A Calculation of Steady Pressure Drop and an Analysis of HT—7U CICC

Under the condition of steady,the pressure drop of coolant is mainly caused by friction along the cable.in the CICC(cable-in-conduit-conductor).helium flow within the conductor consists of two parallel interconnected tubes.The velocity distribution has some differece between the central channel and conductor space.The region of Reynolds number is from 10^3 to 10^6.This paper describes the calculation of pressure drop of HT-7U CICC at various mass flows.It is assumed that the coolant flows in two parallel,rough tudes during the caclulation.     

The AC losses measurement and analysis of superconducting NbTi CICC for HT-TU superconducting Tokamak

Superconducting TF and PF coils have been measured in SULTAN test facility. Segregated copper strands are included in four NbTi CICC and this is a technical innovation. Two AC losses measurement methods, calorimetric and electromagnetic methods, have been used in the experiments, and a broad frequency range (from 0.05 Hz to 6 Hz) is covered in sample test. The purpose of this experiment was to investigate AC losses of TF and PF CICC conductor including segregated copper and to check the design of PF and TF CICC coated with different resistive barriers (Pb-30Sn-2Sb and Ni plating on NbTi strands).     

Nb3Sn超导磁体低温冷却设计

介绍了聚变堆用Nb₃Sn超导磁体管内电缆导体（CICC)的结构型式和参数,以及超导磁体的运行工况,采用一维数学模型Gandalf对超临界氦迫流冷却回路进行压降计算,从理论上确定了较为合理的液氦质量流率。     

The Investigation on Welding Processes for SUS316LN Tubes Used in Superconducting Magnetic System of EAST

The force flow cooled superconducting cable-in-conduit conductor （CICC） is used in both of EAST toroidal field （TF） and poloidal field （PF） coils. The conductor consists of multi-stage NbTi superconducting cable and 1.5 mm thick square jacket. The cable is pulled through in a thin wall circular jacket and then compacted to square cross-section conductor. The jacket material is SUS316LN austenitic stainless steel seamless tubes （about 10 m each）, which is assembled by butt-welding up to 600 m. The results of the welding procedure investigation and quality assurance procedures carrying out are described 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 Nb_3Sn/Nb Ti 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.     

Anomalies on V–I characteristic of NbTi cable-in-conduit conductors

Two kinds of anomaly, observed in the Volt–Ampere Characteristic (VAC) of large NbTi cable-in-conduit conductors (CICC) are discussed. In one case, the wavy behavior of the VAC close to the current sharing range is explained with oscillations of the cooling temperature of the order of 10–30 mK. A simulation of periodic temperature variations is done to reproduce the experimental behavior. In another case, voltage spikes in the VAC are correlated with saw-tooth signals from Hall sensors monitoring the conductor self-field, suggesting the occurrence of local quenches and recovery, with local current re-distribution. The analysis of the two kinds of anomaly, with their own signature on the VAC, provides valuable diagnostic tools for the interpretation of large size CICC test results.     

Calculation of AC Losses of CICC for Superconducting Outsert Coils in a Hybrid Magnet

This paper is devoted to predict AC loss of Cable in Conduit Conductor (CICC) which is of importance in the design of conductors. The consideration for the conductor’s design and main parameters for the magnets are introduced. In order to attain a good accuracy in the calculation of AC losses, the field distribution within superconducting outsert should be considered. Calculation of the AC losses, including hysteresis losses and coupling losses, is conducted. An emphasis is put on the hysteresis loss during the ramp up of the current to the operational current (15.3 kA) and the coupling loss of the conductor in a power-down condition for insert. The results are obtained to be 74.9kJ and 950J for 40 T hybrid magnets, respectively. Based on the calculation, a brief analysis of losses effect on the conductor design and the operation of magnet is given for the purpose that the capacity of the cryogenertor can be evaluated and the stability regime can be improved in our future work on the hybrid magnets.     

The first performance of the facility for testing ITER CC conductor short sample

A new facility had been set up to test the low temperature properties of the short sample of the small-size cable-in-conduit conductor (CICC). The facility consisted of the background magnet which could provide 7 T centric magnetic field, a 50 kA superconducting transformer which provided sample current, a 500 W/4.5 K helium refrigerator which produced both the liquid helium (LHe) and supercritical helium (SHe). An ITER CC conductor short sample was prepared and measured in this testing system. T_cs of 7.02 K (@4.1 T, 10 kA) and I_c of 8.9 kA (@4.1 T, 7.06 K) were measured.     

Results of simulations of stability and quench behavior for pulsed tests of the ENEA 12T Nb3Sn CICC coil

In the ENEA Frascati Laboratory a facility is being assembled to test the ENEA Nb₃Sn CICC coil in pulsed regimes. The characteristics of the coil (dimensions, cable-in-conduit conductor, strand designed for use in variable field) are such to make these tests of primary importance to predict the behaviour of the ITER (International Thermo-nuclear Experimental Reactor) Central Solenoid Model Coil, which will be built in the next two years. In particular, the stability and quench behaviour of the coil will be tested and compared to the predictions of the thermo-hydraulic analysis code SARUMAN. Other important parameters will be the ramp rate limination, the limiting current and the conductor losses. Several testing scenarios (ramp up and discharge) are described and the present status of testing programme definition is given, together with the associated analyses.     

HT-7U NbTi 管内电缆导体瞬态稳定性的实验研究与分析

在SULTAN 测试设备上进行了含分离铜股线CICC瞬态稳定性的实验研究,应用脉冲场对样品的脉冲场区域(390 mm)进行感应加热,发现设计的含分离铜股线CICC能够经受住很大的瞬态磁扰动,分析了这个现象的原因,并就股线上的电阻层对稳定性的影响进行了分析,对4个CICC导体的稳定性差异进行分析和稳定性裕度的理论计算,由理论计算值和实验测量值进行比较分析,为HT-7U纵场和极向场NbTi CICC的选择提供实验依据.     

Stability and design criterion for cable-in-conduit-conductors with a broad transition to normal state

Stability criterion in cable-in-conduit conductors (CICC) is often associated with heat removal rate higher than heat generated in the normal zone, which requires low current density in the strands. We show that this criterion is not a mandatory requirement for serviceability of CICC and that CICC may work reliably at higher current densities. In conditions of limited and well defined perturbations, sufficient stability is provided not by a large amount of copper and high transient heat transfer, but by a smooth transition to the normal state and easy current redistribution. A strand parameter space in terms of I_c and N-value meeting CICC requirements for stability, limited heat generation, and minimum temperature margin is proposed and discussed. The theory predictions are compared with known experimental data on CICC.     

Manufacture of ITER feeder sample conductors

The ITER feeders are the components that connect the ITER magnet systems located inside the main cryostat to the cryogenics, power-supply and control system interfaces outside the cryostat. The feeder busbars rely on the Cable-In-Conduit Conductor (CICC) design concept as all the conductors for the ITER magnet systems. There are two types of busbars for the feeder systems. One is the Main Busbar (MB) for the TF, CS and PF feeders, and the other is the Corrector Busbar (CB) for the CC feeders. The busbar cable is wound from multiple stage sub-cables made with Cu and superconducting strands. The superconducting material is NbTi for the busbar strands of all feeder systems. All Feeder conductors are provided by China. The R&D programs are needed to acquire knowledge on the behavior of such conductors.Since the conductors are new, some full size copper dummy conductors have been produced for the testing of the cabling parameters, definition of automatic TIG welding of seamless jacket section, elaboration of cable insertion and compaction. Then, two short qualification conductor samples (MB and CB) are prepared in ASIPP, and NbTi advanced strands are produced by Western Superconductor Technology (WST).The details of manufacturing procedures for Feeder conductor samples will be described in this paper.     

Influence of mass flow rate on Turbulent Kinetic Energy (TKE) distribution in Cable-in-Conduit Conductors (CICCs) used for fusion grade magnets

Thermohydraulic analysis is beneficial to understand the complex flow behavior in dual channel cable-in-conduit conductors (CICC) used in Tokomaks such as International Thermonuclear Experimental Reactor (ITER). Such dual channel CICC contains an annular and a central channel separated by a spiral. The cable bundle channel of CICC can be assumed to be porous and the central channel a clear region for thermohydraulic analysis using Computational Fluid Dynamics (CFD). Flow through CICC is found to be turbulent and this turbulence is transported in the form of small eddies. These eddies may dissipate the energy in the form of heat while being transported and finally the smaller eddies may combine to form larger eddy or may die out. Such phenomenon can be well explained with the help of a parameter called Turbulent Kinetic Energy (TKE), which determines the energy possessed by the eddies in the turbulent flow.In the present work, a three dimensional model of dual channel CICC is developed in GAMBIT-2.1 and solved using a compatible solver FLUENT-6.3.26. The influence of mass flow rate on Turbulent Kinetic Energy (TKE), which is defined as the mean kinetic energy per unit mass associated with eddies in turbulent flow, is analyzed. The computational results of pressure drop and flow repartition are validated against relevant experimental published results.     

Simulation and test of quench in CICC: The SMES experience

This paper summarizes the work done as part of the U.S. SMES program to simulate quench evolution on the 200 kA CICC developed by the Bechtel Team. As a large-scale CICC with a central tube, this work has led to a number of results applicable to other conductors sharing similarities with the SMES-CICC. The paper presents the evolution in computational models, since 1987 to date, and describes QUIPS, a test intended to validate these computer models. The paper concludes with observations on the directions in the field as perceived by the author.     

CICC Joint Development and Test for the Test Facility

The superconducting joint of the NbTi Cable-in -conduit Conductor (CICC) has been developed and tested on the magnet test facility at Institute of Plasma Physics, Chinese Academy of Sciences. The CICC is composed of (2NbTi+lCu)x3x3x(6+ltube) strands each with 0.85 mm in diameter, which has been developed for a central solenoid model coil. The effective length of the joint is about 500 mm. There have been two common fabrication modes, one of them is to integrate the 2 CICC terminals with the copper substrate via lead-soldering, and the other is to mechanically compress the above two parts into an integrated unit. In the current range from 2 kA to 10 kA the joint resistance changes slightly. Up to now, 11 TF magnets, a central solenoid model coil, a central solenoid prototype coil, and a large PF model coil of PF large coil have been completed via the latter joint in the test facility.     

Entropy generation minimization (EGM) to optimize mass flow rate in dual channel cable-in-conduit conductors (CICCs) used for fusion grade magnets

Dual channel cable-in-conduit conductors (CICCs) used in tokamaks such as International Thermonuclear Experimental Reactor (ITER) consist of annular channel packed with superconducting strands and a clear central channel separated by a spiral from the annular channel. Supercritical helium (SHe) operating at 4.5 K and 0.5 MPa is used for forced convective cooling of CICC. Pressure drop is inevitable in the process of forced convective cooling, leading to the development of velocity gradients and temperature gradients. These velocity gradients and thermal gradients result in entropy generation in CICCs.The present work aims at estimating volumetric rate of entropy generation (EG) in dual channel CICC. Subsequently, entropy generation minimization (EGM) technique is used to find optimum mass flow rate at which volumetric rate of EG is minimum. Pumping power and heat transfer corresponding to minimum rate of EG are also calculated. Computational fluid dynamics (CFD) is used as a tool to estimate EG as the analytical solution for turbulent forced convective flows requires inaccurate simplifications. A three dimensional model of dual channel CICC is developed in GAMBIT-2.1 and solved using a compatible solver FLUENT-6.3.26. The annular region of CICC is assumed to be porous and the central channel is assumed as clear region for EG analysis using CFD. The pressure gradients and heat transfer coefficient estimated from the simulations are validated against relevant experimental results available in the literature. The effect of mass flow rate on volumetric rate of EG in turbulent forced convective flow is studied using CFD.     

Present Status of the KSTAR Superconducting Magnet System Development

The mission of Korea Superconducting Tokamak Advanced Research (KSTAR) project is to develop an advanced steady-state superconducting tokamak for establishing a scientific and technological basis for an attractive fusion reactor. Because one of the KSTAR mission is to achieve a steady-state operation, the use of superconducting coils is an obvious choice for the magnet system. The KSTAR superconducting magnet system consists of 16 Toroidal Field (TF) coils and 14 Poloidal Field (PF) coils. Internally-cooled Cable-In-Conduit Conductors (CICC) are put into use in both the TF and PF coil systems. The TF coil system provides a field of 3.5 T at the plasma center and the PF coil system is able to provide a flux swing of 17 V-sec. The major achievement in KSTAR magnet-system development includes the development of CICC,the development of a full-size TF model coil, the development of a coil system for background magnetic-field generation , the construction of a large-scale superconducting magnet and CICC test facility. TF and PF coils are in the stage of fabrication to pave the way for the scheduled completion of KSTAR by the end of 2006.     

Characterization of superconducting wires and cables by X-ray micro-tomography

Due to their mechanical strength and ability to withstand the large electromagnetic force applied to the superconductors in large magnets during excitation, the Cable-in-Conduit-Conductor (CICC) type superconductors will be employed in the next stage of fusion magnets. Here, we discuss the recent results on the application of a non-invasive method for the characterization of CCIC by X-ray micro-tomography (μXCT). The experiments have been carried out on a high resolution X-ray tomograph in INFLPR (http://tomography.inflpr.ro). An open type nanofocus X-ray source with maximum high voltage of 225 kVp at 15–30 W maximum power and multiple targets of W on different windows materials (Be, Al, Cu or diamond) is the main component. X-rays are detected by means of amorphous silicon flat panel sensor in the cone-beam configuration and high-energy efficient line sensor based on individual scintillators in the fan-beam scanning configuration. The quality of tomographic images (≈40 μm space resolution) allowed the majority of strands of analyzed CICC samples to be fully reconstructed along the investigated segment (up to 300 mm long). Our method provides: (i) local and global void fractions (over a 300 mm length of the sample), (ii) void homogeneity factor as the ratio between void space surface and perimeter and (iii) twist pitch angle of individual strands and its distribution in 3D. It can be used to investigate superconducting CICC during their manufacture, installation or after service inspection, for purposes of QA, characterization or development.     

Test and Analysis of China's First Short Conductor Sample for ITER Toroidal Field Coils

In the framework of the ITER Qualification Tests, the first China TF conductor sample (CNTF1) was tested at the SULTAN facility. The sample was made of two TF conductor sections manufactured from identical internal stannum strands provided by the Oxford Superconducting Technology Company (OST). In order to evaluate the conductor performance, the current sharing temperature (Tcs) was measured at specified electromagnetic load cycling steps. Both conductor sections of the CNTF1 sample showed identical performance. Tcs was 7.2 K before cycling loading, and 6.9 K even after 950 cycles, without significant degradation, which substantially exceeds the ITER requirement of 5.7 K. The tests of the CNTF1 conductor sample showed that the electromagnetic cyclic load exhibited a negligible effect on the conductor performance. The coupling time constant for AC loss was 214 ms and 71.52ms before and after the cycling load, respectively. The test results of the sample are compared with the strand performance and parameter model analysis.