Magnetic Plasma Confinement Research Articles

Development of HL-2M data integration and acquisition system for magnetic diagnostics

Magnetic measurement and diagnostics are critical for the operation of magnetic confinement experimental facilities and plasma analysis, while differential signals are mostly detected by a detector. For this, we have developed and designed a stable and reliable data integration system for HL-2M magnetic measurement and magnetic diagnostics. The system will be used for real-time control of HL-2M after the construction of HL-2M is completed. The system is built based on the PXI platform, and the software system is based on the LABVIEW platform. Key technologies realized by the system primarily include drift compensation, pulse data acquisition technology, multi-threading processing technology and transmission control communication protocol. Trials of the system were successfully carried out on HL-2A, and the results showed that the system could fully meet the construction needs of HL-2M.

Ablation of solid pellets induced by supra-thermal ions in the far scrape-off layer of DIII-D plasmas

Injection of solid pellets is a key element in several aspects of the operation of a magnetic confinement plasma reactor for fusion applications, including plasma fueling, control and diagnosis. This letter reports observations demonstrating that pellet ablation can begin outside the plasma boundary, by effect of supra-thermal ions, whose orbits, under appropriate conditions, can extend well into the vacuum region. The phenomenon was recorded during plasma discharges in the DIII-D tokamak, combining pulsed modulation of heating neutral beams, with high-frequency injection of sub-millimeter lithium pellets, and it is ascribed to the large fraction of trapped beam ions associated with counter current neutral beam injection. The effect was quantitatively evaluated by means of Monte-Carlo simulations of supra-thermal ion orbits, finding that the heat-deposition was of the order of 50–100 W mm−2, in the region traversed by the lithium pellets before reaching the plasma boundary, which is consistent with the severe pellet deterioration observed for low velocity pellets.

Recurrence Plots for Dynamic Analysis of Type-I ELMs at JET With a Carbon Wall

In this paper, the dynamic characteristics of type-I edge-localized modes (ELM) time series from the JET tokamak, the world’s largest magnetic confinement plasma physics experiment, have been investigated through recurrence plots (RPs). The analysis has been focused on RPs of pedestal temperature, line averaged electron density, and outer divertor $D_{ {\alpha }}$ time series during experiments with a carbon wall. The analysis of RPS shows the patterns similar to those characteristics of signals exhibiting type-2 intermittency, in particular, a characteristic kite-like shape; this gives useful hints to model the temperature signal as well as the $D_{ {\alpha }}$ radiation time series, with simple nonlinear maps capturing the nearly periodic behavior of type-I ELMs.

Generation of runaway electrons during the initial stage of the T-10 tokamak plasma discharge

The formation of runaway electron beams in the initial stage of discharge is one of the characteristic features of fusion facilities with magnetic plasma confinement, such as tokamaks. They are generated due to the presence of the high electric fields and strong plasma-wall interaction in plasma. The runaway electrons produced during the breakdown stage also remain in the plasma in the quasistationary stage of the discharge. Studies carried out at the T-10 tokamak show that the electron energy and the heat flux density can reach 5–10 MeV and 1–3 GW/m2, respectively. Thus, the interaction with electrons causes erosion and damage to the limiter surface. In this article, the energy distribution of high-energy electrons formed in the initial stage of plasma discharge in the T-10 tokamak during the formation of runaway electron beams in a strong longitudinal magnetic field was studied. The effect of the plasma density and MHD perturbations on the generation and acceleration of runaway electrons was revealed. The energy distributions of runaway electrons were estimated for different stages of the plasma discharge development.

XLV Zvenigorod International Conference on Plasma Physics and Controlled Fusion

IntroductionThis issue of Journal of Physics: Conference Series includes 32 articles submitted by the participants of the XLV International Zvenigorod Conference on Plasma Physics and Controlled Fusion (April 2-6, 2018). The conference is named after the town of Zvenigorod, Moscow region, where it has been annually held for 45 years. More than 600 scientists took part in the conference this year. These articles showcase a wide range of topical issues in the field of plasma physics that were discussed at the conference.Leading foreign scientists took part even in the first Zvenigorod conferences. They were invited by the conference organizers to give talks on the challenging problems of plasma physics. By now, the conference has truly become international. Several dozens of foreign scientists from the USA, Europe, and Japan take part in the conference annually. They represent about 30 leading research centers working in different fields of plasma physics.Nowadays, the conference has expanded to include a large number of topics. The conference schedule includes sessions on the magnetic confinement of high-temperature plasma, inertial fusion, processes in low-temperature plasma, physical principles of plasma and beam technologies, and topical issues of the ITER project. About 90 Russian research centers are usually represented at the conference. Among them are institutes of the Russian Academy of Sciences, research centers of Russian universities, institutes of the State Corporation ROSATOM, and other scientific organizations of the Russian Federation.The conference talks are selected by the Programming Committee comprised of leading Russian and foreign scientists.Leading scientists from around the world working in the field of plasma physics have become members of the International Advisory Board of the International Zvenigorod Conference on Plasma Physics and Controlled Fusion. The International Advisory Board is aimed to ensure and confirm the international status of the conference, which takes place in Russia.The full list of papers can be viewed on the conference website http://www.fpl.gpi.ru/Zvenigorod/XLV/Zven_XLV.html.The issue was edited by V.A. Ivanov, I.A. Grishina, and E.V. Voronova.

A new method of out-of-focus millimeter wave imaging in fusion plasma diagnostics using Bessel beams.

Electron cyclotron emission imaging (ECEI) and microwave imaging reflectometry diagnostics have been employed on a number of magnetic fusion plasma confinement devices. The common approach is based on a Gaussian beam assumption, which generates good spatial resolution (centimeter level). However, the radial focal depth is limited by the poloidal resolution, which is comparable with the Rayleigh length (∼150 mm). By contrast, a new Bessel beam approach has been developed and demonstrated to generate much longer focal depth with the property of propagation stability. To test the new approach, the DIII-D tokamak LCP ECEI optics have been re-designed to support a Bessel beam approach based on an axicon lens. The achievable radial coverage can exceed that of the current Gaussian approach by 3×. The imaging result is discussed in this paper based on the simulation analysis and laboratory testing result.

Magnetic field enhanced detection of heavy metals in soil using laser induced breakdown spectroscopy

A combination of magnetic field and Laser Induced Breakdown Spectroscopy (LIBS) has been used to improve the detection limit of heavy elements in different Soil samples. The plasma plume was generated by a focused Nd: YAG laser (532 nm) beam on the surface of soil samples in air and the emission spectra were registered in the presence and absence of an external magnetic field (0.3 T) using a set of four spectrometers. The magnetic field is applied transverse to the plasma plume. The emission intensity enhancement factor up to about 8 has been observed and the limit of detection (LOD) of Cr has been improved from 18.2 mg/kg to 7.7 mg/kg in the presence of magnetic field. The effects of magnetic field on the plasma parameters have been studied. The emission intensity enhancement is attributed to magnetic confinement of the laser-generated plasma. The spatial and temporal behavior reveals that the electron number density and electron temperature decreases nearly exponentially in the presence of magnetic field due to the deceleration of the plasma plume.

Detailed design of the RFX-mod2 machine load assembly

An upgrade of the RFX-mod experiment is presently in the final design phase, aimed at widening the explored operational scenarios both in RFP and Tokamak configuration. The main design driver for this machine upgrade is the enhancement of the ‘shell-plasma proximity’, which is expected to provide a significant improvement in the plasma magnetic confinement. The achievement of this aim implies a major change of the internal components of the machine such as the removal of the present vacuum vessel, transferring the function of vacuum barrier to the duly modified toroidal support structure, and the integration of a new in-vessel support system to sustain the conductive stabilizing shell and the whole first wall. The paper presents an overview of the design choices and the proposed implementations, assessed on the base of engineering analyses and results of experimental tests performed on mock-ups of the new components. The solutions conceived to fulfill vacuum and electrical requirements of the in-vessel components, to guarantee their reliability during normal and abnormal operating conditions events, and interface compatibility with existing components and torus assembly sequence are finally highlighted.

Features of the Damage and the Structural Changes in the Tungsten Surface Layer under the Pulsed Action of Laser Radiation, Ion and Plasma Fluxes

The degradation of a bilateral pressed tungsten surface layer by pulsed laser irradiation in the free-running mode (power density q = 105–5 × 106 W/cm2, pulse duration τ = 0.7 ms) and the Q-switched mode (q = 109–1010 W/cm2, τ = 80 ns) as well as under plasma beam irradiation in a plasma focus (PF) device (q = 108–1012 W/cm2, τ = 10–100 ns) has been investigated. The features of the degradation, erosion, and structural changes in the tungsten surface layer under different irradiation conditions have been determined. It has been shown that the use of PF devices in combination with laser equipment is promising for the simulation of the extreme radiation–thermal effects in materials that are typical of thermonuclear fusion devices with magnetic and inertial plasma confinement.

Comparative analysis of damageability produced by powerful pulsed ion/plasma streams and laser radiation on the plasma-facing W samples

Parallel use of directed plasma/fast ion streams from Dense Plasma Focus and of laser radiation (in a free running and Q-switched modes) for irradiations of targets looks perspective for tests of materials designed to withstand extreme thermal loads in the mainstream fusion reactors with inertial and magnetic plasma confinement. It is so because of a wide range of power flux densities and pulse durations generated by them. Tungsten is counted as the most appropriate material for the plasma-facing components. Main features of degradation of the surface layer of double forged tungsten were determined at different conditions of its irradiation by these streams. Chief similarities and differences in damageability obtained in the regimes are fixed – blisters, craters, porosity, microcracks, and discontinuity flaws etc. – that are peculiar characteristics for each mode of irradiation. The observed resemblances and dissimilarities that are specific for each regime of irradiation are explained with the help of numerical modelling of the treatment processes. It is shown that a so-called Integral Damage Factor may be used only in restricted ranges of parameters of an irradiation. It was found that in the regime of irradiation with the well-developed gas dynamic motion of secondary plasma the overall energy of radiation will be spent preferentially either on mass removal from the material's surface or on heating of a small amount of matter to high temperature (and consequently into its fast movement) depending on power flux density of radiation and its pulse structure.

A Waveguide Antenna with an Extended Angular Range for Remote Steering of Wave-Beam Direction

A new method for increasing the angular range of a waveguide antenna for remote steering of the wave-beam direction in thermonuclear-fusion experimental setups with plasma magnetic confinement is proposed. Characteristics for large beam inclination angles can be improved using the synthesized nonuniform waveguide profile. For small angles, the characteristics remain invariable, the waveguide profile differs only slightly from the regular shape, and can be fit to limited waveguide-channel sizes.

Exact Solutions to Several Nonlinear Cases of Generalized Grad–Shafranov Equation for Ideal Magnetohydrodynamic Flows in Axisymmetric Domain

Abstract In this paper, the steady-state equations of ideal magnetohydrodynamic incompressible flows in axisymmetric domains are investigated. These flows are governed by a second-order elliptic partial differential equation as a type of generalized Grad–Shafranov equation. The problem of finding exact equilibria to the full governing equations in the presence of incompressible mass flows is considered. Two different types of constraints on position variables are presented to construct exact solution classes for several nonlinear cases of the governing equations. Some of the obtained results are checked for their applications to magnetic confinement plasma. Besides, they cover many previous configurations and include new considerations about the nonlinearity of magnetic flux stream variables.

Control and data acquisition software upgrade for JET gamma-ray diagnostics

The Joint European Torus (JET), the largest magnetic confinement plasma physics experiment in operation, has a large amount of key diagnostics for physics exploration and machine operation, which include several Gamma-Ray Diagnostics. The Gamma-Ray Spectrometer (GRS), Gamma Camera (GC) and Gamma-Ray Spectrometer Upgrade (GSU) diagnostics have similar Control and Data Acquisition Systems (CDAQ) based on the Advanced Telecommunication Computing Architecture standard, featuring Field Programmable Gate Arrays for data processing and management.During past JET-EP2 enhancements, the GRS and GC diagnostics were successfully installed and commissioned. However, the installed CDAQ software that interfaces these diagnostics to JET Control and Data Acquisition System is different, requiring higher maintenance costs.Benefiting from the Gamma Camera Upgrade (GCU) and new GSU installation and commissioning, the upgrading of the software and controller hardware used in the GRS and GC was evaluated, aiming at software standardization between all three diagnostics for easier maintenance.This paper describes the software standardization process between the diagnostics towards the usage of the same CDAQ software as well as the same Operating System (OS) for the controllers, which allows the operator to minimize the maintenance time, avoiding the need for system specific expertise. The rationale behind the choice of MARTe framework as CDAQ software and Scientific Linux as OS will also be presented.

Plasma expulsion may protect objects within magnetic plasma confinement devices

Computer simulations show how magnetic plasma expulsion might enable researchers to reduce losses and potentially insert instruments into a plasma without significantly affecting plasma properties.

Magnetic plasma expulsion

Magnetic confinement of plasmas is widely studied for restricting a plasma's extent to a given region. Presented here is one scheme for what is referred to as magnetic plasma expulsion, which would prevent the plasma from entering a given region. Magnetic plasma expulsion techniques may allow instrumentation access to the interiors of plasmas. Magnetic plasma expulsion techniques may also make alternative approaches for magnetic plasma confinement possible. Particle-in-cell simulation with the Warp code is used to study magnetic plasma expulsion. Some conditions for achieving magnetic plasma expulsion are reported.

Волноводная антенна с расширенным угловым диапазоном для дистанционного управления направлением волнового пучка

AbstractA new method for increasing the angular range of a waveguide antenna for remote steering of the wave-beam direction in thermonuclear-fusion experimental setups with plasma magnetic confinement is proposed. Characteristics for large beam inclination angles can be improved using the synthesized nonuniform waveguide profile. For small angles, the characteristics remain invariable, the waveguide profile differs only slightly from the regular shape, and can be fit to limited waveguide-channel sizes.

Nonlinear dynamic analysis of Dα signals for type I edge localized modes characterization on JET with a carbon wall

In this paper, the dynamic characteristics of type-I ELM time-series from the JET tokamak, the world’s largest magnetic confinement plasma physics experiment, have been investigated. The dynamic analysis has been focused on the detection of nonlinear structure in Dα radiation time series. Firstly, the method of surrogate data has been applied to evaluate the statistical significance of the null hypothesis of static nonlinear distortion of an underlying Gaussian linear process. Several nonlinear statistics have been evaluated, such us the time delayed mutual information, the correlation dimension and the maximal Lyapunov exponent. The obtained results allow us to reject the null hypothesis, giving evidence of underlying nonlinear dynamics. Moreover, no evidence of low-dimensional chaos has been found; indeed, the analysed time series are better characterized by the power law sensitivity to initial conditions which can suggest a motion at the ‘edge of chaos’, at the border between chaotic and regular non-chaotic dynamics. This uncertainty makes it necessary to further investigate about the nature of the nonlinear dynamics. For this purpose, a second surrogate test to distinguish chaotic orbits from pseudo-periodic orbits has been applied. In this case, we cannot reject the null hypothesis which means that the ELM time series is possibly pseudo-periodic. In order to reproduce pseudo-periodic dynamical properties, a periodic state-of-the-art model, proposed to reproduce the ELM cycle, has been corrupted by a dynamical noise, obtaining time series qualitatively in agreement with experimental time series.

XLIV Zvenigorod International Conference on Plasma Physics and Controlled Fusion (ICPAF2017)

IntroductionThis issue of Journal of Physics: Conference Series includes 28 articles submitted by the participants of the XLIV International Zvenigorod Conference on Plasma Physics and Controlled Fusion (February 13-17, 2017). The conference is named after the town of Zvenigorod, Moscow region, where it has been annually held for 44 years. More than 600 scientists took part in the conference this year. These articles showcase a wide range of topical issues in the field of plasma physics that were discussed at the conference.Leading foreign scientists took part even in the first Zvenigorod conferences. They were invited by the conference organizers to give talks on the challenging problems of plasma physics. By now, the conference has truly become international. Several dozens of foreign scientists from the USA, Europe, and Japan take part in the conference annually. They represent about 30 leading research centers working in different fields of plasma physics.Nowadays, the conference has expanded to include a large number of topics. The conference schedule includes sessions on magnetic confinement of high-temperature plasma, inertial fusion, processes in low-temperature plasma, physical principles of plasma and beam technologies, and topical issues of the ITER project. About 90 Russian research centers are usually represented at the conference. Among them are institutes of the Russian Academy of Sciences, research centers of Russian universities, institutes of the State Corporation ROSATOM, and other scientific organizations of the Russian Federation.The conference talks are selected by the Programming Committee comprised of leading Russian and foreign scientists.Leading scientists from around the world working in the field of plasma physics have become members of the International Advisory Board of the International Zvenigorod Conference on Plasma Physics and Controlled Fusion. The International Advisory Board is aimed to ensure and confirm the international status of the conference, which takes place in Russia.The full list of papers can be viewed on the conference website http://www.fpl.gpi.ru/Zvenigorod/XLIV/Zven_XLIV_e.html.The issue was edited by V.A. Ivanov, I.A. Grishina, and E.V. Voronova.

Optical emission spectroscopy of magnetically confined laser induced vanadium pentoxide (V2O5) plasma

Optical emission spectra of a laser induced plasma of vanadium pentoxide (V2O5) using a Nd:YAG laser (1064 nm, 10 ns) in the presence and absence of the magnetic field of 0.45 T have been investigated. The effect of the magnetic field (B) on the V2O5 plasma at various laser irradiances ranging from 0.64 GW cm−2 to 2.56 GW cm−2 is investigated while keeping the pressure of environmental gases of Ar and Ne constant at 100 Torr. The magnetic field effect on plasma parameters of V2O5 is also explored at different delay times ranging from 0 μs to 10 μs for both environmental gases of Ar and Ne at the laser irradiance of 1.28 GW cm−2. It is revealed that both the emission intensity and electron temperature of the vanadium pentoxide plasma initially increase with increasing irradiance due to the enhanced energy deposition and mass ablation rate. After achieving a certain maximum, both exhibit a decreasing trend or saturation which is attributable to the plasma shielding effect. However, the electron density shows a decreasing trend with increasing laser irradiance. This trend remains the same for both cases, i.e., in the presence and in the absence of magnetic field and for both background gases of Ar and Ne. However, it is revealed that both the electron temperature and electron density of the V2O5 plasma are significantly enhanced in the presence of the magnetic field for both environments at all laser irradiances and delay times, and more pronounced effects are observed at higher irradiances. The enhancement in plasma parameters is attributed to the confinement as well as Joule heating effects caused by magnetic field employment. The confinement of the plasma is also confirmed by the analytically calculated value of magnetic pressure β, which is smaller than plasma pressure at all irradiances and delay times, and therefore confirms the validity of magnetic confinement of the V2O5 plasma.

Topological bifurcations in the evolution of coherent structures in a convection model

Blob filaments are coherent structures in a turbulent plasma flow. Understanding the evolution of these structures is important to improve magnetic plasma confinement. Three state variables describe blob filaments in a plasma convection model. A dynamical systems approach analyzes the evolution of these three variables. A critical point of a variable defines a feature point for a region where that variable is significant. For a range of Rayleigh and Prandtl numbers, the bifurcations of the critical points of the three variables are investigated with time as the primary bifurcation parameter. Bifurcation curves separate the parameter planes into regions with different critical point configurations for the state variables. For Prandtl number equal to 1, the number of critical points of each state variable increases with increasing Rayleigh number. For Rayleigh number equal to 104, the number of critical points is the greatest for Prandtl numbers of magnitude 100.