K. Yagotintsev - Academia.edu (original) (raw)
Papers by K. Yagotintsev
Powder x-ray diffractometry was employed to study infusion of He into $ C_ {60} $ fullerite. It h... more Powder x-ray diffractometry was employed to study infusion of He into $ C_ {60} $ fullerite. It has been shown that the intercalation at a pressure of 1 Bar is a two-stage process, the first stage being the saturation of the octahedral voids, virtually complete after 55 hr. ...
Solid State Phenomena, 2001
ABSTRACT
Low Temperature Physics, 2010
ABSTRACT Intercalation of fullerite C60 with oxygen molecules is performed by two methods—under o... more ABSTRACT Intercalation of fullerite C60 with oxygen molecules is performed by two methods—under ordinary conditions of saturation at room temperature and gas pressure 1 atm as well as at elevated temperature (373 K) and pressure (10 atm). The time dependences of the lattice parameter of fullerite during intercalation are determined. This made it possible to evaluate the activation energy and the coefficient of diffusion of oxygen molecules in fullerite C60. It is shown that increasing the temperature and pressure of the gas increases the diffusion coefficient almost five-fold: from D≈(1.6±1.9)⋅10−14 cm2∕s at atmospheric pressure and room temperature to D≈(7.1±1.9)⋅10−14 cm2∕s for pressure P=10 atm and temperature T=373 K. The oxygen concentration in octahedral voids and the temperatures of phase transitions in solutions are determined on the basis of an analysis of the results obtained together with published data on the effect of atomic and molecular impurities on the properties of C60. The effect of oxygen impurity on the properties of an orientational phase transition and the temperature dependence of the lattice parameter is investigated.
Low Temperature Physics, 2009
The process of normal hydrogen infusion into a C60 powder at 1 bar and room temperature is monito... more The process of normal hydrogen infusion into a C60 powder at 1 bar and room temperature is monitored using x-ray diffraction. The effect of the intercalation on the lattice proves to be rather weak: the volume expansion upon complete saturation does not exceed 0.13%. The characteristic saturation time is found to be 320 h the corresponding diffusion coefficient amounts to
Journal of Applied Physics, 2003
This article reports the temperature dependence of the structural and photoelectrical properties ... more This article reports the temperature dependence of the structural and photoelectrical properties of C 60 thin films with varying crystal structure and oxygen content near the orientational disorder/order phase transition at about 260 K. X-ray diffraction data demonstrate that highly crystalline oxygen-free C 60 films undergo the first-order phase transition at 252 K with a lattice parameter discontinuity ⌬a/a of 0.22%; no discontinuity was observed in C 60 films with coexisting amorphous and nanocrystalline phases. A strong effect of the phase transition on the dark-and photoconductivity in those films is presented: In highly crystalline C 60 films both dark-and photoconductivity increase as the temperature is lowered through the transition region. However, opposite temperature changes of the conductivity are observed in nanocrystalline/amorphous C 60 films. In situ exposure of samples to oxygen gas suppresses any critical behavior. The experimental results are interpreted in terms of trap-controlled mobility of the dominant charge carriers such that the temperature changes of the conductivity are attributed to variations in the concentration, energy distribution, and population of the carrier traps at the phase transition. Differences in the parameters of the traps, which are associated with the freeze-out of the molecular orientations, may also explain the strong variations in the temperature dependence of the conductivity observed in our C 60 films and reported by other authors.
Physica B: Condensed Matter, 2001
Structural and chemical changes in C 60 thin films, grown on a Cu substrate and exposed to air or... more Structural and chemical changes in C 60 thin films, grown on a Cu substrate and exposed to air or I 2 atmosphere, at room temperature, were monitored by X-ray diffraction, Auger electron and X-ray photoelectron spectroscopy. Exposure to air is demonstrated to result not only in oxygen diffusion but also in a counter diffusion of the metal from the substrate into the C 60 matrix. In particular, 10 months of air-exposure led to the presence of Cu and O atoms at all depths over the sample and the formation of a complex which we refer to as Cu x O y C 60. The new phase is quasi-stable at room temperature, but a relatively short thermal annealing at 1501C destroys it and restores the initial C 60 FCC lattice. After 10 min of exposure of the Cu-supported C 60 films to an I 2 atmosphere the Cu sub-layer disappears completely and macroscopic amounts of a stable CuI phase are formed over the entire thickness of the C 60 film. To explain the results a model of chemically-induced counter electro-diffusion is proposed. We propose the possible usefulness of this counter diffusion approach for tailoring C 60-based materials doped with various compounds in the form of both phaseseparated composites and solid solutions (intercalated fullerides).
Fusion Engineering and Design
In fabricating REBa2Cu3Oy (REBCO) superconducting coated conductors (CCs), the CCs are required t... more In fabricating REBa2Cu3Oy (REBCO) superconducting coated conductors (CCs), the CCs are required to increase deposition rate and crystallinities in order to reduce the cost of CCs fabrication. However, using the conventional pulsed laser deposition (PLD) method, the deposition rate is enhanced as the energy density of the pulsed laser is increased, while the crystallinities of the REBCO layer are deteriorated. In this work, in order to improve both the deposition rate and superconducting properties, we fabricated SmBa2Cu3Oy (Sm123) coated conductors using VLS growth technique. VLS growth technique is expected rapid growth rate and good crystallinity of REBCO films [1]. Furthermore, REBCO films fabricated using VLS growth technique by several group is reported that this films indicate high deposition rate and crystallinities [2,3]. The VLS growth technique consists of the following three steps by PLD method. The first step is to fabricate a solid Sm123 layer. The second step is to for...
Superconductor Science and Technology, Oct 22, 2018
Due to an error in the production process, the caption for figure 2 is incorrect. It should corre... more Due to an error in the production process, the caption for figure 2 is incorrect. It should correctly read 'Figure 2. Configuration of SuperPower 2G HTS Tape SCS#030'.
Superconductor Science and Technology
Many high-temperature superconductor (HTS) applications require superconducting cables with high ... more Many high-temperature superconductor (HTS) applications require superconducting cables with high currents while operating in an alternating magnetic field. HTS cables should be composed of numerous superconducting tapes to achieve the required current capacity. Alternating current and magnetic fields cause AC losses in such cables and can provoke conductor instability. AC losses and contact resistances were measured of several cable designs based on commercially available REBCO tapes at the University of Twente. The AC loss was measured under identical conditions for eight REBCO conductors manufactured according to three types of cabling methods—CORC® (Conductor on Round Core), Roebel, and stacked tape, including a full-size REBCO CICC (cable in conduit conductor). The measurements were done at T = 4.2 K without transport current in a sinusoidal AC magnetic field of 0.4 T amplitude and frequencies from 5 to 55 mHz. The AC loss was measured simultaneously by calibrated gas flow calor...
Superconductor Science and Technology
A CORC ® cable is composed of several layers of helically wound high-temperature superconducting ... more A CORC ® cable is composed of several layers of helically wound high-temperature superconducting (HTS) tapes on a round core with the winding direction reversed in each successive layer. The cable is flexible but the flexibility is limited by the critical strain value causing breakage of the HTS layer when this strain level is exceeded. The cables for magnets in fusion reactors experience large mechanical and electromagnetic loads. These loads arise from the cabling, coil manufacturing, cooling, and magnet operation. In order to optimize the manufacture and operating conditions, the mechanical behavior of CORC ® cables must be understood for the different relevant loading conditions. The cable configuration with many contact interactions between tapes and the non-linear behavior of the materials during the production and operating conditions makes the modeling challenging. Detailed finite element (FE) modeling is required to account for these complexities. The FE modeling allows an accurate calculation of the stress-strain state of the cable components under various loads and avoids time-consuming large-scale experimental optimization studies. This work presents a detailed FE modeling of the 3D stress-strain state in a CORC ® wire under bending load. The elastic-plastic properties of the individual tape composite materials and its temperature dependence are taken into account. The FE model is experimentally validated by a multi-layer CORC ® bending test performed by Advanced Conductor Technologies LLC. A critical intrinsic tensile strain value of 0.45% is taken as the threshold where the individual tape performance becomes irreversibly degraded. The proposed FE model describes the bending test of the CORC ® wire adequately and thus can be used to study other types of loads. A parametric study is ongoing with dependent variables to pursue a further optimization of CORC ® cables and wires for various applications.
IEEE Transactions on Applied Superconductivity
The central solenoid model coil (CSMC) project of the China Fusion Engineering Test Reactor was l... more The central solenoid model coil (CSMC) project of the China Fusion Engineering Test Reactor was launched in 2014 to verify the technological feasibility of a large-scale superconducting magnet at the Institute of Plasma and Physics Chinese Academy of Sciences. The short twist pitch design recommended by CEA is chosen for the CSMC Nb 3 Sn cable-in-conduit conductors. In order to better understand the evolution of transport properties and coupling losses related to the effect of electromagnetic load cycles, the mechanical and electrical properties were measured and investigated employing a special cryogenic press facility for the transverse mechanical loadings. The results show that the transverse compression (d y) versus applied load force (F y) is different from first to subsequent loading cycles. This mechanical behavior can be interpreted by the combination of strands bending between the crossovers and strands deformation at the crossovers. The fitting relations of d y versus F y are also presented. The evolution of interstrand contact resistance (R c) in the cabling stages with cyclic history and pressure effects are discussed. In addition, a fitting relation of R c versus F y is presented based on a combination of strand's microsliding and copper matrix resistivity. A clear correlation between intrapetal resistance R c and coupling loss is also found.
Superconductor Science and Technology
Two prototype Nb 3 Sn cable-in-conduit conductors conductors were designed and manufactured for t... more Two prototype Nb 3 Sn cable-in-conduit conductors conductors were designed and manufactured for the toroidal field (TF) magnet system of the envisaged European DEMO fusion reactor. The AC loss, contact resistance and mechanical properties of two sample conductors were tested in the Twente Cryogenic Cable Press under cyclic load up to 30 000 cycles. Though both conductors were designed to operate at 82 kA in a background magnetic field of 13.6 T, they reflect different approaches with respect to the magnet winding pack assembly. The first approach is based on react and wind technology while the second is the more common wind and react technology. Each conductor was tested first for AC loss in virgin condition without handling. The impact of Lorentz load during magnet operation was simulated using the cable press. In the press each conductor specimen was subjected to transverse cyclic load up to 30 000 cycles in liquid helium bath at 4.2 K. Here a summary of results for AC loss, contact resistance, conductor deformation, mechanical heat production and conductor stiffness evolution during cycling of the load is presented. Both conductors showed similar mechanical behaviour but quite different AC loss. In comparison with previously tested ITER TF conductors, both DEMO TF conductors possess very low contact resistance resulting in high coupling loss. At the same time, load cycling has limited impact on properties of DEMO TF conductors in comparison with ITER TF conductors.
Superconductor Science and Technology
The ITER magnet system uses cable-in-conduit conductor (CICC) technology with individual strands ... more The ITER magnet system uses cable-in-conduit conductor (CICC) technology with individual strands twisted in several stages resulting in a rope-type cable, which is inserted into a stainless steel conduit. The combination of high current (up to 68 kA) and background magnetic field (up to 13 T) results in large transverse Lorentz forces exerted on the conductors during magnet system operation. The high transverse forces, accompanied with the cyclic nature of the load, have a strong influence on the conductor properties. The Twente Cryogenic Cable Press is used to simulate the effect of the Lorentz forces on a conductor comparable to the ITER magnet operating conditions. An overview is presented of the AC coupling and hysteresis loss, mechanical deformation characteristics and inter-strand contact resistance measurement results obtained on full-size ITER CICCs measured in the Twente Cryogenic Cable Press. The aim of this work is to characterize conductors' electromagnetic and mechanical properties during cycling of the load up to 30 000 cycles. The evolution of the magnetization (AC coupling loss time constant nτ), mechanical properties and inter-strand resistance R c between selected strands is presented along with loading history. The R c between first triplet strands is also measured as a function of applied load. It is shown that transverse load cycling has a strong influence on the CICC properties. An overview of the results for eight toroidal field conductors, two central solenoid conductors, three poloidal field conductors of different types (PF1&6, PF4, PF5), one main bus-bar and one correction coil conductor is presented.
Fusion Engineering and Design
In the framework of the DEMOnstration fusion power plant (DEMO) design coordinated by the EUROfus... more In the framework of the DEMOnstration fusion power plant (DEMO) design coordinated by the EUROfusion consortium, a pre-conceptual design of the superconducting magnet system has been developed. For the toroidal field coils (TFCs), three winding pack (WP) options have been proposed; exploring different winding approaches (pancakes vs. layers), and manufacturing techniques (react & wind vs. wind & react Nb 3 Sn). Thermal-hydraulic and mechanical analyses on the three WPs have produced encouraging results, with some critical issues to be solved in future studies and optimizations. The experimental tests on TF prototype short sample conductors have demonstrated a limited performance degradation with electromagnetic cycles and significantly lower effective strains than most of the large-size Nb 3 Sn conductors reported in literature. The toroidal field quench protection circuit has been studied, starting from different topologies and focusing on the most promising one. Two designs are also presented for the central solenoid magnet, with preliminary evaluations on the AC losses during the plasma breakdown. Finally, the design of a TF winding pack based on HTS conductors and the experimental tests on "fusion-relevant" HTS cables are illustrated.
Low Temperature Physics, 2016
X-ray studies of polycrystalline and pressure compacted barium manganite powder Ba6Mn24O48 were c... more X-ray studies of polycrystalline and pressure compacted barium manganite powder Ba6Mn24O48 were conducted at room and low temperatures. It was found that the compacting process that leads to the accumulation of macro- and microstress in the sample exerts a substantial amount of influence on the diffraction pattern. We obtained data for the temperature dependence of the lattice parameters a and c, as well as the linear thermal expansion coefficient in the basal plane of the tetragonal phase at temperatures 20–100 K. In the region of the magnetic phase transition temperature 45 K, we found an abnormal change in lattice parameter a and negative values for the linear thermal expansion coefficients αa. However, at the same time there were no singularities along the c(T) dependence. We suggest that one possible reason for this temperature behavior of the structural and thermal characteristics of barium manganite, is the significant anisotropy of the crystal lattice.
IEEE Transactions on Applied Superconductivity, 2016
The DEMO reactor is expected to be the first application of fusion for electricity generation in ... more The DEMO reactor is expected to be the first application of fusion for electricity generation in the near future. To this aim, conceptual design activities are progressing in Europe (EU) under the lead of the EUROfusion Consortium in order to drive on the development of the major tokamak systems. In 2014, the activities carried out by the magnet system project team were focused on the toroidal field (TF) magnet system design and demonstrated major achievements in terms of concept proposals and of consolidated evaluations against design criteria. Several magnet system R&D activities were conducted in parallel, together with broad investigations on high temperature superconductor (HTS) technologies. In this paper, we present the outcomes of the work conducted in two areas in the 2014 magnet work program: 1) the EU inductive reactor (called DEMO1) 2014 configuration (power plant operating under inductive regime) was the basis of conceptual design activities, including further optimizations; and 2) the HTS R&D activities building upon the consolidated knowledge acquired over the past years.
IEEE Transactions on Applied Superconductivity, 2016
EUCARD2 aims to research ReBCO superconducting magnets for future accelerator applications. The p... more EUCARD2 aims to research ReBCO superconducting magnets for future accelerator applications. The properties of ReBCO conductors are very different from low temperature superconductors. To investigate dynamic field quality, stability and normal zone propagation an electrical network model for coated conductor cables was developed. To validate the model two identical samples were prepared at CERN after which measurements were taken at the University of Twente and Southampton University. The model predicts that for Roebel cable, in a changing magnetic field applied in the perpendicular direction, the hysteresis loss is much larger than the coupling loss. In the case of a changing magnetic field applied parallel to the cable coupling loss is dominant. In the first case the experiment is in good agreement with the model. In the second case the data can only be compared qualitatively because the calibration for the inductive measurement is not available.
Powder x-ray diffractometry was employed to study infusion of He into $ C_ {60} $ fullerite. It h... more Powder x-ray diffractometry was employed to study infusion of He into $ C_ {60} $ fullerite. It has been shown that the intercalation at a pressure of 1 Bar is a two-stage process, the first stage being the saturation of the octahedral voids, virtually complete after 55 hr. ...
Solid State Phenomena, 2001
ABSTRACT
Low Temperature Physics, 2010
ABSTRACT Intercalation of fullerite C60 with oxygen molecules is performed by two methods—under o... more ABSTRACT Intercalation of fullerite C60 with oxygen molecules is performed by two methods—under ordinary conditions of saturation at room temperature and gas pressure 1 atm as well as at elevated temperature (373 K) and pressure (10 atm). The time dependences of the lattice parameter of fullerite during intercalation are determined. This made it possible to evaluate the activation energy and the coefficient of diffusion of oxygen molecules in fullerite C60. It is shown that increasing the temperature and pressure of the gas increases the diffusion coefficient almost five-fold: from D≈(1.6±1.9)⋅10−14 cm2∕s at atmospheric pressure and room temperature to D≈(7.1±1.9)⋅10−14 cm2∕s for pressure P=10 atm and temperature T=373 K. The oxygen concentration in octahedral voids and the temperatures of phase transitions in solutions are determined on the basis of an analysis of the results obtained together with published data on the effect of atomic and molecular impurities on the properties of C60. The effect of oxygen impurity on the properties of an orientational phase transition and the temperature dependence of the lattice parameter is investigated.
Low Temperature Physics, 2009
The process of normal hydrogen infusion into a C60 powder at 1 bar and room temperature is monito... more The process of normal hydrogen infusion into a C60 powder at 1 bar and room temperature is monitored using x-ray diffraction. The effect of the intercalation on the lattice proves to be rather weak: the volume expansion upon complete saturation does not exceed 0.13%. The characteristic saturation time is found to be 320 h the corresponding diffusion coefficient amounts to
Journal of Applied Physics, 2003
This article reports the temperature dependence of the structural and photoelectrical properties ... more This article reports the temperature dependence of the structural and photoelectrical properties of C 60 thin films with varying crystal structure and oxygen content near the orientational disorder/order phase transition at about 260 K. X-ray diffraction data demonstrate that highly crystalline oxygen-free C 60 films undergo the first-order phase transition at 252 K with a lattice parameter discontinuity ⌬a/a of 0.22%; no discontinuity was observed in C 60 films with coexisting amorphous and nanocrystalline phases. A strong effect of the phase transition on the dark-and photoconductivity in those films is presented: In highly crystalline C 60 films both dark-and photoconductivity increase as the temperature is lowered through the transition region. However, opposite temperature changes of the conductivity are observed in nanocrystalline/amorphous C 60 films. In situ exposure of samples to oxygen gas suppresses any critical behavior. The experimental results are interpreted in terms of trap-controlled mobility of the dominant charge carriers such that the temperature changes of the conductivity are attributed to variations in the concentration, energy distribution, and population of the carrier traps at the phase transition. Differences in the parameters of the traps, which are associated with the freeze-out of the molecular orientations, may also explain the strong variations in the temperature dependence of the conductivity observed in our C 60 films and reported by other authors.
Physica B: Condensed Matter, 2001
Structural and chemical changes in C 60 thin films, grown on a Cu substrate and exposed to air or... more Structural and chemical changes in C 60 thin films, grown on a Cu substrate and exposed to air or I 2 atmosphere, at room temperature, were monitored by X-ray diffraction, Auger electron and X-ray photoelectron spectroscopy. Exposure to air is demonstrated to result not only in oxygen diffusion but also in a counter diffusion of the metal from the substrate into the C 60 matrix. In particular, 10 months of air-exposure led to the presence of Cu and O atoms at all depths over the sample and the formation of a complex which we refer to as Cu x O y C 60. The new phase is quasi-stable at room temperature, but a relatively short thermal annealing at 1501C destroys it and restores the initial C 60 FCC lattice. After 10 min of exposure of the Cu-supported C 60 films to an I 2 atmosphere the Cu sub-layer disappears completely and macroscopic amounts of a stable CuI phase are formed over the entire thickness of the C 60 film. To explain the results a model of chemically-induced counter electro-diffusion is proposed. We propose the possible usefulness of this counter diffusion approach for tailoring C 60-based materials doped with various compounds in the form of both phaseseparated composites and solid solutions (intercalated fullerides).
Fusion Engineering and Design
In fabricating REBa2Cu3Oy (REBCO) superconducting coated conductors (CCs), the CCs are required t... more In fabricating REBa2Cu3Oy (REBCO) superconducting coated conductors (CCs), the CCs are required to increase deposition rate and crystallinities in order to reduce the cost of CCs fabrication. However, using the conventional pulsed laser deposition (PLD) method, the deposition rate is enhanced as the energy density of the pulsed laser is increased, while the crystallinities of the REBCO layer are deteriorated. In this work, in order to improve both the deposition rate and superconducting properties, we fabricated SmBa2Cu3Oy (Sm123) coated conductors using VLS growth technique. VLS growth technique is expected rapid growth rate and good crystallinity of REBCO films [1]. Furthermore, REBCO films fabricated using VLS growth technique by several group is reported that this films indicate high deposition rate and crystallinities [2,3]. The VLS growth technique consists of the following three steps by PLD method. The first step is to fabricate a solid Sm123 layer. The second step is to for...
Superconductor Science and Technology, Oct 22, 2018
Due to an error in the production process, the caption for figure 2 is incorrect. It should corre... more Due to an error in the production process, the caption for figure 2 is incorrect. It should correctly read 'Figure 2. Configuration of SuperPower 2G HTS Tape SCS#030'.
Superconductor Science and Technology
Many high-temperature superconductor (HTS) applications require superconducting cables with high ... more Many high-temperature superconductor (HTS) applications require superconducting cables with high currents while operating in an alternating magnetic field. HTS cables should be composed of numerous superconducting tapes to achieve the required current capacity. Alternating current and magnetic fields cause AC losses in such cables and can provoke conductor instability. AC losses and contact resistances were measured of several cable designs based on commercially available REBCO tapes at the University of Twente. The AC loss was measured under identical conditions for eight REBCO conductors manufactured according to three types of cabling methods—CORC® (Conductor on Round Core), Roebel, and stacked tape, including a full-size REBCO CICC (cable in conduit conductor). The measurements were done at T = 4.2 K without transport current in a sinusoidal AC magnetic field of 0.4 T amplitude and frequencies from 5 to 55 mHz. The AC loss was measured simultaneously by calibrated gas flow calor...
Superconductor Science and Technology
A CORC ® cable is composed of several layers of helically wound high-temperature superconducting ... more A CORC ® cable is composed of several layers of helically wound high-temperature superconducting (HTS) tapes on a round core with the winding direction reversed in each successive layer. The cable is flexible but the flexibility is limited by the critical strain value causing breakage of the HTS layer when this strain level is exceeded. The cables for magnets in fusion reactors experience large mechanical and electromagnetic loads. These loads arise from the cabling, coil manufacturing, cooling, and magnet operation. In order to optimize the manufacture and operating conditions, the mechanical behavior of CORC ® cables must be understood for the different relevant loading conditions. The cable configuration with many contact interactions between tapes and the non-linear behavior of the materials during the production and operating conditions makes the modeling challenging. Detailed finite element (FE) modeling is required to account for these complexities. The FE modeling allows an accurate calculation of the stress-strain state of the cable components under various loads and avoids time-consuming large-scale experimental optimization studies. This work presents a detailed FE modeling of the 3D stress-strain state in a CORC ® wire under bending load. The elastic-plastic properties of the individual tape composite materials and its temperature dependence are taken into account. The FE model is experimentally validated by a multi-layer CORC ® bending test performed by Advanced Conductor Technologies LLC. A critical intrinsic tensile strain value of 0.45% is taken as the threshold where the individual tape performance becomes irreversibly degraded. The proposed FE model describes the bending test of the CORC ® wire adequately and thus can be used to study other types of loads. A parametric study is ongoing with dependent variables to pursue a further optimization of CORC ® cables and wires for various applications.
IEEE Transactions on Applied Superconductivity
The central solenoid model coil (CSMC) project of the China Fusion Engineering Test Reactor was l... more The central solenoid model coil (CSMC) project of the China Fusion Engineering Test Reactor was launched in 2014 to verify the technological feasibility of a large-scale superconducting magnet at the Institute of Plasma and Physics Chinese Academy of Sciences. The short twist pitch design recommended by CEA is chosen for the CSMC Nb 3 Sn cable-in-conduit conductors. In order to better understand the evolution of transport properties and coupling losses related to the effect of electromagnetic load cycles, the mechanical and electrical properties were measured and investigated employing a special cryogenic press facility for the transverse mechanical loadings. The results show that the transverse compression (d y) versus applied load force (F y) is different from first to subsequent loading cycles. This mechanical behavior can be interpreted by the combination of strands bending between the crossovers and strands deformation at the crossovers. The fitting relations of d y versus F y are also presented. The evolution of interstrand contact resistance (R c) in the cabling stages with cyclic history and pressure effects are discussed. In addition, a fitting relation of R c versus F y is presented based on a combination of strand's microsliding and copper matrix resistivity. A clear correlation between intrapetal resistance R c and coupling loss is also found.
Superconductor Science and Technology
Two prototype Nb 3 Sn cable-in-conduit conductors conductors were designed and manufactured for t... more Two prototype Nb 3 Sn cable-in-conduit conductors conductors were designed and manufactured for the toroidal field (TF) magnet system of the envisaged European DEMO fusion reactor. The AC loss, contact resistance and mechanical properties of two sample conductors were tested in the Twente Cryogenic Cable Press under cyclic load up to 30 000 cycles. Though both conductors were designed to operate at 82 kA in a background magnetic field of 13.6 T, they reflect different approaches with respect to the magnet winding pack assembly. The first approach is based on react and wind technology while the second is the more common wind and react technology. Each conductor was tested first for AC loss in virgin condition without handling. The impact of Lorentz load during magnet operation was simulated using the cable press. In the press each conductor specimen was subjected to transverse cyclic load up to 30 000 cycles in liquid helium bath at 4.2 K. Here a summary of results for AC loss, contact resistance, conductor deformation, mechanical heat production and conductor stiffness evolution during cycling of the load is presented. Both conductors showed similar mechanical behaviour but quite different AC loss. In comparison with previously tested ITER TF conductors, both DEMO TF conductors possess very low contact resistance resulting in high coupling loss. At the same time, load cycling has limited impact on properties of DEMO TF conductors in comparison with ITER TF conductors.
Superconductor Science and Technology
The ITER magnet system uses cable-in-conduit conductor (CICC) technology with individual strands ... more The ITER magnet system uses cable-in-conduit conductor (CICC) technology with individual strands twisted in several stages resulting in a rope-type cable, which is inserted into a stainless steel conduit. The combination of high current (up to 68 kA) and background magnetic field (up to 13 T) results in large transverse Lorentz forces exerted on the conductors during magnet system operation. The high transverse forces, accompanied with the cyclic nature of the load, have a strong influence on the conductor properties. The Twente Cryogenic Cable Press is used to simulate the effect of the Lorentz forces on a conductor comparable to the ITER magnet operating conditions. An overview is presented of the AC coupling and hysteresis loss, mechanical deformation characteristics and inter-strand contact resistance measurement results obtained on full-size ITER CICCs measured in the Twente Cryogenic Cable Press. The aim of this work is to characterize conductors' electromagnetic and mechanical properties during cycling of the load up to 30 000 cycles. The evolution of the magnetization (AC coupling loss time constant nτ), mechanical properties and inter-strand resistance R c between selected strands is presented along with loading history. The R c between first triplet strands is also measured as a function of applied load. It is shown that transverse load cycling has a strong influence on the CICC properties. An overview of the results for eight toroidal field conductors, two central solenoid conductors, three poloidal field conductors of different types (PF1&6, PF4, PF5), one main bus-bar and one correction coil conductor is presented.
Fusion Engineering and Design
In the framework of the DEMOnstration fusion power plant (DEMO) design coordinated by the EUROfus... more In the framework of the DEMOnstration fusion power plant (DEMO) design coordinated by the EUROfusion consortium, a pre-conceptual design of the superconducting magnet system has been developed. For the toroidal field coils (TFCs), three winding pack (WP) options have been proposed; exploring different winding approaches (pancakes vs. layers), and manufacturing techniques (react & wind vs. wind & react Nb 3 Sn). Thermal-hydraulic and mechanical analyses on the three WPs have produced encouraging results, with some critical issues to be solved in future studies and optimizations. The experimental tests on TF prototype short sample conductors have demonstrated a limited performance degradation with electromagnetic cycles and significantly lower effective strains than most of the large-size Nb 3 Sn conductors reported in literature. The toroidal field quench protection circuit has been studied, starting from different topologies and focusing on the most promising one. Two designs are also presented for the central solenoid magnet, with preliminary evaluations on the AC losses during the plasma breakdown. Finally, the design of a TF winding pack based on HTS conductors and the experimental tests on "fusion-relevant" HTS cables are illustrated.
Low Temperature Physics, 2016
X-ray studies of polycrystalline and pressure compacted barium manganite powder Ba6Mn24O48 were c... more X-ray studies of polycrystalline and pressure compacted barium manganite powder Ba6Mn24O48 were conducted at room and low temperatures. It was found that the compacting process that leads to the accumulation of macro- and microstress in the sample exerts a substantial amount of influence on the diffraction pattern. We obtained data for the temperature dependence of the lattice parameters a and c, as well as the linear thermal expansion coefficient in the basal plane of the tetragonal phase at temperatures 20–100 K. In the region of the magnetic phase transition temperature 45 K, we found an abnormal change in lattice parameter a and negative values for the linear thermal expansion coefficients αa. However, at the same time there were no singularities along the c(T) dependence. We suggest that one possible reason for this temperature behavior of the structural and thermal characteristics of barium manganite, is the significant anisotropy of the crystal lattice.
IEEE Transactions on Applied Superconductivity, 2016
The DEMO reactor is expected to be the first application of fusion for electricity generation in ... more The DEMO reactor is expected to be the first application of fusion for electricity generation in the near future. To this aim, conceptual design activities are progressing in Europe (EU) under the lead of the EUROfusion Consortium in order to drive on the development of the major tokamak systems. In 2014, the activities carried out by the magnet system project team were focused on the toroidal field (TF) magnet system design and demonstrated major achievements in terms of concept proposals and of consolidated evaluations against design criteria. Several magnet system R&D activities were conducted in parallel, together with broad investigations on high temperature superconductor (HTS) technologies. In this paper, we present the outcomes of the work conducted in two areas in the 2014 magnet work program: 1) the EU inductive reactor (called DEMO1) 2014 configuration (power plant operating under inductive regime) was the basis of conceptual design activities, including further optimizations; and 2) the HTS R&D activities building upon the consolidated knowledge acquired over the past years.
IEEE Transactions on Applied Superconductivity, 2016
EUCARD2 aims to research ReBCO superconducting magnets for future accelerator applications. The p... more EUCARD2 aims to research ReBCO superconducting magnets for future accelerator applications. The properties of ReBCO conductors are very different from low temperature superconductors. To investigate dynamic field quality, stability and normal zone propagation an electrical network model for coated conductor cables was developed. To validate the model two identical samples were prepared at CERN after which measurements were taken at the University of Twente and Southampton University. The model predicts that for Roebel cable, in a changing magnetic field applied in the perpendicular direction, the hysteresis loss is much larger than the coupling loss. In the case of a changing magnetic field applied parallel to the cable coupling loss is dominant. In the first case the experiment is in good agreement with the model. In the second case the data can only be compared qualitatively because the calibration for the inductive measurement is not available.