Future International Thermonuclear Experimental Reactor Research Articles

Study of mechanisms of crack formation on tungsten composites using the three-point method

The aim of this study was evaluated the ductile-to-brittle transition temperature (DBTT) and microstructure of miniaturized tungsten composites by three point bending method. Tungsten and tungsten composites are the best technical materials candidates for the manufacture of a diverter in the future fusion reactor ITER (International Thermonuclear Experimental Reactor). Because tungsten has the highest melting point off all metals, it is candidate for plasma-facing materials. The ITER plasma temperatures to between 150 and 300 million °C, so it is important to study the effect of temperature on materials. The effect of temperature on the mechanical properties of tungsten composites was studied by performing a number of three point bending tests at different temperatures (100-600 С). Three different types of materials were assessed: first one – IGP commercial pure tungsten (W > 99,97%), grades produced according to International Thermonuclear Experimental Reactor specifications in Europe and China and two laboratory types W - 0.5%ZnC, W - 2%Y2O3. The resulting DBTT ranges depending on the type of material, grain orientation affects and rolled. The IGP and W - 0.5%ZnC were rolled and tested in two different orientations of grains (L and T): WZC_L, WZC_T, IGP_L, IGP_T. It is shown that the temperature transition from brittle to plastic fracture occurs sharply for composites WZC_L (120-180 ° C) and IGP_L (160-180 ° C), slower for WZC_T (260-380 ° C) and (350-500 °C). The yield stress decrease linearly with temperature. The materials tested in the L- orientation of the grains have a higher elasticity and better strength characteristics. There are two types of fracture researched in work. After the crack has initiated in a metal it grows through the grains, which is called transgranular fracture (WZC_L, WZC_T, IGP_L, IGP_T), or along the grain boundaries, known as intergranular fracture (W-YO), or by a combination of transgranular and intergranular fracture (WZC_L, WZC_T, IGP_T).

Nonlinear Cone Model for Investigation of Runaway Electron Synchrotron Radiation Spot Shape

The runaway electron event is the fundamental physical phenomenon and tokamak is the most advanced conception of the plasma magnetic confinement. The energy of disruption generated runaway electrons can reach as high as tens of mega-electron-volt and they can cause a catastrophic damage of plasma-facing-component surfaces in large tokamaks and International Thermonuclear Experimental Reactor (ITER). Due to its importance, this phenomenon is being actively studied both theoretically and experimentally in leading thermonuclear fusion centers. Thus, effective monitoring of the runaway electrons is an important task. The synchrotron radiation diagnostic allows direct observation of such runaway electrons and an analysis of their parameters and promotes the safety operation of present-day large tokamaks and future ITER. In 1990 such diagnostic had demonstrated its effectiveness on the TEXTOR (Tokamak Experiment for Technology Oriented Research, Germany) tokamak for investigation of runaway electrons beam size, position, number, and maximum energy. Now this diagnostic is installed practically on all the present-day’s tokamaks. The parameter v┴/|v||| strongly influences on the runaway electron synchrotron radiation behavior (v|| is the longitudinal velocity, v┴ is the transverse velocity with respect to the magnetic field B). The paper is devoted to the theoretical investigation of runaway electron synchrotron radiation spot shape when this parameter is not small that corresponds to present-day tokamak experiments. The features of the relativistic electron motion in a tokamak are taken into account. The influence of the detector position on runaway electron synchrotron radiation data is discussed. Analysis carried out in the frame of the nonlinear cone model. In this model, the ultrarelativistic electrons emit radiation in the direction of their velocity v→ and the velocity vector runs along the surface of a cone whose axis is parallel to the magnetic field B. The case of the small parameter v┴/|v||| (v┴/|v|||<<1, linear cone model) was considered in the paper: Plasma Phys. Rep. 22, 535 (1996) and these theoretical results are used for experimental data analysis.

TRIPOLI-4 simulation of the FNG copper benchmark experiment and the tritium production in the lithium diamond detector for ITER-TBM

Abstract For the future ITER (International Thermonuclear Experimental Reactor) operation needs, several D–T fusion neutron experiments have been conducted at FNG (Frascati Neutron Generator) facility. These FNG experimental results are useful to validate neutron transport codes and nuclear data libraries. The TRIPOLI-4 Monte-Carlo radiation transport code has been widely used on radiation shielding, criticality safety and fission reactor physics fields to support nuclear energy research and industrial applications. With the growing interest in using the TRIPOLI-4 code for ITER applications, a key issue that arises is whether or not the released TRIPOLI-4 code and its associated nuclear data libraries are verified and validated for the 14 MeV fusion neutronics calculations. Copper is a key material used in different components of ITER tokamak machine and the FNG copper benchmark experiment funded by F4E (Fusion for Energy) was recently introduced into the OECD/NEA SINBAD database. In the first part of this work, TRIPOLI-4 calculations were performed to simulate the D–T fusion neutron transport in a pure copper block of FNG-Cu experiments. The reaction rates were evaluated for various activation foils (93Nb(n,2n), 27Al(n,α), 58Ni(n,p), 115In(n,n’), 197Au(n,2n), 186W(n,γ), and 197Au(n,γ)) versus penetration depth in the Cu block. To study the measurement tool of tritium production for the future ITER Test Blanket Module (TBM), the second FNG experiment analyzed in this work arranged a thin layer of 6LiF (LiDia detector) placed inside a polyethylene cylinder and irradiated with FNG 14 MeV neutrons. TRIPOLI-4 simulation models were run to evaluate the tritium production in the LiDia detector. The purpose of this study is to investigate the TRIPOLI-4 calculations against the FNG experimental ones. TRIPOLI-4 calculation methods and results are reported.

14 MeV neutron streaming calculations for JET-like maze entrance using TRIPOLI-4 Monte Carlo code

For the future ITER (International Thermonuclear Experimental Reactor) operation needs, D-T fusion experiments named DTE2 will be conducted in 2020 at JET (Joint European Torus). During the DTE2 operations, 14 MeV fusion neutrons will be generated. One of the aims of the DTE2 neutronics experiments is to investigate the D-T neutron streaming along the penetrations of biological shield of the JET Torus Hall. The TRIPOLI-4 Monte-Carlo radiation transport code has been extensively used on radiation shielding analyses. The purpose of this study is to evaluate the variance reduction (VR) techniques of TRIPOLI-4 on the 14 MeV neutron streaming calculations for a JET-like maze entrance. A JET-like torus hall building of 40 m x 40 m x 4.2 m and a maze entrance of 11.8 m length in 5-section configuration of concrete were first modeled. The standard INIPOND VR method and the new developed VR method AMS (Adaptive Multilevel Splitting) were then presented and discussed. Using the single-step approach combined with AMS techniques, the TRIPOLI-4 calculations results including neutron flux and ambient dose equivalent maps, the VR performance, and the user-friendly AMS input of TRIPOLI-4 code are reported.

Demonstration of two-laser Polarimeter-Interferometer (PIer) scheme for simultaneous measurements of Faraday rotation angle and electron density on HL-2A

A novel two-laser Polarimeter-Interferometer (PIer) diagnostic scheme, in which Faraday rotation angle (αF) and electron density (ne) can be simultaneously measured by taking advantage of two lasers and two detectors for each channel, has been successfully demonstrated on HL-2A tokamak through upgrading one channel of existing monofunctional Faraday-effect polarimeter. In comparison with the conventional three-laser PIer diagnostic, two-laser PIer generates only one intermediate frequency (IF), avoiding the overlap of IF frequency bands, so as to increase the time resolution and decrease the phase noise of system. The single channel two-laser PIer was firstly put into operation in 2016 HL-2A experimental campaign, and both Faraday rotation angle and electron density phase have been measured with a fast time resolution of 1.0 μs and a phase resolution of 0.1̂ and 1.0̂, respectively. This work is valuable for next step far-infrared (FIR) laser PIer construction on HL-2M tokamak, as well as the future International Thermonuclear Experimental Reactor (ITER).

Fully relativistic atomic structure calculations for W XLIV for determination of plasma diagnostic terms

We report accurate calculations of W XLIV through application of multi-configuration Dirac–Fock wave functions. We have calculated the energies for the lowest 100 fine structure levels, transition wavelengths, radiative rates, oscillator strengths, and line strengths for electric (E1) and magnetic dipole (M1) transitions with the extended average level multi-configurational Dirac–Fock method in the General-Purpose Relativistic Atomic Structure Package (GRASP). We have taken into account the electron correlations, quantum electrodynamics (QED) and Breit corrections in our calculations. We have also performed parallel calculations with the flexible atomic code (FAC) to assess the accuracy of our calculations. This is a fully relativistic code that provides a variety of atomic parameters, and (generally) yields results for energy levels and radiative rates comparable to GRASP. Our calculated results match well with experimentally observed results that are obtained in ASDEX upgrade Tokamak. Additionally, we have also provided the line intensity ratios and electron density for W XLIV, which is useful and important in plasma diagnostics and modeling in future International Thermonuclear Experimental Reactor (ITER) experiments. We believe that our results would be beneficial in the areas of fusion plasma research and astrophysical investigations and applications.

Modelling of the soft X-ray tungsten spectra expected to be registered by GEM detection system for WEST

Abstract In the future International Thermonuclear Experimental Reactor (ITER), the interaction between the plasma and the tungsten chosen as the plasma-facing wall material imposes that the hot central plasma loses energy by X-ray emission from tungsten ions. On the other hand, the registered X-ray spectra provide alternative diagnostics of the plasma itself. Highly ionized tungsten emits extremely complex X-ray spectra that can be understood only after exhaustive theoretical studies. The detailed analyses will be useful for proper interpretation of soft X-ray plasma radiation expected to be registered on ITER-like machines, that is, Tungsten (W) Environment in Steady-state Tokamak (WEST). The simulations of the soft X-ray spectra structures for tungsten ions have been performed using the flexible atomic code (FAC) package within the framework of collisional-radiative (CR) model approach for electron temperatures and densities relevant to WEST tokamak.

Modeling of the L and M x-ray line structures for tungsten in high-temperature tokamak plasmas

We present the results of modeling of the L and M x-ray line structures for tungsten in high-temperature plasmas predicted with temperatures relevant to large tokamaks including the Joint European Tokamak and the future International Thermonuclear Experimental Reactor. The simulations have been performed using the Flexible Atomic Code within the framework of the collisional–radiative (CR) model. For L x-ray lines, our results predicted for various levels of CR model sophistication have been compared with the spectrum measured using the electron beam ion trap (EBIT) calorimeter spectrometer at the Livermore SuperEBIT that constitutes a rigorous atomic benchmark for tokamak plasmas. In the case of M x-ray lines, we have reproduced the experimental SuperEBIT spectra as a superposition of theoretical contributions for different ions. The obtained results enable us to propose an approach allowing the decomposition of registered experimental tungsten spectra produced in tokamaks into the theoretically predicted contributions, corresponding to different degrees of ionization.

Temperature dependent defects evolution and hardening of tungsten induced by 200 keV He-ions

Tungsten has been selected as one of the potential candidate materials to cover some parts of the divertor in the future International Thermonuclear Experimental Reactor (ITER). The accumulation of defects and He induced by neutron irradiation and their impact on the mechanical properties of tungsten are of very importance. In this work, the high pure polycrystalline tungsten samples were implanted by 200keV He+ with a fluence of 5×1016He+/cm2 at temperatures of room temperature (RT), 200, 400 and 800°C. Vacancy-type defects were detected in all implanted samples by means of positron annihilation spectroscopy. Vacancy-type defects produced by He implantation exist in the damaged layer and are decorated by He atoms. At higher implantation temperature, He–V complexes could grow larger through absorbing mobile vacancies. The nano-hardness values were measured by nano-indentation technique. It is observed that implantation hardening occurred for all the implanted samples. With increasing implantation temperature from 200°C to 800°C, the change of the average hardness values which are lower than the value at RT has a tendency of enhancement for the shallower layer and degradation for the deeper layer. The hardness variations are discussed to be the pinning effects of the defects with different density or size.

Biparametric fracture toughness characterization of Eurofer steel plates

Reduced activation ferritic/martensitic (RAFM) steels are considered promising candidates for the test blanket modules (TBM) of the future international thermonuclear experimental reactor (ITER), being Eurofer steel the EU reference material specifically developed for this application. It is a 9%CrWVTa RAFM steel which exhibits a tempered martensite microstructure, giving way to a good combination of mechanical strength andtoughness, even under long periods of in-service neutron irradiation.Eurofer steel was cast in a laboratory high vacuum inductionmelting furnace. The 60kg ingot was hot rolled to obtain a 14mm thickness plate, which was finally quenched and tempered. The room temperature fracture toughness behaviour of the hot rolled and heat treated Eurofer plates (critical J integral, JQ) was determined using standard elastoplastic fracture mechanics tests and the constraint effect on its fracture behaviour was also obtained using fracture specimens subjected to different triaxialities in order to finally define the Eurofer fracture toughness evolution against triaxiality conditionsKewywordsRAFM steels, Eurofer, biparametric fracture, constraint, elasto-plastic fracture

Methods and Instruments for Assessing the in-Core Gamma Heating of Materials

The reliable estimate gamma heating of materials in a research reactor core, including irradiated samples or core compartments, is recognized as directly related to reactor safety. A review of related reports indicates that the capability of accurate assessment of gamma heating of materials in nuclear reactor cores remains a matter of investigation. Numerous works, theoretical and/or experimental, have been performed in the frame of the design of the future fusion reactor ITER (International Thermonuclear Experimental Reactor) while relevant work is also reported concerning the future material testing reactor Jules Horowitz (RJH). In the present work, an extended review is presented about methods and instruments that have been developed in order to assess the heating of materials due to absorption of gamma radiation in a research reactor core. This compilation may contribute to define coherent measurement and computational strategies in order to reliably assess gamma heating.

Radiation tolerance qualification for maintenance tasks in the future fusion reactors: from fibre-optic components to robust data links

The future International Thermonuclear Experimental Reactor (ITER) requires remote handling tools for its maintenance that will operate in a harsh environment. The numerous instrumentation cables for this maintenance equipment call for (de)multiplexing solutions, in order to reduce the umbilical size. Fibre-optic data links, using commercial-off-the-shelf (COTS) components, are seriously considered as a radiation tolerant solution, offering wavelength encoded multiplexing possibilities. However, an adapted modus operandi for a reliable assessment of this evolving technology is needed, to enable their long-term implementation in a radiation environment. In this paper, we present a methodology towards qualification methods for these instrumentation data links, and illustrate it with results obtained for different individual components. These results should enable the future design of robust architectures for communication links.

Advanced high-power gyrotrons

Gyrotrons at high frequency with high-output power are mainly developed for microwave heating and current drive in plasmas for thermonuclear fusion. For the stellarator Wendelstein 7-X, now under construction at IPP Greifswald, Germany, a 10-MW electron-cyclotron-resonance-heating (ECRH) system is foreseen. A 1-MW 140-GHz gyrotron with synthetic diamond window for continuous wave operation and with a single stage depressed collector for energy recovery and improvement of efficiency has been designed, constructed, and tested in collaboration with CRPP Lausanne and TED Ve/spl acute/lizy. It operates in the TE/sub 28,8/-cavity mode and provides a linearly polarized TEM/sub 0,0/ Gaussian RF beam. In short pulse operation at the design current of 40 A, an output power of 1-MW could be achieved for an accelerating voltage of 82 kV without depression voltage, an output power of 1.15 MW at an accelerating voltage of 84 kV with a depression voltage of 25 kV. These values correspond to an efficiency of 49%. After some problems with the RF-load, long-pulse operation was performed. The power measurements were done by the calibrated signal of the diode detector placed at the second mirror. Output powers of 1 MW could be achieved for 10 s, and an energy as high as 90 MJ per pulse has been produced with an output power of 0.64 MW. The pulselengths were mainly determined by the preset values. Only for the 100-s pulse at 0.74 MW, a limitation was found due to a pressure increase beyond about 10/sup -7/ hPa. The ITER task (task for the future international thermonuclear experimental reactor) on development of coaxial cavity gyrotrons ended in 2001. In accordance with the goal of the task, the potential of coaxial gyrotrons has been investigated and, as a result, data necessary for an industrial realization of a 2-MW CW 170-GHz tube have been obtained. In addition, first work on tube integration has been done. The results will be presented and discussed. By biasing the coaxial insert a fast (within 0.1 ms) frequency tuning has been demonstrated. In particular, a fast step tuning between the 165-GHz nominal mode and the azimuthal neighbors at 162.5 and 167.2 GHz have been performed. In addition, at the nominal mode a continuous frequency variation within the bandwidth of up to 70 MHz has been done.