Superconducting Test Facility Research Articles

Cable Modeling and DC Resistance Analysis of Terminations for 16 T Superconductor Test Facility

Cable Modeling and DC Resistance Analysis of Terminations for 16 T Superconductor Test Facility

Conceptual design study of a large bore superconducting test facility magnet, SUCCEX

A 16 Tesla, large bore superconducting magnet for testing the superconducting Cable-in-Conduit Conductor (CICC) is being designed in parallel with the design of the steady state Korea fusion demonstration reactor (K-DEMO) magnet system. The test facility magnet, named SUperConducting Conductor Experiment (SUCCEX), was designed in 2014 and some design modifications of the magnet have been conducted since 2020. The peak magnetic field of the K-DEMO toroidal field coil is about 16 T, and thus the required background field of the conductor test magnet is expected to be over 15 T in a large bore of 600 mm diameter. The background field will be in addition to the K-DEMO conductor sample's self-field. To reach the target magnetic field, high current density Nb3Sn strands (Jc > 1100 A/mm2 at 4.2 K, 16 T) were employed in the design of the high field CICC. The modified SUCCEX magnet consists of concentric solenoids, with a high field inner coil (IC) and low field outer coil (OC). They are connected in series with each other, and the operating current is about 24 kA. In this study, the overall design concept is presented in relation to the results of electro-magnetic, structural analyses.

Status of the High Field Cable Test Facility at Fermilab

Fermi National Accelerator Laboratory (FNAL) and Lawrence Berkeley National Laboratory (LBNL) are building a new High Field Vertical Magnet Test Facility (HFVMTF) for testing superconducting cables in high magnetic field. The background magnetic field of 15 T in the HFVMTF will be produced by a magnet provided by LBNL. The HFVMTF is jointly funded by the US DOE Offices of Science, High Energy Physics (HEP), and Fusion Energy Sciences (FES), and will serve as a superconducting cable test facility in high magnetic fields and a wide range of temperatures for HEP and FES communities. This facility will also be used to test high-field superconducting magnet models and demonstrators, including hybrid magnets, produced by the US Magnet Development Program (MDP). The paper describes the status of the facility, including construction, cryostat designs, top and lambda plates, and systems for powering, and quench protection and monitoring.

Construction Strategy for the Future K-DEMO Superconductor Test Facility

The 16 T superconducting magnet for the next generation fusion reactor, called K-DEMO would be a great engineering challenge with current technology. The project on the test facility, named SUCCEX (Super Conducting Conductor Experiment) is prerequisite for the development of K-DEMO superconducting magnet. It would generate an external magnetic field of 16 T for developing and testing K-DEMO superconductors. Also, this project will give a guideline to fabricate future superconducting conductors for the next generation nuclear fusion reactor construction. It will be an essential facility for the production of superconducting magnets for K-DEMO. In 2021, the Korean government has approved this project and the project is in its early stages of construction. The construction strategy and the current progress are discussed in this paper.

SELFIE: ITER superconducting joint test facility

In the frame of a contract with ITER Organization (IO) on magnets assembly support, CEA designed and built a superconducting joint test facility called SELFIE (ITER SELf-FIEld joint test facility). This facility is installed at CEA Cadarache and started to operate in 2022.This project was initiated by IO for quality control of critical assembly activities. Indeed, the magnet superconducting joints assembly is a special process, for which the performance cannot be verified until the full Tokamak is at cryogenic temperature and obviously repair cannot be envisaged once the machine is assembled. Therefore, the quality control of these joints assembly relies on procedures and qualification of the workers in charge of their implementation.As the joints assemblies will span over three years of the ITER construction, the qualified workers will have to assemble periodically some Production Proof Samples (PPS) joints to train and keep their certification valid. The purpose of SELFIE is to test these PPS in a timely manner.The tests scope is the measurement of the PPS resistance (few nOhms). For that purpose, PPS integrated in ITER conductors length (∼200 kg weight and 3600 mm length) are tested in a liquid helium bath (4.2 K), at nominal current (up to 70 kA), in self-field. The current is provided by a superconducting transformer integrated in the same cryostat as the sample.CEA finalized the preliminary design in 2019, complying with the requirement to achieve a full test sequence within one week (controlled cool down, test and warm-up), with an optimised operation cost. The detailed design phase was started in April 2020 followed by the manufacturing phase up to mid 2021. SELFIE integration and installation were achieved in December 2021 and the cold commissioning done in January 2022. This paper presents the SELFIE test facility and the first results.

Design and Construction of a High Field Cable Test Facility at Fermilab

Fermi National Accelerator Laboratory, together with Lawrence Berkeley National Laboratory, is building a new High Field Vertical Magnet Test Facility (HFVMTF) to be situated in the Magnet Test Facility at Fermilab. The HFVMTF is jointly funded by the US DOE Offices of Science, High Energy Physics, and Fusion Energy Sciences, and will serve as a superconducting cable test facility for both communities. The background magnetic field for test samples is 15 T and will be produced by a magnet provided by LBNL operating at 1.9 K in superfluid helium. The samples will be placed in the background magnetic field, cooled to between 4.5 K and a user-specified upper limit, and will be powered with a superconducting transformer at up to 100 kA. Additionally, this facility will be used to test high-field superconducting magnet models and demonstrators, including hybrid magnets, produced by the US Magnet Development Program. Currently, the various tasks of the project are at different stages of execution, from conceptual to ready-for-construction designs. This paper describes the parameters and design status of the pit construction, cryostat, heat exchanger, lambda plate, power system, and quench protection and monitoring systems of the facility.

Preliminary Design of Pulse Inductor Applied for 100-kA Quench Protection System

The quench protection system in a large-scale superconductor test facility (LSTF) aims to protect the superconducting magnets from being damaged by long time and severe conducting current. A super-high pulse current from oscillation between a pulse inductor and a storage capacitor flows reversely into the main circuit to force the current in the main circuit cross zero, which ensures the reliable turn-off of the mechanical switch to protect the superconducting magnets. Furthermore, the pulse inductor also plays an essential role in adjusting the pulsewidth and the limiting pulse peak value. For the inductor, the pulse current is up to 130 kA and the rated inductance is 30 μH. To release the electromagnetic (EM) force largely and reinforce the structure and insulation properties, a circular multi-winding structure with epoxy resin-casting technique is presented. Based on the 2-D/3-D model built in finite element analysis software, the structure resist, deformation, heat, and EM environment of the design are simulated. The terminals are also optimized to minimize the damage from the EM force and extend the operation life of the inductor. In addition, a fatigue analysis is carried out to estimate the working life of the inductor and verify the reliability of the structure under the 130-kA pulse current working condition.

Analysis and Design of Fast Discharge Resistor System Based on Forced-Air Cooling Method

The quench protection (QP) system is crucial to transfer the quench energy out within specific time when the quench phenomenon occurs in the superconducting magnet. The fast discharge resistor (FDR) system in the QP system is responsible for transferring and consumption of the quench energy. In large-scale superconductor test facility (LSTF), with extreme quench parameters concerning about the large current up to 90 kA, high inductance up to 2 H, and huge energy up to 8.1 GJ, the structure stability, heat controlling, and power feasibility of the FDR system are hard to be guaranteed. Therefore, a novel FDR system based on forced-air cooling method is put forward and discussed. The FDR system is with the characteristic of effectiveness protection, safety operating, and economic efficiency when compared with previous systems. In addition, based on the designed concept, the analysis and test process of the FDR system are carried out to testify the effectiveness and veracity. In particular, the structure stability of the shape deformation and cooling method of the temperature rise are analyzed. With the proof of simulation and testing results, the FDR system can serve for the QP system development of the new fusion device, the LSTF.

Integral Resonance Control In Continuous Wave Superconducting Particle Accelerators

Superconducting accelerating cavities for continuous wave low-current particle accelerators requires a tight resonance control to optimize the RF power costs and to minimize the beam delivery downtime. When the detuning produced by radiation pressure becomes comparable to the RF bandwidth, the monotonic instability starts to affect the cavity operation. When this instability is triggered by external vibrations or drifts, the accelerating field amplitude drops rapidly, and the beam acceleration has to be stopped. Past experiments showed that using an integral control of the piezoelectric tuners installed on the cavity prevents the adverse effects of the monotonic instability. This paper derives theoretically why an integral controller is an effective way to counteract the monotonic instability. To perform the study a linearized state-space model of the cavity is derived. Simulations and experiments in a superconducting test facility indicate that the use of this kind of control has the additional benefit of bringing the cavities to the resonance condition automatically.

Structure Optimization of Fast Discharge Resistor System for Quench Protection System

In the quench protection (QP) process of superconducting fusion devices, the operating reliability and efficiency of power components are affected by stray parameters of the fast discharge resistor (FDR) system, especially the system stray inductance. In this paper, the fundamental condition of the QP operating process and the large power FDR system structure layout for the Large-scale Superconductor Test Facility (LSTF) are presented. The negative affected VCB, CPC circuit action, and the energy discharging process are further analyzed. The stray inductance optimization method of the resistor module and structure connections are proposed to reduce the stray inductance value. Finally, the optimization results are presented by the Q3D module of the FEA software.

Parameter Optimization of Thyristor Snubber Circuit in LSTF Quench Protection System

The Large-scale Superconductor Test Facility (LSTF) is an important part of comprehensive research facilities in support of China Fusion Engineering Test Reactor (CFETR). In order to protect the superconducting magnets from being damaged in quench accident, the Quench Protection System (QPS) should be designed to commutate the energy stored in the coils. The snubber circuit is used to reduce the reverse recovery current and voltage of thyristor in QPS, and it can impact the reliability and stability of the QPS. In general, the studies of snubber circuit are focused on the DC turn-off process of thyristor used in HVDC, which has small turn-off current. However, the turn-off current can reach to 100 kA in the QPS of LSTF. In this paper, a thyristor reverse recovery model is described, and the key parameters of reverse recovery current are obtained from the testing experiment. Based on the transient analysis of snubber circuit, a systematic approach is used to minimizing the resistance and capacitance of snubber circuit of QPS working condition is proposed. By the MATLAB simulation and comparison, minimum parameters of snubber circuit were obtained, and proved that the approach can improve the reliability and stability of system, while reduce the cost of QPS.

Temperature- and field-dependent characterization of a conductor on round core cable

The conductor on round core (CORC) cable is one of the major high temperature superconductor cable concepts combining scalability, flexibility, mechanical strength, ease of fabrication and high current density; making it a possible candidate as conductor for large, high field magnets. To simulate the boundary conditions of such magnets as well as the temperature dependence of CORC cables a 1.16 m long sample consisting of 15, 4 mm wide SuperPower REBCO tapes was characterized using the ‘FBI’ (force—field—current) superconductor test facility of the Institute for Technical Physics of the Karlsruhe Institute of Technology. In a five step investigation, the CORC cable’s performance was determined at different transverse mechanical loads, magnetic background fields and temperatures as well as its response to swift current changes. In the first step, the sample’s 77 K, self-field current was measured in a liquid nitrogen bath. In the second step, the temperature dependence was measured at self-field condition and compared with extrapolated single tape data. In the third step, the magnetic background field was repeatedly cycled while measuring the current carrying capabilities to determine the impact of transverse Lorentz forces on the CORC cable sample’s performance. In the fourth step, the sample’s current carrying capabilities were measured at different background fields (2–12 T) and surface temperatures (4.2–51.5 K). Through finite element method simulations, the surface temperatures are converted into average sample temperatures and the gained field- and temperature dependence is compared with extrapolated single tape data. In the fifth step, the response of the CORC cable sample to rapid current changes (8.3 kA s−1) was observed with a fast data acquisition system. During these tests, the sample performance remains constant, no degradation is observed. The sample’s measured current carrying capabilities correlate to those of single tapes assuming field- and temperature dependence as published by the manufacturer.

Temperature-and field dependent characterization of a twisted stacked-tape cable

The twisted stacked-tape cable (TSTC) is one of the major high temperature superconductor cable concepts combining scalability, ease of fabrication and high current density making it a possible candidate as conductor for large scale magnets. To simulate the boundary conditions of such a magnets as well as the temperature dependence of TSTCs a 1.16 m long sample consisting of 40, 4 mm wide SuperPower REBCO tapes is characterized using the ‘FBI’ (force–field–current) superconductor test facility of the Institute for Technical Physics of the Karlsruhe Institute of Technology. In a first step, the magnetic background field is cycled while measuring the current carrying capabilities to determine the impact of Lorentz forces on the TSTC sample performance. In the first field cycle, the critical current of the TSTC sample is tested up to 12 T. A significant Lorentz force of up to 65.6 kN m−1 at the maximal magnetic background field of 12 T result in a 11.8% irreversible degradation of the current carrying capabilities. The degradation saturates (critical cable current of 5.46 kA at 4.2 K and 12 T background field) and does not increase in following field cycles. In a second step, the sample is characterized at different background fields (4–12 T) and surface temperatures (4.2–37.8 K) utilizing the variable temperature insert of the ‘FBI’ test facility. In a third step, the performance along the length of the sample is determined at 77 K, self-field. A 15% degradation is obtained for the central part of the sample which was within the high field region of the magnet during the in-field measurements.

1 ms Pulse Beam Generation and Acceleration by Photocathode Radio Frequency Gun and Superconducting Accelerator

We report the successful generation and acceleration of a 1-ms-long pulse and multibunch electron beam by a normal conducting photocathode RF gun and a super conducting accelerator at the KEK Superconducting Test Facility (STF). A 1.3 GHz normal conducting RF gun generates a 1 ms and 10 mA macropulse that fully satisfies the designed parameters. This is the longest macropulse generated by a normal conducting RF gun with a frequency of more than 1 GHz. A beam acceleration of up to 40 MeV was demonstrated with more than 60% of the designed average current. The accelerated beam properties were evaluated: the intensity and energy fluctuations were 3.8% and less than 0.08%, respectively. These beam properties are sufficient for the requirement of the STF operation including that in the quantum beam project, which is high-brightness-X-ray generation by inverse laser Compton scattering. The intensity fluctuation should be improved toward the International Linear Collider (ILC) for uniform acceleration.

A new facility for investigation on neutron irradiation effect on superconducting properties of Nb3Sn strand for fusion magnet

To perform post irradiation tests of superconducting strands, a 15.5T superconducting magnet and a variable temperature insert (VTI) were installed at a radiation control area in Oarai center, Institute for Materials Research, Tohoku University. Both of the 15.5T magnet and the VTI are conductively cooled with GM refrigeration. The commissioning test of the system is still ongoing because unexpected troubles occurred during the commissioning. Also, a SQUID system with the maximum field of 7T has been installed at another radiation control area to investigate the magnetic property of uranium and its isotopes. These devices are very useful to study the electro-magnetic properties of the neutron irradiated superconducting strands. This paper will introduce the new superconducting test facility, and some data recently obtained will be presented together with the data of magnetization evaluated with the SQUID, and the discussion on the irradiation effect on superconducting properties will be performed.

New Superconducting Test Facility in Radiation Control Area for Neutron Irradiation Study

To perform post irradiation tests of superconducting strands, a 15.5 T superconducting magnet and a variable temperature insert were installed at a radiation control area in Oarai center, Institute for Materials Research, Tohoku University. Both of the 15.5 T magnet and the VTI are conductively cooled without liquid coolant. The commissioning test of the system is ongoing and this paper will present the new superconducting test facility and some data obtained recently.

EDIPO Quench Detection System: Concept and Development

EDIPO is the new 12.5 T superconducting test facility that is being installed at CRPP in Villigen, Switzerland. It will be placed beside the existing test facility SULTAN. The main purpose of both facilities is testing samples for the ITER project. EDIPO will provide a uniform high field region of 1 m, i.e. longer than SULTAN's ( 45 cm). EDIPO includes the main magnet and a superconducting transformer to power it with a current up to 100 kA in the test sample. The energy stored in the dipole is 16 MJ and in the undesired event of a quench this energy must be safely extracted. A Quench Detection System (QDS) is required to trigger the quench protection system for both the dipole and the transformer. This paper describes the overall QDS from the conceptual design, components, manufacture and commissioning as well as interactions with related systems.

ENFASI: Conceptual Design of a 15 T Large Bore Superconducting Test Facility

The present work illustrates the conceptual design of a new superconducting test facility, ENFASI (Enea FAcility for Superconducting Inserts), which has been mainly conceived to test long length wound conductors. It consists of a background 15 T Nb3Sn solenoid, with a warm bore of 90 cm diameter, divided into three concentric sections corresponding to high field (15 T), medium field (13 T) and low field (8 T), and globally composed of 983 turns. The three different CIC (cable-in-conduit) conductor layouts, one for each section and with rectangular cross-sections, operate at 20 kA and are made of strands with different Cu/nonCu ratios and segregated copper when needed. The facility permits to feed the sample with a current up to 70 kA and to vary the sample temperature in the range [4.5 K-77 K]. The main results of electro-magnetic, structural and thermo-hydraulic analysis which brought to the definition of the main aspects of the design, are presented.

Upgrading the NIFS superconductor test facility for JT-60SA cable-in-conduit conductors

The superconductor test facility at the National Institute for Fusion Science (NIFS) was upgraded to test cable-in-conduit (CIC) conductors for the JT-60SA equilibrium field (EF) coil. Supercritical helium (SHe) lines were assembled with transfer tubes and a heat exchanger. The CIC conductor was covered with a thermal insulation vessel, filled with gas helium at atmospheric pressure. The temperature of the conductor was varied using a film heater attached to an inlet pipe. Critical current (Ic) and current sharing temperature (Tcs) measurements of the prototype CIC conductor were carried out successfully in the upgraded test facility. During the measurements, the conductor temperature was precisely controlled.

Finite Element Analyses and Instrumentation Layout for Single Coil Testing of TF Coils in HT-7U

The HT-7U tokamak is a magnetically-confined full superconducting fusion device, consisting of superconducting toroidal field (TF) coils and superconducting poloidal field (PF) coils. These coils are wound with cable-in-conductor (CICC) which is based on UNK NbTi wires made in Russian [1]. A single D-shaped toroidal field magnet coil will be tested for large and expensive magnets systems before assembling them in the toroidal configuration. This paper describes the layout of the instrumentation for a superconducting test facility based on the results of a finite element modeling of the single coil of toroidal magnetic field (TF) coils in HT-7U tokamak device. At the same time, the design of coil support structure in the test facility is particularly discussed in some detail.