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The International Thermonuclear Experimental Reactor (ITER) magnet system is one of the most sophisticated superconducting magnet systems ever designed, with a stored energy of 51 GJ. The coils are wound from cable-in-conduit conductors made of superconducting and copper strands assembled into a multistage rope-type cable, inserted into a conduit of austenitic steel tubes. The ITER central solenoid (CS) works in pulsed mode, reaching a peak field of 13 T, thus allowing the induction of a high intensity current in the plasma of the ITER tokamak. This magnet consists of a stack of six modules which include around 125 t of Nb3Sn strands. The production of all CS conductors has been completed and module manufacturing is well underway; throughout the production phase, samples were cut at the extremities of the conductor unit lengths to undergo quality control tests. About 25% of the conductor short samples were tested in current and field at cryogenic conditions at the SULTAN facility in Villigen, Switzerland. This work reports the comparative analysis of the short samples set of test results.

On ITER, plasma start-up will be performed in limiter configuration on the inboard equatorial beryllium first wall panels (FWP). In contrast to most present tokamaks, however, this ramp-up phase will be comparatively long (∼10 s) and the use of actively cooled components means that power flux management is key if FWP lifetime is not to be compromised. Shaping of the FWPs is mandatory to ensure that leading edges do not appear between neighbouring units. For the ITER inboard panels, this has been optimized to account for the discovery in recent years on current devices of narrow scrape-off layer power flux channels for inner wall limited plasmas. However, the shaping results in power densities which are particularly sensitive to the overall ‘longwave’ (LW) alignment of the central column FWP ring with the structure of the toroidal magnetic field (TF), placing tight constraints on the target alignment. This target is currently based on a pure n = 1 LW alignment, but simulations of TF coil (TFC) locking upon energization show that, depending on the initial configuration of the gaps between the TFC inner legs, the field structure can be more complex. Although the TFC manufacture and machine assembly strategy is to make every effort possible to approach the ideal TF structure, an NMR sensor-based TF mapping diagnostic will be implemented to measure the field structure during the first plasma and engineering operation phase. An analytic framework has been developed and verified against numerical simulations to assess the capability for measurements from a set of discrete sensors located on the vacuum vessel inner column to be used to reconstruct the field structure at the FWP locations, a further ∼60 cm radially inward. In parallel with the alignment optimization and TF mapping strategies, modified ramp-up scenarios are also being designed which may be used to reduce inner wall limiter power fluxes if this proves to be necessary during operation.

Cone-beam CT (CBCT) is an imaging technique used in conjunction with radiation therapy. For example CBCT is used to verify the position of lung cancer tumours just prior to radiation treatment. The accuracy of the radiation treatment of thoracic and upper abdominal structures is heavily affected by respiratory movement. Such movement typically blurs the CBCT reconstruction and ideally should be removed. Hence motion-compensated CBCT has recently been researched for correcting image artefacts due to breathing motion. This paper presents a new dual-modality approach where CBCT is aided by using electrical impedance tomography (EIT) for motion compensation. EIT can generate images of contrasts in electrical properties. The main advantage of using EIT is its high temporal resolution. In this paper motion information is extracted from EIT images and incorporated directly in the CBCT reconstruction. In this study synthetic moving data are generated using simulated and experimental phantoms. The paper demonstrates that image blur, created as a result of motion, can be reduced through motion compensation with EIT.

Nb3Sn cable in conduit-type conductors were expected to provide an efficient way of achieving large conductor currents at high field (up to 13 T) combined with good stability to electromagnetic disturbances due to the extensive helium contact area with the strands. Although ITER model coils successfully reached their design performance (Kato et al 2001 Fusion Eng. Des. 56/57 59–70), initial indications (Mitchell 2003 Fusion Eng. Des. 66–68 971–94) that there were unexplained performance shortfalls have been confirmed. Recent conductor tests (Pasztor et al 2004 IEEE Trans. Appl. Supercond. 14 1527–30) and modelling work (Mitchell 2005 Supercond. Sci. Technol. 18 396–404) suggest that the shortfalls are due to a combination of strand bending and filament fracture under the transverse magnetic loads. Using the new model, the extensive database from the ITER CS insert coil has been reassessed. A parametric fit based on a loss of filament area and n (the exponent of the power-law fit to the electric field) combined with a more rigorous consideration of the conductor field gradient has enabled the coil behaviour to be explained much more consistently than in earlier assessments, now fitting the Nb3Sn strain scaling laws when used with measurements of the conductor operating strain, including conditions when the insert coil current (and hence operating strain) were reversed. The coil superconducting performance also shows a fatigue-type behaviour consistent with recent measurements on conductor samples (Martovetsky et al 2005 IEEE Trans. Appl. Supercond. 15 1367–70). The ITER conductor design has already been modified compared to the CS insert, to increase the margin and provide increased resistance to the degradation, by using a steel jacket to provide thermal pre-compression to reduce tensile strain levels, reducing the void fraction from 36% to 33% and increasing the non-copper material by 25%. Test results are not yet available for the new design and performance predictions at present rely on models with limited verification.

The crucial multi-physics problem of how to extrapolate from the performance of an isolated Nb3Sn strand measured in the laboratory to the performance of a superconducting coil using multi-strand twisted cables is addressed here. We consider the particular case of the path going from the LMI strand to the international thermonuclear experimental reactor (ITER) toroidal field model coil (TFMC), through its associated Full Size Joint Sample, the TFMC-FSJS. Mechanical, electromagnetic and thermal–hydraulic conditions are simulated using the ANSYS, ENSIC and Mithrandir/M&M codes, respectively. At least in this case, the DC performance of the short sample turns out to be relatively close to (considering error bars) but not fully representative of that of the coil, showing higher (less compressive) effective thermal strain but also higher sensitivity to the electromechanical load.

Nb3Sn superconductors show a dependence of the critical current and temperature on the strain state of the superconducting material. The basic causes of Nb3Sn strain effects, primarily differential thermal contraction between elements of the strand, have been known for 30 years, but have received more attention lately as part of a drive to achieve much higher operating current densities and make use of them in practical multistrand cables. The use of the cable-in-conduit (CICC) type of conductors to achieve high current capacity has proved popular, as the conductors offer good local cooling of the strands and distributed electrical contact between strands that is essential to provide stability against the inevitable current non-uniformity that arises with parallel connection of the strands. However, the essential openness of the cable means that the strands have to support local magnetic loads as well as being exposed to the overall magnet strain displacements. Simple structural models are developed based on mechanical measurements on cable-in-conduit conductors which are able to successfully simulate the measured superconducting performance. These suggest that degradation observed in large cables is due to a combination of the repeated bending strain experienced by the strands and filament fracture, which is starting to occur to a significant extent in some large cables. Superconducting performance improvements in strands can only be properly utilized with improved support of the strands in the cable, implying a more ordered structure than in a multistage.

This paper describes the structure, fabrication and detailed characterization of a polycrystalline silicon passive microvalve. The microvalves were fabricated utilizing micromachining techniques, and automated measurement systems were developed for device characterization. The valves were successfully characterized to determine the effect of dimensions on fluid flow rate and valve deflection. Methanol, deionized water and nitrogen were used for fluid flow tests, and nitrogen gas was used in the deflection measurements. The ratio of reverse to forward flow rates of methanol was found to be less than 3% at a pressure of 11 kPa. The measured data are in good agreement with a first-order model for the device taking into account applied pressure, valve plate deflection and the resistance of the inlet hole. Using nitrogen gas, analysis of the device was extended to measure the valve plate deflection as a function of inlet pressure. Valve plate deflections of up to 15.3 μm were recorded at 31 kPa. The nitrogen gas flow characteristics differ significantly from the liquid flow characteristics due to the compressible nature of the fluid, but agree well with the theoretical flow for gases.

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 (T-cs) 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 T-cs values of 6.0-6.9 K, after 700-1000 electromagnetic cycles. These T-cs 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.

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.

Single-photon emission computerized tomography (SPECT) is a tool which can be used to image perfusion in the brain. Clinicians can use such images to help diagnose dementias such as Alzheimer's disease. Due to the intrinsic stochasticity in the photon imaging system, some form of statistical comparison of an individual image with a 'normal' patient database gives a clinician additional confidence in interpreting the image. Due to the variations between SPECT camera systems, ideally a normal patient database is required for each individual system. However, cost or ethical considerations often prohibit the collection of such a database for each new camera system. Some method of adapting existing normal patient databases to new camera systems would be beneficial. This paper introduces a method which may be regarded as a 'first-pass' attempt based on 2-norm regularization and a codebook of discrete spatially stationary convolutional kernels. Some preliminary illustrative results are presented, together with discussion on limitations and possible improvements.

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.

The physical properties of the first In analog of the PuMGa5 (M = Co, Rh) family of superconductors, PuCoIn5, are reported. With its unit cell volume being 28% larger than that of PuCoGa5, the characteristic spin-fluctuation energy scale of PuCoIn5 is three to four times smaller than that of PuCoGa5, which suggests that the Pu 5f electrons are in a more localized state relative to PuCoGa5. This raises the possibility that the high superconducting transition temperature Tc = 18.5 K of PuCoGa5 stems from the proximity to a valence instability, while the superconductivity at Tc = 2.5 K of PuCoIn5 is mediated by antiferromagnetic spin fluctuations associated with a quantum critical point.

The electronic structure of PuCoGa5, Pu metal, and PuO2 is explored using photoelectron spectroscopy. Ground state electronic properties are inferred from temperature dependent photoemission near the Fermi energy for Pu metal. Angle-resolved photoemission details the energy vs. crystal momentum landscape near the Fermi energy for PuCoGa5 which shows significant dispersion in the quasiparticle peak near the Fermi energy. For the Mott insulators AnO2(An = U, Pu) the photoemission results are compared against hybrid functional calculations and the model prediction of a crossover from ionic to covalent bonding is found to be reasonable.

Electrical impedance tomography (EIT) is a new and emerging tomographic imaging system, which is able to provide high temporal resolution with low spatial resolution. In past few years, the EIT has been extensively studied for lung monitoring. Cone beam CT (CBCT) is an imaging system used in radiation therapy unit. The CBCT suffers from motion artefacts, making treatment planning inaccurate. This problem is very severe in lung cancer therapy. In this study a dual modality of EIT-CBCT has been proposed. Feasibility of such a dual system has been investigated using preliminary simulated phantom data. The motion information is extracted from the EIT images and has been used to compensate for the motion in CBCT through our recently developed iterative image reconstruction for CBCT. The results show that blurring artefacts around a tumour can be reduced for the motion compensated images using this dual modality combination. The dual EIT-CBCT imaging benefits from complementary high spatial resolution of CBCT and high temporal EIT resolution.

Plutonium is the element with the greatest number of allotropic phases. Thermally induced transformations between these phases are typically characterized by thermal hysteresis and incomplete phase reversion. With Ga substitutional in the lattice, low symmetry phases are replaced by a higher symmetry phase. However, the low temperature martensitic phase transformation (δ→α') in Ga stabilized δ-phase Pu is characterized by a region of thermal hysteresis which can reach 200°C in extent. These regions of thermal hysteresis offer a unique opportunity to study thermodynamics in inhomogeneous systems of coexistent phases. The results of thermophysical properties measured for samples of inhomogeneous unalloyed and Ga alloyed Pu will be discussed and compared with similar measurements of their single phase constituents.

The temperature range of the δ-phase field of plutonium can be expanded by alloying with Group IIIA elements. Ga is a particularly potent δ-stabilizer and effectively stabilizes the δ-phase to room temperature. Due to a strong propensity to wards s olute redistribution during cooling through the e→δ phase field, regions of the material often do not contain enough solute to stabilize the δ-phase even after extensive homogenization annealing in the δ-phase field. The result is a small, but persistent, fraction of α-phase in the material. A technique using differential scanning calorimetry to measure the enthalpy of transformation of the plutonium α→β transformation is described which can detect and quantify α-phase in a δ-phase matrix at levels as low as ~0.1 wt. %. Complications arise due to interference from the pressure-induced α-phase, and a peak separation method was developed to accurately measure the heat signal from each phase. A set of δ-stabilized Pu-1.7 atomic % Ga alloys was examined using the technique and found to contain 0.32 ± 0.06 weight % α-phase. The onset temperature of the α→β transformation in these specimens was found to be 140.2°C, significantly higher than that for the transformation in pure plutonium, 126.2°C. This increase in onset temperature is a consequence of significant Ga content in the α-phase.

The effects of various chemical substitutions and induced lattice disorder in the Ce- and Pu-based 115 superconductors are reviewed, with particular emphasis on results from x-ray absorption fine structure (XAFS) measurements.

Nb3Sn cable in conduit type conductors (CICC) are a popular choice for high current conductors operating in steady or slowly changing current/field conditions. They provide a low cost way of bundling strands together to achieve large conductor currents at high field (up to 13 T), allowing a reduction in coil voltage requirements. The extensive strand contact, although giving relatively high AC losses, gives resilience against current non-uniformity and local strand damage, and there is good stability to electromagnetic disturbances due to the extensive helium contact area with the strands. In the last 5–6 years there has been clear evidence of Nb3Sn CICC performance degradation compared to expectations based on strand measurements. Investigations have linked this to filament bending and fracture under the mechanical loads, and particularly their accumulation from top to bottom of a cable. These effects were not widely expected to occur in small cables, and even in large ones their extent was expected to be limited. However, in 2006 testing of a small 15 kA conductor intended for a dipole showed severe degradation that continuously increased with cycling and some large 70 kA CICC have also shown a higher than expected performance drop. Experimental evidence strongly suggests that the degradation is dependent not only on the cable pattern but also on the sensitivity of different types of Nb3Sn strands to bending and pinching. The variability of results, with some strand–cable combinations giving a satisfactory performance, has provided an incentive to improve the modelling of the degradation to provide better predictions at the strand level of the characteristics needed for successful cable performance. Modelling was being developed as early as 2005 with an analytic cable mechanical model but a simplified and non-physical procedure to then derive the superconducting performance. The mechanical model was successfully benchmarked against overall mechanical property measurements on cables. This paper continues the development towards a complete predictive cable degradation model, this time covering the link between filament bending and damage (available from the earlier mechanical model and also increasingly from more sophisticated numerical simulations) and the overall superconducting performance, benchmarked using data from strand tests.

Current designs for tokamak based fusion reactors usually consider deuterium-tritium reactions with a 50–50% mixture of D-T, to give a maximum power density, although design studies for pure D-D, He3-catalysed and T-catalysed tokamak fusion reactors have been performed. The letter considers a reactor burning a D-T mixture with an enhanced percentage of deuterium to increase the possibility of D-D reactions (a so-called T-catalysed D reactor). Most of the energy needed to maintain the burning plasma comes from D-T reactions, but the D-D reaction results in the generation of extra neutrons (or equally useful tritons or 3He nuclei), which can contribute to the overall neutron economy of the reactor. – A simple plasma energy balance for an ignited tokamak is used to study the usefulness of D-D reactions, with confinement times, safety factors, and beta limits as predicted by existing experimental devices. The authors consider both the improvements necessary in present plasma performance limits to produce useful D-D reaction rates as well as the effect of a lower plasma energy density on reactor size. – The object of the study has not been to consider the economics of such types of reactor, but rather to assess the potential of the D-D reaction to introduce some flexibility into a fusion reactor design. It is evident from design studies on next generation tokamaks that the overall neutron economy will be a major challenge in a fusion reactor and that the reduction of the necessary blanket breeding ratio could improve the feasibility of the overall design.

Experiments are reported in which (1) the resistivity has been measured as a function of thickness in 82–18 nickel-iron thin films; (2) the ferromagnetic resistance anisotropy and the fractional anisotropy in magnetoresistance have been measured as a function of thickness; (3) the fractional anisotropy in magnetoresistance is measured as a function of temperature. The resistivity exhibits a higher value and lower mean free path than earlier measurements due to a different method of evaporation. Furthermore the functional dependence of the ferromagnetic anisotropy in resistivity and the fractional anisotropy in magnetoresistance are shown to be dependent on the method of evaporation. The fractional anisotropy in magnetoresistance is observed to fall off approximately linearly with temperature in the range from 20°C to 300°C, and to approach zero at a temperature well below the Curie point.