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The last acceleration stage of the deuteron beam of the LIPAc linear accelerator is provided by eight superconducting cavities in a cryomodule (SRF Linac). Each cavity needs a magnet package, which consists of a solenoid for beam focusing and two vertical and horizontal dipole correctors for beam steering. The superconducting coils are fed by vapour cooled current leads. The beam position monitor is part of the magnet helium vessel. The series fabrication of eight sets of magnets and current leads has been performed by Elytt Energy, under CIEMAT follow-up. This paper describes the final design used for production, the main challenges addressed during fabrication, together with the quality control procedure, acceptance tests and qualification criteria to validate both the magnets and current leads. Currently some activities are being performed in the magnet helium vessels for improvement of surfaces for handling inside the clean room and reducing the risk of presence of particulate contaminations in the beam tube. [ABSTRACT FROM AUTHOR]

Flux pumps provide a contact-free method of energizing dc currents in superconducting coils. Since a predictive quantitative theory for dynamo-type flux pumps does not exist yet, the optimization of device designs must proceed through empirical experiment. In this paper, we investigate the effect of varying the annularwidth of the iron stator yokewithin a high-temperature superconducting dynamo. Reducing the dimensions of this iron yoke reduces the mass of cold iron within the dynamo, and hence has advantages in terms of weight, cryogenic efficiency, and eddy current losses. In this paper, we have investigated the dc output from an experimental high-temperature superconductor (HTS) dynamo in which the annular width of the iron yoke Δr is varied across a factor of four. Varying this dimension affects the reluctance of the magnetic circuit formed between the rotor and stator. We have shown that the dynamo output is surprisingly insensitive to the size of the iron yoke. The maximum current output (Isc ) is independent of Δr at all flux gaps. At the closest magnet-stator flux gap, a fourfold increase in Δr results in only a ~30% increase in the open circuit voltage (Voc ) and internal resistance (Rd) of the dynamo. Our results indicate that the smallest yoke studied (Δr = 6 mm) can be utilized with a 25.4-mm Nd-Fe-B rotor magnet, without adverse impact on the electrical performance of this type of HTS dynamo. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Dynamo-type high-temperature superconductor (HTS) flux pumps are fully superconducting dc current sources for HTS magnet coils, which eliminate the need for external current leads. Previous work has focussed on dynamos employing a single-coated conductor stator wire, and the maximum output current is found to be limited by the effective internal resistance of the stator wire. It is expected that adding additional stator wires in parallel will increase the maximum output current. However, there have been few experimental reports of this effect, nor of the influence of the rotor magnet configuration in a multiply parallel stator arrangement. In this paper, we report on the design and experimental characterization of an HTS dynamo employing eight parallel HTS stator wires, which are arranged in a cylindrical geometry and excited by an axially concentric rotor carrying one or more permanent Nd-Fe-B magnets. We investigate the effect of changing the number of rotor magnets, and find that the maximum output current is achieved when the number of rotor magnets is less than half the number of stator wires. We have demonstrated output currents of up to 700 A from this device. This is the highest reported output to date from a flux pump operating at liquid nitrogen temperatures. Furthermore, our results indicate that the squirrel-cage architecture used here is capable of achieving a maximum output current of ~ 1.3 kA. At present, the heat load associated with a kA+ conduction cooled current leads prevents such large currents being injected into present-day cryo-cooled HTS magnets. Our results now indicate that this issue could be circumvented through employing an HTS dynamo, opening up new opportunities to consider novel designs of very high-current cryo-cooled HTS magnets. [ABSTRACT FROM AUTHOR]

TheKarlsruhe Institute of Technology (KIT) agreed to construct and test the high-temperature superconductor (HTS) current leads for the tokamak JT-60SA presently under construction in the frame of the Broader Approach agreement between Europe and Japan. In total 6 HTS-CLs for 25.7 kA for the TF coils and 20 HTS-CLs for 20 kA for the PF and CS coils are needed. In addition, the acceptance tests of the HTS current leads were performed in the test facility CuLTKa at KIT. The manufacturing started in 2014 and the last current leads were tested in July 2017. The main parts of the acceptance test are the determination of the heat load at 4 K and the 50 K He mass flow rate through the heat exchanger as well as the simulation of a loss of flow accident. One test of the PF current leads also included a pulse test at 20 kA to demonstrate their PF operation capability. In this paper, an overview of the manufacture and acceptance tests of the HTS current lead is given. The results for the different current leads are summarized and compared to the specifications. [ABSTRACT FROM AUTHOR]

Superconducting flux pumps enable dc supercurrents to be injected into a superconducting coil without direct connection to an external current supply. Here, we report experimental data from a dynamo-type flux pump employing a high-$T_{{c}} superconducting stator. This device employs a mechanical rotor that rotates outside the cryogenic envelope, and excites the superconducting circuit through the cryostat wall via a magnetic circuit formed between the rotor and stator. We show that the width of the stator wire employed in this device has a significant effect on its output performance. At low frequencies, both the short circuit current, I\rm{sc}, and the open-circuit voltage, V\rm{oc} increase with stator width, and we obtain a maximum value of I\rm{sc}> 340 A using a stator wire width of 46 mm. However at higher operating frequencies, we observe that I\rm{sc} reaches a maximum value before dropping with any further increase in stator width. We attribute this to thermally dissipative effects due to circulating eddy currents in these wide superconducting stators. At frequencies above ∼400 Hz, we observe a sharp rise in the internal resistance of the stator wire that we attribute to a local quench due to the eddy currents driven by the local electromotive force (EMF) beneath the rotor magnet. This paper emphasizes the importance of frequency dependence when defining optimum operating parameters of a high- $T_{{c}}$ superconductor (HTS) flux pump. Our results also offer the promise that very high current flux pumps may be developed through maximizing the ratio of the stator wire width to the peak width of the rotor field profile. [ABSTRACT FROM AUTHOR]

This paper describes new kind of HTS (High Temperature Superconducting) element for current leads, which can transfer large electric current in the nuclear fusion system. Since the HTS tapes have no resistance and the generated Joule heat is also very small compared to the conventional current leads, cooling costs of the current leads can be reduced. For this reason, the various feasibility researches for HTS current leads have been promisingly progressed in the superconducting power applications. However, there is a limitation on the capability of current carrying for single HTS tape. In addition, the cross-sectional area of the current leads should be small enough to minimize the heat conducted through the HTS current leads. In order to improve the current carrying capacity of the current leads, multiple HTS tapes are required. In this paper, we proposed several structures of compact HTS current leads and compare them other 2 kA class current leads. We report on the calculated characteristics of stabilized HTS current leads and on the performance measured during critical current measurement tests. [ABSTRACT FROM PUBLISHER]

The preliminary design of the heat exchanger part for the pair of 30 kA hybrid current leads that will be installed in the ENEA 12 T CICC facility is presented. To limit the overall length and the amount of cooling gas to be employed, a hybrid resistive/HTS configuration has been conceived. Regarding the resistive part, a screw-like solution has been adopted for the following reasons: first to guarantee that helium would wet all the finned surfaces of the heat exchanger limiting possible short-path typically present in braided solutions, then to guarantee a proper insulation by creating a counter screw that seals this component and finally to limit the manufacture cost. Starting from the conceptual design were the hybrid model has been studied, in the present paper the resistive section is analysed in greater detail making use of a dedicated 1-D convective tool and 3-D finite element analyses. [ABSTRACT FROM AUTHOR]

The Karlsruhe Institute of Technology (which is a merger of former Forschungszentrum Karlsruhe and Karlsruhe University) is responsible for the design, construction and testing of the high temperature superconductor (HTS) current leads for the stellarator Wendelstein 7-X (W7-X) which is presently under construction at the Greifswald branch of the Max-Planck-Institute for Plasma Physics. The current leads are of the binary type, the HTS part covering the temperature range between 4.5 K and 60 K while the heat exchanger covers the range between 60 K and room temperature being cooled by 50 K He. In total 2 prototypes and 14 series current leads are required with a nominal current of 14 kA and a maximum current of 18.2 kA. The paper describes the design and first test results of the prototype HTS current leads. [ABSTRACT FROM AUTHOR]

A 3 T central field Superconducting Electromagnetic Iron Separator (SEIS) has been designed, fabricated and tested at Institute of High Energy Physics (IHEP) of China. The SEIS system is deliberately designed to separate small pieces of hazardous ferromagnetic materials, such as detonators, from coal to achieve high purity and good yield. The SEIS system mainly consists of a NbTi superconducting magnet, a LHe recondensation type cryostat with two GM cryocoolers (31 W/40 K, 1 W/4.2 K), a pair of binary current leads (CL). The 1 ton cold mass was located in the cryostat of the system with 630 mm room temperature bore. The system is powered with a 250 A/50 V power supply, and has charging time and discharging time of 15 minutes and 20 minutes, respectively. It took 10 days for SEIS magnet to cool down from 300 K to 4.2 K and 6 days to accumulate LHe at designed level 360 mm. The SEIS magnet suffered no quench to reach its designed current, and operated stably during many experiments afterwards. The experiment research of the SEIS system is detailedly presented in this paper. [ABSTRACT FROM AUTHOR]

Forschungszentrum Karlsruhe has taken over the responsibility for the design, construction and testing of the High Temperature Superconductor (HTS) current leads for two fusion experiments, i.e. the stellarator WENDELSTEIN 7-X. (W7-X) and the satellite tokamak JT-60SA. W7-X is presently under construction at the Greifswald branch of the Max-Planck-Institute for Plasma Physics and consists of 50 non-planar and 20 planar coils with a maximum conductor current of 17.6 kA. In total 14 current leads are required with a nominal current of 14 kA that are mounted upside down with the warm end at the bottom. In the frame of the Broader Approach Agreement between Japan and the EU and concomitantly to the ITER project, the satellite tokamak project JT-60SA has been agreed in 2006. The magnet system of JT-60SA consists of 18 toroidal field coils, 4 central solenoid modules and 7 poloidal field coils. In total 26 leads mounted in vertical, normal position are required. For W7-X and JT-60SA a common basic design will be used which will be adapted to the special needs of the machines. All current leads will be of the Cu-HTS binary type. The HTS part covers the range between 4.5 K and 60 K and is cooled by heat conduction from the 4.5 K end, only. The Cu heat exchanger is cooled with 50 K He and covers the range between 60 K and room temperature. The paper describes the status of the HTS current lead development for W7-X and JT-60SA. [ABSTRACT FROM AUTHOR]

For the superconducting magnet system of the International Thermonuclear Experimental Reactor, ITER, 60 current leads for a total current of more than 2500 kA are needed. The use of High Temperature Superconductor current leads (HTS-CL) will reduce the resultant large refrigerator load considerably. Within the EU Fusion Technology Programme, the Forschungszentrum Karlsruhe and CRPP have developed and built a 70 kA HTS-CL demonstrator optimized for 50 K Helium operation. In 2004-2005, the CL was successfully tested with 50 K as well as 80 K Helium, and finally with LN2. In the meantime, ITER has decided to use HTS-CLs for the magnet system and China has taken the responsibility to provide the sc feeders for ITER including the current leads. In this paper, the performance of a 70 kA HTS-CL in fault conditions will be analysed using the FZK-CRPP demonstrator as a model. In particular, the quench performance and the safety behavior in case of a loss-of-flow accident (LOFA) will be described and an extrapolation of the leads performance in real ITER conditions will be given. Finally the effect of different shunt materials is discussed. [ABSTRACT FROM AUTHOR]

The superconducting magnet system of the W7-X stellarator presently under construction at the Max-Planck-Institute for Plasmaphysics in Greifswald, Germany, requires 7 pairs of current leads for a maximum current of 18.2 kA. The Forschungszentrum Karlsruhe is responsible for construction, manufacturing and performance testing of the current leads prior to installation in the W7-X machine. To reduce the overall cooling power for the refrigerator as well as the free convection problem due to the upside-down orientation of the leads, it was decided to use HTS material in the temperature range between approx. 5 K and 60 K. The optimization of the HTS part requires to know exactly the electrical, mechanical and thermal parameters of the HTS material. Actually two suppliers, EHTS and Sumitomo offer such Bi-2223/AgAu material. Single tapes as well as stacks were used to measure the critical current as a function of applied magnetic field for various temperatures. The thermal conductivity, the stress-strain dependence and the thermal contraction were also measured. In the paper the electrical, mechanical and thermal performance of different tapes and stacks will be described and discussed. [ABSTRACT FROM AUTHOR]

The development of the semi-retractable current leads for a 21 T Fourier Transform Ion Cyclotron Resonance (FT-ICR) superconducting magnet system is presented. The semi-retractable current leads are composed of a normal metal element, conducting the current from room temperature to intermediate temperature, and an HTS element, conducting the current down to liquid helium temperature. An HTS element is partly immersed in liquid helium and the joint between the normal metal and HTS element is continuously refrigerated by a cryocooler. After magnet energization the metal element is disengaged from the HTS element without breaking vacuum to the insulating vacuum space. In the paper, the optimized dimensions of the leads are presented in order to minimize the thermal heat load when carrying operational current with some margin. The intermediate block with a lockable set point and the insulating vacuum system are fabricated and the adaptability and reliability are tested during engage and disengage performance. The effects of vacuum level and performance cycle on the electrical contact resistance in a lockable set are also investigated. [ABSTRACT FROM AUTHOR]

The powering of the LHC machine requires more than 1000 High Temperature Superconducting (HTS) current leads. These leads contain, at their cold end, HTS conductors made of stacks of Bi-2223 tape with gold-doped silver matrix. CERN specified and purchased 31 km of this material, which was delivered on spools in unit lengths of 100 to 300 m. On reception the tape was inspected, cut into short length and vacuum soldered into stacks. All stacks were characterized in liquid nitrogen using a measuring procedure and set-up specifically developed for this purpose. Contact resistance values and critical currents at different electric field criteria were measured, from which the n-values have been extrapolated from the experimental V-I characteristics. This paper reports on the assembly and electrical characterization (up to 800 A) of more than ten thousand Bi-2223 stacks. Three types of stack were made from tape from two manufacturers. The assembly and soldering procedures and the set-up for the series electrical characterization are described. An analysis of the measured data is presented, with particular regard to the homogeneity of the electrical properties of both the tape and the derived stacks. [ABSTRACT FROM AUTHOR]

HTS based leads have established themselves for high current carrying applications. This work revisits the issues for commercial magnets with a view to minimizing heat load and space for both the resistive and HTS parts. The paper describes the experimental work carried out to develop up to 300 A HTS current leads for Oxford Instruments' Cryofree and liquid helium cooled magnets. The current-voltage, temperature, and quench measurements are reported. The leads make use of BSCCO-2223 HTS wire and have been characterized at 4.2 K, 77 K, and some intermediate temperatures for quench purposes to test their robustness. The leads are in thermal equilibrium with their environment and require no additional cooling, unlike in the case of large current leads for accelerator magnets. The current work on the combined resistive and HTS parts has achieved a boil-off of 20 ml/hr in a liquid cooled cryostat. [ABSTRACT FROM AUTHOR]

For full cryogenic test of CERN 600 A High Temperature Superconducting (HTS) current leads prior to integration into the Large Hardron Collider (LHC), a dedicated facility has been designed, constructed and operated at the University of Southampton. The facility consists of purpose-built test cryostats, 20 K helium gas supply, helium gas flow and temperature control systems and quench protection system. Over 400 such leads have already been successfully tested and qualified for installation at CERN. This paper describes various design and operation aspects of the test facility and presents the detailed cryogenic test results of the CERN 600 A current leads, including steady state 20 K flow rates. [ABSTRACT FROM AUTHOR]

A new concept of current leads for a 21 T Fourier Transform Ion Cyclotron Resonance (FT-ICR) superconducting magnet system is presented. The binary current lead, a series combination of a normal conductor in the high-temperature section and an HTS conductor in the low-temperature section, is employed. The HTS section is partly immersed in liquid helium and the joint between the normal metal and HTS conductor is cooled by the contact with a cryocooler. After excitation, the normal metal conductor section is thermally disengaged from the HTS section without disturbance to the insulating vacuum space and without requiring complete removal of the current leads. The present paper describes the so-called semi-retractable current leads for a 21 T FT-1CR magnet system application. The optimized dimensions of the leads are presented in order to minimize the thermal heat load when carrying operational current with some margin. [ABSTRACT FROM AUTHOR]

Today the Bi-2223 tape represents a suitable candidate for the use in various HTS devices. The LHC current leads use Bi-2223 tapes soldered together in short lengths, forming stacks of rugged HTS conductors. Critical current and AC loss measurements were performed on BSCCO stacks, in the temperature range of 65 K and 77 K and in magnetic fields of up to 0.5 T. The experimental results reported in this paper give a broad description of the stacks behavior in the range of current and field values of practical interest, and provide design parameters for the optimization of current leads operating both in DC and pulsed conditions. [ABSTRACT FROM AUTHOR]

For the superconducting magnet system of the International Thermonuclear Experimental Reactor, ITER, 60 current leads for a total current of more than 2500 kA are needed. To reduce the resultant large refrigerator load at 4.5 K, High Temperature Superconductor current leads (HTS-CL) could be used. Therefore, EFDA CSU Garching had launched a development program for a 70 kA HTS-CL demonstrator. The Forschungszentrum Karlsruhe and CRPP developed and built this CL optimized for 50 K Helium operation. In 2004, the CL was successfully tested in the TOSKA facility at the Forschungszentrum Karlsruhe. The very encouraging results lead to testing this CL with 80 K Helium because ITER provides a large 80 K Helium cooling capacity for the thermal shields. At the end of last year, the test could be successfully performed demonstrating that high current capacity current leads can be stably operated at about 80–85 K. Recently, the CL was retested using liquid nitrogen which would be an interesting alternative option. In this paper, the test results for the 80 K He cooling operation as well as for the operation with LN2 are presented and compared to the results obtained before for nominal conditions. [ABSTRACT FROM AUTHOR]

In the frame of the European Fusion Technology Programme, the Forschungszentrum Karlsruhe and the CRPP Villigen have designed and built a 70 kA current lead for the ITER TF Coils using High Temperature Superconductors (HTS). At the beginning of 2004 the HTS current lead was installed and tested in the TOSKA facility of the Forschungszentrum Karlsruhe. The scope of the experiment was to characterize the current lead in steady state conditions and to explore the operation limits as well. For this, the temperature profile, the contact resistances, the heat load at 4.5 K, the required 50 K He mass flow rate, and the temperature margin were evaluated. The safety margin in case of a loss of He mass flow was studied, too. The paper describes the experimental results as well as the thermal and electrical models developed. [ABSTRACT FROM AUTHOR]