Additional Plasma Heating Research Articles

Neutral Injection Complex for Globus-M2 Spherical Tokamak

The injection complex that heats plasma of Globus-M2 spherical tokamak consists of two injectorswhich supply high-energy beams of hydrogen (deuterium) atoms into the device’s plasma. Injectors areautonomous and allow for preparing and setting up the device and measuring the parameters of the atomicbeam independently of the other injector and of the tokamak. The authors provide detailed analysis of eachinjector’s configuration, substantiate their selection of the experiment layout for introducing beams into thetokamak 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 byinjecting two atomic beams.

Implications for Additional Plasma Heating Driving the Extreme-ultraviolet Late Phase of a Solar Flare with Microwave Imaging Spectroscopy

Extreme-ultraviolet late phase (ELP) refers to the second extreme-ultraviolet (EUV) radiation enhancement observed in certain solar flares, which usually occurs tens of minutes to several hours after the peak of soft X-ray emission. The coronal loop system that hosts the ELP emission is often different from the main flaring arcade, and the enhanced EUV emission therein may imply an additional heating process. However, the origin of the ELP remains rather unclear. Here we present the analysis of a C1.4 flare that features such an ELP, which is also observed in microwave wavelengths by the Expanded Owens Valley Solar Array. Similar to the case of the ELP, we find a gradual microwave enhancement that occurs about 3 minutes after the main impulsive phase microwave peaks. Radio sources coincide with both foot points of the ELP loops and spectral fits on the time-varying microwave spectra demonstrate a clear deviation of the electron distribution from the Maxwellian case, which could result from injected nonthermal electrons or nonuniform heating to the footpoint plasma. We further point out that the delayed microwave enhancement suggests the presence of an additional heating process, which could be responsible for the evaporation of heated plasma that fills the ELP loops, producing the prolonged ELP emission.

Propagation of dipole structure in an inhomogeneous-density plasma using two-dimensional particle-in-cell simulation

We have investigated the propagation of a magnetic dipole assuming a simple model of forward and return flow of fast electrons under a condition of plasma-density inhomogeneity by a particle-in-cell simulation. An exact propagating depiction of the dipolar structure is given under the framework of a simplified ‘electron magnetohydrodynamic’ fluid model (Yadav et al 2008 Phys. Plasmas 15 062308; Yadav et al 2009 Phys. Plasmas 16 040701; Yadav and Das 2010 Phys. Plasmas 17 052306) in a dense plasma. We reproduce this structure in our kinetic calculations. The results indicate that, with a steep plasma density gradient, the structure evolves rapidly toward plasma in a process involving shock formation and rapid dissipation of beam energy, which is consistent with the fluid simulations. In addition, new features are also reported, such as the pinching of the two dipole lobes to form a very strong shear layer, which develops into a Kelvin–Helmholtz instability. The magnetic energy is rapidly converted to kinetic energy of electrons leading to additional plasma heating in inhomogeneous regions, such as the core region in an imploded plasma.

H-mode plasmas in the pre-fusion power operation 1 phase of the ITER research plan

The optimum conditions for access to and sustainment of H-mode plasmas and their expected plasma parameters in the pre-fusion power operation 1 (PFPO-1) phase of the ITER research plan, where the additional plasma heating will be provided by 20 MW of electron cyclotron heating, are assessed in order to identify key open R&D issues. The assessment is performed on the basis of empirical and physics-based scalings derived from present experiments and integrated modelling of these plasmas including a range of first-principle transport models for the core plasma. The predictions of the integrated modelling of ITER H-mode plasmas are compared with ITER-relevant experiments carried out at JET (low-collisionality high-current H modes) and ASDEX Upgrade (significant electron heating) for both global H-mode properties and scale lengths of density and temperature profiles finding reasonable agreement. Specific integration issues of the PFPO-1 H-mode plasma scenarios are discussed taking into account the impact of the specificities of the ITER tokamak design (level of ripple, etc).

Current status of tokamak T-15MD

Abstract At the present time, the preparation to physical start-up of tokamak T-15MD is completed in the National Research Center “Kurchatov Institute”. The main parameters of T-15MD are: R = 1.48 m, a = 0.67 m, B = 2.0 T, Ipl = 2.0 MA. The magnet system is capable to maintain without overheating (more 60 °C) the plasma current of 2 MA for 4 s, 1 MA for 20 s, 700 kA for 40 s, 500 kA for 80 s, 300 kA for 160 s and 250 kA for 400 s. Plasma current drive can be maintained either by injection of fast neutrals or by electron cyclotron (EC)-, ion cyclotron (IC)- and low hybrid (LH) - waves. In August 2019 the electromagnetic system, consisting of TF and PF coils, together with vacuum vessel have been assembled in experimental hall. Power supply system of Tokamak T-15MD includes: two substations 110/10 kV, two substations 10/0.83 kV, thyristor convertors and different equipment. Total power consumption during the pulse with plasma current 2 MA and additional plasma heating of 20 MW will consist of 300 MVA. Power supply system is in the commissioning. Tokamak T-15MD will be operate using the information and control system. All the information and control system equipment, required for the implementation of physical start-up of tokamak T-15MD, is available. For plasma control the 250 different electromagnetic probes are installed inside vacuum vessel. The gyrotron with frequency 82.6 GHz and power of 1 MW will be used for pre-ionization.

Discharges with Reduced-Volume Plasma Filament in T-15 Upgrade Tokamak

The formation in the T-15 Upgrade tokamak of plasma filaments with a smaller volume than in the base discharge scenario, keeping the total plasma current constant, has been studied by numerical simulation. The purpose of such operating regimes is to raise the specific power of additional plasma heating. These regimes are of interest for attaining highest possible temperatures under limited additional heating power, e.g., for attaining AT (Advanced Tokamak) regimes. Additionally, these operating regimes can be investigated in the early stage of the T-15 Upgrade experiments when the total available heating power is low. Calculations with the Tokameq code have produced stationary equilibrium configurations for reduced plasma volume regimes. Three variants of plasma-volume reduction have been considered: displacing the plasma filament to the strong magnetic field region near the inner chamber wall while maintaining the filament center in the equatorial plane, and also displacing the plasma filament up or down. Numerical calculations have shown that such regimes may reduce the plasma-filament volume by a factor of 2 to 5, thus significantly raising the specific power of additional heating.

Explanation of Experimentally Observed Phenomena in Hot Tokamak Plasmas from the Nonequilibrium Thermodynamics Position.

In studying the hot plasma behavior in tokamak devices, the classical approach for collisional processes is traditionally used. This approach leaves unexplained a number of phenomena observed in experiments related to plasma energy confinement. Further, it is well known that tokamak plasma is always turbulent and self-organized. In the present paper, we show that the nonequilibrium thermodynamics approach allows us to explain many observed dependences and paradoxes; for example, puffing of impurities results in confinement improvement if zones of plasma cooling by impurities and additional plasma heating are not overlapped. The analysis of the experimental results shows the important role of radiation losses at the plasma edge in the processes determining its total energy confinement. It is shown that the generally accepted dependence of energy confinement on plasma density is not quite adequate because it is a consequence of dependence on radiation losses. The phenomenon of the appearance of internal transport barriers and magnetic islands can also be explained by plasma self-organization. The obtained results may be taken into account when calculating the operation of a future tokamak reactor.

Ignition threshold in cylindrical fast ignition targets

In this paper, the ignition stage of heavy ion driven fast ignition is evaluated numerically by using a quasi-1D model. Recently, the minimum value of the fuel areal density in cylindrical fast ignition was reported by Ramis and Meyer-ter-Vehn [Laser Part. Beams 32, 41–47(2014)]. Here, we intend to examine the impact of the initial fuel temperature on the ignition threshold. It is expected that the initial temperature and fuel areal density provide an acceptable practical framework to manage a successful ignition scenario. Assuming a precompressed DT fuel with temperature between 0.1 keV and 1.0 keV and the areal density ⟨ρr⟩DT ≥ 0.45 g/cm2, the minimum required ignition energy has been derived. It is found that as the ignition energies decrease, the burn wave propagation into the fuel layer is suppressed and the ignition condition becomes more sensitive to the initial fuel temperature. Moreover, at fixed fuel areal density, the ignition threshold energy reveals a weak dependence on the fuel radius smaller than rDT ≤ 40 μm. In order to attain the high energy gain, G > 30, the minimum ignition energy of 250 kJ corresponding to beam intensity higher than 1.6 × 1019 W/cm2 is recommended. While, in the burn strategy, fb ≥ 0.33, it has been found that the threshold ignition energy scales exponentially with the fuel radius, which becomes vivid for the critical areal density of ⟨ρr⟩crt= 0.45 g/cm2. Finally, it has been shown that the contribution of the released fast neutrons provides the additional plasma heating, which generally improves the burn stage.

Commissioning of vacuum pumping devices of the second KSTAR neutral beam injection system

The Korea Superconducting Tokamak Advanced Research (KSTAR) Neutral Beam Injection (NBI) system is designed to provide additional plasma heating and current drive for high performance and long pulse operation of the KSTAR tokamak using two co-current beam injection systems. Each neutral beam injection system is designed to consist of three ion sources, and each ion source is designed to deliver more than 2.0 MW of deuterium neutral beam power for the 100 keV beam energy. Consequently, the final goal of the KSTAR NBI system is to inject 12 MW of deuterium beam power for the long pulse operation of the KSTAR. The first NBI (NBI-1) has been installed since 2010, which provides a 100 keV deuterium neutral beam of 6.0 MW maximum using three ion sources.The second NBI (NBI-2) also consist with three ion sources which arranged vertically with tangency radius of 1.56 m to provide balanced core heating and off-axis current drive will be constructed until 2019. An ion source will be commissioned 2018 KSTAR campaign, and the other two ion source will be applied to KSTAR from 2019. As the vacuum condition can substantially affect the beam performance, the vacuum pumping system for NBI-2 has been carefully designed. The cryopumps for NBI-2 were designed and the overall vacuum pumping system of NBI-2 was installed including turbo pumps, mechanical booster-pumps, and dry-pumps. In this paper, the detailed engineering design, fabrication, and installation results of large condensation cryopumps and vacuum sub-components were explained. The effective pumping speed and pressure distribution will be evaluated through the commissioning of the vacuum pumping system for NBI-2. Finally, we present the operation procedures of the NBI-2 vacuum pumping system.

Impact of additional plasma heating on detached plasma formation in divertor simulation experiments using the GAMMA 10/PDX tandem mirror

The transition of a detached to attached plasma experiment has been performed in GAMMA 10/PDX by applying an additional plasma heating pulse of electron cyclotron heating (ECH). In a plasma detachment experiment, a short pulse (25 ms) of ECH was applied at the east plug-cell to examine the effects of electron heating on the plasma parameters in the D-module. It was found that the ion flux increased significantly during ECH injection. In the ECH injection period, the ion flux increased with the increasing impurity injection, which indicates the impurity ion components are enhanced by ionization in the D-module due to the application of ECH. During ECH injection period, the increase of the ion flux near the corner of the target plate shows a clear dependence on the gas species. The 2D visible emission has been captured by the high-speed camera and a bright emission near the corner of the target has been observed. The spectroscopic measurement in the D-module shows that the impurity ion emission increases remarkably during ECH injection. These results indicate the detached plasma change to the attached state.

Hole Production in High-Strength Steels by Plasma Incision and Reaming

Hole production in high-strength steels (in particular, manganese steels) by plasma incision and reaming is considered. Thermal conditions are identified for preliminary plasma incision of holes with subsequent reaming. Phase and structural transformations in the surface layer after plasma treatment greatly improve the efficiency of subsequent cutting. Additional plasma heating of the machined hole surface after plasma incision is proposed.

The Spectrum of Ion Cyclotron Emission from Neutral Beam Injection Heated Plasma on the TUMAN-3M Tokamak

Radiation at the ion cyclotron resonance frequencies in both the ohmic mode and the injection heating mode—ion cyclotron emission (ICE)—is observed on the TUMAN-3M tokamak (minor radius a = 0.25 m, major radius R0 = 0.5 m, toroidal field BT = 1 T, plasma current Ip ≤ 180 kA, and average plasma electron density ne ≤ 5 × 1019 m–3). Usually, the ICE is associated with the presence of high-energy ions in the plasma. Such ions may be products of a thermonuclear reaction or arise as a result of additional plasma heating, e.g., by means of electromagnetic waves or by injection of beams of high-energy atoms (neutral beam injection, NBI). The properties of the ICE in the TUMAN-3M tokamak in the NBI-heating mode and their possible connection with the features of fast ion trajectories and their energy spectrum are considered.

External resonance magnetic field control system based on the Siemens S7-400 controllers at the T-10 tokamak

A multilevel control system of a tokamak-reactor should provide measurements of the physical and technological plasma parameters in real time under conditions of high radiation fluxs. For the control systems of the ITER tokamak-reactor, it is planned to use automatic control systems based on the Siemens S7 programmable logic controllers (PLCs) which can operate under these conditions. Along with the possibility of multilevel remote control of the equipment, the PLC provides timely responses in emergency situations without human involvement and adaptive control in real time. This article presents results of using the Siemens S7 417-4 controllers for external resonant magnetic field control in the T-10 tokamak in the regimes with increased electromagnetic fields and radiation fluxs in shots with ohmic and additional microwave plasma heating.

DOUBLE code simulations of emissivities of fast neutrals for different plasma observation view-lines of neutral particle analyzers on the COMPASS tokamak

Neutral particle analyzers (NPA) measure line-integrated energy spectra of fast neutral atoms escaping the tokamak plasma, which are a product of charge-exchange (CX) collisions of plasma ions with background neutrals. They can observe variations in the ion temperature Ti of non-thermal fast ions created by additional plasma heating. However, the plasma column which a fast atom has to pass through must be sufficiently short in comparison with the fast atom’s mean-free-path. Tokamak COMPASS is currently equipped with one NPA installed at a tangential mid-plane port. This orientation is optimal for observing non-thermal fast ions. However, in this configuration the signal at energies useful for Ti derivation is lost in noise due to the too long fast atoms’ trajectories. Thus, a second NPA is planned to be connected for the purpose of measuring Ti. We analyzed different possible view-lines (perpendicular mid-plane, tangential mid-plane, and top view) for the second NPA using the DOUBLE Monte-Carlo code and compared the results with the performance of the present NPA with tangential orientation. The DOUBLE code provides fast-atoms’ emissivity functions along the NPA view-line. The position of the median of these emissivity functions is related to the location from where the measured signal originates. Further, we compared the difference between the real central Ti used as a DOUBLE code input and the TiCX derived from the exponential decay of simulated energy spectra. The advantages and disadvantages of each NPA location are discussed.

Спектр ионно-циклотронного излучения из плазмы токамака ТУМАН-3М при инжекционном нагреве

AbstractRadiation at the ion cyclotron resonance frequencies in both the ohmic mode and the injection heating mode—ion cyclotron emission (ICE)—is observed on the TUMAN-3M tokamak (minor radius a = 0.25 m, major radius R _0 = 0.5 m, toroidal field B _ T = 1 T, plasma current I _ p ≤ 180 kA, and average plasma electron density n _ e ≤ 5 × 10^19 m^–3). Usually, the ICE is associated with the presence of high-energy ions in the plasma. Such ions may be products of a thermonuclear reaction or arise as a result of additional plasma heating, e.g., by means of electromagnetic waves or by injection of beams of high-energy atoms (neutral beam injection, NBI). The properties of the ICE in the TUMAN-3M tokamak in the NBI-heating mode and their possible connection with the features of fast ion trajectories and their energy spectrum are considered.

Energy composition of high-energy neutral beams on the COMPASS tokamak

Abstract The COMPASS tokamak is equipped with two identical neutral beam injectors (NBI) for additional plasma heating. They provide a beam of deuterium atoms with a power of up to ~(2 × 300) kW. We show that the neutral beam is not monoenergetic but contains several energy components. An accurate knowledge of the neutral beam power in each individual energy component is essential for a detailed description of the beam- -plasma interaction and better understanding of the NBI heating processes in the COMPASS tokamak. This paper describes the determination of individual energy components in the neutral beam from intensities of the Doppler-shifted Dα lines, which are measured by a high-resolution spectrometer viewing the neutral beam-line at the exit of NBI. Furthermore, the divergence of beamlets escaping single aperture of the last accelerating grid is deduced from the width of the Doppler-shifted lines. Recently, one of the NBI systems was modified by the removal of the Faraday copper shield from the ion source. The comparison of the beam composition and the beamlet divergence before and after this modification is also presented.

Laser ablation coupled with DAPNe-NSI-MS applied to redacted documents

Laser ablation has been applied to redacted documents, where the text has been concealed by other ink. This technique strips the redacting ink revealing the text that was once redacted. Once removed, a nanomanipulation technique is used to extract the ink of the underlying text where mass spectrometry is then implemented to analyze its ink chemistry. In order to facilitate microscopy with direct analyte-probed nanoextraction coupled to nanospray ionization mass spectrometry (DAPNe-NSI-MS), laser ablation must be executed prior to ink extraction. Laser ablation has a nondestructive approach of stripping the ink used to redact the document. Not only does this reveal the text, it clears an area for DAPNe to directly extract ink, in miniscule amounts, from the document without inducing destruction. The redacting ink was concluded to affect the aging process of the concealed handwritten ink more than the printed text. The redacted handwritten sample obtained higher relative peak area (%) values than the control samples (text that was not redacted) and the control for the printed text produced higher amounts of low molecular weight products than the sample. Implementing laser ablation on these samples could also affect the chemical properties of the underlying ink due to the additional UV radiation and plasma heating. Results indicate by using laser ablation to remove the redacting ink, the relative peak area of the underlying ink deviates by 1.25%. The thermal degradation of binding agents such as polymethylene, polyethylene glycol, and diethylene glycol was monitored by calculating the relative peak area for five days which, in turn, tracks the oxidation process. The relative peak area values were also used to determine the chemical kinetics of polyethylene glycol, where degradation and polymerization occur.

Metallic targets ablation by laser plasma production in a vacuum

A model of metallic target ablation and metallic plasma production by laser irradiation is reported. The model considers laser energy absorption by the plasma, electron emission from hot targets and ion flux to the target from the plasma as well as an electric sheath produced at the target-plasma interface. The proposed approach takes into account that the plasma, partially shields the laser radiation from the target, and also converts absorbed laser energy to kinetic and potential energies of the charged plasma particles, which they transport not only through the ambient vacuum but also through the electrostatic sheath to the solid surface. Therefore additional plasma heating by the accelerated emitted electrons and target heating caused by bombardment of it by the accelerated ions are considered. A system of equations, including equations for solid heat conduction, plasma generation, and plasma expansion, is solved self-consistently. The results of calculations explain the measured dependencies of ablation yield (μ g/pulse) for Al, Ni, and Ti targets on laser fluence in range of (5–21)J/cm2 published previously by Torrisi et al.

Initial Plasma Formation in the GLAST-II Spherical Tokamak

This paper reports the initial plasma formation in glass spherical tokamak (GLAST-II) with electron cyclotron resonance pre-ionization assisted startup. Initially, a plasma current of 3 kA has been produced for duration of about 0.5 ms after establishing optimum conditions for microwave absorption at 2.45 GHz. Plasma current is then enhanced up to 5 kA by applying a small vertical magnetic field that provides additional plasma heating and shaping. Applied vertical field is optimized experimentally and optimal value is found to be 40 Gauss for this experiment. Plasma current and loop voltage are monitored by using Rogowski coil and toroidal loop of wire. A fast framing camera (5000 fps) is used for temporal investigation of plasma during the discharge scenario. A fast photodiode (BPX-65) and USB4000 spectrometer are used to record the signature of plasma current and the impurity content (O2, H etc.). Cross-sectional average electron temperature is also estimated from plasma resistivity and found to be 6.1 eV for maximum plasma current of 5 kA.

Important problems of future thermonuclear reactors*

Abstract This paper concerns important and difficult problems connected with a design and construction of thermonuclear reactors, which have to use nuclear fusion reactions of heavy isotopes of hydrogen, i.e., deuterium (D) and tritium (T). There are described conditions in which such reactions can occur, and different methods of a high-temperature plasma generation, i.e., high-current electrical discharges, intense microwave pulses, and injection of energetic neutral atoms (NBI). There are also presented experimental facilities which can contain hot plasma for an appropriate period, and particularly so-called tokamaks. The second part presents the technical problems which must be solved in order to build a thermonuclear reactor, that might be used for energetic purposes. There are considered problems connected with a choice of constructional materials for a vacuum chamber, its internal parts, external windings generating a magnetic field, and necessary shields. The next part considers the handling of radioactive tritium; the using of alpha particles (4He) for additional heating of plasma; recuperation of hydrogen isotopes absorbed in the tokamak internal parts, and a removal of a helium excess. There is presented a scheme of a future thermonuclear power plant and critical comments on a road map which should enable the construction of an industrial thermonuclear reactor (DEMO).