Controlled Thermonuclear Reactor Research Articles

Point-defect modulation of hydrogen migration in Pd−based membranes

Pure hydrogen is not only one of the key ingredients in chemistry industries, but also the future fuel sources for proton-exchange membrane fuel cells and especially controlled fusion reactors. Pd and Pd−based membranes are the only commercial products for H separation and purification, which are influenced by various point defects, including vacancies and substitutional atoms. In this work, the design rationale for H diffusion process in Pd−based membranes is elucidated by intentionally modulating the electronic interaction between vacancy and H. Adding (removing) one itinerant electron in the Pd-Vacancy system strengthens (weakens) the directional bonding between H and Pd, thus facilitating (impeding) H diffusion in Pd. Extra condition is supplemented to the Hume-Rothery rules for the design of solid-solution Pd−based membranes for faster H diffusion, that is a lower-electronegativity (χ) element accelerates H diffusion by providing extra bonding electrons, while a higher one has opposite effect. Solute elements Ag (χ = 1.93), Ir (2.20), and W (2.36) in Pd (2.20) are chosen to demonstrate our design principle in real Pd-based membranes. The good agreement between experimental and theoretical results confirms the effectiveness and soundness of this new rationale, and also sheds insights into the physical picture of the complex interaction between point defects.

Microstructural evolution of Ti2ZrHfV0.5Mo0.2 refractory multi-principal alloy under low-energy, high-flux He ion irradiation

The irradiation response of refractory multi-principal element alloys (RMPEAs) has gained increasing attention for the potential applications in future fusion devices. In controlled fusion reactors, plasma-facing materials have to suffer continuous low-energy high flux helium (He) ion irradiations. During high flux He irradiation, vacancy-interstitial pairs can be generated through trap mutation mechanism even without cascade collision. To simplify the model, Ti2ZrHfV0.5Mo0.2 RMPEA was irradiated with 50 eV He+ (less than the minimum He displacement energy of the alloy EdTi = 67 eV) under 1200 K to various fluences of 5 × 1024 - 1 × 1026 ions/m2, and the microstructural evolution was investigated. In the irradiated RMPEA, the intense sputtering of Ti, the growth and degradation of fuzz mainly composed of Zr, Hf elements on the surface, as well as the formation of V, Mo enriched band and high density large He cavities in the subsurface layer were observed. Although the sputtering threshold energy for He of V is similar to that of Ti (ETi = 24 eV, EV = 29 eV), V showed anomalous enrichment in the subsurface layer. Moreover, unlike the W fuzz growth process, the adatoms used to form fuzz in Ti2ZrHfV0.5Mo0.2 were derived from the Zr, Hf atoms diffusing through the vacancy-solute exchange mechanism, rather than from the atoms formed by the loop-punching mechanism. The anomalous enrichment of V atoms and the different fuzz growth mechanism were attributed to (i) different migration rates for different species of atoms in the alloy under vacancy diffusion mechanism and (ii) the formation of AB2 (A = Ti, Zr, Hf; B = V, Mo) phase blocking the continued formation of prismatic dislocation loops mainly composed of V and Mo.

A new array eddy current testing probe for inspection of small-diameter tubes in Tokamak fusion devices

Abstract Nuclear power plant (NPP) is the final goal of the research and developments on the controlled nuclear fusion technologies. Small-diameter tubes, such as the mono-block tubes in divertors, are widely used in Tokamak fusion reactors and other NPPs. To ensure safety of controlled fusion reactors, pre-service and in-service non-destructive testing (NDT) for small-diameter tubes are of great importance. In view of this background, this paper proposes a new array eddy current testing (ECT) probe of high efficiency and detectability aiming for NDT of the small-diameter tubes. The excitation unit of the probe contains large coils of spiral configuration, and the pick-up unit consists of four small pancake coils with rectangle arrangement. The detection signal is taken as the specific difference of the outputs of the pick-up coils. The unique coil arrangement and signal mode can significantly reduce the wobbling noise due to both the probe lift-off change and inclination. The validity and efficiency of the probe configuration are verified in this paper through numerical simulation and experiments. A hybrid FEM-BEM code of A-φ formulation is adopted in the ECT signal simulation, and experiments are conducted by using simplified probe for plate specimen and an array ECT instrument. Both the simulation and experimental results reveal that the configuration of new array ECT probe is capable to detect both axial and circumferential crack in either inside or outside surface of a small-diameter tube.

Vortex Method of Localization of Thermonuclear Plasma

An important task of world energy is to solve the problem of controlled thermonuclear fusion and the information presented in the article can be used in power engineering to create a controlled thermonuclear reactor. The method now used magnetic localization of plasma does not allow sustaining stable thermonuclear plasma in a closed chamber, and so another solution to the problem is necessary. In this paper, we propose an alternative dynamic approach of the stationary localization of plasma through centrifugal force. Localization of plasma as plasma whirlwind allows us to control the process of stable thermonuclear fusion.

Dependence of the gyrotron efficiency on the azimuthal index of non-symmetric modes

Development of MW-class gyrotrons for future controlled fusion reactors requires careful analysis of the stability of high efficiency operation in very high-order modes. In the present paper, this problem is analyzed in the framework of the non-stationary self-consistent theory of gyrotrons. Two approaches are used: the one based on the wave envelope representation of the resonator field and the second one based on representation of this field as a superposition of eigenmodes, whose fields are determined by a self-consistent set of equations. It is shown that at relatively low beam currents, when the maximum efficiency can be realized in the regime of soft self-excitation, the operation in the desired mode is stable even in the case of a very dense spectrum of competing modes. At higher currents, the maximum efficiency can be realized in the regimes with hard self-excitation; here the operation in the desired mode can be unstable because of the presence of some competing modes with low start currents. Two 170 GHz European gyrotrons for the international thermonuclear experimental reactor are considered as examples. In the first one, which is the 2 MW gyrotron with a coaxial resonator, the stability of operation in a chosen TE34,19-mode in the presence of two sideband modes with almost equidistant spectrum is analyzed and the region of magnetic fields in which the oscillations of the central mode are stable is determined. The operation of the second gyrotron, which is the 1 MW gyrotron with a cylindrical cavity currently under development in Europe, is studied by using the wave envelope approach. It is shown that high efficiency operation of this gyrotron in the TE32,9-mode should be stable.

Low-voltage gyrotrons

For a long time, the gyrotrons were primarily developed for electron cyclotron heating and current drive of plasmas in controlled fusion reactors where a multi-megawatt, quasi-continuous millimeter-wave power is required. In addition to this important application, there are other applications (and their number increases with time) which do not require a very high power level, but such issues as the ability to operate at low voltages and have compact devices are very important. For example, gyrotrons are of interest for a dynamic nuclear polarization, which improves the sensitivity of the nuclear magnetic resonance spectroscopy. In this paper, some issues important for operation of gyrotrons driven by low-voltage electron beams are analyzed. An emphasis is made on the efficiency of low-voltage gyrotron operation at the fundamental and higher cyclotron harmonics. These efficiencies calculated with the account for ohmic losses were, first, determined in the framework of the generalized gyrotron theory based on the cold-cavity approximation. Then, more accurate, self-consistent calculations for the fundamental and second harmonic low-voltage sub-THz gyrotron designs were carried out. Results of these calculations are presented and discussed. It is shown that operation of the fundamental and second harmonic gyrotrons with noticeable efficiencies is possible even at voltages as low as 5–10 kV. Even the third harmonic gyrotrons can operate at voltages about 15 kV, albeit with rather low efficiency (1%–2% in the submillimeter wavelength region).

Ceramics for fusion reactors: The role of the lithium orthosilicate as breeder

Lithium-based oxide ceramics are studied as breeder blanket materials for the controlled thermonuclear reactors (CTR). Lithium orthosilicate (Li 4 SiO 4 ) is one of the most promising candidates because of its lithium concentration (0.54 g/cm 3 ), its high melting temperature (1523 K) and its excellent tritium release behavior. It is reported that the diffusion of tritium is closely related to that of lithium, so it is possible to find an indirect measure of the trend of tritium studying the diffusivity of Li + . In the present work, the synthesis of the Li 4 SiO 4 is carried out by Spray drying followed by pyrolysis. The study of the Li + ion diffusion on the sintered bodies, is investigated by means of electrical conductivity measurements. The effect of the γ-ray irradiation is evaluated by the impedance spectroscopy method (EIS) from room temperature to 1173 K. The results indicate that the síntesis process employed can produce Li 4 SiO 4 in the form of pebbles, finally the best ion species for the electrical conduction is the Li + and is shown that the g-irradiation to a dose of 5MGy, facilitate its mobility through the creation of defects, without change in its conduction process.

Heat removal from the controlled thermonuclear reactor

Heat removal from the controlled thermonuclear reactor

Design of a GEM-based detector for the measurement of fast neutrons

A novel neutron detector has been developed and tested in collaboration between LNF-INFN and ENEA-Frascati. The aim is to obtain a versatile system that can be employed for the simultaneous measurement of the neutron flux in various energy bands from 1 to 20 MeV. The main drive for this development is the need of neutron detectors with low sensitivity to γ -rays and high count rate capability for operation in the neutron flux environment ~ 3 × 10 8 n / cm 2 s expected in future controlled thermonuclear fusion reactors. In these devices the fusion power is assessed through the measurement of the 2.5 and 14 MeV neutrons emitted by the plasma. A multilayer detector architecture, including a proton recoil converter, a proton absorber and a triple Gas Electron Multiplier (GEM), has been adopted. The detector read-out system consists of 128 pads ( 12.3 × 6 mm 2 ) in a 8 × 16 matrix. The work on the detector design and optimization carried out with the MCNPX code and the experimental tests at the Frascati Neutron Generator (FNG) on a detector prototype for 2.5 and 14 MeV measurements are presented.

Optimization for the tritium isotope separation factor and permeation by selecting temperature and thickness of the diffusion Pd–Ag alloy cathode

Large quantities of tritiated water will be produced in the controlled fusion reactors for power generation. To eliminate the concentrated tritiated water and for recycling tritium, an industrial electrolyzer was developed. The aim of this paper is to give the design of this electrolyzer and the results for optimization in diffusion and in isotopic exchange by selecting thickness of a thimble-shaped Pd–25%Ag cathode working at high temperature and current. In this process, the tritium recovery system is based on the principle of the tritium diffusion Pd–Ag cathode which produces very pure hydrogen isotopes from enriched tritiated water.

Experimental estimate of tritium production parameters for RF test blanket module

Tritium breeding ratio (TBR) is a most value among controlled fusion reactor parameters. One in targets of test blanket module (TBM) program is experimental investigation of the value. On the whole TBR can be submitted for consideration TBR = BTB/BTP (BTB: breaded tritium in blanket; BTP: burned tritium in plasma). To investigate a numerator of the formula a tritium production in breeding zone (TBZ) of the TBM has to be measured under ITER plasma experiments. Tritium and neutron monitoring system with some lithium and neutron sensors are proposed. Lithium ortho-silicate and lithium carbonate and the neutron detectors fit the task. Differences isotope lithum-6 and lithium-7 can be applied. For delivery/withdrawal of the detectors into/from the TBZ a pneumatic concept is suggested with using canals allocated in module. The canals pass through the module back wall and reach the attended area. These canals allow the insertion of activation foil and capsules with material probes during the dwell time or operational pauses. Casks for the detectors and the canal for conveying of the casks in the TBM before pulse and extraction after pulse are presented in this paper.

A kinetic stochastic model of blistering and nanofilm islands deposition: self-organization problem

First-order phase transition at a fluctuation stage into non-linear dissipative plasma-like media is considered. The clustering of new phase germs (or nucleation) is represented by stochastic Wiener processes. Brownian motion of clusters induced by a long-range potential of indirect (through acoustic phonons and Friedel's oscillation of electron density) interaction between one another is taken into account. Kinetic models for blistering materials in a controlled thermonuclear reactor and for melted metal thin film islands deposition during surface CVD modification are both put forward. The non-steady-state distribution of clusters versus their size and position in space is calculated using Ito–Stratonovich stochastic differential equations. Formation of radiation stimulated porosity layers in a lattice as well as liquid island chains on the surface are to be discussed as characteristics of phase transition at fluctuation stages as well as a new kind of self-organization phenomenon.

Azimuthal instability of radiation in gyrotrons with overmoded resonators

Stability of efficient operation at one of the high-order modes is of great importance for the development of megawatt-level gyrotrons intended for plasma experiments in controlled fusion reactors. Typically such gyrotrons operate at modes with large azimuthal indices, which form a rather dense spectrum of eigenfrequencies. Therefore, instead of considering interaction of electrons with a large number of such modes it is more convenient to analyze the spatial-temporal evolution of an envelope formed by a superposition of these modes with the electrons. In all previous studies of stability of such envelopes it was assumed that some kind of azimuthal nonuniformity is present in the initial condition for the wave envelope. However, the physical reason for this nonuniformity, which is apparently the nonuniformity of the electron emission, was not analyzed. In the present paper, the relation between the emission nonuniformity and resulting nonuniformity of the wave envelope is established. Then, results of numerical simulations are given, which demonstrate various changes in the gyrotron dynamics caused by the azimuthal instability of the wave envelope. These results allow one to determine the maximum azimuthal index of the operating mode and show that this maximum index can depend on the degree of azimuthal nonuniformity of the electron emission.

Coaxial Gyrotrons: Past, Present, and Future (Review)

Most of the present-day millimeter-wave gyrotrons developed for plasma experiments in controlled fusion reactors utilize cylindrical cavities operating in high-order modes. The choice of modes should obey certain restrictions dictated by the achievable mode selection and the maximum admissible level of the density of microwave ohmic losses in the cavity walls. Even with these restrictions, developers have successfully manufactured quasi-continuous-wave gyrotrons operating in the short millimeter wavelength bands that are capable of delivering microwave power on the order of 1 MW. To upgrade gyrotron power to the level of several megawatts, more complicated coaxial microwave circuits should be used. This statement is also valid for relativistic gyroklystrons, which are currently under development for driving future linear accelerators. This paper presents an overview of the history of the development of coaxial gyrodevices, a discussion of the physics-based issues which are the most important for their operation, a description of the state of the art in the development of coaxial gyrodevices for the above-mentioned applications, and a brief forecast for their future.

Activation of stainless steel with high energy neutrons

The development of the next generations of nuclear reactors (accelerator driven systems, ADS, or controlled fusion reactors) needs an important database of cross-sections for various nuclear reactions with high energy neutrons. At the cyclotron of Louvain-la-Neuve, a neutron beam has been developed on the base of a 9 Be (d,n) 10 B reaction. The energy spectrum of the neutron beam is centered on 20 MeV. By using this tool, the activation of iron, chromium and nickel sheets has been measured, and the cross-section of various reactions has been calculated. Some of those cross-sections were available in the literature, and the comparison with our results shows the effect of delayed nucleon emission. The evaluation of the production rate of various isotopes, as well as the energy and relative intensity of their transitions, is very important to evaluate the activation of most stainless steels.

The initial period in the history of nuclear fusion research at the Kurchatov Institute

The problem of controlled nuclear fusion (CNF) is a colossal scientific and technological challenge on a global scale; enormous teams of scientists in many countries are still trying to solve this problem. 50 years ago, on May 5, 1951, the USSR Council of Ministers Resolution enacted a governmental program, apparently the first in the world, ``On conducting research and experimental work to clarify the feasibility of building a magnetic thermonuclear reactor''. The three papers below briefly outline the history and sequence of events together with the evolution of ideas that led to the first governmental decisions to carry out the work that would clarify whether the creation of a controlled thermonuclear reactor was feasible, and also summarize the results of the first decades of research. DOI:10.1070/PU2001v044n08ABEH001068 The initial period in the history of nuclear fusion research at the Kurchatov Institute

Effect of the azimuthal inhomogeneity of electron emission on gyrotron operation

Gyrotrons are typically driven by electron beams produced by magnetron-type thermionic electron guns operating in the regime of temperature limited emission. Very often, the current density in such annular electron beams is azimuthally nonuniform. To describe the effect of this nonuniformity on gyrotron operation, the code MAGY [M. Botton et al., IEEE Trans. Plasma Sci. 26, 882 (1998)], which is widely used for modeling of slow and fast microwave sources, was properly modified. The results of numerical simulations demonstrate the effect of azimuthal inhomogeneity of the emission on the excitation of low- and high-frequency satellites of the operating mode and on the efficiency degradation. The calculations are done for parameters typical for megawatt-class, long-pulse, millimeter-wave gyrotrons, which are currently under development for electron cyclotron plasma heating and current drive experiments in controlled fusion reactors.

Tritium Recovery from Tritiated Water by Electrolysis

In addition to the tritiated water produced by the Commissariat à l’Energie Atomique, large quantities result from the development of controlled fusion reactors for power generation (International Thermonuclear Experimental Reactor). To obtain a new industrial method of reducing tritiated water, an electrolytic rather than a chemical process was developed. A prototype electrolyzer is described and the results obtained are given. In this process, the tritium recovery system is based on the principle of a gas diffusion Pd-Ag electrode incorporating a tritium charging cathode, which produces very pure hydrogen isotope gases. This is for converting 3H2O to high-purity 3H2 and its isotopes from tritiated water with >30 TBq/cm3 radioactivity (>50% 3H2O). The prototype module has been tested in a hot laboratory. The overall operating time exceeded 1500 h, and 6 g of gaseous tritium were produced without difficulty.

Irradiated steel properties degradation while hydrogenation and annealing alternation

Abstract Controlled thermonuclear reactor (CTR) will be subjected by the multi-factor in fluence including irradiation, hydrogenation, thermocycling etc.1-2. One of the most complex problem for candidate materials usage in CTR is the hydrogen–radiation defects interaction during operation. Structural materials embrittlement may affect the integrity of CTR construction and therefore it is one of the critical auestion of CTR safety. The above-mentioned factors are considered for their possible combined embrittlement effects. It was found that such treatment result in degradation of the steel; the mechanical properties thus obtained differ significantly from originally received.

Sustainable Development – On the Way to the Second Solar Civilization

Industrialized societies once embraced a vision of sustainable energy that called for fission breeder reactors, controlled fusion reactors, and futuristic concepts for energy transport. A more realistic and fundamentally more attractive vision calls for a portfolio of technologies relying primarily on indigenous and distributed sources rather than a single solution based on huge central energy generation complexes. Major ingredients in the new sustainable energy portfolio are the technologies known as “renewables”. Over the past twenty years several have quietly become “real”, both technically and economically. Wind turbines, central station solar thermal plants, solar photovoltaics, and biomass and urban waste fueled power plants are all now ready to compete with fossil fuel based systems, in spite of the market structures that still favor fuel based choices. Not only is their use expandable and sustainable, but there is still room for major improvement of these technologies, unlike the “leamed out” fossil and nuclear technologies we rely on now. A vision is nothing; its fulfillment is everything. We must make good choices now if we are to put in place the new sustainable infrastructures in time to avert the consequences of our current profligate and unsustainable resource use. Specifically, our energy policies must be informed by an overarching ethic that emphasizes stewardship versus ownership. Likewise, we must engage a relentless practice of energy efficiency involving informed decisions at every level of production, delivery and use. Cost-effective efficiency technologies not only mitigate environmental harm and strengthen regional economies, but they open the economic window for renewable sources as well. Further, we must carefully attend to business and economic issues, learning lessons from commercialization successes and failures, and tearing down barriers to renewables and efficiency that are imbedded in current markets. Government R&D priorities and risk sharing policies must also change, creating new structures for risk sharing in commercialization and market regulation, and a balance between funding for “efficiency technologies” and “supply technologies”.