Common Coil Configuration Research Articles

Design and Fabrication of a 13-T Twin-Aperture Superconducting Dipole Magnet With Graded Common-Coil Configuration

Design and Fabrication of a 13-T Twin-Aperture Superconducting Dipole Magnet With Graded Common-Coil Configuration

Development of superconducting model dipole magnets beyond 12 T with a combined common-coil configuration

The superconducting magnet group at IHEP (the Institute of High Energy Physics, Chinese Academy of Sciences, China) has been engaging in the R&D of high field accelerator magnets since 2014 for the pre-study of the next-generation high energy particle accelerators like CEPC-SPPC (Circular Electron Positron Collider-Super Proton Proton Collider), FCC (Future Circular Collider), etc. A superconducting model dipole magnet named LPF1 was first fabricated with NbTi and Nb3Sn in a combined common-coil configuration in 2017 and tested in 2018, a main field of 10.23 T was reached within two 10 mm apertures. The magnet was reassembled with higher pre-stress in 2019 to investigate the influence of the pre-stress loading level on the performance of common-coil dipole magnets. The main field of this upgraded magnet named LPF1-S was increased to 10.71 T within two 12 mm apertures. By improving the key processing technologies in Rutherford cable fabrication, coil winding, Nb3Sn & NbTi splices soldering and coil impregnation, the recently fabricated model dipole magnet named LPF1-U attained a 12.47 T main field in two 14 mm apertures in 2021. To fully take advantage of Nb3Sn and NbTi superconductors in different field regions, LPF1-U was still designed and developed with a combined coil configuration with Nb3Sn for the inner two coils and NbTi for the outer four coils. Additionally, graded coil topology and different coil LSS (length of straight section) settings were adopted in the optimization of LPF1-U layouts. Bladder and key technology was used for the support structure, and fiber optic sensors based on FBG (fiber Bragg grating) were utilized to monitor the stress distribution and variation in the structures and coils through the whole process from magnet assembly to cool-down and excitation. During the performance test, a relatively large number of trainings were carried out and LPF1-U became more stable after the thermal cycle. A peak field of 12.7 T in the coils (12.47 T main field in apertures) corresponds to an operating current of 6865 A and a load line ratio of 90% was finally attained. It is worth mentioning that LPF1-U is the first hybrid—Nb3Sn, NbTi—common coil dipole magnet that has achieved a main field of more than 12 T in two apertures. The design, fabrication and performance analysis of the LPF series dipole magnets are presented in this paper.

Mechanical Design and Analysis of the Baby-IAXO Magnet Cold Mass, Cryostat and Support System

According to the so-called Primakoff effect, axions and axion-like particles can transform into photons in the presence of a strong magnetic field. To continue the search for these hypothetical particles, a new helioscope called the International Axion Observatory IAXO, and its subscale but fully functional demonstrator Baby-IAXO, are being designed. To increase the detector's sensitivity by a factor of 10 compared to the present CAST helioscope, the experiment needs a stronger magnetic field and in a much larger volume. The superconducting magnet of Baby-IAXO features two 10 m long flat racetrack coils spaced by 0.8 m, arranged in a common coil configuration and generating an average magnetic field of 2.1 T in the two 700 mm detection bores positioned in between the coils. The cold mass structure based on using mainly Al6061-T651, is designed to guarantee pre-stress of the coils during curing and sustain the magnetic loads by the Lorentz force. At ultimate current of 12 kA, the repelling force between the two coils is 33 MN. Furthermore, the supporting structure has to keep the coils in position as they are in an unstable equilibrium in the plane parallel to the racetracks. To support the cold mass in the cryostat, an arrangement of rods was chosen in order to minimize the cryogenic load. The system is composed of 16 titanium rods, which in addition to supporting the expected force loads also keeps the magnet centered. The total mass of the magnet is 35 t comprising an 18 t cold mass and a 15 t cryostat. The magnet is installed on an elevated 360° rotating platform further constraining the cryostat design. Here the mechanical design of cold mass, cold mass supporting system and cryostat of the Baby-IAXO magnet are presented.

Mechanical Design and Stress Analysis of LPF2: A 12-T Hybrid Common-Coil Dipole Magnet

The Institute of High Energy Physics (IHEP, China) has been engaged in the development of shell-based dipole magnets with a common-coil configuration for the pre-study of the Super proton-proton Collider (SPPC) project. The first subscale magnet LPF1, with two Nb3Sn coils and four NbTi coils, reached a bore field of 10.2 T at 4.2 K. Subsequently a higher safety margin model has been proposed as LPF2, which has six Nb3Sn coils and two NbTi coils to reach a 12-T main field in both apertures with an operating current of 5300 A. The shell and yoke are reused from LPF1, as well as the two Nb3Sn coils and two inner NbTi coils of LPF1. The pre-loaded method of LPF2 is much alike that in LPF1: using the Bladder & Key technology to overcome the Lorentz forces in horizontal and vertical directions and pre-tightening six aluminum rods to pre-load the coil packs in the axial direction. In addition, the strain gauges are positioned at the surface of the aluminum shell to monitor the pre-loading effect. The main design parameters and stress analyses results will be presented.

Electromagnetic Design and Fabrication of LPF2: A 12-T Hybrid Common-Coil Dipole Magnet With Inserted IBS Coil

High field dipole magnets with common-coil configuration are under development at IHEP (the Institute of High Energy Physics, Chinese Academy of Sciences) for key technology pre-study of high energy colliders. A model magnet named LPF1 has been fabricated and tested in 2018, which was made up of four flat racetrack NbTi coils and two flat racetrack Nb3Sn coils, and a main dipole field of 10.2 T has been reached in the two apertures at 4.2 K. A new model magnet LPF2 is being designed and fabricated in 2019, with four new Nb 3 Sn coils included comparing with LPF1, and the magnet is expected to reach a much higher field. To reduce the field enhancement at the coil ends, the newly fabricated Nb 3 Sn coils are designed with different straight lengths and bending radii. This hybrid dipole magnet is designed to provide a 12-T main field in the two apertures with an operating current of 5300 A, corresponding to a load line ratio of 78% at 4.2 K. A single-pancake racetrack IBS (Iron-based superconducting) coil wound with a 100-m IBS tape would be inserted into the middle of the magnet (between the inner-most two Nb 3 Sn coils). This magnet is also used to test the IBS coil performance under high field and high stress. The main design parameters, fabrication process of the magnet will be presented.

Mechanical Design, Assembly, and Test of LPF1: A 10.2 T Nb3Sn Common-Coil Dipole Magnet With Graded Coil Configuration

An Nb3Sn/NbTi subscale dipole magnet named LPF1 with graded coil design and common-coil configuration has been designed, assembled, and tested at the Institute of High Energy Physics, Beijing, China. Compared to the previously proposed FECD1, LPF1 is designed with a longer outer NbTi racetrack coil to reduce the peak field in the coil end. The computed bore field and peak coil field of LPF1 is 12.0 T and 12.1 T, if it works at 6100 A with a safety margin of 17% at 4.2 K. The horizontal and vertical directions of the coil packs are preloaded by using bladder and key technology while the axial direction of the coil packs is preloaded by pretightening four aluminum rods. Before assembly, we tested the electron-beam welded bladders in a subscale shell-support structure and verified the strain measurement system. During assembly, we preloaded the coil packs gradually by referring to the measured shell strain after inserting stainless steel keys and removing the bladders. After assembly, we started to test the subscale dipole magnet vertically at 4.2 K. LPF1 reached a bore field of 10.2 T after 13 training quenches and then it reached a stable quench current without detraining. This paper presents the updated design parameters, the stress analysis, the magnet assembly, and test of LPF1.

Conceptual design study of iron-based superconducting dipole magnets for SPPC

A conceptual design study of 12-T two-in-one dipole magnets is ongoing with the iron-based superconducting (IBS) technology, as a candidate option for Super Proton Proton Collider (SPPC), which is designed with a circumference of 100 km and a center-of-mass energy of 70 TeV. Compared with Nb3Sn, the IBS design is competitive because of the potential much higher performance and lower cost of IBS conductors in the future. The design study is carried out with an expected Je level of IBS in 10 years. Besides, we also expect the IBS superconductor to have much better mechanical properties compared to stress-sensitive conductors like Nb3Sn and Bi-2212 wires. The 12-T dipole magnet is designed with common-coil configuration. We have optimized the field uniformity with two different layouts of the coil ends, including the soft-way bending and the hard-way bending. We also have explored the influence of a mid-plane gap on the field uniformity. The main parameters, the coil layouts, and the optimization of the field quality are presented.

Magnetic and Mechanical Design of a 16 T Common Coil Dipole for an FCC

A EuroCirCol is a conceptual design study for a post-LHC research infrastructure based on an energy-frontier 100 TeV circular hadron collider. In the frame of the high-field accelerator magnet design work package of this study, the feasibility of a 16 T dipole in a common coil configuration is being studied. This paper shows the electromagnetic design optimization performed to achieve the required field quality while minimizing the superconductor volume and taking into account the input parameters and assumptions of the EuroCirCol study. The finite element models have been used to analyze the stress distribution and deformations under the large Lorentz forces due to the very high magnetic field. Several iterations have been necessary to obtain a feasible magnet design. The 3-D electromagnetic calculations are also included in this paper.

Electromagnetic design of a 12 T twin-aperture dipole magnet

A 12 T twin-aperture subscale magnet is under development at the Institute of High Energy Physics (IHEP, Beijing, China), as the R&D of high-field accelerator magnet technology for SPPC (Super Proton–Proton Collider) pre-study. Four NbTi coils and two Nb3Sn coils will be fabricated firstly, to provide a 12 T dipole field in two apertures with the load line ratio of 20% at 4.2 K. After that, the HTS (ReBCO and Bi-2212) coils will be inserted between the Nb3Sn coils to realize a higher dipole field. The ReBCO coils with the block-type configuration will be inserted between the Nb3Sn coils with common-coil configuration (Combined Common-coil and Block type configuration, CCB), to make the broad plane of the tape parallel with the magnetic flux and maximize current-carrying capacity. The electromagnetic design, mechanical design and quench protection design have been completed. The fabrication is ongoing. The magnet will be assembled and tested in 2017.

Electromagnetic Design Study of a 20-T Cos-Theta 2-in-1 Dipole Magnet for High-Energy Accelerators

High-field superconducting magnets are the key components of the high-energy particle accelerators. The Institute of High Energy Physics, Beijing, China, has been working on the related R&D since 2014. In parallel with the baseline R&D roadmap with common coil configuration, preliminary electromagnetic design of a 20-T 2-in-1 dipole magnet with cos-theta configuration has been carried out as an option for the model magnet R&D in future. Totally six layers of coils are required for each aperture of this dipole with the high temperature superconductor for the inner two layers and the low temperature superconductor for the outer four layers. Graded coil design is selected to increase the efficiency of the conductor utilization. For each aperture, the clear bore diameter is 50 mm. Asymmetric coil configuration has been adopted to obtain a good geometrical field quality. After optimization, the field uniformity of 10 -4 within 2/3 of the aperture is achieved. The coil ends of the dipole magnet have also been designed and optimized. The detailed magnetic analysis and the main characteristics of this magnet are presented.

R&D steps of a 12-T common coil dipole magnet for SPPC pre-study

IHEP (the Institute of High Energy Physics, Beijing, China) has started the R&D of high field accelerator magnet technology from 2014 for recently proposed CEPC-SppC (Circular Electron Positron Collider, Super proton–proton Collider) project. The conceptual design study of a 20-T dipole magnet is ongoing with the common coil configuration, and a 12-T model magnet will be fabricated in the next two years. A 3-step R&D process has been proposed to realize this 12-T common-coil model magnet: first, a 12-T subscale magnet will be fabricated with Nb3Sn and NbTi superconductors to investigate the fabrication process and characteristics of Nb3Sn coils, then a 12-T subscale magnet will be fabricated with only Nb3Sn superconductors to test the stress management method and quench protection method of Nb3Sn coils; the final step is fabricating the 12-T common-coil dipole magnet with HTS (YBCO) and Nb3Sn superconductors to test the field optimization method of the HTS and Nb3Sn coils. The characteristics of these R&D steps will be introduced in the paper.

20-T Dipole Magnet With Common-Coil Configuration: Main Characteristics and Challenges

The Institute of High Energy Physics (Beijing, China) is pursuing R&D of high-field accelerator magnet technology for the recently proposed CEPC-SPPC project, which will need thousands of 20-T level accelerator magnets in 20 years. A long-term plan has been made aiming to realize the 20-T magnets in 15 years. The conceptual design study has been ongoing from 2014 based on the current J c level of superconductors. As both Nb 3 Sn and high-temperature superconductor superconducting materials are strain sensitive, the common-coil configuration has been chosen as the first option for the design study of the 20-T dipoles, to simplify the coil structure, raise the bending radius, and lower the strain level in superconducting coils. The magnetic analysis, mechanical analysis, and preliminary design study of the straight section and the coil ends have been completed for a 20-T common-coil dipole magnet. The main characteristics and challenges of this design concept will be presented in this paper.

Test Results of a Nb<sub>3</sub>Al/Nb<sub>3</sub>Sn Subscale Magnet for Accelerator Application

The High Energy Accelerator Research Organization (KEK) has been developing a Nb3Al and Nb3Sn subscale magnet to establish the technology for a high-field accelerator magnet. The development goals are a feasibility demonstration for a Nb3Al cable and the technology acquisition of magnet fabrication with Nb3Al superconductors. KEK developed two double-pancake racetrack coils with Rutherford-type cables composed of 28 Nb3Al wires processed by rapid heating, quenching, and transformation in collaboration with the National Institute for Materials Science and the Fermi National Accelerator Laboratory. The magnet was fabricated to efficiently generate a high magnetic field in a minimum-gap common-coil configuration with two Nb3Al coils sandwiched between two Nb3Sn coils produced by the Lawrence Berkeley National Laboratory. A shell-based structure and a “bladder and key” technique have been used for adjusting coil prestress during both the magnet assembly and the cool down. In the first excitation test of the magnet at 4.5 K performed in June 2014, the highest quench current of the Nb3Sn coil, i.e., 9667 A, was reached at 40 A/s corresponding to 9.0 T in the Nb3Sn coil and 8.2 T in the Nb3Al coil. The quench characteristics of the magnet were studied.

Development of a $\hbox{Nb}_{3}\hbox{Al}$ and $\hbox{Nb}_{3}\hbox{Sn}$ Subscale Magnet

A 13 T class Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al and Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn subscale magnet has been in development at the High Energy Accelerator Research Organization (KEK) to establish technology for a high-field accelerator magnet. The magnet was designed to generate a high magnetic field efficiently in a minimum-gap, common coil configuration with 200-mm-long racetrack coils. Two of the five coils in the magnet are Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn-produced by Lawrence Berkeley National Laboratory. The other three coils are Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al -produced by KEK. The Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al Rutherford cables are comprised of 28 RHQ-Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al wires and were developed at KEK in collaboration with National Institute for Materials Science and Fermi National Accelerator Laboratory. Presently, the fabrication of two double pancake Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al coils with the same configuration of 13 turns per layer was completed using the wind and react method. The magnet assembly and the preparations for excitation tests are currently in progress.

Design and Test of a ${\hbox{Nb}}_{3}{\hbox{Sn}}$ Subscale Dipole Magnet for Training Studies

As part of a collaboration between CEA/Saclay and the Superconducting Magnet Group at LBNL, a subscale dipole structure has been developed to study training in Nb3Sn coils under variable pre-stress conditions. This design is derived from the LBNL Subscale Magnet and relies on the use of identical Nb3Sn racetrack coils. Whereas the original LBNL subscale magnet was in a dual bore common-coil configuration, the new subscale dipole magnet (SD) is assembled as a single bore dipole made of two superposed racetrack coils. The dipole is supported by a new mechanical structure developed to withstand the horizontal and axial Lorentz forces and capable of applying variable vertical, horizontal and axial preload. The magnet was tested at LBNL as part of a series of training studies aiming at understanding of the relation between pre-stress and magnet performance. Particular attention is given to the coil ends where the magnetic field peaks and stress conditions are the least understood. After a description of SD design, assembly, cool-down and tests results are reported and compared with the computations of the OPERA3D and ANSYS magnetic and mechanical models.

Study of the effects of high temperatures during quenches on the performance of a smallNb3Sn racetrack magnet

Several high field Nb3Sn magnets of different design are under development for future particle accelerators. The highlevels of stored energy in these magnets and the high current densities in theconductor can cause high peak temperatures during a quench. The thermal gradientsgenerated in the epoxy-impregnated magnet coils during the fast temperaturerise can result in high thermo-mechanical stresses. Considering the sensitivity ofNb3Sn to strain and epoxy cracks, it is important to define a maximum acceptable temperature inthe coils during a quench which does not cause degradation of the magnet performance. Aprogram was launched at Fermilab to study the effects of thermo-mechanical stress inNb3Sn coils, supported by experiments and by analysis. In collaboration with LBNL,a sub-scaled magnet was built and instrumented to measure the effect of thethermo-mechanical shock during magnet quenches. The magnet consisted of tworacetrack coils, assembled in a common coil configuration with a small gap inbetween. During the test, the magnet reached the maximum field of T at the short sample current of 9100 A. Temperature excursions up to 400 K did notdiminish the magnet quench performance; only after temperature excursions over 430 Kdid the magnet show detraining effects, which occasionally reduced the quenchcurrent to about 6%. Signs of irreversible degradation (reducing the maximumcurrent of about 3%) appeared only after temperature excursions over 550 K.

Fabrication and test of a racetrack magnet using pre-reacted Nb/sub 3/Sn cable

A racetrack magnet, using Nb/sub 3/Sn superconducting cable reacted before winding, has been fabricated and tested at Fermilab. It consists of two flat racetrack coils, connected in a common-coil configuration, separated by a 5 mm thick fiberglass plate. Synthetic oil was used to prevent sintering of the strands during the heat treatment. The coils were wound and vacuum impregnated in the mechanical structure. The turn-to-turn insulation, consisting of Kapton/spl reg/ and pre-impregnated fiberglass tapes as wide as the cable, was wound together with the bare cable in order to form a continuous inter-turn spacer. The coils were instrumented with voltage taps, temperature sensors, spot heaters and quench heaters. The maximum current achieved was 12675A which is 78% of the short sample limit at 5.1 K (minimum temperature in the coil during 75 A/s ramp). Measurement of the temperature margin revealed a low degradation in the innermost turns. Quench performances at different temperatures and ramp rate effects have been measured and are presented and discussed.

The performance of BSCCO racetrack windings for a common coil dipole

The first of a series of 90 cm long racetrack shaped coils has been tested at 77 K and 4.2 K in a common coil configuration. The conductor used was selected from a number of available lengths by testing in liquid nitrogen in pancake form. The performance of this coil is compared with shorter versions fabricated from similar conductor.