Thermonuclear Fusion Reactors Research Articles

Modeling of Iter Equatorial Neutron Diagnostics Equipment

In the course of a controllable thermonuclear fusion reaction the state of the plasma in the reactor must be monitored. Neutron diagnostics can provide some parameters of the plasma in the thermonuclear reactor. In the present work, the neutron diagnostics of the equatorial port of the ITER is checked by means of Monte Carlo modeling of seven external fast-neutron spectrometers based on solid stilbene scintillators distributed in the port with their collimators and the efficiency of the spectrometers is determined.

Rigorous Dynamic Simulation of Cryogenic Distillation of Hydrogen Isotopologues in the Fuel Cycle of a Thermonuclear Reactor Based on UV Flash

Operation of the fuel cycle of a thermonuclear fusion reactor naturally leads to accumulation of surplus protium, but in some cases it can also lead to accumulation of surplus deuterium. Both surplus protium and deuterium have to be separated, detritiated, and discharged to the environment, normally passing a final detritiation stage based on either the liquid phase catalytic exchange or water distillation process. The concept of a multicolumn cryogenic distillation (CD) system capable of discharging a time-varying surplus of deuterium is presented in this paper. A model of a CD column based on a UV (internal energy U – volume V) flash formulation and equation of state (EOS) thermodynamic model for hydrogen isotopologue mixtures is also presented at the principal step to a comprehensive model of the isotope separation system. Although fundamental for constant volume systems, the UV formulation of the thermodynamic state has not been widely used in transient simulations; in particular, for distillation dynamics modeling, other approaches are much more common. At the same time, in helium cryogenics the UV formulation has gained wide usage in large-scale dynamic simulations. It is known from the literature that a UV formulation of the distillation problem is very challenging for a numerically stable implementation. To cope with this situation, we present our findings on the sources of numerical instabilities and approaches.

Thermonuclear Fusion, as a Source of Seismic Phenomena?

The theory of Mr. Reid The elastic recoil, which interprets the origin of earthquakes as the emission of elastic deformation by the earth’s crust, does not allow us to describe in detail the mechanism and kinematics of the earthquake process. This applies not only to the description of the exotic of seismology in the form of frost-earthquakes but also to the classics of Elastic recoil associated with the movement of tectonic plates: seismic events at great depths, a swarm of tectonic and volcanic earthquakes. Do not fit into the framework of the theory of Elastic recoil and the phenomenon of mega earthquakes with their colossal release of energy. For example, the power of the Great Chilean earthquake of 1960 was equivalent to an explosion of 32 billion tons of TNT or 1.33 × 1020 J, which is comparable to the world electricity consumption in 2005 (5⋅1020 J). The energy of a nuclear bomb explosion over Hiroshima was ≈ 15 Kt TNT, which corresponds to the complete conversion of approximately 0.7 g of matter into energy: 15 Kt TNT = 63⋅1012 J, E = mc2, m = E / c2 = 63⋅1012 J. / (3⋅108 m / s) 2 = 0. 0007 kg. Accordingly, during the Great Chilean earthquake, 1477.77 kg of the matter was converted into energy! These gigantic figures clearly demonstrate the incomparability of the mechanical strength of terrestrial rocks with such an energy level! Consequently, the earthquake source does not have the physical ability to accumulate so much energy of elastic deformations and it is necessary to find the source of energy of earthquakes not associated with elastic deformations. In our opinion, such a force can be a force generated by chemical processes in the lithosphere. The ideological and practical basis of the article was the work of numerous groups of physicists and chemists in which the theoretical and experimental results were obtained in the leading laboratories of the world of condensed plasma [1], or the so-called Warm Dense Matter (WDM). The article presents a hypothesis based on the possibility of natural forces not only to form a condensed plasma in the depths of our planet but also through WDM to carry out thermonuclear fusion reactions — muon catalyzed melting (μCF) with the possibility of transition of the process into nuclear reactions “under the uranium blanket” and the process the formation of a catastrophic earthquake. Models of deep-focus, shallow-focus, and volcanic earthquakes are shown…

Deuterium Permeation Through Reduced Activation V-4Cr-4Ti Alloy and V-4Cr-4Ti Alloy with AlN/Al Coatings

Vanadium alloys are considered as candidate structural materials for thermonuclear fusion reactors (FR) and fast neutron reactors. Some properties of vanadium alloys are especially attractive for FR: fast decay of induced activity, durability in liquid lithium, high temperature strength. At the same time vanadium alloys absorb and dissolve hydrogen isotopes, and hydrogen fluxes through them are quite high. Hydrogen affects on plasticity of vanadium alloys and significantly decreases it at high concentrations. This should be taken into account considering the possibility of vanadium alloys usage as the material of fusion and fission reactors, especially if these materials are assumed to be in contact with radioactive tritium. In this work deuterium permeation through V-4Cr-4Ti alloy with deposited AlN coatings on an adhesion sublayer of Al on it was investigated. Deposition of insulating coatings on blanket structural materials allows to reduce the influence of strong magnetic fields of the tokamak on liquid metal coolant (e.g., lithium flow). It has been demonstrated that the coatings also reduce deuterium permeating fluxes by several times in comparison with V-4Cr-4Ti covered with natural oxide film and about 3–4 orders of magnitude in comparison with literature data for vanadium and its alloys with oxide-free surfaces. Taking into account thermomechanical and insulating properties, moderate swelling under neutron irradiation, thermal conductivity an order of magnitude higher than that of oxide coatings AlN coatings seem to be attractive for application in FR both as insulating and as a coating for hydrogen permeability suppression.

Growth of nanostructured highly porous surface on refractory metals under plasma treatment in the PLM device

Refractory metals are irradiated with powerful plasma in the PLM plasma device which is a linear magnetic trap with a 8-pole multicusp magnetic confinement. A feature of this device is the many hours stationary confinement, which is an advantage for testing materials of the divertor and wall of a thermonuclear fusion reactor and for the development of novel plasma technologies for metal processing. Helium plasma parameters were measured in the PLM by using the reciprocated Langmuir probe. Tungsten, titanium and molybdenum test plates were tested in stationary helium discharges in the PLM during 200 minutes. The thermal load on the surface of the test plates was more than 1 MW / m2. The temperature of the plates reached 1000 °C. Scanning electron microscopy analysis revealed a stochastic nanostructured surface with dimensions of structural elements less than 100 nm. Such materials are of interest for using in nuclear, chemical and biomedical technologies.

Simulation of Spectra Code (SOS) for ITER Active Beam Spectroscopy

The concept and structure of the Simulation of Spectra (SOS) code is described starting with an introduction to the physics background of the project and the development of a simulation tool enabling the modeling of charge-exchange recombination spectroscopy (CXRS) and associated passive background spectra observed in hot fusion plasmas. The generic structure of the code implies its general applicability to any fusion device, the development is indeed based on over two decades of spectroscopic observations and validation of derived plasma data. Four main types of active spectra are addressed in SOS. The first type represents thermal low-Z impurity ions and the associated spectral background. The second type of spectra represent slowing-down high energy ions created from either thermo-nuclear fusion reactions or ions from injected high energy neutral beams. Two other modules are dedicated to CXRS spectra representing bulk plasma ions (H+, D+, or T+) and beam emission spectroscopy (BES) or Motional Stark Effect (MSE) spectrum appearing in the same spectral range. The main part of the paper describes the physics background for the underlying emission processes: active and passive CXRS emission, continuum radiation, edge line emission, halo and plume effect, or finally the charge exchange (CX) cross-section effects on line shapes. The description is summarized by modeling the fast ions emissions, e.g., either of the α particles of the fusion reaction or of the beam ions itself.

Tritium Extraction From HCLL/WCLL/DCLL PbLi BBs of DEMO and HCLL TBS of ITER

The tritium balance in DEMO reactor is a key factor for the success of the production of energy from the thermonuclear fusion reactor. Three of the four breeder blankets (BBs) concepts candidates for DEMO used the eutectic Pb–16Li enriched at 90% in 6Li as breeder, the water-cooled lithium–lead, dual-coolant lithium–lead, and helium-cooled lithium–lead (HCLL) BBs; therefore, the design and characterization of the tritium extraction and removal system (TER) from PbLi with high efficiency are a critical issue in the European Roadmap. In ITER research reactor, a PbLi BB concept will be qualified, the HCLL BB. An HCLL test blanket module, PbLi loop, instrumentations, and auxiliary systems will be characterized with the support of European infrastructures. However, the tritium extraction unit from PbLi (TEU) selected and designed for ITER is based on the gas–liquid contactor technology, a reliable technology but with less than 40% efficiency. Instead, the candidates TER technologies for the lead–lithium loops of DEMO BBs, the permeator against vacuum (PAV) and vacuum sieve tray (VST), will not qualified in ITER, because these systems will not be fully mature by the start of the reactor. PAV and VST can theoretically achieve efficiency above 80%. The present works aim to analyze the technologies candidates for ITER and DEMO reactors, describe and compare TEU and TER design for each concept of BB and the integration of TER in DEMO tokamak building taking into account two design requirements: self-sufficient sustainable of fusion nuclear reactor and safety requirements.

Dependence of inertial confinement fusion ignition energy threshold on electron thermal conduction

In inertial confinement fusion, ignition conditions of the thermonuclear deuterium–tritium fusion reactions depend on the electron thermal heat conduction that affects the hot-spot mass accretion and energy balance. One-dimensional hydrodynamic calculations have been performed to simulate the implosion of a capsule directly irradiated by laser beams. For these calculations, the laser-capsule configuration has been scaled using homothetic transformations to scan the transition to ignition while keeping the implosion velocity constant. The electronic heat conduction has been modified by two alternative ways: (i) the classical Spitzer heat flux has been harmonically limited to the free streaming limit using a flux limit factor φ, and (ii) the classical Spitzer coefficient is reduced by a multiplicative factor α < 1. A change of the thermal conductivity affects the performances of the implosion and it can be beneficial or harmful. Parametric studies have been performed for both alternatives, looking for the kinetic energy threshold that generates a unitary energy gain as a function of parameters φ or α, respectively. These studies show how the energy threshold is modified by acting on the heat flux and that there is a minimum ignition energy that can be tuned by appropriately reducing the heat conduction. A simple qualitative model is developed to understand the relation between energy threshold and heat conduction.

Action of Shocks Generated in Solid Targets by Dense Plasma Focus Devices and at Pulsed Laser Irradiation

Shock waves actions upon materials perspective for using in future thermonuclear fusion reactors are investigated experimentally and by means of numerical modelling. The shocks are generated by powerful streams of plasma and fast ions in Dense Plasma Focus devices as well as by irradiation with a laser operating in a Q-spoiled mode. Power flux densities of these streams on the targets’ surfaces are in the range 1014 – 1016 W/m2. They are used for tests of the above materials, and their influences are compared for a number of substances. It is shown that in the above-mentioned identical conditions Plasma Foci generate shock waves with amplitudes of approximately two times higher than that for the laser case. Fronts of the shocks are formed here faster than at the laser irradiation. A simple analytical formula for calculations of the amplitudes of shock waves in radiation material science experiments provided with Dense Plasma Focus devices are advanced.

Fabrication and Characterization of Li&lt;sub&gt;4&lt;/sub&gt;SiO&lt;sub&gt;4&lt;/sub&gt; Ceramic Pebbles Doped with Y&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3 &lt;/sub&gt;and Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;

Tritium breeder blanket has been considered as one of the most important components of thermonuclear fusion reactor. Recently, Li4SiO4has been regarded as one of the favored ceramics breeders as it exhibits excellent tritium release properties. In order to further improve the comprehensive properties of Li4SiO4pebbles, the grain size and crush load of Li4SiO4pebbles doped with Y2O3and Nb2O5were systematically studied in this work. The results showed that the relative density of Li4SiO4pebbles was increased to 87.2% and the crush load was increased from 43N to 48N when Y2O3doping was used. In view of inhibiting grain growth and increasing the crush load and relative density of Li4SiO4pebbles, the effect of Nb2O5doping was better than that of Y2O3doping.

Radio-frequency current drive for thermonuclear fusion reactors

Principal research on energy from thermonuclear fusion uses Deuterium-Tritium plasmas magnetically trapped in toroidal devices. As major scientific problem for an economic (i.e., really feasible) reactor, we must understand how to lead strongly heated plasmas to sustain a high fusion gain while large fraction of current is self-produced via the presence of strong pressure gradient. To suppress turbulent eddies that impair thermal insulation and pressure tight of the plasma, current drive (CD) is necessary. However, tools envisaged so far in ITER (International Thermonuclear Experiment Rector) are unable accomplishing this task that requires efficiently and flexibly matching the natural current profiles of plasma. Consequently, viability of a thermonuclear reactor should be problematic. Multi-megawatt radio-frequency (RF) power coupled to plasma would produce the necessary CD, but modelling results based on previous understanding found difficult the extrapolation of this CD concept to reactor conditions of high temperature plasma, and greater flexibility of method would also be required. Here we present new model results based on standard quasilinear (QL) theory that allow establish conditions to drive efficiently and flexibly the RF-driven current at large radii of the plasma column, as necessary for the goal of a reactor.

Reaching to a featured formula to deduce the energy of the heaviest particles producing from the controlled thermonuclear fusion reactions

Thermonuclear fusion reaction plays an important role in developing and construction any power plant system. Studying the physical behavior for the possible mechanism governed energies released by the fusion products to precise understanding the related kinematics. In this work a theoretical formula controlled the general applied thermonuclear fusion reactions is achieved to calculating the fusion products energy depending upon the reactants physical properties and therefore, one can calculate other parameters governed a given reaction. By using this formula, the energy spectrum of 4He produced from T-3He fusion reaction has been sketched with respect to reaction angle and incident energy ranged from (0.08-0.6) MeV.

Li vaporization property of Li8ZrO6 and Li5AlO4 as tritium breeders

New tritium breeding materials that maintain large tritium breeding ratio for thermonuclear fusion reactors should be developed. In this study, we investigate the lithium-vaporization behavior from the sintered bodies of Li8ZrO6 and Li5AlO4 having high lithium atom densities. From the viewpoint of lithium density, we investigate the possibility of using the sintered compacts of Li8ZrO6 and Li5AlO4 as a tritium breeder. Lithium vaporization rates from the sintered bodies of Li8ZrO6 and Li5AlO4 are high. However, for both materials, the lithium vaporization rate gradually decreases with the annealing time by “self-stabilization” in which the surfaces of each sintered body are covered by the stable layer of the second phase. Considering the temperature dependency of equivalent vapor pressure and the volume fraction of tritium breeding material loaded at high-temperature region, it is suggested that the sintered compacts of Li8ZrO6 and Li5AlO4 have high potentials for the tritium breeder.

Investigation of material homogenisation on the nuclear heating estimates of the electron cyclotron-heating upper launcher blanket shield module

The electron cyclotron-heating upper launcher (ECHUL) will be installed in four upper ports of the ITER tokamak thermonuclear fusion reactor. Each ECHUL is able to deposit 8 MW power into the plasma for plasma mode stabilization via microwave beam lines. These beam lines and other components needed for the guidance of the microwaves are mounted into the upper port plug. In order to protect these components and to mitigate radiation leaving the reactor, several shield blocks are also included in the port plugs design. The ECHUL components which are closest to the fusion plasma are heated by the gamma and neutron radiation and therefore will need to be actively cooled. This paper reports on the influence of material homogenization by comparing results obtained in the neutronic analyses performed for the cooling system of the ECHUL blanket shield module (BSM). A small reduction in shielding performance of the BSM was found in the case of a heterogeneous description of the BSM compared to the standard approach of homogenizing the materials of the BSM by removing pipes and cooling circuits for the neutronic analyses.

Effects of fusion relevant transient energetic radiation, plasma and thermal load on PLANSEE double forged tungsten samples in a low-energy plasma focus device

Tungsten is the leading candidate for plasma facing component (PFC) material for thermonuclear fusion reactors and various efforts are ongoing to evaluate its performance or response to intense fusion relevant radiation, plasma and thermal loads. This paper investigates the effects of hot dense decaying pinch plasma, highly energetic deuterium ions and fusion neutrons generated in a low-energy (3.0 kJ) plasma focus device on the structure, morphology and hardness of the PLANSEE double forged tungsten (W) samples surfaces. The tungsten samples were provided by Forschungszentrum Juelich (FZJ), Germany via International Atomic Energy Agency, Vienna, Austria. Tungsten samples were irradiated using different number of plasma focus (PF) shots (1, 5 and 10) at a fixed axial distance of 5 cm from the anode top and also at various distances from the top of the anode (5, 7, 9 and 11 cm) using fixed number (5) of plasma focus shots. The virgin tungsten sample had bcc structure (α-W phase). After PF irradiation, the XRD analysis showed (i) the presence of low intensity new diffraction peak corresponding to β-W phase at (211) crystalline plane indicating the partial structural phase transition in some of the samples, (ii) partial amorphization, and (iii) vacancy defects formation and compressive stress in irradiated tungsten samples. Field emission scanning electron microscopy showed the distinctive changes to non-uniform surface with nanometer sized particles and particle agglomerates along with large surface cracks at higher number of irradiation shots. X-ray photoelectron spectroscopy analysis demonstrated the reduction in relative tungsten oxide content and the increase in metallic tungsten after irradiation. Hardness of irradiated samples initially increased for one shot exposure due to reduction in tungsten oxide phase, but then decreased with increasing number of shots due to increasing concentration of defects. It is demonstrated that the plasma focus device provides appropriate intense fusion relevant pulses for testing the structural, morphological and mechanical changes on irradiated tungsten samples.

Hydrogen is a Friend, or an Enemy, of the Environment?

Hydrogen is the best friend of man and the environment. Actually, it is the core element from that can extract energy, at infinity, in various forms. Until now has not been sufficiently exploited, but once with the evolution of the human species is the time to start to pool all types of energy which the hydrogen and its isotopes may donate them to us. Obviously the most abundant are nuclear energies which may be extracted from the hydrogen, either by well-known reaction of fission or through the much-desired fusion. In the reaction of a merger Deuterium-Tritium, for example, the energy required to overcome the Coulomb barrier is 0.1 MeV. Conversion between the energy and the temperature shows that the barrier of 0.1 MeV would be exceeded at a temperature of over 1.2 billion Kelvin degrees. According to the static calculations required a temperature of fusion to warm temperature is about 4 billion degrees. There is already an increase of almost four times than the latest calculations indicated by specialists. But calculating using radius determined dynamically, when the energy required is much higher, we come to a temperature necessary for the attainment of the thermonuclear fusion reaction of 40 trillion degrees, as for any 1 keV is needed about 10 million degrees temperature. Hot temperatures the merger being elusive, scientists have thought of achieving cold fusion.

Friction Factors in Fully Developed MHD Laminar Flows for Oblique Magnetic Fields and High Hartmann Numbers in Rectangular Channels

Self-cooled liquid metal blanket of a thermonuclear fusion reactor has the most critical issue of strong MHD effects which influence the thermal efficiency of the reactor. Special attention needs to be paid to the MHD friction factors for flow in rectangular channels at low as well as at high Hartmann numbers. The effect on MHD friction factors of a magnetic field oblique to the channel walls for various channel wall conductivities and aspect ratios at different Hartmann numbers is investigated numerically. Even for relatively small channel wall conductivity at high Hartmann numbers, velocity jets are developed near the channel walls. Due to these jets, MHD friction factors increase by the orders of magnitude which can be observed in the numerical results. The finite-difference method has been used to discretize the coupled second-order linear partial differential equations of MHD by using both uniform and nonuniform grids. Nonuniform discretization of the mesh is more efficient than the uniform mesh due to steep velocity gradients near the walls. For parallel plates, an analytical solution for MHD friction factor has been developed, and then compared with the numerical solutions. It is found that an oblique magnetic field has a significant effect on MHD friction factors for different channel wall conductivities and aspect ratios at various Hartmann numbers.

Design Features of the Neutral Particle Diagnostic System for the ITER Tokamak

The control of the deuterium–tritium (DT) fuel isotopic ratio has to ensure the best performance of the ITER thermonuclear fusion reactor. The diagnostic system described in this paper allows the measurement of this ratio analyzing the hydrogen isotope fluxes (performing neutral particle analysis (NPA)). The development and supply of the NPA diagnostics for ITER was delegated to the Russian Federation. The diagnostics is being developed at the Ioffe Institute. The system consists of two analyzers, viz., LENPA (Low Energy Neutral Particle Analyzer) with 10–200 keV energy range and HENPA (High Energy Neutral Particle Analyzer) with 0.1–4.0MeV energy range. Simultaneous operation of both analyzers in different energy ranges enables researchers to measure the DT fuel ratio both in the central burning plasma (thermonuclear burn zone) and at the edge as well. When developing the diagnostic complex, it was necessary to account for the impact of several factors: high levels of neutron and gamma radiation, the direct vacuum connection to the ITER vessel, implying high tritium containment, strict requirements on reliability of all units and mechanisms, and the limited space available for accommodation of the diagnostic hardware at the ITER tokamak. The paper describes the design of the diagnostic complex and the engineering solutions that make it possible to conduct measurements under tokamak reactor conditions. The proposed engineering solutions provide a safe—with respect to thermal and mechanical loads—common vacuum channel for hydrogen isotope atoms to pass to the analyzers; ensure efficient shielding of the analyzers from the ITER stray magnetic field (up to 1 kG); provide the remote control of the NPA diagnostic complex, in particular, connection/disconnection of the NPA vacuum beamline from the ITER vessel; meet the ITER radiation safety requirements; and ensure measurements of the fuel isotopic ratio under high levels of neutron and gamma radiation.

Preliminary study of a fast massive gas injection system for plasma disruption mitigation

In fusion experiments, and for future international thermonuclear experimental reactor-like fusion reactors, the mitigation of plasma disruptions is a key issue to reduce the severe damage that can be caused to the machine by high heat loads and runaway electrons. Pellet injection (PI) and massive gas injection (MGI) are present among the most promising candidate techniques to mitigate disruption effects. PI consists of injecting into the plasma solid cryogenic pellets, while MGI involves the injection of large amounts of different species of noble gases by means of a fast valve. In present day facilities, a suitable fast disruption mitigation valve (FDMV) typically must be able to deliver [Bozhenkov et al., Rev. Sci. Instrum. 78, 033503 (2007)] about 10 bar × l of a noble gas in 10 ms (although this figure depends on the plasma stored energy). An almost unique know-how has been developed in the Special Technologies Laboratory, at ENEA Frascati, concerning high-speed cryogenic pellet injectors based on two-stage pneumatic light-gas guns [Frattolillo et al., Rev. Sci. Instrum. 67, 1834 (1996).]. The possible use of the fast valve, integrated inside the first stage of the gun driver, as a FDMV, is proposed in this article. Preliminary laboratory tests, conducted using an existing device, demonstrate the considerable potential of this particular fast valve concept, which is actuated by a difference in pressure exerted on the opposite sides of the valve shutter. Although the equipment used in these preliminary laboratory tests was not specifically designed for this purpose, its performances (about 20 bar × l of He injected in the test volume in roughly 10.5 ms) are comparable with those of other FDMV concepts; moreover, it proved to be reliable, flexible, and repeatable, allowing an accurate control of the amount of gas released by the valve. The results of these exploratory experiments are reported and compared with other FDMV concepts.

ITER: A unique international collaboration to harness the power of the stars

Abstract Harnessing the energy of thermonuclear fusion reactions is one of the greatest challenges of our time. Fusion, the nuclear reaction that powers the Sun and stars would provide mankind with a safe, environmentally benign, and virtually limitless source of energy.