High Efficient Numerical Methods for Viscous and Nonviscous Wave Problems

This paper is concerned with accurate and efficient numerical methods for solving viscous and nonviscous wave problems. The paper first introduces a new second-order PR-ADI like scheme. For an efficient simulation, the scheme is also extended to a high-order compact PRADI like method. Both of them have the advantages of unconditional stability, less impact of the perturbing terms on the accuracy, and being convenient to compute the boundary values of the intermediates. Besides this, the compact scheme has high-order accuracy and costs less in computational time. Numerical results are presented to show the accuracy and efficiency of the new algorithms

Heat Transfer Analysis of MgB₂ Coil in Heat Treatment Process for Future Fusion Reactor

State of the art MgB2 is reviewed as a potential material for the poloidal field (PF) coils of the future fusion reactor due to its high critical temperature and low material cost. The heat treatment process is a crucial step in the development of MgB2 magnets. The temperature lag in heat treatment of large magnets can lead to insufficient thermal reaction time. It may be infeasible to control the temperature of a magnet according to the heat treatment scheme recommended for the MgB2 wire. Hence, the heat treatment process of a large magnet needs to be evaluated. Therefore, the dynamic temperature distribution of a MgB2 PF coil is obtained by simulating the heat transfer in heat treatment process. A suitable heat treatment schedule for a large magnet is proposed and the experimental results of a sub-size Cable-In-Conduit Conductor manufactured with MgB2 strand confirmed the feasibility of the newly proposed heat treatment process. The results provide a reference for the heat treatment method of a future larger MgB2 coil.</p

Metallographic investigation of first full-size high-J_c Nb₃Sn cable-in-conduit conductor after cyclic loading tests

In order to verify the feasibility of applying high-Jc Nb3Sn strand in fusion magnet, a full-size cable-in-conduit conductor (CICC) with short twist pitch (STP) cable pattern was manufactured and tested in SULTAN facility at SPC, Switzerland. Three levels of cyclic electromagnetic (EM) load were applied on the sample stepwise, no visible decrease of current sharing temperature (Tcs) was observed until the EM load increased to 80 kA × 10.8 T, after that the Tcs decreased dramatically with the EM cycles, which suggested that irreversible deformation, causing a change in the strain state, or even damage has occurred in the superconducting strands. For investigating the reason which caused the conductor performance degradation, the tested conductor was dissected for metallographic observation. Eight segments which subjected to different EM loads were extracted from one of the legs, the geometric feature changes of the cable cross-sections were analyzed and compared. A good correlation was found between the decrease of the Tcs and deformation of the cable cross section. A mass of cracks were found on the sub-elements of strands in the segment which subjected to highest EM load, but the amount of crack is much lower in other segments. Combining the analyses, it is speculated that the critical EM load which causes irreversible degradation is between 850 kN/m and 870 kN/m for this conductor. The results could be a reference in high-Jc Nb3Sn CICC design.</p

Mechanical and Electrical Properties of a CFETR CSMC Conductor under Transverse Mechanical Loadings

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 Nb3Sn 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 (dy) versus applied load force (Fy ) 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 dy versus Fy are also presented. The evolution of interstrand contact resistance (Rc) in the cabling stages with cyclic history and pressure effects are discussed. In addition, a fitting relation of Rc versus Fy is presented based on a combination of strand's microsliding and copper matrix resistivity. A clear correlation between intrapetal resistance Rc and coupling loss is also found

Manufacture and performance test result of a 95 kA-class Nb-Ti cable-in-conduit conductor for the low field winding-package of CFETR-TF coil

The engineering design of the CFETR TF prototype coil and conductors has been completed. The wind-package (WP) of the coil is graded into three regions based on the magnetic field distribution for saving cost. High-Jc Nb3Sn strand, ITER-like Nb3Sn strand and Nb-Ti strand are applied for high-field, mid-field and low-field WP respectively. In order to verify the conductor design, full-size short samples have been manufactured for the three types of conductors. The samples are tested in the SULTAN facility at CRPP in Villigen, Switzerland. At present, the test of Nb-Ti conductor for low-field WP is finished, DC and AC tests were performed. In DC test, several current sharing temperature (Tcs) measurements were performed with 500 electromagnetic cycles and one thermal cycle. Additionally, minimum quench energy (MQE) measurement was performed for investigating the stability of the conductor. The test results and analysis are reported in this paper.</p

Research on mechanical properties of high-performance cable-in-conduit conductors with different design

The China Fusion Engineering Test Reactor (CFETR) is a new tokamak fusion reactor under preliminary design, where the toroidal field (TF) coil has been designed to create a magnetic field of over 14.3 T. The TF conductors need to operate stably at 14.3 T, requiring the exclusion of conductor performance degradation from thermal and electromagnetic loading as much as possible. The maximum Lorentz force will reach about 1200 kN m-1, which is much higher than that of ITER conductors. In previous research, performance degradation was found during electromagnetic cycles and warm-up-cool-down cycles. A correlation was found between a conductor's degradation and its mechanical properties. According to the analysis, a conductor with a short twist pitch (STP) scheme or a copper wound superconducting strand (CWS) design has large stiffness, which enables significant performance improvement in terms of the electromagnetic and thermal load cycling. The cable stiffness is closely related to the number of inter-strand contact points inside the conductor. Based on this concept, four types of prototype cable-in-conduit conductor samples with STP and CWS design were manufactured. The number of inter-strand contact points was analyzed, and mechanical transverse load testing was performed at 77 K. The results show that the conductors with more contact points per unit length exhibit a higher stiffness. However, the cable designed with high cable stiffness caused strand indentation, which was also investigated. In this paper, the conductor design and experimental results are discussed and compared with ITER TF and central solenoid conductors.</p

Performance of first insert coil with REBCO CICC sub-size cable exceeding 6 kA at 21 T magnetic field

The Institute of Plasma Physics at the Chinese Academy of Sciences is developing the REBCO cable in conduit conductor (CICC) technology for applications in next-generation nuclear fusion devices. The aim is to develop a CICC comprised of six REBCO sub-cables to satisfy the requirements of operation with a current of around 40 kA and a peak field of up to 20 T. To qualify the performance of the sub-size REBCO cable to be used in the CICC, two 25-turn insert solenoids have been designed, manufactured and tested at a current exceeding 6 kA subjected in a background field supplied by a water-cooled resistive magnet. The insert solenoid, wound from a 11.5 m long REBCO CORC$^{®}$ cable, was designed to investigate its current carrying capacity under high field and electromagnetic (EM) load at 4.2 K. Tests were performed under a background magnetic field up to 18.5 T, resulting in a peak magnetic field on the innermost layer turns of around 21.1 T at an operating current of 6.3 kA. The effects of operation with cyclic EM loads were tested by repeated current ramps to around 95% of the critical current. Moreover, the V–I characteristics were measured at 77 K and the self-field, to check the effects from warm-up and cool-down (WUCD) cycles between room temperature and 77 K with liquid nitrogen. The results show no obvious degradation after dozens of high-current test cycles in background fields ranging from 10 T to 18.5 T. The insert solenoid demonstrates the stable operation of the REBCO sub-size cable for CICC with EM loads of about 90 kN m$^{−1}$ and WUCD cycles between room temperature and 77 K. These promising results indicate the potential of this technology for further applicationsin particular, for full-size CICC for high-performance fusion magnets

Building damages in Deyang city by the 2008 Wenchuan earthquake

The Ms8.0 Wenchuan earthquake in 2008 caused huge casualties, economic losses, and building damages, which are analyzed. The results show that damages of houses designed according to the current seismic code were significantly smaller than those without such design, suggesting that the code has achieved the desired goal of seismic fortification. Buildings of different kinds of structures showed large differences in damages : Houses with steel-frames and shear walls or steel structures suffered the least damages: those with frames or with brick-and-concrete structures suffered more; old cottages, the most