Bi Yanfang

R&D on Resistive Heat Exchangers for HTS High Rated Current Leads

The HTS current leads of superconducting magnets for large scale fusion devices and high energy particle colliders can reduce the power consumption for cooling by 2/3 compared with conventional leads. The resistive sections of high-rated current leads are usually made of a heat exchanger cooled by gas flow. The supply of the cooling mass flow incurs more than 90% of the cooling cost for the HTS leads. The mass flow rate requirement depends not only on the length and material of the resistive heat exchanger, but also on the heat transfer coefficient and HEX surface, the joint resistance at the cold end and its cooling approach. The design and operation of a sheet-stack HEX with a larger specific surface and a much smaller hydraulic diameter are presented in the paper. The test results of an HTS lead optimized for 8 kA show that a 98.4% efficiency can be achieved.

Investigation on the Relation of CICC Stability Margin to Mass Flow Rate and Operating Temperature of Helium

To circulate supercritical helium, a differential pressure between inlet and outlet has to be applied. A differential pressure can be generated by a refrigerating compressor which forces the coolant through cooling channels. A differential pressure corresponds to a constant flow rate in a constant length. The coolant flow rate was set at different values from 0.2 to 2.8 g/s. The numerical simulation was performed using the 1-D mathematical model (Gandalf). The results of the experiment and simulation show that the larger the coolant flow rate, the higher the stability margin is. It is also showed that the shorter the cooling channel, the higher the stability margin is with the same coolant flow rate. Meanwhile, we also introduce the influence of temperature and pressure on the stability margin of CICC.

Evaluation of AC Losses for HT-7U CICC on Plasma Disruption

AC loss is one of the main issues in the design of the CICC used for PF and TF coils of superconducting tokamak. A preliminary calculation of AC loss for the designed HT-7U CICCs used for TF magnets is given in this paper. We only consider the hysteresis and coupling losses related to transversal and longitudinal kinds. In addition to the strand resistive barriers (Pb-30Sn-2Sb coating for NbTi strands), a stainless steel strip has been used inside these cables to reduce the AC loss in this kind of conductor. The available theory has enabled us to emphasize the role played by the stainless steel strip in the reduction of total AC losses in this kind of conductor. In this paper, it was shown that AC losses of cable were affected by the structure and change rate of magnetic field.

Construction of a 2 kW /4 K Helium Refrigerator for HT-7U

Superconducting magnets of toroidal field (TF) and poloidal field (PF) of HT-7U tokamak are all made of NbTi/Cu Cable-in-Conduit Conductor (CICC), and cooled with a forced flow supercritical helium of 3.8 K. A helium refrigerator with an equivalent capacity of 2 kW/4 K will be constructed. This paper presents the design of the helium refrigerator process, the thermodynamics of the refrigeration cycle and the refrigerator equipments.

A 4m 2kA HTS Power Cable System

A high temperature superconductor (HTS) cable system of both a length of 4 metre and a normal current of 2 KA with terminations and a cooling system has been built up and tested. The cable conductor was made of Bi-2223 tape. A space maintained vacuum between two corrugated stainless steel tubes functions as the cryostat surrounding the superconductor. A series of tests were carried out to verify the functions of the system. The important data obtained can be used to make longer HTS cable systems.

20kA HTS current leads for EAST tokamak project

Publisher Summary This chapter describes the design consideration, manufacture technology, and some test results of 20kA HTSCL. According to investigation the heat load of HTS current leads (HTSCL) at 4.5K can reduce to 0.1–0.18W/kA of the nominal leads. Using HTSCL for EAST tokamak can reduce refrigeration power of 900 W/4.5K at least and save operating cost greatly. Two 20kA current leads are made of different materials. Module 1 consists of melt cast processed Bi-2212 tube and two layers of Bi-2223/Ag-Au alloy tapes as the shunt and also to enhance current-carrying capacity. The critical current of the Bi-2212 tube alone is 9.052 kA at 77 K. The preliminary test results show that module 2 made of CryoBlock has better performance on the higher critical current and lower contact resistance. Correct solder technique and intervals between the stacks as small as possible are most important for HTSCL to reach a high performance without degradation of Bi-2223/AgAu tapes.

Superconducting Busline Design for HT-7U Tokamak

Superconducting (SC) tokamak HT-7U has seven pairs of buslines connecting toroidal/poloidal coils and the current leads. These SC buslines (SCBLs) share a common cryostat and are made of the cable in conduit conductors (CICCs) arranged as a decoupling configuration. In order to reduce the heat loads conducted from the seven current leads with a capacity of 15 kA during the magnets cooldown, the buslines with a much lower thermal conduction were employed in comparison with the current leads, and a special cooling loop was designed.

Trial Manufacture of a 30 m Cable-in-Conduit-Conductor (CICC) for HT-7U

This paper reports the working procedure of a 30 m cable-in-conduit-conductor (CICC), which has been first successfully fabricated by a working group of IPP in Jan. 1999. A series of problems along with measures for their solution were put forward at the request of engineering design on the basis of an in-depth understanding of the basic performance of the related techniques for the manufacture of CICC. Through a full-scale trial manufacture of a 30 m conductor including a series of test on performance technology such as tube-tube butted welding, pulling, equaring, prebending and take-up, the trial manufacture of the first home-made CICC conductor has been accomplished, demonstrating that the fabrication of a long-length CICC is entirely possible theorically and practically through our own efforts. Results and problems concerned in this trial fabrication are also presented in the paper.

New CICC Design Versions with High Copper Fraction for HT-7U Tokamak

The peak fields of HT-7U TF/PF coils are designed at 5.8 T and 4.5 T, respectively. The superconducting (SC) NbTi/Cu strands for the coils have a quite low copper fraction (0.58). To increase the ratio of the limiting current Vs. critical current for the cable in conduit conductor (CICC), the first-stage subcable consists of several copper strands twisted around a SC composite one. The copper strand diameter is different from the SC one. Based on Botturas CICC design approach we take the product of total copper cross-section and wetted perimeter as one of the key design parameters to meet with stability margin requirement. The product reaches 114 cm3 for 15.5 kA TF CICC at operating temperature of 4.2 K and 139 cm3 for 15 kA PF CICC at 3.8 K to obtain stability margins of 280 and 700 mJ/cm3, respectively.