HTS Current Lead Research Articles

Results of HTS Current Lead Series Manufacturing for ITER

Results of HTS Current Lead Series Manufacturing for ITER

HTS Current Lead with Varying Cross-sectional Area for Superconducting Magnet systems

HTS Current Lead with Varying Cross-sectional Area for Superconducting Magnet systems

Design and experimental research on a new structure of 20 kA ReBCO high temperature superconducting current lead

This paper proposes and introduces a new design structure for a 20 kA ReBCO high temperature superconducting current lead (HTSCL). The main parameters of the new structure, such as heat load and safety performance, were studied through theoretical calculations. Subsequently, critical performance experiments were conducted on the samples. The results show that the new design structure is significantly superior to the first generation HTSCL and the simple ReBCO design structure in many performance aspects and thus has certain application prospects. This research will accumulate valuable experience for the application of ReBCO high-temperature superconducting materials.

Test Results of a Prototype HTS Current Lead With MgB2 and NbTi Superconducting Joints

Conventional vapor cooled current leads (CL) based on low temperature superconductor are the major consumer of liquid helium in large-scale superconducting magnets based nuclear fusion devices. Use of conduction cooled, high temperature superconductors (HTS) current leads enable operation up to 80 K and saves significant cold capacity of cryo plant. Recently at Institute for Plasma Research, India, a 3.3 kA rated prototype HTS CL pair is developed with the help of Indian industries. It exploits various superconducting materials operating from 5 K to 80 K. HTS module is based up on commercially available rare earth cuprate oxide superconductor based BSCCO-2223 tapes. For testing purpose, we have developed bottom lap joints using composite magnesium diboride (MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) wires as an intermediate between HTS module and NbTi: Cu cable that act as a shunt between CL pair. Such a hybrid concept is adopted as a next step to developing MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconducting current feeder which could be operated near 20 K and save cryogenic cost in future fusion machines. Here, we report the salient features, basic details of HTS CL, superconducting joints fabrication, its test set-up and experimental results. The inference from test results are then reported and discussed in detail.

Structure, design, and test of 13 kA HTS current lead

The 13 kA High Temperature Superconducting Current Leads (HTSCL) were designed and manufactured by the Institute of plasma physics, Chinese Academy of Sciences (ASIPP). This lead differs from former HTS current leads, in that it features an integrated heat exchanger (HEX) structure, a HTS magnetic shield and protective sleeve, and a Low Temperature Superconducting (LTS) module with a through cold conduction channel. The HTS and LTS module is cooled by SHe. In November 2020, the 13 kA steady-state test, Loss Of Flow Accident (LOFA) test, joint resistance test, pulse current test, insulation voltage test and other low-temperature electrical test items of the leads were completed. The test results indicate that all parameters meet the design requirements.

Copper electroplating technique for development of HTS current leads bottom joints using MgB2 wires

Low resistance, helium leak tight, cryo-stable superconducting (SC) joints with sufficient strength to absorb thermo-mechanical stress are commonly used in large sized magnets, their feeders and current leads (CL). Among high temperature superconductor (HTS), cuprate oxide based tapes are the popular options for CL applications. Recently composite magnesium diboride (MgB2) wires with superconducting transition temperature of 39 K are getting wide attention for low field applications. Use of Monel as a sheath material in MgB2 wires poses a major challenge while fabricating SC joints due to its low wettability and flowability using PbSn alloy based solder material. To tackle this issue, we exploited Cu electroplating technique to ease fabrication of MgB2 – NbTi: Cu as well as HTS: Cu - MgB2 joints. The details of in-house electroplating technique developed to fabricate bottom joints of BSCCO-2223 based HTS CL using MgB2 wires are reported. To study the morphology of such Cu coated MgB2 wires microstructural investigation is performed using Scanning Electron Microscope with energy dispersive X-ray spectroscopy (SEM/EDX) analysis. Similar Cu plated MgB2 wires are used to fabricate bottom joints of a prototype HTS CL. The performance of joints is preliminary attempted in the HTS CL test experiment up to 1.5 kA at 20 K.

Progress of engineering design of CFETR magnet feeder system

The engineering design project of the China Fusion Engineering Test Reactor (CFETR) was almost done by the end of 2020. The superconducting magnets system of CFETR is significantly different from International Thermonuclear Experimental Reactor (ITER), so as a lifeline of Tokamak system, a new magnet feeder system needs to be designed to meet the CFTER operation requirement. According to the operating requirements of the CFETR magnet system, 23 feeder lines were designed for different coils. In this paper, the progress of the preliminary engineering design of the CFETR magnet feeder system was presented. Combined with the overall design consideration of the CFETR's buildings and other auxiliary systems, the overall layout of feeder system has been completed. The engineering design of main substructures and components were almost completed, including CTB (Coil Terminal Box, 100 kA HTSCL (High Temperature Superconducting Current Lead), CFT (Cryostat Feed-through), ICF (In-Cryostat-Feeder), etc. And some important analysis results were presented to give discussion and conclusion support for the design.

Analysis and Design of a 100 kA HTS Current Lead for CFETR

High temperature superconductors have zero resistance under critical temperature and the HTS tapes have low thermal conductivity. The China Fusion Engineering Test Reactor(CFETR) project requires current leads with current carrying capacity up to 100 kA, making high temperature superconducting current leads the ideal choice. The main work of this paper is the theoretical analysis and optimization design of the 100 kA HTS current lead. Current leads are designed to minimize heat leakage to the cryogenic system and to reduce the mass flow of cooling gas. In this paper, some important design parameters are introduced firstly, and then one dimensional thermal analysis is carried out for the heat exchanger and high temperature superconductor parts. The LOFA time and overheating time of the current lead were calculated through simulation, and it was verified that the design meets the requirements of the project. Finally, the factors that have great influence on the performance of current leads are analyzed. In view of the four influencing factors, which are joint resistance, GHe inlet temperature, hPw and RRR, we respectively produced an optimized design.

Overview and first operation of the high temperature superconductor current leads during integrated commissioning of JT-60SA

The Karlsruhe Institute of Technology (KIT) has constructed and tested the High Temperature Superconductor Current Leads (HTS-CL) for the tokamak JT-60SA within the frame of the Broader Approach agreement between Europe and Japan. In total six HTS-CLs for 25.7 kA for the Toroidal Field (TF) coils and 20 HTS-CLs for 20 kA for the Equilibrium Field (EF) and Central Solenoid (CS) coils were manufactured and all of them were tested at operating temperatures in the test facility CuLTKa at KIT. After delivery, the CLs were integrated into the coil-terminal boxes (CTB) and connected to the TF, EF and CS coils via superconducting feeders. In the present paper the design, manufacture and acceptance tests of the HTS-CL at KIT, their integration into the CTBs, and first results of their operation during integrated commissioning are presented.

Cold Performance Tests of the ITER 68 kA HTS Current Lead Prototypes

• The cold performance test under 4 K is crucial and essential for the most challenged TF prototype HTS current leads. Detailed test process and method are presented. • Many overcurrent and over cooling case were performed to study the TF current leads, and the 1-hand test results and some analysis were presented • The test process and result is important for all the series TF current leads and for the operation in the future. The Toroidal Field (TF) current leads which supply 68 kA DC current for the TF coils are the largest capacity High Temperature Superconducting (HTS) current leads among the three types of HTS current leads for ITER. Two TF HTS current leads prototypes have been successfully built and cold tested at the Institute of Plasma Physics of the Chinese Academy of Sciences (ASIPP). The cold performance test is a crucial step to verify the design parameters and manufacturing process before starting the series production. The cold performance test includes rated current steady state operation and Loss Of Flow Accident (LOFA) test, different Heat eXchanger (HX) boundary operation, over-current, joint resistance, and heat conduction tests. This paper will present the major results of those tests.

Experimental Research of a 10 kA HTS Current Lead Using YBCO Tapes

A 10 kA high-temperature superconductor current lead (HTS-CL) using a double-tube stainless steel (SS) shunt has been designed, fabricated, and tested at Institute of plasma physics, Chinese Academy of Sciences (ASIPP). The current lead consists of 80 parallel the second generation HTS coated conductor with critical current of 220 A at 77 K in self-field, a double-tube SS shunt, and Cu connectors. The 80 YBCO tapes are divided into 20 so-called panels, which are soldered into the 20 grooves on the surface of the double-tube SS shunt and Cu connectors, each panel contains four parallel YBCO tapes. A double-tube shunt consisting of two coaxial tubes is designed. A series of tests were performed to verify the feasibility of the HTS-CL. The measured joint resistance is about 0.3-0.4 μΩ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The transport current of 10.515 kA was carried between 5 and 65 K for 1010 s with no quenching. The LOFA time of 569 s and the burnout time over 15 s meeting the design requirements.

Design and Test of Current Leads With Parallel HTS Tapes for MRI Applications

The design, analysis and experimental test of a High Temperature Superconductor (HTS) current lead with parallel HTS tapes for MRI applications are presented. Two HTS tapes are electrically shunted in parallel in each current lead to increase its current-carrying capability. Analytical and finite element analysis has been conducted to investigate the current distribution of parallel HTS tapes under the impact of various design parameters, including the geometry, symmetricity and resistance of copper terminals, and the resistance of the interface between copper terminals and the HTS tapes. The analysis concludes that the electric resistance from the copper terminal to each of the parallel HTS tapes needs to be relatively close in order to balance the current sharing between two tapes. Making the copper terminal electrical resistance dominantly greater than the interface resistance would result in a robust current leads design. The FEA simulation meets well with prototype HTS leads test result.

Self-Protecting HTS Current Lead-Demonstration of a New Technology

A straight forward solution to reduce the heat load of Current Leads to superconducting magnets operating at 4 K is the use of high temperature superconductors (HTS) thereby eliminating the ohmic heating at the range below 50–77 K. The heat input from the current leads is then determined by heat conduction in the HTS section only, leading to some factor 10 reduction in the heat load in comparison to fully normal conducting conventional leads. Modern HTS conductors demonstrate extremely high current density and further decrease of the current lead heat load is limited not by the material properties but by the requirement of robustness and reliable protection of the leads in the case of cryogenic failures in order to avoid lead burnout. While accelerator magnets are designed for a fast dump at quench events within a fraction of a second, larger stored energy magnets like detector magnets may have discharge times of tens of seconds or even more. In this case the HTS part of the lead has to withstand the ohmic heating for a relatively long time and this requirement then determines the heat input at operation conditions. A new idea to reduce the heat load while keeping full reliability of the HTS leads is using a thermo-mechanical switch that is connected electrically in parallel to the HTS lead section. In the case of a quench in the HTS lead section, by using the differential thermal expansion between materials, the switch turns on and the overheated section is bypassed by the high cross-section of the conductive part of the switch. We wish to use this new technology for the first time for the BabyIAXO detector magnet. In this paper the design and test of the first and unique Self-Protecting HTS Current Lead with a current rating of 800 A is presented.

Safety analysis of the 100 kA HTS current lead for CFETR

Based on the Agreement of Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) and Ministry of Science and Technology of China during the Thirteen Five-Years Plan (so called 13∙5 plan), a dedicated test facility of superconducting magnet for China Fusion Engineering Test Reactor (CFETR) will be constructed in Hefei, China. A pair of high temperature superconducting (HTS) current leads rated at 100 kA for the CFETR magnet test facility is being designed at ASIPP. Because magnetic energy stored in the toroidal field magnet is 134 Giga Joules which are 3 times higher than the ITER case, HTS current leads must work at nominal current without performance degradation during the HTS current lead quench. In order to verify the safety and reliability of HTS current lead, the analysis of static magnetic field is done by ANSYS iteration to predict the maximum current carrying capacity of HTS module. This paper also give the numerical calculation of loss of flow accident(LOFA) of HTS current lead and temperature margin analysis of HTS module. The analysis results indicate that the HTS module has a current carrying capacity of 165 kA without external field at 65 K and a current carrying capacity of 149 kA with external 30 mT vertical field at 65 K. The LOFA time is about 580 s and the burnout time is about 30 s, which is better than the requirement of the toroidal field coil fast discharge time of 24 s.

Operation Experience of the Wendelstein 7-X High-Temperature Superconductor Current Leads

The fusion device Wendelstein 7-X is a modular stellarator, which went into operation at the Greifswald branch of the Max-Planck-Institut fur Plasmaphysik in December 2015. The main component is the superconducting magnet system that consists of 50 nonplanar and 20 planar coils, 14 high-temperature superconductor (HTS) current leads (CLs), and more than 100 superconducting bus bars. The HTS CLs with a maximum current of 18.2 kA were constructed, tested, and delivered by the Karlsruhe Institute of Technology (KIT). In the first plasma physics campaign, the nonplanar coils were operated with a maximum current of 12.4 kA, whereas the planar coils were energized up to 4.9 kA. This paper describes the performance of the HTS CLs during plasma operation. A comparison to the acceptance test results performed after the construction of the CLs at KIT will be presented.

Development of a Zero Rate Evaporation Cryogenic System for 200 MeV Proton Cyclotron

Based on the collaboration of ASIPP (Hefei, China)–JINR (Dubna, Russia) for proton therapy, a 200-MeV compact superconducting proton cyclotron project (SC-200 project) has been launched at ASIPP. The superconducting coil of the main magnet system for cyclotron is cooled by liquid helium. A zero rate evaporation cryogenic system has been designed and tested for the main superconducting magnet system. Three GM-cry coolers (40 W at 50 K, 1.5 W at 4.2 K) were worked as the cold source to cooling the thermal shield, a pair of high-temperature superconducting current leads (HTSCL) and liquid helium container. The test results show that the thermal shield and HTSCL can be cooler lower than 77 K, the heat load of the cryogenic system is less than 2.8 W. The detail design of the cryogenic system and test process will be described in the paper.

Manufacture and Test of the ITER TF Type HTS Current Lead Prototypes

High temperature superconducting current leads (HTS-CL) are designed to supply the current to the large superconducting ITER magnets for the operation with reduced heat load to the cryogenic system. The Toroidal field (TF) current leads are the largest with a current capacity of 68 kA each. The Institute of Plasma Physics of the Chinese Academy of Sciences (ASIPP) is responsible for the supply of the current leads based on a design jointly developed with the ITER organization. Before the supply of the TF HTS-CL series, a pair of prototypes was manufactured in 2014 by ASIPP and associated manufacturers according to previously qualified manufacturing procedures. Rigorous quality control measures were developed and applied in preparation for series manufacturing. To verify compliance of the prototypes with the ITER specification, thorough testing was conducted in 2015. The test items under particular scrutiny were: the pressure drop in the counter-flow heat exchanger, the loss of flow accident test after steady state operation at 68 kA current, the so-called overheating time of the HTS module following an induced quench, the electrical resistances of the soldered joints inside the lead assembly (i.e., the low temperature superconducting (LTS) to busbar and the HTS to LTS joints), and the conduction heat load per lead to the 4.5 K end. In this paper, the main manufacturing steps are discussed, and test results are presented and discussed.

AC Loss Analysis of High-Temperature Superconducting Current Leads With Nonsinusoidal Current Waveform

For some high-temperature superconducting (HTS) devices, such as fusion magnet, fault current limiters (FCLs), and superconducting energy magnetic system, the ac loss of the HTS current leads is one of the most important heat sources in the cryogenic system. When HTS current lead is carrying alternating current, ac loss occurs. However, the HTS current leads of the above HTS devices usually carry the nonsinusoidal current, and the ac loss is difficult to be analyzed when the applied transport current is nonsinusoidal waveform. In this paper, we firstly proposed two kinds of structure of HTS current leads, and the ac losses of these two current leads with the specific current waveform were calculated subsequently by using finite element method software COMSOL. Furthermore, the ac losses of two structure current leads were measured by using the integral method, respectively. Finally, the ac loss results of these two structures of current leads were compared and analyzed theoretically and experimentally, which aims to select the preferred structure of current lead for HTS applications in terms of ac loss.

Monitoring and control of the magnet system of JT-60SA

The construction of the full-superconducting tokamak JT-60 Super Advanced (JT-60SA) is in progress under the JA-EU broader approach agreement. The Cryogenic System of JT-60SA has five circuits to cool the Poloidal field coils, Toroidal field coils, thermal shields, high temperature superconducting current leads (HTS-CLs) and feeders, and divertor cryopumps. The physical conditions such as pressures, temperatures and mass flows of the magnet cooling loops are monitored by a Magnet Controller The magnet controller also performs local control of the helium flows. A particular abnormal situation is a quench or a fast discharge of a magnet which would require many hours for recovery to normal operation. In order to avoid fast discharges as far as possible, the MC uses “safety interlocks” to supervise the magnet coils and the HTS CL. This safety interlocks are called slow discharge. In this paper, the slow discharge thresholds of the HTS-CLs are derived from simulations of the cryogenic loops using the thermal analysis programs FLOWER, HEATER, and SUPERMAGNET.

Test Results of ITER 52-kA HTS Current Lead Prototypes

The Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) is responsible for the construction and performance testing of the 30 pairs of the international thermonuclear experimental reactor high-temperature superconducting (HTS) current leads. The first pair of poloidal field (PF) coil type, 52-kA HTS current lead prototypes was built and cold tested in ASIPP in mid-2016. The test results demonstrated their excellent performance on low joint resistance, long loss of flow accident time, and high current-sharing temperature. The overheating time, mass flow, and heat loads to 5-K ends also meet the requirements. This paper summarizes the major test results for the PF 52-kA HTS current lead prototypes.