juan knaster - Academia.edu (original) (raw)
Papers by juan knaster
Nature Physics, 2016
Fusion materials research started in the early 1970s following the Q.1 observation of the degrada... more Fusion materials research started in the early 1970s following the Q.1 observation of the degradation of irradiated materials used in the first Q.2 38 eventually used for the generation of electricity by the conventional 39 scheme of a thermal power plant. 40 Primary neutron irradiation damage 41 Neutrons have about the same mass as protons; however, unlike 42 protons, they can strongly interact with atoms at very low 43 energies (their charge neutrality implies that no Coulomb barrier 44 has to be overcome). Degradation of materials under neutron 45 irradiation was already anticipated in 1946 by Eugene Wigner, who 46 argued theoretically that neutrons could displace atoms through 47 irradiation: 'The matter has great scientific interest because pile 48 irradiations should permit the artificial formation of displacements 49 in definite numbers and a study of the effect of these on thermal and 50 electrical conductivity, tensile strength, ductility, etc., as demanded 51 by the theory' 3. 52 The integration of the flux in a certain period of time-the 53 fluence-and the absorbed dose are typically the two parameters 54 used to characterize the exposure of a given material to irradiation, 55 irrespective of the nature of the irradiated material. However, the 56 number of factors that play a primary role in the eventual damage of 57 a material exposed to a particular irradiation makes this description 58 incomplete. 59 Under neutron irradiation, in the first stage after collision, a 60 primary knock-on atom (PKA) is generated: the primary atom that 61 recoils after being impacted by the neutron. This initial interaction 62 can be both elastic and inelastic. In the latter case, some of 63 the neutron's energy is transferred to a specific excited state of 64 the collided atom, leaving the neutron and the recoiling primary 65 atom with substantially less kinetic energy. Figure 1 illustrates the 66 pathways of irradiation damage. Following the first impact, if no 67 excited state is generated, the PKA recoils quasi-elastically and 68 dissipates its initial kinetic energy by exciting the electrons of the 69 medium and by elastic collisions with surrounding atoms of the 70 impacted material. The total kinetic energy of the atoms involved 71 in the recoiling is nearly conserved; the sum of the energies of 48 reactor can be sized down, a fusion reactor retains certain size and 49 complexity limitations, which tend to correlate with cost. 50 Progress in plasma-facing materials research 51 Materials capable of withstanding extreme heat loads in addition 52 to neutron bombardments are required for the plasma-facing 53 components. The irradiation damage becomes secondary compared 54 to the high generated thermal power densities (up to 20 MW m −2 ; 55 refs 85,86) in the divertor armour, the lifetime of which could be 56 limited to two years owing to erosion phenomena (which could 57 still be affordable given the relative ease of removal compared 58 with that of the blanket). The key properties of plasma-facing 59 components are thermal conductivity, strength, ductility, thermal 60 shock resistance, thermal fatigue resistance, structural stability at 61 high temperature, low activation and stability of all these properties 62 under long-term irradiation with 14.1 MeV neutrons 87. Finding a 63 material with optimal behaviour regarding all these properties is an 64 impossible challenge. Despite the partly contradictory properties, 65 of an inexhaustible and safe source of energy. Lev Artsimovich, one 2 of the founders of the tokamak concept, was asked, at the dawn 3 of fusion research, when commercial fusion power would become 4 available. He said: 'Fusion will be ready when society needs it, maybe even a short time before that' .
LIPAc, under installation in Rokkasho aims to produce a 125 mA CW deuteron beam accelerated from ... more LIPAc, under installation in Rokkasho aims to produce a 125 mA CW deuteron beam accelerated from 100 keV up to 5 MeV through the world longest RFQ and up to 9 MeV after a SRF Linac housing eight 175 MHz HWR superconducting cavities. It will become the validating prototype of IFMIF’s accelerators. The objective of 18 -2 -1 IFMIF is to generate a neutron flux of 10 m s at 14 MeV for fusion materials testing, by using 2 x 125 mA CW 40 MeV D + beams impacting on a 25 mm thick liquid lithium jet flowing at 15 m/s. The first attempt to validate the high current accelerator required for fusion materials testing was in the US in the early 80s under FMIT project with a H2 + 100 mA CW 2 MeV linac. The accelerator know-how has matured since the times of FMIT concep tion in the 70s. Today, operating the required accelerator seems feasible thanks to the understanding of the beam halo physics and the three main technological break throughs in accelerator technology: a) the ECR ion source for li...
Fusion Engineering and Design, 2020
Nuclear Fusion, 2017
As part of the Engineering Validation and Engineering Design Activities (EVEDA) phase for the Int... more As part of the Engineering Validation and Engineering Design Activities (EVEDA) phase for the International Fusion Materials Irradiation Facility IFMIF, major elements of Lithium Target Facility and the Test Facility were designed, prototyped and validated. For the Lithium Target Facility, the ELTL lithium loop was built and used to test the stability (waves and long term) of the lithium flow in the target, work out the startup procedures, and test lithium purification and analysis. It was confirmed by experiments in the Lifus 6 plant, that Lithium corrosion on ferritic martensitic steels is acceptably low. Furthermore, complex remote handling procedures for the remote maintenance of the target in the Test Cell environment were successfully practiced. For the Test Facility, two variants of a High Flux Test Module were prototyped and tested in helium loops, demonstrating their good capabilities of maintaining the material specimens at the desired temperature with a low temperature spread. Irradiation tests were performed for heated specimen capsules and irradiation instrumentation in the BR2 reactor. The Small Specimen Test Technique (SSTT), essential for obtaining material test results with limited irradiation volume, was advanced by evaluating specimen shape and test technique influences.
Nuclear Materials and Energy, 2016
The International Fusion Materials Irradiation Facility (IFMIF), presently in the Engineering Val... more The International Fusion Materials Irradiation Facility (IFMIF), presently in the Engineering Validation and Engineering Design Activities (EVEDA) phase was started from 2007 under the frame of the Broader Approach (BA) agreement. In the activities, a prototype Li loop with the world's highest flow rate of 30 0 0 L/min was constructed in 2010, and it succeeded in generating a 100 mm wide and 25 mm thick with a free-surface lithium flow along a concave back plate steadily at a high-speed of 15 m/s at 250 °C for 1300 h. In the demonstration operation it was needed to develop the Li flowing measurement system with precious resolution less than 0.1 mm, and a new wave height measuring method which is laserprobe method was developed for measurements of the 3D geometry of the liquid Li target surface. Using the device, the stability of the variation in the Li flowing thickness which is required in the IFMIF specification was ± 1 mm or less as the liquid Li target, and the result was satisfied with it and the feasibility of the long-term stable liquid Li flow was also verified. The results of the other engineering validation tests such as lithium purification tests of lithium target facility have also been evaluated and summarized.
Journal of Nuclear Engineering and Radiation Science, 2017
A liquid Li jet flowing at 15 m/s under a high vacuum of 10−3 Pa is intended to serve as a beam t... more A liquid Li jet flowing at 15 m/s under a high vacuum of 10−3 Pa is intended to serve as a beam target (Li target) in the planned International Fusion Materials Irradiation Facility (IFMIF). The engineering validation and engineering design activities (EVEDA) for the IFMIF are being implemented under the broader approach (BA) agreement. As a major activity of the Li target facility, the EVEDA Li test loop (ELTL) was constructed by the Japan Atomic Energy Agency. A stable Li target under the IFMIF conditions (Li temperature: 523.15 K, velocity: 15 m/s, and vacuum pressure: 10−3 Pa) was demonstrated using ELTL. This study focuses on a cavitationlike acoustic noise detected in a downstream conduit where the Li target flowed under vacuum conditions. This noise was investigated using acoustic-emission (AE) sensors installed at eight locations via acoustic wave guides. The sound intensity of the acoustic noise was examined against the cavitation number of the Li target. In addition, two t...
Reviews of Accelerator Science and Technology, 2015
Fusion materials research is a worldwide endeavor as old as the parallel one working toward the l... more Fusion materials research is a worldwide endeavor as old as the parallel one working toward the long term stable confinement of ignited plasma. In a fusion reactor, the preservation of the required minimum thermomechanical properties of the in-vessel components exposed to the severe irradiation and heat flux conditions is an indispensable factor for safe operation; it is also an essential goal for the economic viability of fusion. Energy from fusion power will be extracted from the 14 MeV neutron freed as a product of the deuterium–tritium fusion reactions; thus, this kinetic energy must be absorbed and efficiently evacuated and electricity eventually generated by the conventional methods of a thermal power plant. Worldwide technological efforts to understand the degradation of materials exposed to 14 MeV neutron fluxes [Formula: see text] m[Formula: see text]s[Formula: see text], as expected in future fusion power plants, have been intense over the last four decades. Existing neutr...
Fusion Engineering and Design, 2016
h i g h l i g h t s • Nitrogen contained in solid Lithium is converted into Ammonium ion. • Ammon... more h i g h l i g h t s • Nitrogen contained in solid Lithium is converted into Ammonium ion. • Ammonium ion is suitably quantified by ionic chromatograph or by Ammonia sensor. • Good agreement of the partner's results has been achieved. • Maximum operative reproducibility and blank subtraction are necessary.
Vacuum, 2004
The LHC will be the world next generation accelerator to be operational in 2007 at CERN. The UHV ... more The LHC will be the world next generation accelerator to be operational in 2007 at CERN. The UHV requirements force the installation of ion pumps in the experimental areas of ATLAS. Due to the unacceptable particle background that standards ion pumps may generate, a reduction in the amount of material constitutive of the pump body is required. Hence, an stainless steel 0.8 mm thick body annular triode ion pump has been designed. A pumping speed of ~ 20 l/s at 10-9 mbar is provided by 15 pumping elements. Finite elements analysis and destructive tests have been performed in its design. Final vacuum tests results are shown.
Journal of Nuclear Materials, 2014
The d-Li based International Fusion Materials Irradiation Facility (IFMIF) will provide a high ne... more The d-Li based International Fusion Materials Irradiation Facility (IFMIF) will provide a high neutron intensity neutron source with a suitable neutron spectrum to fulfil the requirements for testing and qualifying fusion materials under fusion reactor relevant irradiation conditions. The IFMIF project, presently in its Engineering Validation and Engineering Design Activities (EVEDA) phase under the Broader Approach (BA) Agreement between Japan Government and EURATOM, aims at the construction and testing of the most challenging facility subsystems , such as the first accelerator stage, the Li target and loop, and irradiation test modules, as well as the design of the entire facility, thus to be ready for the IFMIF construction with a clear understanding of schedule and cost at the termination of the BA mid-2017. The paper reviews the IFMIF facility and its principles, and reports on the status of the EVEDA activities and achievements.
Vacuum, 2002
The Large Hadron Collider (LHC) is a proton-proton collider with a centre of mass energy of 14 Te... more The Large Hadron Collider (LHC) is a proton-proton collider with a centre of mass energy of 14 TeV presently in construction at CERN. The four colliding experiments will require special vacuum chamber designs to allow the best physics performance. New technologies such as very thin beampipes to increase transparency, optimized rotatable flanges, wired supports with special layers to reduce dynamic effects, special heating jackets, double wall chambers and mass minimized annular ion pumps are being developed by CERN for this application.
IEEE Transactions on Applied Superconductivity, 2012
The Toroidal Field Coils (TFC) are subject to mandatory geometrical tolerances constraints for ac... more The Toroidal Field Coils (TFC) are subject to mandatory geometrical tolerances constraints for acceptance by ITER Organization. As a consequence, pre-assembly tests are foreseen to verify if each single coil meets such criteria, including laser tracking, and possibly warm magnetic measurements on each of the finished winding packs. Possible performance limitations of the acceptance tests for the winding pack are
IEEE Transactions on Applied Superconductivity, 2012
The Paschen breakdown is the outcome of an avalanche effect related with the ionization of a gas ... more The Paschen breakdown is the outcome of an avalanche effect related with the ionization of a gas under electric stress. Paschen's law defines the voltage breakdown of rarefied (low pressure) gases as a function of the product of pressure PPP and distance ddd between electrodes showing a minimum value (typically of the order of hundreds V) below which the breakdown cannot take place. The actual field level depends on the gas, on the shape, material and surface conditions (roughness, cleanness and presence of oxide layers) of the electrodes; hence there is a big dispersion in the results available due to the referred number of parameters influencing the voltage breakdown. The design of the electrical insulation of superconducting magnets targets a safety factor of times\timestimes10 on dielectric strength over specified voltages using the intrinsic dielectric strength of the materials. A crack in the insulation or a flaw not detected by visual inspection would not necessarily lead to an electrical break during the acceptance tests in air given the high dielectric strength of air (typically values over 1 kV/mm). However, it would lead to an electrical failure during operation if Paschen conditions take place. Since the Paschen minimum occurs under vacuum, it is irrelevant for conventional High Voltage (HV) engineering. The application of superconducting technology for plasma fusion devices with a growing size and complexity of magnets has shown Paschen testing as an essential tool. During magnet operation inside the cryostat conditions, if a He leak takes place, critical pressures can be reached locally and Paschen breakdown might occur at voltages significantly lower than the designed ones. The present paper covers an existing gap in International Standards and scientific literature addressing Paschen testing of superconducting magnets and explains why it is needed and how the tests should be done in the most efficient way.
AIP Conference Proceedings, 2012
ABSTRACT During the last years, two cyanate ester epoxy blends supplied by European and US indust... more ABSTRACT During the last years, two cyanate ester epoxy blends supplied by European and US industry have been successfully qualified for the ITER TF coil insulation. The results of the qualification of a third CE blend supplied by Industrial Summit Technology (IST, Japan) will be presented in this paper. Sets of test samples were fabricated exactly under the same conditions as used before. The reinforcement of the composite consists of wrapped R-glass / polyimide tapes, which are vacuum pressure impregnated with the resin. The mechanical properties of this material were characterized prior to and after reactor irradiation to a fast neutron fluence of 2×1022m-2 (E>0.1 MeV), i.e. twice the ITER design fluence. Static and dynamic tensile as well as static short beam shear tests were carried out at 77 K. In addition, stress strain relations were recorded to determine the Young's modulus at room temperature and at 77 K. The results are compared in detail with the previously qualified materials from other suppliers.
Superconductor Science and Technology, 2013
ABSTRACT The ITER toroidal field (TF) system features eighteen coils that will provide the magnet... more ABSTRACT The ITER toroidal field (TF) system features eighteen coils that will provide the magnetic field necessary to confine the plasma. Each winding pack is composed of seven double pancakes (DP) connected through praying hands joints. Shaking hands joints are used to interface the terminals of the conductor with the feeder and inter-coil U-shaped bus bars. The feasibility of operating plasma scenarios depends on the ability of the magnets to retain sufficient temperature and current margins. In this respect, the joints represent a possible critical region due to the combination of steady state Joule heating in the resistance of the joint and coupling losses and currents in ramped operation. The temperature and current margins of both DP and terminal joints are analysed during the 15 and 17 MA plasma scenarios. The effect on the joint performance of feasible optimization solutions, such as rotation of the terminal joints and sole RRR increase, is explored. The characterization of the TF coil joints is completed by the estimation of the coupling loss time constant for different inter-strand and strand-to-joint resistance values. The study is carried out with the code JackPot-ACDC, allowing the analysis of lap-type joints with a strand-level detail.
IEEE Transactions on Applied Superconductivity, 2012
The Toroidal Field Coils (TFC) for the ITER magnet system are large 'D' shaped coils consisting o... more The Toroidal Field Coils (TFC) for the ITER magnet system are large 'D' shaped coils consisting of a Winding Pack (WP) enclosed in a stainless steel (316LN) casing. The WP is a bonded structure of 7 Double Pancakes (DP), each made up of a stainless steel radial plate (RP) housing the reacted Nb3Sn circular cable-in-conduit superconductor (CICC), which operate at 4.5 K. The cooling of the WP is assured by helium feed in the CICC through one inlet for each DP at an average mass flow of 7.9 g/s in the conductor. The helium inlet is critical from a structural point of view because it has to withstand both static and cyclic strains in the order of coming from energization of the TFC and plasma operation conditions. The assembly of the helium inlet around the conductor includes a fillet weld that makes it even more critical. This paper describes the analyses results performed for the (static and fatigue) structural assessment of the helium inlet. It describes the statistical approach followed to determine the number of cycles to be used in the validation tests.
IEEE Transactions on Applied Superconductivity, 2012
ABSTRACT The insulation of the ITER TF coils consists of multiple wrapped layers of glass fiber p... more ABSTRACT The insulation of the ITER TF coils consists of multiple wrapped layers of glass fiber polyimide sandwich tapes. In order to simplify the fabrication process, the polyimide tape can be bonded to the glass fiber tape, mainly to avoid misalignments of the polyimide tape. However, due to the intense neutron and gamma-radiation exposure, bonding agents have to be radiation resistant, otherwise the composite will be severely damaged, as was observed for the ITER TF model coil insulation. Two bonded glass fiber polyimide tapes (40 mm wide, similar to 0.175 mm thick) were supplied by Arisawa, Japan, and Advanced Composites Group, United Kingdom. Test materials were fabricated based on the build-up of the ITER TF turn insulation and vacuum pressure impregnated with a 40: 60 cyanate ester/epoxy blend supplied by Huntsman, Switzerland. The mechanical properties of these materials were characterized prior to and after reactor irradiation to a fast neutron fluence of 2 x 10(22) m(-2) (E > 0.1 MeV), i.e. twice the ITER design fluence. Static and dynamic tensile tests were carried out at RT and 77 K. The Arisawa tape showed excellent mechanical properties.
IEEE Transactions on Applied Superconductivity, 2012
The ITER superconducting magnet structures (Toroidal Field coils (TF), Central Solenoid (CS), Pol... more The ITER superconducting magnet structures (Toroidal Field coils (TF), Central Solenoid (CS), Poloidal Field coils (PF), Correction Coils (CC) and Feeders), representing a total weight of approximately 10 000 tons, are submitted to gravitational and seismic forces, stresses induced by constrained thermal contractions during cool-down from 300 K to 4.5 K, and large Lorentz forces in the superconducting coils. Although not classified as Safety Important Class (SIC) components, the sensors (stress, displacements, thermometers) used to monitor the thermo-mechanical behaviour of the structures are important diagnostic means to assess the designs, give support to operation and survey possible fatigue effects over the 20 years lifetime of the tokamak. Environmental operating conditions are unique and severe. Sensors and their wiring have to operate under cryostat vacuum (<10-4 Pa total gas pressure), under magnetic inductions of several Tesla, at low temperature (4.5 K), in presence of a neutron fluence in the order of 10 22 n/m 2 and a maximum associated gamma dose of 10MGy over a period of 20 years. In addition, the fast and slow cycling of very large currents in the superconducting magnets and plasma generate large eddy currents, thus heat loads and electro-motive forces (voltages) in the various parts of the structures, and a large electromagnetic noise. The design philosophy and the choice of sensor technologies, some of which are at the frontier of present technology and as such require development in collaboration with industry, are presented that satisfy objectives and severe working conditions. Specifically, the near to 1 000 measuring points for thermo-mechanical data of the ITER magnet structures will rely for 20% on "classical", copper-wired technologies, and for 80% on specially developed optical fibrebased sensors.
IEEE Transactions on Applied Superconductivity, 2012
ABSTRACT The ITER Magnet System contains 18 Toroidal Field Coils (TFC). These are large D-shaped ... more ABSTRACT The ITER Magnet System contains 18 Toroidal Field Coils (TFC). These are large D-shaped coils of about 300 t, 17.5-m height and 9-m width. They consist of a Winding Pack (WP) enclosed in a rigid structural steel case, the Toroidal Field Coil Case (TFCC). The WP is a bonded structure of 7 Double Pancakes (DP), each made up of a radial plate (RP) housing the reacted rmNb3rmSn{\rm Nb}_{3}{\rm Sn}rmNb3rmSn cable-in-conduit superconductor (CICC), which operate at 4.5 K in supercritical helium. The conductor carries a current of 68 kA in operation to produce a nominal peak field of 11.8 T. The total stored magnetic energy in the 18 TFCs is 41 GJ. While the Japanese and European Domestic Agencies that are in charge of the procurement of the TFCs are progressing with the manufacturing design and the fabrication trials prior to launch the production of the real coils, the ITER Organization (IO) is completing the development and qualification of the most critical items, e.g. cyanate ester and resin blends for the conductor and WP insulation system, the terminal region, the helium inlet, a charged resin system for the filling of the gap between the WP and the TFCC and the general tolerancing especially at the interfaces between the neighboring systems. This paper presents the final design of the TFCs and the results of the developments carried out in the aforementioned areas in the last 2 years.
Nature Physics, 2016
Fusion materials research started in the early 1970s following the Q.1 observation of the degrada... more Fusion materials research started in the early 1970s following the Q.1 observation of the degradation of irradiated materials used in the first Q.2 38 eventually used for the generation of electricity by the conventional 39 scheme of a thermal power plant. 40 Primary neutron irradiation damage 41 Neutrons have about the same mass as protons; however, unlike 42 protons, they can strongly interact with atoms at very low 43 energies (their charge neutrality implies that no Coulomb barrier 44 has to be overcome). Degradation of materials under neutron 45 irradiation was already anticipated in 1946 by Eugene Wigner, who 46 argued theoretically that neutrons could displace atoms through 47 irradiation: 'The matter has great scientific interest because pile 48 irradiations should permit the artificial formation of displacements 49 in definite numbers and a study of the effect of these on thermal and 50 electrical conductivity, tensile strength, ductility, etc., as demanded 51 by the theory' 3. 52 The integration of the flux in a certain period of time-the 53 fluence-and the absorbed dose are typically the two parameters 54 used to characterize the exposure of a given material to irradiation, 55 irrespective of the nature of the irradiated material. However, the 56 number of factors that play a primary role in the eventual damage of 57 a material exposed to a particular irradiation makes this description 58 incomplete. 59 Under neutron irradiation, in the first stage after collision, a 60 primary knock-on atom (PKA) is generated: the primary atom that 61 recoils after being impacted by the neutron. This initial interaction 62 can be both elastic and inelastic. In the latter case, some of 63 the neutron's energy is transferred to a specific excited state of 64 the collided atom, leaving the neutron and the recoiling primary 65 atom with substantially less kinetic energy. Figure 1 illustrates the 66 pathways of irradiation damage. Following the first impact, if no 67 excited state is generated, the PKA recoils quasi-elastically and 68 dissipates its initial kinetic energy by exciting the electrons of the 69 medium and by elastic collisions with surrounding atoms of the 70 impacted material. The total kinetic energy of the atoms involved 71 in the recoiling is nearly conserved; the sum of the energies of 48 reactor can be sized down, a fusion reactor retains certain size and 49 complexity limitations, which tend to correlate with cost. 50 Progress in plasma-facing materials research 51 Materials capable of withstanding extreme heat loads in addition 52 to neutron bombardments are required for the plasma-facing 53 components. The irradiation damage becomes secondary compared 54 to the high generated thermal power densities (up to 20 MW m −2 ; 55 refs 85,86) in the divertor armour, the lifetime of which could be 56 limited to two years owing to erosion phenomena (which could 57 still be affordable given the relative ease of removal compared 58 with that of the blanket). The key properties of plasma-facing 59 components are thermal conductivity, strength, ductility, thermal 60 shock resistance, thermal fatigue resistance, structural stability at 61 high temperature, low activation and stability of all these properties 62 under long-term irradiation with 14.1 MeV neutrons 87. Finding a 63 material with optimal behaviour regarding all these properties is an 64 impossible challenge. Despite the partly contradictory properties, 65 of an inexhaustible and safe source of energy. Lev Artsimovich, one 2 of the founders of the tokamak concept, was asked, at the dawn 3 of fusion research, when commercial fusion power would become 4 available. He said: 'Fusion will be ready when society needs it, maybe even a short time before that' .
LIPAc, under installation in Rokkasho aims to produce a 125 mA CW deuteron beam accelerated from ... more LIPAc, under installation in Rokkasho aims to produce a 125 mA CW deuteron beam accelerated from 100 keV up to 5 MeV through the world longest RFQ and up to 9 MeV after a SRF Linac housing eight 175 MHz HWR superconducting cavities. It will become the validating prototype of IFMIF’s accelerators. The objective of 18 -2 -1 IFMIF is to generate a neutron flux of 10 m s at 14 MeV for fusion materials testing, by using 2 x 125 mA CW 40 MeV D + beams impacting on a 25 mm thick liquid lithium jet flowing at 15 m/s. The first attempt to validate the high current accelerator required for fusion materials testing was in the US in the early 80s under FMIT project with a H2 + 100 mA CW 2 MeV linac. The accelerator know-how has matured since the times of FMIT concep tion in the 70s. Today, operating the required accelerator seems feasible thanks to the understanding of the beam halo physics and the three main technological break throughs in accelerator technology: a) the ECR ion source for li...
Fusion Engineering and Design, 2020
Nuclear Fusion, 2017
As part of the Engineering Validation and Engineering Design Activities (EVEDA) phase for the Int... more As part of the Engineering Validation and Engineering Design Activities (EVEDA) phase for the International Fusion Materials Irradiation Facility IFMIF, major elements of Lithium Target Facility and the Test Facility were designed, prototyped and validated. For the Lithium Target Facility, the ELTL lithium loop was built and used to test the stability (waves and long term) of the lithium flow in the target, work out the startup procedures, and test lithium purification and analysis. It was confirmed by experiments in the Lifus 6 plant, that Lithium corrosion on ferritic martensitic steels is acceptably low. Furthermore, complex remote handling procedures for the remote maintenance of the target in the Test Cell environment were successfully practiced. For the Test Facility, two variants of a High Flux Test Module were prototyped and tested in helium loops, demonstrating their good capabilities of maintaining the material specimens at the desired temperature with a low temperature spread. Irradiation tests were performed for heated specimen capsules and irradiation instrumentation in the BR2 reactor. The Small Specimen Test Technique (SSTT), essential for obtaining material test results with limited irradiation volume, was advanced by evaluating specimen shape and test technique influences.
Nuclear Materials and Energy, 2016
The International Fusion Materials Irradiation Facility (IFMIF), presently in the Engineering Val... more The International Fusion Materials Irradiation Facility (IFMIF), presently in the Engineering Validation and Engineering Design Activities (EVEDA) phase was started from 2007 under the frame of the Broader Approach (BA) agreement. In the activities, a prototype Li loop with the world's highest flow rate of 30 0 0 L/min was constructed in 2010, and it succeeded in generating a 100 mm wide and 25 mm thick with a free-surface lithium flow along a concave back plate steadily at a high-speed of 15 m/s at 250 °C for 1300 h. In the demonstration operation it was needed to develop the Li flowing measurement system with precious resolution less than 0.1 mm, and a new wave height measuring method which is laserprobe method was developed for measurements of the 3D geometry of the liquid Li target surface. Using the device, the stability of the variation in the Li flowing thickness which is required in the IFMIF specification was ± 1 mm or less as the liquid Li target, and the result was satisfied with it and the feasibility of the long-term stable liquid Li flow was also verified. The results of the other engineering validation tests such as lithium purification tests of lithium target facility have also been evaluated and summarized.
Journal of Nuclear Engineering and Radiation Science, 2017
A liquid Li jet flowing at 15 m/s under a high vacuum of 10−3 Pa is intended to serve as a beam t... more A liquid Li jet flowing at 15 m/s under a high vacuum of 10−3 Pa is intended to serve as a beam target (Li target) in the planned International Fusion Materials Irradiation Facility (IFMIF). The engineering validation and engineering design activities (EVEDA) for the IFMIF are being implemented under the broader approach (BA) agreement. As a major activity of the Li target facility, the EVEDA Li test loop (ELTL) was constructed by the Japan Atomic Energy Agency. A stable Li target under the IFMIF conditions (Li temperature: 523.15 K, velocity: 15 m/s, and vacuum pressure: 10−3 Pa) was demonstrated using ELTL. This study focuses on a cavitationlike acoustic noise detected in a downstream conduit where the Li target flowed under vacuum conditions. This noise was investigated using acoustic-emission (AE) sensors installed at eight locations via acoustic wave guides. The sound intensity of the acoustic noise was examined against the cavitation number of the Li target. In addition, two t...
Reviews of Accelerator Science and Technology, 2015
Fusion materials research is a worldwide endeavor as old as the parallel one working toward the l... more Fusion materials research is a worldwide endeavor as old as the parallel one working toward the long term stable confinement of ignited plasma. In a fusion reactor, the preservation of the required minimum thermomechanical properties of the in-vessel components exposed to the severe irradiation and heat flux conditions is an indispensable factor for safe operation; it is also an essential goal for the economic viability of fusion. Energy from fusion power will be extracted from the 14 MeV neutron freed as a product of the deuterium–tritium fusion reactions; thus, this kinetic energy must be absorbed and efficiently evacuated and electricity eventually generated by the conventional methods of a thermal power plant. Worldwide technological efforts to understand the degradation of materials exposed to 14 MeV neutron fluxes [Formula: see text] m[Formula: see text]s[Formula: see text], as expected in future fusion power plants, have been intense over the last four decades. Existing neutr...
Fusion Engineering and Design, 2016
h i g h l i g h t s • Nitrogen contained in solid Lithium is converted into Ammonium ion. • Ammon... more h i g h l i g h t s • Nitrogen contained in solid Lithium is converted into Ammonium ion. • Ammonium ion is suitably quantified by ionic chromatograph or by Ammonia sensor. • Good agreement of the partner's results has been achieved. • Maximum operative reproducibility and blank subtraction are necessary.
Vacuum, 2004
The LHC will be the world next generation accelerator to be operational in 2007 at CERN. The UHV ... more The LHC will be the world next generation accelerator to be operational in 2007 at CERN. The UHV requirements force the installation of ion pumps in the experimental areas of ATLAS. Due to the unacceptable particle background that standards ion pumps may generate, a reduction in the amount of material constitutive of the pump body is required. Hence, an stainless steel 0.8 mm thick body annular triode ion pump has been designed. A pumping speed of ~ 20 l/s at 10-9 mbar is provided by 15 pumping elements. Finite elements analysis and destructive tests have been performed in its design. Final vacuum tests results are shown.
Journal of Nuclear Materials, 2014
The d-Li based International Fusion Materials Irradiation Facility (IFMIF) will provide a high ne... more The d-Li based International Fusion Materials Irradiation Facility (IFMIF) will provide a high neutron intensity neutron source with a suitable neutron spectrum to fulfil the requirements for testing and qualifying fusion materials under fusion reactor relevant irradiation conditions. The IFMIF project, presently in its Engineering Validation and Engineering Design Activities (EVEDA) phase under the Broader Approach (BA) Agreement between Japan Government and EURATOM, aims at the construction and testing of the most challenging facility subsystems , such as the first accelerator stage, the Li target and loop, and irradiation test modules, as well as the design of the entire facility, thus to be ready for the IFMIF construction with a clear understanding of schedule and cost at the termination of the BA mid-2017. The paper reviews the IFMIF facility and its principles, and reports on the status of the EVEDA activities and achievements.
Vacuum, 2002
The Large Hadron Collider (LHC) is a proton-proton collider with a centre of mass energy of 14 Te... more The Large Hadron Collider (LHC) is a proton-proton collider with a centre of mass energy of 14 TeV presently in construction at CERN. The four colliding experiments will require special vacuum chamber designs to allow the best physics performance. New technologies such as very thin beampipes to increase transparency, optimized rotatable flanges, wired supports with special layers to reduce dynamic effects, special heating jackets, double wall chambers and mass minimized annular ion pumps are being developed by CERN for this application.
IEEE Transactions on Applied Superconductivity, 2012
The Toroidal Field Coils (TFC) are subject to mandatory geometrical tolerances constraints for ac... more The Toroidal Field Coils (TFC) are subject to mandatory geometrical tolerances constraints for acceptance by ITER Organization. As a consequence, pre-assembly tests are foreseen to verify if each single coil meets such criteria, including laser tracking, and possibly warm magnetic measurements on each of the finished winding packs. Possible performance limitations of the acceptance tests for the winding pack are
IEEE Transactions on Applied Superconductivity, 2012
The Paschen breakdown is the outcome of an avalanche effect related with the ionization of a gas ... more The Paschen breakdown is the outcome of an avalanche effect related with the ionization of a gas under electric stress. Paschen's law defines the voltage breakdown of rarefied (low pressure) gases as a function of the product of pressure PPP and distance ddd between electrodes showing a minimum value (typically of the order of hundreds V) below which the breakdown cannot take place. The actual field level depends on the gas, on the shape, material and surface conditions (roughness, cleanness and presence of oxide layers) of the electrodes; hence there is a big dispersion in the results available due to the referred number of parameters influencing the voltage breakdown. The design of the electrical insulation of superconducting magnets targets a safety factor of times\timestimes10 on dielectric strength over specified voltages using the intrinsic dielectric strength of the materials. A crack in the insulation or a flaw not detected by visual inspection would not necessarily lead to an electrical break during the acceptance tests in air given the high dielectric strength of air (typically values over 1 kV/mm). However, it would lead to an electrical failure during operation if Paschen conditions take place. Since the Paschen minimum occurs under vacuum, it is irrelevant for conventional High Voltage (HV) engineering. The application of superconducting technology for plasma fusion devices with a growing size and complexity of magnets has shown Paschen testing as an essential tool. During magnet operation inside the cryostat conditions, if a He leak takes place, critical pressures can be reached locally and Paschen breakdown might occur at voltages significantly lower than the designed ones. The present paper covers an existing gap in International Standards and scientific literature addressing Paschen testing of superconducting magnets and explains why it is needed and how the tests should be done in the most efficient way.
AIP Conference Proceedings, 2012
ABSTRACT During the last years, two cyanate ester epoxy blends supplied by European and US indust... more ABSTRACT During the last years, two cyanate ester epoxy blends supplied by European and US industry have been successfully qualified for the ITER TF coil insulation. The results of the qualification of a third CE blend supplied by Industrial Summit Technology (IST, Japan) will be presented in this paper. Sets of test samples were fabricated exactly under the same conditions as used before. The reinforcement of the composite consists of wrapped R-glass / polyimide tapes, which are vacuum pressure impregnated with the resin. The mechanical properties of this material were characterized prior to and after reactor irradiation to a fast neutron fluence of 2×1022m-2 (E>0.1 MeV), i.e. twice the ITER design fluence. Static and dynamic tensile as well as static short beam shear tests were carried out at 77 K. In addition, stress strain relations were recorded to determine the Young's modulus at room temperature and at 77 K. The results are compared in detail with the previously qualified materials from other suppliers.
Superconductor Science and Technology, 2013
ABSTRACT The ITER toroidal field (TF) system features eighteen coils that will provide the magnet... more ABSTRACT The ITER toroidal field (TF) system features eighteen coils that will provide the magnetic field necessary to confine the plasma. Each winding pack is composed of seven double pancakes (DP) connected through praying hands joints. Shaking hands joints are used to interface the terminals of the conductor with the feeder and inter-coil U-shaped bus bars. The feasibility of operating plasma scenarios depends on the ability of the magnets to retain sufficient temperature and current margins. In this respect, the joints represent a possible critical region due to the combination of steady state Joule heating in the resistance of the joint and coupling losses and currents in ramped operation. The temperature and current margins of both DP and terminal joints are analysed during the 15 and 17 MA plasma scenarios. The effect on the joint performance of feasible optimization solutions, such as rotation of the terminal joints and sole RRR increase, is explored. The characterization of the TF coil joints is completed by the estimation of the coupling loss time constant for different inter-strand and strand-to-joint resistance values. The study is carried out with the code JackPot-ACDC, allowing the analysis of lap-type joints with a strand-level detail.
IEEE Transactions on Applied Superconductivity, 2012
The Toroidal Field Coils (TFC) for the ITER magnet system are large 'D' shaped coils consisting o... more The Toroidal Field Coils (TFC) for the ITER magnet system are large 'D' shaped coils consisting of a Winding Pack (WP) enclosed in a stainless steel (316LN) casing. The WP is a bonded structure of 7 Double Pancakes (DP), each made up of a stainless steel radial plate (RP) housing the reacted Nb3Sn circular cable-in-conduit superconductor (CICC), which operate at 4.5 K. The cooling of the WP is assured by helium feed in the CICC through one inlet for each DP at an average mass flow of 7.9 g/s in the conductor. The helium inlet is critical from a structural point of view because it has to withstand both static and cyclic strains in the order of coming from energization of the TFC and plasma operation conditions. The assembly of the helium inlet around the conductor includes a fillet weld that makes it even more critical. This paper describes the analyses results performed for the (static and fatigue) structural assessment of the helium inlet. It describes the statistical approach followed to determine the number of cycles to be used in the validation tests.
IEEE Transactions on Applied Superconductivity, 2012
ABSTRACT The insulation of the ITER TF coils consists of multiple wrapped layers of glass fiber p... more ABSTRACT The insulation of the ITER TF coils consists of multiple wrapped layers of glass fiber polyimide sandwich tapes. In order to simplify the fabrication process, the polyimide tape can be bonded to the glass fiber tape, mainly to avoid misalignments of the polyimide tape. However, due to the intense neutron and gamma-radiation exposure, bonding agents have to be radiation resistant, otherwise the composite will be severely damaged, as was observed for the ITER TF model coil insulation. Two bonded glass fiber polyimide tapes (40 mm wide, similar to 0.175 mm thick) were supplied by Arisawa, Japan, and Advanced Composites Group, United Kingdom. Test materials were fabricated based on the build-up of the ITER TF turn insulation and vacuum pressure impregnated with a 40: 60 cyanate ester/epoxy blend supplied by Huntsman, Switzerland. The mechanical properties of these materials were characterized prior to and after reactor irradiation to a fast neutron fluence of 2 x 10(22) m(-2) (E > 0.1 MeV), i.e. twice the ITER design fluence. Static and dynamic tensile tests were carried out at RT and 77 K. The Arisawa tape showed excellent mechanical properties.
IEEE Transactions on Applied Superconductivity, 2012
The ITER superconducting magnet structures (Toroidal Field coils (TF), Central Solenoid (CS), Pol... more The ITER superconducting magnet structures (Toroidal Field coils (TF), Central Solenoid (CS), Poloidal Field coils (PF), Correction Coils (CC) and Feeders), representing a total weight of approximately 10 000 tons, are submitted to gravitational and seismic forces, stresses induced by constrained thermal contractions during cool-down from 300 K to 4.5 K, and large Lorentz forces in the superconducting coils. Although not classified as Safety Important Class (SIC) components, the sensors (stress, displacements, thermometers) used to monitor the thermo-mechanical behaviour of the structures are important diagnostic means to assess the designs, give support to operation and survey possible fatigue effects over the 20 years lifetime of the tokamak. Environmental operating conditions are unique and severe. Sensors and their wiring have to operate under cryostat vacuum (<10-4 Pa total gas pressure), under magnetic inductions of several Tesla, at low temperature (4.5 K), in presence of a neutron fluence in the order of 10 22 n/m 2 and a maximum associated gamma dose of 10MGy over a period of 20 years. In addition, the fast and slow cycling of very large currents in the superconducting magnets and plasma generate large eddy currents, thus heat loads and electro-motive forces (voltages) in the various parts of the structures, and a large electromagnetic noise. The design philosophy and the choice of sensor technologies, some of which are at the frontier of present technology and as such require development in collaboration with industry, are presented that satisfy objectives and severe working conditions. Specifically, the near to 1 000 measuring points for thermo-mechanical data of the ITER magnet structures will rely for 20% on "classical", copper-wired technologies, and for 80% on specially developed optical fibrebased sensors.
IEEE Transactions on Applied Superconductivity, 2012
ABSTRACT The ITER Magnet System contains 18 Toroidal Field Coils (TFC). These are large D-shaped ... more ABSTRACT The ITER Magnet System contains 18 Toroidal Field Coils (TFC). These are large D-shaped coils of about 300 t, 17.5-m height and 9-m width. They consist of a Winding Pack (WP) enclosed in a rigid structural steel case, the Toroidal Field Coil Case (TFCC). The WP is a bonded structure of 7 Double Pancakes (DP), each made up of a radial plate (RP) housing the reacted rmNb3rmSn{\rm Nb}_{3}{\rm Sn}rmNb3rmSn cable-in-conduit superconductor (CICC), which operate at 4.5 K in supercritical helium. The conductor carries a current of 68 kA in operation to produce a nominal peak field of 11.8 T. The total stored magnetic energy in the 18 TFCs is 41 GJ. While the Japanese and European Domestic Agencies that are in charge of the procurement of the TFCs are progressing with the manufacturing design and the fabrication trials prior to launch the production of the real coils, the ITER Organization (IO) is completing the development and qualification of the most critical items, e.g. cyanate ester and resin blends for the conductor and WP insulation system, the terminal region, the helium inlet, a charged resin system for the filling of the gap between the WP and the TFCC and the general tolerancing especially at the interfaces between the neighboring systems. This paper presents the final design of the TFCs and the results of the developments carried out in the aforementioned areas in the last 2 years.