Huan Jin

Magnetic relaxation and critical current density of the new superconductor MgB2

Magnetic relaxation rate, critical current density and transport properties have been investigated on MgB2 bulks from 1.6 K to Tc at magnetic fields up to 8 T. A vortex phase diagram is depicted based on these measurements. A large separation between the bulk irreversibility field Hirr(T) and the upper critical field Hc2(T) has been found. It is thus proposed that there is a quantum vortex liquid due to strong quantum fluctuation of vortices at 0 K. It is also found that the magnetic relaxation rate is weakly dependent on temperature but strongly dependent on field indicating a trivial influence of thermal fluctuation on the vortex depinning process. Therefore, the phase line Hirr(T) is attributed to quantum vortex melting in the rather clean system at a finite temperature.

Status of the ITER Conductors in China

The ITER magnet system is made up of four main subsystems: the 18 toroidal field (TF) coils, the central solenoid, the six poloidal field (PF) coils, and the correction coils (CCs). The feeder system, with its main busbar (MB) and CC busbar (CB), represents one of the main magnet components as well. All coils and busbars with different dimensions used cable-in-conduit conductors. China has signed three conductor packages, which are the so-called procurement arrangements, between ITER and the Chinese Domestic Agency (CN DA): a TF conductor package, a PF conductor package, and a CC and feeder conductor package. They include 7.5% of the TF conductors (11); all the PF2 (12), PF3 (16), PF4 (16), and PF5 (16) conductors; all the CC (18) conductors; and the MB (3) and CB (2) conductors for the feeders. Complex technologies have been developed by ASIPP for the serial production of all ITER conductors, in terms of cabling parameter design, welding, and elaboration of cable insertion, compaction, and winding processes. China has finished all qualification phases and is well into the main series production. All conductor samples required for quality control have successfully passed the SULTAN tests with good performance. The status of the production of ITER conductors in China is described in this paper.

Research on the Mechanical Properties of Jacket Used for Bi-2212 Cable-In-Conduit Conductor

The China fusion engineering test reactor is a new tokamak device. It is a commercial reactor, which demands a superconducting magnet with higher magnetic field. The maximum field of CS and TF will get around 15 T, which is much higher than that of present reactors. In order to meet the requirements, the new conductor with Bi2Sr2 CaCu2Ox is considered as one potential material for the superconducting magnets. Because Bi2212 wire needs to endure special heat treatment with oxygen, the jacket material is one key issue. As one new material, Ni80Cr has an excellent performance, which cannot react with Bi-2212 wire. It could be one potential material as Bi-2212 cable-in-conduit conductor jacket. In order to understand the mechanical properties of Ni80Cr, the samples with different conditions were prepared, and tested at high, room, and low temperature (4.2 K). The results are analyzed in this paper.

Manufacturing of Nb3Sn Sample Conductor for CFETR Central Solenoid Model Coil

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. In order to develop the manufacturing process for the full-size CS coil, the CS model coil (CSMC) project was launched first. The cable-in-conduit conductor used for CFETR CSMC refers to ITER CS conductor with the same short twist pitch cable pattern. They have the similar layout. In order to qualify the manufacturing process and performance of conductor, two short sample conductors with two different jacket materials (316LN and high-Mn steel) were manufactured. The conductors were tested at Swiss Plasma Center successfully. In future, the CSMC will be tested at the Institute of Plasma Physics, CAS (ASIPP). In this paper, the manufacturing processes for conductor are described in detail. The strand damage analysis and conductor performance were also discussed.

Mechanical Properties of Preliminary Designed Insulation for CFETR CSMC

Glass-fiber reinforced plastics is commonly designed as insulation materials for fusion magnet coils and is selected for the turn and ground insulation for the China Fusion Engineering Test Reactor (CFETR) Central Solenoid Model Coil (CSMC). The mechanical properties are being subjected to investigations with respect to the design requirements and operating conditions at present. The preliminary designed insulation system for CFETR CSMC mainly consists of S-glass fiber reinforced tape, interleaved with corona-treated Kapton HN, and vacuum-pressure impregnated in a DGEBF epoxy system. For the composite structure, the tensile and shear performance of the insulation system at room temperature and liquid nitrogen temperature (77 K) were assessed. Meanwhile, effects on the tensile and inter-laminar shear performance from cycling in liquid nitrogen were investigated. The failed specimens were observed to verify the insulation system failure mechanisms.

Mechanical Performances of ITER In-Vessel Coil’s Conductor

The design and R&D for ITER In-Vessel Coils (IVCs) is being deployed. The concerned issue of “Edge Localized Modes” (ELMs) and “Vertical Stabilization” (VS) of the ITER plasma can be addressed by the implemented IVCs. The ELM and VS coils will be installed in the vessel just behind the blanket shield modules to reach the requirement of keeping strong coupling with the plasma. The 59mm Stainless Steel Jacketed Mineral Insulated Conductor (SSMIC) using MgO as the insulation is being designed for the IVCs to resist the special challenges, including the nuclear radiation, high temperature, electromagnetic and thermal fatigue. It is necessary to take the mechanical performances of the SSMIC and the feasibility of fabrication techniques into consideration of the R&D program. The mechanical performances of the SSMIC close to the actual work conditions, including the three point bend modulus, three point bend cyclical performance and the cyclical performance with a U-bend sample of the SSMIC prototypes have been investigated and the results are presented in this paper.Copyright

Effect of Cold Working and Aging Treatment on Mechanical Performance of SS316LN Tube

Abstract Modified stainless steel 316LN is selected as a candidate material for the China Fusion Engineering Test Reactor (CFETR) central solenoid model coil (CSMC) because of the high strength combined with good ductility at cryogenic temperature. The tensile properties, fatigue crack growth rate, and fracture toughness of the SS316LN tube in solution-annealed and aged (575°C/100 h and 650°C/100 h) conditions were evaluated at 4.2 K. The fatigue crack growth and tensile properties for the solution-annealed conduit were high enough to satisfy the design requirements for CFETR CSMC. However, the fracture toughness of the aged conduit is not satisfied, since there was a significant decline from 280 to 110 MPa·m1/2 after cold working and aging treatments. The chemical compositions and fractures have been analyzed to assess the reason and recommend modifications that could improve fracture toughness and fatigue crack growth properties.

Axial Tensile Stress–Strain Characterization of Bi-2212 Round Wire With Different Heat Treatments

The China Fusion Engineering Test Reactor is a new tokamak device whose magnet system includes toroidal field (TF), central solenoid (CS), and poloidal field (PF) coils which are made up of cable-in-conduit conductor (CICC). The maximum field of CS and TF will reach around 15 T, which is much higher than that of present reactors. In this case, the high-temperature superconducting material Bi-2212 is considered as one potential magnet material for CICC because it has an outstanding conductor-carrying capacity at 4.2 K in magnetic field, especially for that with high-pressure heat treatment. However, Bi-2212 phase is a ceramic structure, which is sensitive to strain. The mechanical property is important for its application. In this paper, the axial tensile measurements on Bi-2212 round wires with different heat treatments were performed at room temperature, 77 K and 4.2 K, respectively. It was found that the wires with high pressure heat treatment had higher mechanical strength than that with normal pressure. The compared results were given, and SEM of cross sections for tested samples was also made and analyzed.

Preliminary Investigation on Brazing Performance of OFHC Tube Butt-Joints

The OFHC C10200 tube with an outer diameter of 45mm, and the thickness of 7.5mm was used as the conductor for ITER vertical stabilization (VS) coil. The limited length of the OFHC tube sections require to be connected by induction brazing. A thin BCuP-5 foil with thickness of 0.3 mm and BCuP-5 wire with a diameter of 1.2 mm served as the brazing filler metal. The inert gas of Argon was used for protecting the OFHC tube away from oxidation during induction brazing. An investigation was carried out to observe the brazing performance of OFHC tubes with four kinds of brazing structures. NDE and stretching tests was conducted on the brazed OFHC joints. The results showed that the Butt-OD sleeve joint structure was much easier for operation, and the quality of the brazed joints are better than the others, which was preliminarily chosen for manufacturing the prototype VS coil.

Effect of ITER ELM Conductor Manufacturing Process on the Properties of the Inconel 625 Jacket

Abstract Nickel based alloy Inconel 625 is proposed as the jacket material for the ITER edge localized mode (ELM) conductor. Based on some investigation works finished in the Institute of Plasma Physics (ASIPP), the ELM conductor manufacturing process involves a compaction procedure of cold rolling and a joining procedure of argon-arc welding for the jackets. The effects of the fabrication processes on the physical and mechanical properties of the Inconel 625 steel have been investigated by observing the metallurgical structure and tensile performance. The test results show that the Inconel 625 jacket has high strength and good ductility after the ELM conductor fabrication, which conclude that the results are accordant with the ITER requirements.