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A reduced kinetic method (RKM) with a first-principles collision operator is introduced in a 1D2V planar geometry and implemented in a computationally inexpensive code to investigate non-local ion heat transport in multi-species plasmas. The RKM successfully reproduces local results for multi-species ion systems and the important features expected to arise due to non-local effects on the heat flux are captured. In addition to this, novel features associated with multi-species, as opposed to single species, cases are found. Effects of non-locality on the heat flux are investigated in mass and charge symmetric and asymmetric ion mixtures with temperature, pressure, and concentration gradients. In particular, the enthalpy flux associated with diffusion is found to be insensitive to sharp pressure and concentration gradients, increasing its significance in comparison to the conductive heat flux driven by temperature gradients in non-local scenarios. The RKM code can be used for investigating other kinetic and non-local effects in a broader plasma physics context. Due to its relatively low computational cost it can also serve as a practical non-local ion heat flux closure in hydrodynamic simulations or as a training tool for machine learning surrogates. [ABSTRACT FROM AUTHOR]

The impact of electromagnetic (EM) and thermal cyclic loading (referred as warm-up-cool-down—WUCD) on the Nb3Sn cable in conduit conductors for the toroidal field magnets of the ITER tokamak should be carefully assessed for the proper operation of the machine. The experience gained during the production phases of the TF conductors revealed that a degradation occurs when thermal and EM cyclic loading is applied at the nominal operating conditions of 10.78 T and 68 kA. Since at the beginning of the tokamak operation the nominal conditions will not be achieved, it is worth investigating to what extent lower EM loads affect the conductor performance, and the threshold of EM load that triggers the WUCD degradation. The aim of this investigation is to identify critical levels which determine the onset of this degradation, both in terms of thermal and EM cycles, and to study the performance of strands from different suppliers. For this assessment, a set of conductor samples were manufactured including all types of strands to be used in the TF coils of the ITER machine. These samples were subjected to a set of EM and thermal cycles representing in a realistic way the actual operation of the conductors in the ITER machine. The tests were performed in the SULTAN facility of the Swiss Plasma Center at working conditions ranging from 5.4 T–34 kA to 10.78 T–68 kA. This work presents the results obtained in these tests in terms of current sharing temperature (Tcs), effective strain, rate of degradation at different working conditions and their implications for the prospected conductor performance in the machine. [ABSTRACT FROM AUTHOR]

The overall 30 year Nb3Sn conductor program for ITER provides an unusual opportunity to look at the issues created by the application of novel Nb3Sn technology on a large scale. ITER design criteria have evolved to make use of the features of the industrialized material, exploiting advantages as well as managing the disadvantages. There are lessons from the successes and failures to be learned for the future application of very high current Nb3Sn strands in fusion and high energy physics. The behaviour of Nb3Sn strands in the large compound ITER conductors is still producing surprises after 25 years of development, industrial production and testing, with the Nb3Sn strain sensitivity and brittleness producing many more subtle design impacts than originally foreseen. The results now obtained at the end of the ITER production suggest that, as a novelty for Nb3Sn, there are options for conditioning the strands in the ITER conductors that can be applied during commissioning and which could reduce the impact of brittleness by as much as one third. [ABSTRACT FROM AUTHOR]

Taking the relay of the large Hadron collider (LHC) at CERN, ITER has become the largest project in applied superconductivity. In addition to its technical complexity, ITER is also a management challenge as it relies on an unprecedented collaboration of seven partners, representing more than half of the world population, who provide 90% of the components as in-kind contributions. The ITER magnet system is one of the most sophisticated superconducting magnet systems ever designed, with an enormous stored energy of 51 GJ. It involves six of the ITER partners. The coils are wound from cable-in-conduit conductors (CICCs) made up of superconducting and copper strands assembled into a multistage cable, inserted into a conduit of butt-welded austenitic steel tubes. The conductors for the toroidal field (TF) and central solenoid (CS) coils require about 600 t of Nb3Sn strands while the poloidal field (PF) and correction coil (CC) and busbar conductors need around 275 t of Nb–Ti strands. The required amount of Nb3Sn strands far exceeds pre-existing industrial capacity and has called for a significant worldwide production scale up. The TF conductors are the first ITER components to be mass produced and are more than 50% complete. During its life time, the CS coil will have to sustain several tens of thousands of electromagnetic (EM) cycles to high current and field conditions, way beyond anything a large Nb3Sn coil has ever experienced. Following a comprehensive R&D program, a technical solution has been found for the CS conductor, which ensures stable performance versus EM and thermal cycling. Productions of PF, CC and busbar conductors are also underway. After an introduction to the ITER project and magnet system, we describe the ITER conductor procurements and the quality assurance/quality control programs that have been implemented to ensure production uniformity across numerous suppliers. Then, we provide examples of technical challenges that have been encountered and we present the status of ITER conductor production worldwide. [ABSTRACT FROM AUTHOR]

Observing the Sun at high time and spatial scales is a step toward understanding the finest and fundamental scales of heating events in the solar corona. The high-resolution coronal (Hi-C) instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 2012 July 11 that exhibits several interesting features in the EUV line at 193 Å. One of them is the existence of short, small brightenings “sparkling” at the edge of the active region; we call these EUV bright dots (EBDs). Individual EBDs have a characteristic duration of 25 s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength; however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA, which suggests a temperature between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time series, we define four different categories of EBDs: single peak, double peak, long duration, and bursty. Based on a potential field extrapolation from an SDO/HMI magnetogram, the EBDs appear at the footpoints of large-scale, trans-equatorial coronal loops. The Hi-C observations provide the first evidence of small-scale EUV heating events at the base of these coronal loops, which have a free magnetic energy of the order of 1026 erg. [ABSTRACT FROM AUTHOR]

Construction of the ITER magnet systems has been started at the end of 2007 following the signature of the first procurement arrangements (PA) for the toroidal field (TF) conductors. Six ITER members are involved in the share of the ITER magnet components and, to date, eighteen PA between the ITER Organization and six domestic agencies have been signed. Substantial progress towards full-scale construction has been achieved with the placement of the first large manufacturing contracts, the production of several tens of tons of advanced Nb3Sn and NbTi strand, and the set-up of large cabling and jacketing facilities. The detailed design of the coils and support structures has also been finalized. The qualification of the fabrication processes for the TF coils and poloidal field (PF) coils has been initiated. The detailed design of the central solenoid (CS) coils is being developed. The design of the correction coils (CCs) with their support structures has been finalized, as well as for the TF gravity supports and clamps of the PF coils. The manufacture of prototypes of the feeder lines and current leads has been started, while ITER is in charge of the procurement of the required magnet instrumentation. This paper provides a progress report on the ITER magnet construction as per December 2010. [ABSTRACT FROM AUTHOR]

The strong strain sensitivity of the critical properties of Nb3Sn is well established. However, the roles played by both the reversible strain sensitivity and the susceptibility to brittle fracture of Nb3Sn filaments is still leading to unexpected results and resulting design modifications of conductors. Practical conductors require acceptance of less than perfect superconducting behaviour because such conductors actually operate continuously in a slightly resistive mode. Performance testing of the ITER conductors has provided a unique database of both strand and corresponding conductor performance. The test database includes strand characterization under uniaxial and bending strain, superconducting measurements on full-size conductor samples and microscopic investigations into filament fracture. A simple mechanical and electrical model of the strands and a multistage cable (capable of operation at 12 T and 45 kA) that focuses on predicting the imperfect superconducting behaviour is used to provide insight into the processes governing the observed conductor behaviour.The conclusions show that a short twist pitch at the first cabling stage provides the best operating conditions for the strands, and further that some strand mechanical properties, essentially a high stiffness to bending and a low stiffness to pinching, increase the ability of the strands to tolerate less well optimized cables. [ABSTRACT FROM AUTHOR]

The differences in thermal contraction of the composite materials in a cable in conduit conductor (CICC) for the International Thermonuclear Experimental Reactor (ITER), in combination with electromagnetic charging, cause axial, transverse contact and bending strains in the Nb3Sn filaments. These local loads cause distributed strain alterations, reducing the superconducting transport properties. The sensitivity of ITER strands to different strain loads is experimentally explored with dedicated probes. The starting point of the characterization is measurement of the critical current under axial compressive and tensile strain, determining the strain sensitivity and the irreversibility limit corresponding to the initiation of cracks in the Nb3Sn filaments for axial strain. The influence of spatial periodic bending and contact load is evaluated by using a wavelength of 5 mm. The strand axial tensile stress-strain characteristic is measured for comparison of the axial stiffness of the strands. Cyclic loading is applied for transverse loads following the evolution of the critical current, n-value and deformation. This involves a component representing a permanent (plastic) change and as well as a factor revealing reversible (elastic) behavior as a function of the applied load. The experimental results enable discrimination in performance reduction per specific load type and per strand type, which is in general different for each manufacturer involved. Metallographic filament fracture studies are compared to electromagnetic and mechanical load test results. A detailed multifilament strand model is applied to analyze the quantitative impact of strain sensitivity, intrastrand resistances and filament crack density on the performance reduction of strands and full-size ITER CICCs. Although a full-size conductor test is used for qualification of a strand manufacturer, the results presented here are part of the ITER strand verification program. In this paper, we present an overview of the results and comparisons. [ABSTRACT FROM AUTHOR]

The U-238 series of radionuclides is of relevance in a variety of environmental contexts ranging from the remediation of former uranium mining and milling facilities to the deep geological disposal of solid radioactive wastes. Herein, we review what is known concerning the behaviour of radionuclides from the U-238 decay chain in soils and plants. This review is intended to provide a single comprehensive source of information to anyone involved in undertaking environmental impact assessment studies relating to this decay chain. Conclusions are drawn relating to values and ranges of distribution coefficients appropriate to uranium, thorium, radium, lead and polonium in different soil types and under various environmental conditions. Similarly, conclusions are drawn relating to plant:soil concentration ratios for these elements for different plant and soil types, and consideration is given to the distribution of these elements within plants following both root uptake and foliar application. [ABSTRACT FROM AUTHOR]

The performance of the toroidal field (TF) magnet conductors for the ITER machine are qualified by a short full-size sample (4 m) current sharing temperature (Tcs) test in the SULTAN facility at CRPP in Villigen, Switzerland, using the operating current of 68 kA and the design peak field of 11.8 T. Several samples, including at least one from each of the six ITER Domestic Agencies participating in TF conductor fabrication (China, European Union, Japan, Russia, South Korea and the United States), have been qualified by the ITER Organization after achieving Tcs values of 6.0-6.9 K, after 700-1000 electromagnetic cycles. These Tcs values exceed the ITER specification and enabled the industrial production of these long-lead items for the ITER tokamak to begin in each Domestic Agency. Some of these samples did not pass the qualification test. In this paper, we summarize the performance of the qualified samples, analyze the effect of strand performance on conductor performance, and discuss the details of the test results. [ABSTRACT FROM AUTHOR]

Recent results on short samples of ITER-type Nb3Sn cable-in-conduit conductors have shown degradation, with the current-sharing temperature dropping slowly over several thousand current cycles. However, although such behaviour has been linked to the magnetic loads on the strands, which cause filament fracture and plastic yielding of the surrounding copper, the detailed examination of the results shows a number of inconsistencies. These suggest that the degradation may be exaggerated by artefacts of the short sample and may provide an over-conservative assessment of the in-coil performance. The behaviour of a short sample and its frictional interaction with the jacket have been analysed to consider the impact of local material modulus changes. Both an analytical approach and a finite-element simulation have been used. This paper shows that, if transverse magnetic loading causes a local reduction in the longitudinal elastic modulus of the cable in the high-field region, then the thermal compression along the cable becomes non-uniform, with a higher compression in the high field. The process develops with load cycles, due to the jacket/cable friction. If the strain change is interpreted using Jc, T, B and the strain scaling law, the predicted current-sharing temperature drop is similar to those observed during testing. [ABSTRACT FROM AUTHOR]