Central Solenoid Model Coil Research Articles

A New Numerical Model for the Quench Simulation in CFETR CSMC Conductor

Modeling of cable-in-conduit conductor (CICC) is available for its advantage in efficiency and usually performed for optimizing CICC in a magnetic system. It is an important part of design and analysis of the central solenoid model coil (CSMC) for the China Fusion Engineering Test Reactor (CFETR). This paper is intended to provide a finite-element method with an ANSYS module to deal with the integrated analysis of thermal and fluid models of CICC. The CICC model is based on the NbTi conductor of the CFETR CSMC. It cooled by supercritical helium. One-dimensional elements of thermal and fluid are used to represent CICC components of conduit, strands, and two separated fluid areas of the bundle and the central hole, respectively. Test verification of a short length of the full-size conductor in the SULTAN facility is also presented.

Cabling Technology of Nb3Sn Conductor for CFETR Central Solenoid Model Coil

The China Fusion Engineering Test Reactor (CFETR) is a new tokamak device, whose magnet system includes the toroidal field, central solenoid (CS), and poloidal field coils. To develop the manufacturing technique for the full-size CS coil, the Central Solenoid Model Coil (CSMC) project was launched first. The cable-in-conduit conductor used for CFETR CSMC refers to the International Thermonuclear Experimental Reactor CS conductor with the same short twist pitch cable pattern. As the short twist pitch and low void fraction, a higher compaction ratio during cabling is required, and the possibility of damages occurring on strands is increased. After numerical analysis and experimental trials on cabling technology, one short cable sample was manufactured, which shows good results compared with former experimental cables.

Research on Nondestructive Examination of Jacket Sections for CFETR Central Solenoid Model Coil

The central solenoid model coil (CSMC) is a large superconducting “model” coil, which is responsible for developing and verifying the key manufacturing methods of the China Fusion Engineering Test Reactor. Therefore, all subcomponents have very strict requirements, including the conductors which are cable-in-conduit conductor (CICC) type. The jacket section as an important component of the CSMC CICC is circular-in-square type, which is nonmagnetic stainless steel. Severe requirements not only high mechanical performances but also the size of initial defects in the jacket section were specified. Based on the linear elastic fracture mechanics, maximum acceptable defect sizes inside the jacket material have been estimated. Phased array ultrasonic test (PAUT) supplemented with eddy current test (ECT) were studied and developed for nondestructive examination. The defects inside the jacket section can be detected by PAUT with 11 runs by 4 probes. The defects on inner surfaces can be detected by ECT. Focal laws on PAUT and parameters of ECT are also discussed in this paper.

Process Design of Cryogenic Distribution System for CFETR CS Model Coil

The superconducting magnet of Central Solenoid (CS) model coil of China Fusion Engineering Test Reactor (CFETR) is made of Nb3Sn/NbTi cable-in-conduit conductor (CICC), and operated by forced-flow cooling with a large amount of supercritical helium. The cryogenic circulation pump is analyzed and considered to be effective in achieving the supercritical helium (SHe) circulation for the forced-flow cooled (FFC) CICC magnet. A distributed system will be constructed for cooling the CFETR CS model coil. This paper presents the design of FFC process for the CFETR CS model coil. The equipment configuration, quench protection in the magnet and the process control are presented.

ITER-CS インサート･コイル試験

The Japan Atomic Energy Agency (JAEA) is procuring conductors for the ITER central solenoid (CS). To evaluate the superconducting performance of the CS conductor, a test coil “CS insert” was fabricated and tested at the CS model coil test facility in JAEA Naka. The CS insert is a single-layer, nine-turn solenoid using a piece of the actual CS conductor. The test was performed in 2015, and its duration was five months including initial cool-down and final warm-up. At the beginning, the nominal conditions of 40 kA - 13 T and 45.1 kA - 12.5 T were achieved. The change in current-sharing temperature (Tcs) was then measured during 16,000 cycles of electromagnetic force and three cycles of warm-up to room temperature and cool-down. There was no apparent degradation of Tcs observed. The variation in Tcs resulting from conductor strain in the longitudinal direction was also measured using direct and reverse charges. Quenching behavior was measured using an inductive heater installed at the middle point of the CS insert. From the tests, a database to estimate the performance of the CS conductor for the actual ITER CS was established.

Structural Design and Simulated Analysis of the Cryostat and Its Affiliated Parts of CFETR CSMC Cryogenic Test Facility

According to the CFETR CSMC properties test requirements, a large cryogenic test platform will be set up. The cryostat and its affiliated parts, as one of the important components of the platform, should be studied to make sure them could afford the much valued help for the basic test facilities. This paper focuses on the structural design and the finite element analysis of the cryostat and its affiliated parts. All of the work could not only provide necessary help for building CFETR CS model coil test platform, but also provide the important experience of the large cryogenic test platform in future.

Optimization of CFETR CSMC cabling based on numerical modeling and experiments

The China Fusion Engineering Test Reactor (CFETR) is a new tokamak device, whose magnet system includes toroidal field (TF), central solenoid (CS) and poloidal field (PF) coils. The main goal is to build a fusion engineering tokamak reactor with 50–200 MW fusion power and self-sufficiency by blanket, which means that the deuterium–tritium reaction in the plasma produces neutrons and alpha particles, and the neutrons react with the lithium-containing blanket surrounding the plasma, breeding the tritium by lithium–neutron reaction. To develop the manufacturing technique for the full-size CS coil, the Central Solenoid Model Coil (CSMC) project for CFETR was launched first. A Nb3Sn conductor is to be used in the CFETR CSMC, whose design refers to the ITER CS conductor with the same short-twist-pitch cable pattern. Due to the short twist pitch and relatively low void fraction, a high compaction ratio is required during cabling and the risk of strand damage is increased significantly. Although it is impossible to avoid strand deformation for this design, it is crucial to find a way to reduce strand damage as much as possible. A numerical model was used to analyze the causes of strand damage, including variation in twist pitch length as well as different mechanical properties for copper and Nb3Sn strands. Several experiments have been performed to verify the numerical results, including cabling trials for different conditions and critical current (Ic) tests on strands with/without deformation. The results show that the numerical analysis is consistent with the experiments and provides the optimal cabling conditions for the CFETR CSMC.

Performance verification tests of JT-60SA CS model coil

As a final check of the coil manufacturing method of the JT-60 Super Advanced (JT-60SA) central solenoid (CS), we verified the performance of a CS model coil. The model coil comprised a quad-pancake wound with a Nb3Sn cable-in-conduit conductor. Measurements of the critical current, joint resistance, pressure drop, and magnetic field were conducted in the verification tests. In the critical-current measurement, the critical current of the model coil coincided with the estimation derived from a strain of −0.62% for the Nb3Sn strands. As a result, critical-current degradation caused by the coil manufacturing process was not observed. The results of the performance verification tests indicate that the model coil met the design requirements. Consequently, the manufacturing process of the JT-60SA CS was established.

Numerical analysis of modified Central Solenoid insert design

The United States ITER Project Office (USIPO) is responsible for fabrication of the Central Solenoid (CS) for ITER project. The ITER machine is currently under construction by seven parties in Cadarache, France. The CS Insert (CSI) project should provide a verification of the conductor performance in relevant conditions of temperature, field, currents and mechanical strain. The US IPO designed the CSI that will be tested at the Central Solenoid Model Coil (CSMC) Test Facility at JAEA, Naka. To validate the modified design three-dimensional numerical simulations were performed using coupled solver for simultaneous structural, thermal and electromagnetic analysis. Thermal and electromagnetic simulations supported structural calculations providing necessary loads and strains. According to current analysis design of the modified coil satisfies ITER magnet structural design criteria for the following conditions: (1) room temperature, no current, (2) temperature 4K, no current, (3) temperature 4K, current 60kA direct charge, and (4) temperature 4K, current 60kA reverse charge. Fatigue life assessment analysis is performed for the alternating conditions of: temperature 4K, no current, and temperature 4K, current 45kA direct charge. Results of fatigue analysis show that parts of the coil assembly can be qualified for up to 1 million cycles. Distributions of the Current Sharing Temperature (TCS) in the superconductor were obtained from numerical results using parameterization of the critical surface in the form similar to that proposed for ITER. Special ADPL scripts were developed for ANSYS allowing one-dimensional representation of TCS along the cable, as well as three-dimensional fields of TCS in superconductor material.

Fabrication of an Insert to Measure Performance of ITER CS Conductor

The Japan Atomic Energy Agency (JAEA) and Mitsubishi Electric Corporation are fabricating the insert coil needed to evaluate the performance of final design conductor for the International Thermonuclear Experimental Reactor (ITER) Central Solenoid (CS). The insert, designed by the US ITER Project Office, is a nine-turn single-layer solenoid of 1.5-m diameter. Major operations, such as winding, terminal fabrication, heat treatment, and turn insulation, have thus far been successfully completed. Fabrication will be completed in September 2014, and testing will begin at JAEA's CS Model Coil test facility in early 2015. The results of qualification and fabrication of the insert are reported.

Magnetic field measurements of JT-60SA CS model coil

In a cold test of the JT-60SA CS model coil, which has a quad-pancake configuration consisting of a Nb3Sn cable-in-conduit (CIC) conductor, magnetic fields were measured using Hall sensors. For a holding coil current of 20kA, measured magnetic fields varied slightly with long time constants in the range 17–571s, which was much longer than the time constant derived from a measurement using a short straight sample. To validate the measurements, the magnetic fields of the model coil were calculated using a computational model representing the positions of Nb3Sn strands inside the CIC conductor. The calculated results were in good agreement with the measurements. Consequently, the validity of the magnetic field measurements was confirmed. Next, we investigated other coils consisting of CIC conductors and having long time constants. The only commonality among the coils was the use of CIC conductors. At present, there is no obvious way to prevent generation of such magnetic-field variations with long time constants.

Development and Test of JT-60SA Central Solenoid Model Coil

A central solenoid (CS) model coil (CSMC) was manufactured by using real manufacturing jigs and procedure to validate the CS manufacturing processes for JT-60SA. The winding accuracy and the temperature control precision during the heat treatment met the requirements. The vacuum pressure impregnation process was also successfully finished. The cold test of the CSMC was performed as a final check of the manufacturing process. The joint resistance, the Ic, and the pressure drop measurements were conducted as the verification test. The results of verification test satisfied the design requirements. These results indicate that the manufacturing processes of the JT-60SA CS has been established. The manufacturing of real CS pancakes just started after finishing the CSMC test.

Analysis of TF Insert Coil

The United States ITER Project Office (USIPO) is responsible for the design of the oroidal Field (TF) insert coil, which will allow validation of the performance of significant lengths of the conductors to be used in the full scale TF coils in relevant conditions of field, current density and mechanical strain. The Japan Atomic Energy Agency (JAEA) will build the TF insert which will be tested at the central solenoid model coil (CSMC) test facility at JAEA, Naka, Japan. Three dimensional mathematical model of TF insert was created based on the initial design geometry data, and included the following features: orthotropic material properties of superconductor material and insulation; external magnetic field from CSMC, temperature dependent properties of the materials; precompression and plastic deformation in lap joint. Major geometrical characteristics of the design were preserved including cable jacket and insulation shape, mandrel outline, and support clamps and spacers. The model is capable of performing coupled structural, thermal, and electromagnetic analysis using ANSYS. Numerical simulations were performed for room temperature conditions; cool down to 4 K, and the operating regime with 68 kA current at 11.8 Tesla background field. Numerical simulations led to the final design of the coil producing the required strain levels on the cable, while simultaneously satisfying the ITER magnet structural design criteria.

Pressure drop test and analysis of Nb3Sn superconducting magnet

In order to test the performance of experimental advanced superconducting tokamak (EAST) central solenoid (CS) model coil, which was made by the cable-in-conduit conductor using Nb3Sn strands and a 316L stainless steel jacket, a cryogenic experiment system was designed. The experimental results showed that the superconducting magnet was cooled down to 5K, which could meet the test requirements successfully. Meanwhile, we measured the pressure drop in CICC of Nb3Sn superconducting magnet under the circulating mode of forced flow cooling which used supercritical helium as coolant compared with the result calculated by the Katheder fraction factor correlation, it showed that calculated pressure drop underestimates the experimental data. We corrected the Katheder correlation and compared with the experimental data, it proved that the corrected correlation is much more suitable for the kind of CICC of Nb3Sn superconducting magnet.

Development of Central Solenoid for JT-60SA

Several components for central solenoid (CS) of JT-60 Super Advanced (JT-60SA) were newly developed and tested. The butt-type joint, the electrical resistance of which is about 2 nΩ, was developed to increase the winding diameter. The insulation system, which consists of Glass/Kapton/Glass tape and Bisphenol A diglycidyl ether (DGEBA) epoxy, showed sufficient tensile strength after the irradiation of 100 kGy. Insulation characteristics of 4 × 4 winding stack sample after the compression of 705 kN 36 000 times was able to withstand voltages larger than 21 kV. The heat treatment and transfer of the CS model coil with superconductor were conducted. The pancake temperature during flat top was maintained at 923 ± 4 K. The maximum temperature difference in the pancake was 30 K. All manufacturing processes were confirmed so that the mass production of CS will be started in 2013.

Test Results for the East Central Solenoid Model Coil

The central solenoid (CS) of the experimental advanced superconducting tokamak (EAST) consists of six independent coils. In order to improve the performance of the EAST CS coils, a new pulsed superconducting model coil was developed and tested by the Institute of Plasma Physics, the Chinese Academy of Sciences (ASIPP). The Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strand was used to manufacture the cable-in-conduit conductor of the model coil. The model coil had similar dimension with the CS coils used in the EAST facility. The operation current of the model coil was designed to be 12 kA. The peak magnetic field of the model coil was 4.7 T. The maximum rate of change of magnetic field was designed to be 8 T/s. The stored energy of the model coil was 0.9 MJ. A 500 W/4.5 K refrigerator was used to provide the model coil supercritical helium (SHe). The model coil was successfully cooled down to 5 K. The coil current was ramped up to 12 kA and the peak magnetic field was calculated to be 4.7 T. The maximum rate of change of magnetic field was about 10.6 T/s. The coil outlet temperature increased to 5.8 K due to ac losses. This paper presents test results of the model coil.

Optimization of ITER Central Solenoid Insert design

The United States ITER Project Office (USIPO) is responsible for fabrication of the Central Solenoid (CS) for International Thermonuclear Experimental Reactor (ITER). The CS Insert (CSI) project should provide a verification of the conductor performance in relevant conditions of temperature, field, currents and mechanical strain. The US IPO will build the CSI that will be tested at the Central Solenoid Model Coil (CSMC) Test Facility at JAEA, Naka. One of the design goals of the CSI is to assure that the properties of the conductor near the median plane are measured accurately. Since Nb3Sn is strain sensitive and electromagnetic forces generate a significant strain that increases the current sharing temperature (Tcs), we need to design the Insert in such a way that the most strained conductor near the median plane would still have the lowest Tcs of all the rest of the conductor in the Insert. The difference between thermal contraction of the jacket and spacer material allows controlling axial distribution of the coil radial deformation. Numerical analysis of the CSI was performed using stainless steel, titanium and invar spacer material variants. Distribution of the Tcs was obtained from numerical results in the form similar to one proposed for ITER.

Electromagnetic and Structural Analysis of ITER Central Solenoid Insert Coil

The United States ITER Project Office (USIPO) is responsible for fabrication of the Central Solenoid (CS) for International Thermonuclear Experimental Reactor (ITER). The CS Insert (CSI) project should provide verification of the conductor performance in relevant conditions of temperature, field, currents and mechanical strain. The USIPO will build the CSI that will be tested at the Central Solenoid Model Coil (CSMC) Test Facility at JAEA, Naka, Japan. This paper presents three-dimensional mathematical model of CSI based on the design. Simulations were performed in order to verify structural integrity and compliance with the Japanese High Gas Pressure Safety Law. Numerical simulations lead to the design of the CSI that produced a required strain levels during operation on the superconductor cable, while simultaneously satisfy the ITER magnet structural design criteria.

Superconducting Property and Strain Effect Study of the ${\rm Nb}_{3}{\rm Sn}$ Strands Developed for ITER

Japan Atomic Energy Agency has developed Nb3Sn strands for the ITER magnet, whose critical current density is about 1.4 times as large as that of ITER CS Model Coil. The magnetic field, temperature, and strain dependence on the critical current (Ic) of the strands were measured with apparatus that were developed by the authors. The strain properties in particular were investigated in detail, with strain tensor analysis revealing that the upper critical field dependence on strain can be naturally formulated using a high order polynomial terms of strain taking into account residual strain due to thermal contraction difference inside the strand and strain applied externally. A correlation formula for field, temperature, strain and Ic of the strand is discussed and presented. Recent results of fabricating strands for ITER TF coil are then finally provided.

EU contribution to the test and analysis of the ITER poloidal field conductor insert andthe central solenoid model coil

The PFCI is a single-layer solenoid wound from a 45 m long ITER-type NbTi dual-channelcable-in-conduit conductor, designed to be representative of the one currently proposed forthe ITER PF1&6 coils. The PFCI, installed in the bore of the ITER central solenoid modelcoil (CSMC) at JAEA Naka, Japan, and well instrumented from both the thermalhydraulic and the electromagnetic points of view, has been successfully tested inJune–August 2008. The test concentrated on DC performance (current sharing temperatureand critical current measurements) and AC loss measurements. The results of the analysisof those measurements are reported in the paper, with particular attention to thecomparison with the PFCI short sample, which was previously tested in the SULTANfacility. The evolution of the DC performance of the CSMC is also discussed.