR-T1 tokamak, with and without external field (electric biasing), and then compared it with each other. After the Fourier analysis of Mirnov coil data, the diagram of power spectrum density was depicted in different angles of Mirnov coils in the ‘presence of external field’ as well as in the ‘absence of external field’. The power spectrum density (PSD) interprets the manner of power distribution of a signal with frequency. In this article, the number of plasma modes and the safety factor q were obtained by using the mode number of q = m /n (m is the mode number). The maximum MHD activity was obtained in 30–35 kHz frequency, using the density of the energy spectrum. In addition, the number of different modes across 0–35 ms time was compared with each other in the presence and absence of the external field.     

Influence of molecular clustering on the interpretation of diffractograms of hydrocarbon films from tokamak T-10

The influence of molecular clustering on the formerly suggested interpretation of diffraction patterns of hydrocarbon films formed in the vacuum vessel of the tokamak T-10 is analyzed numerically. The simulation of clustering of simple hydrocarbon molecules C(D, H)₄, C₂(D, H)₄, and C₆(D, H)₆ and molecules composed of curved graphene (fullerenes and toroidal nanotubes) is carried out with the rigid body molecular dynamics method. It is shown that formerly neglected atomic correlations C–C and C–D(H) in the amorphous hydrocarbon component decrease the calculated values of the scattered intensity in the range of scattering vector modulus 5 < q < 20 nm^–1 because of homogenization of scatters on the spatial scale of ~1 nm. The allowance for these correlations does not change the diffraction patterns in the range q > 20 nm^–1. The results suggest the necessity to introduce to the procedure of determining the structural content of the films, similar to those from the tokamak T-10, the clusters formed by the van der Waals adhesion of hydrocarbon molecules to “graphene” nanoparticles. This simplifies the mathematical optimization to the former level of complexity—but for an extended ensemble of objects—and makes it possible to calculate the diffraction patterns of these objects using the distributed computing resources. A modified algorithm of structural content identification on the basis of joint X-ray and neutron diffractometry is suggested.     

Thermonuclear Power Engineering: 60 Years of Research. What Comes Next?

This paper summarizes results of more than half a century of research of high-temperature plasmas heated to a temperature of more than 100 million degrees (10⁴ eV) and magnetically insulated from the walls. The energy of light-element fusion сan be used for electric power generation or as a source of fissionable fuel production (development of a fusion neutron source—FNS). The main results of studies of tokamak plasmas which were obtained in the Soviet Union with the greatest degree of thermal plasma isolation among all other types of devices are presented. As a result, research programs of other countries were redirected to tokamaks. Later, on the basis of the analysis of numerous experiments, the international fusion community gradually came to an opinion that it is possible to build a tokamak (ITER) with Q > 1 (where Q is the ratio of the fusion power to the external power injected into the plasma). The ITER program objective is to achieve Q = 1–10 for a discharge time of up to 1000 s. The implementation of this goal does not solve the problem of a steadystate operation. The solution to this problem is a reliable first wall and current generation. This is a task of the next fusion power plant construction stage, called DEMO. Comparison of DEMO and FNS parameters shows that, at this development stage, the operating parameters and conditions of these devices are identical.     

On the verification of atomic data for <Emphasis Type="Italic">K</Emphasis><Subscript>α</Subscript> radiation spectra from the TEXTOR tokamak

High-resolution spectra from the Ar¹⁶⁺ and Ar¹⁵⁺ ions measured at the TEXTOR tokamak are used to verify atomic data necessary for simulation and diagnostics of a hot coronal plasma with an accuracy of about 5%. A self-consistent approach based on solving the inverse problem by the Bayesian iteration method in the framework of the proposed semiempirical “spectroscopic” model is used. The perturbation calculations of the atomic characteristics for [He] and [Li] argon ions by means of the ATOM and MZ codes require 10% correction of the ratios of the effective excitation rates for the intercombination line of the [He] ion and the group of dielectronic satellites corresponding to the 1s2p3l — 1s ²3l′ transitions in the [Li] ion to the resonance line of the [He] ion. The spectra calculated with this correction are in agreement with the measured spectra within the measurement accuracy ?10% in the wide ranges ～0.8–2.5 keV and ～10¹³–10¹⁴ cm^?3 of the central electron temperature and density, respectively. It is found that the central temperature value can be determined in the framework of the spectroscopic model with an accuracy of ～5%, and the abundances of the [Li] and [II] argon ions with respect to the [He] ions can be determined with an accuracy of ～20 and 50%, respectively. It has been shown that the use of the isothermal approximation when measuring the temperature from the ratio of the intensities of the dielectronic satellites to the resonance line can lead to a large error of ～20% in the presence of gradients typical for tokamak plasmas.     

X-ray spectroscopy diagnostics of a recombining plasma in laboratory astrophysics studies

The investigation of a recombining laser plasma is topical primarily because it can be used to simulate the interaction between plasma jets in astrophysical objects. It has been shown that the relative intensities of transitions of a resonance series of He-like multicharged ions can be used for the diagnostics of the recombining plasma. It has been found that the intensities of the indicated transitions for ions with the nuclear charge number Z _n ~ 10 are sensitive to the plasma density in the range N _e ~ 10¹⁶–10²⁰ cm^–3 at temperatures of 10–100 eV. The calculations performed for the F VIII ion have determined the parameters of plasma jets created at the ELFIE nanosecond laser facility (Ecole Polytechnique, France) in order to simulate astrophysical phenomena. The resulting universal calculation dependences can be used to diagnose different recombining plasmas containing helium-like fluorine ions.     

Calculation of<Emphasis Type="Italic">Z</Emphasis><Subscript>eff</Subscript> from plasma resistivity in IR-T1 tokamak

The effective ion charge,Z _eff, represents the average charge of ionsZ _i of gasses inside the system, which indicates the level of the impurities in the plasma. Several techniques have been applied to estimateZ _eff, like mass spectroscopy, anomaly factor and Bremsstrahlung radiation.

We estimatedZ _eff in the IR-T1 tokamak through anomaly factor. The IR-T1 tokamak is a small air-core transformer tokamak with circular cross section and with out conducting shell and divertor. Its aspect ratio is

$$\frac{R}{a} = \frac{{45 cm}}{{12.5 cm}}.$$

For a tokamak discharge of 30 kA plasma current and 1.5 V of loop voltage and by anomaly factor we observed thatZ _eff value is about 1.5.     

Converting heat to electricity by a graphene stripe with heavy chiral fermions

A conversion of thermal energy into electricity is considered in the electricallypolarized graphene stripes with zigzag edges where the heavy chiral fermion (HCF) statesare formed. The stripes are characterized by a high electric conductance G _e and by a significantSeebeck coefficient S. The electric current in the stripes is induced due toa non-equilibrium thermal injection of “hot” electrons. This thermoelectric generationprocess might be utilized for building of thermoelectric generators with an exceptionallyhigh figure of merit ZδT ?1 and with an appreciable electric power densities ~1 MW/cm².     

Ignition curves for deuterium/helium-3 fuel in spherical tokamak reactor

In this paper, ignition curve for deuterium /helium-3 fusion reaction is studied. Four fusion reactions are considered. Zero-dimensional model for the power balance equation has been used. The closed ignition curves for ρ=constant (ratio of particle to energy confinement time) have been derived. The results of our calculations show that ignited equilibria for deuterium /helium-3 fuel in a spherical tokamak is only possible for ρ= 5.5 and 6. Then, by using the energy confinement scaling and parameters of the spherical tokamak reactor, the plasma stability limits have been obtained in n_e, T plane and, to determine the thermal instability of plasma, the time-dependent transport equations have been solved.     

Hard antineutrino source based on a lithium blanket: A version for the accelerator target

The β^–-active ⁸Li isotope has a hard and well-defined antineutrino spectrum (E _ν ^max= 13.0 MeV, E _ν= 6.5 MeV) that ensures the reliable detection of the threshold reactions (ν _e, p) and (ν _e, d). An intense ν _e source is proposed within a scheme comprising an accelerator with a neutron-producing target and a lithium blanket. The density analysis of ⁸Li production in this blanket shows that the mass of highly pure ⁷Li can be reduced to 100–200 kg, as compared to ~19.5 t in the option with metallic ⁷Li, and the size of the source can be decreased by a factor of ~2.5, which is important for the proposed short-base experiments on the search for sterile neutrinos.     

Multiphoton SRS-Lasing in a Monoclinic β-BaYb<Subscript>2</Subscript>F<Subscript>8</Subscript> Crystal

The discovery of stimulated Raman scattering (SRS) in monoclinic fluoride β-BaYb₂F₈ known as a host matrix for Ln³⁺ lasant ions was reported. All the recorded spectral components of Stokes and anti-Stokes χ⁽³⁾-nonlinear picosecond generation were assigned to the three SRS-active photon A_g- and B_g-modes of a crystal (ω_SRS1 ~ 362 cm^–1, ω_SRS2 ~ 295 cm^–1, and ω_SRS3 ~ 230 cm^–1).     

Thermal quenching of luminescence of BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystals activated with Er<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> ions

Thermal quenching of interconfigurational 5d-4f luminescence of Er³⁺ and Tm³⁺ ions in BaY₂F₈ crystals is studied in the temperature range of 330–790 K. The quenching temperatures are ~575 and ~550 K for Er³⁺ and Tm³⁺, respectively. It is shown that quenching of 5d-4f luminescence of Tm³⁺ ions is caused by thermally stimulated ionization of 5d electrons to the conduction band.     

Anti-Stokes Luminescence in LiYF<Subscript>4</Subscript>:Ho<Superscript>3+</Superscript>, Yb<Superscript>3+</Superscript> Ceramics Excited at 1.93 μm

Conversion of IR radiation of a Tm:YAP laser with a wavelength of 1930 nm into visible light by ceramics of composition LiY_(1–x–y) Ho _x Yb _y , where х = 1–5 mol % and y = 0–15 mol %, is demonstrated. It is shown that the threshold power density of IR light visualization decreases with increasing concentration of Ho³⁺ ions, while additional doping of ceramic samples with Yb³⁺ ions changes the anti-Stokes luminescence spectrum. The threshold power density of visualization of the Tm:YAP laser radiation decreases with increasing concentration of holmium ions and is I_thr ≈ 0.8 W cm^–2 in the samples of composition LiYF₄:5%Ho³⁺–15%Yb³⁺.