Applied superconductivity
The characterization of superconductors under magnetic field conditions is a long-standing activity of the laboratory. We have studied low-critical-temperature superconductors (LTS) as part of the development of a large-diameter (800 mm) superconducting magnet which is the outer coil of our new hybrid magnet. We are are currently studying high-critical-temperature superconductors (HTS) for the production of very high magnetic field.
The recent and rapid development of HTS, in particular REBCO coated conductors (REBCO tapes), represents a potential major breakthrough for societal applications of superconductivity. Unlike LTS, which are limited to 25 T, HTS can produce much higher magnetic fields (> 30 T) at low temperatures (4 K).
The LNCMI offers a unique characterization platform with several magnetic field configurations (Grenoble: 34 mm/36 T, 50 mm/30 T, 170 mm/20T, 367mm/10 T; Toulouse: 25 mm / 60 T pulsed). A wide range of objects can be tested: small samples for physics, centrimetric lengths of ribbon, decimetric windings, conductors made up of several tapes, magnet sub-elements (inserts), allowing thus to cover problems from tapes to magnet.
Research staff
Research topics
Research & development of a new type of Nb-Ti/Cu superconducting conductor, as an alternative to CICC (Cable In Conduit Conductor) for the LNCMI hybrid electromagnet.
Contact : pierre.pugnat [a] lncmi.cnrs.fr
One of the special features of hybrid electromagnets is the electro-thermo-magnetic-mechanical coupling between the resistive and superconducting windings, which must be kept under control even in the event of major malfunctions such as rapid, untimely power supply cuts. In this case, the magnetic field variation produced by the resistive coils is of the order of 40 T/s. An eddy-current screen cooled to 50 K was specially developed for the Grenoble hybrid coil, enabling this magnetic field variation to be attenuated to around 3 T/s at the level of the superconducting conductor, which is not enough to prevent quenching [1]. The initial idea for solving this problem was to introduce an enthalpy reservoir supplied by superfluid He at a pressure of 1200 mbar, stored in the channel of a copper stabilizer onto which a multi-strand, multi-filament Rutherford-type Nb-Ti/Cu cable is welded (see photo), so as to limit heating below the limit temperature of the superconducting conductor. In an initial study, only the heat generated by induced currents in the Cu-Ag duct was considered, while the heat generated by induced inter-strand and inter-filament currents in the superconducting cable was neglected. Taking them into account in order to minimize them has led to a radical change in the way this superconducting conductor is manufactured, christened RCOCC (Rutherford Cable On Conduit Conductor) as an alternative to the more expensive CICC (Cable In Conduit Conductor) generally used for this type of application.
The production of this innovative superconducting conductor had to be entirely internalised at LNCMI-Grenoble, after a major R&D phase to develop the assembly line, subcontracting parts of the equipment to Ravni Technologies. The innovative concept for this production line is the strict control of the quantity of filler metal for the soft solder, the choice of compound for the latter, and the induction heating method including its optimization.
[1] As a reminder, one of the definitions of the term “quench” that can be given in this context is that of an irreversible transition from the superconducting state to the normal state via thermal runaway. All too often, the quench is confused with the resistive transition to the normal state, which is a transition to local thermodynamic equilibrium, i.e. in the hydrodynamic regime that allows transport coefficients to be defined. This confusion leads to another, that between critical current and quench current, which must be avoided when characterizing superconducting conductors.
Fig. 1 : a) RCOCC Nb-Ti/Cu superconductor specially developed for the Grenoble hybrid magnet project and assembled in-house at LNCMI. It should be noted that all other hybrid magnet projects use a different type of conductor, called Cable In Conduit Conductor (CICC), which is more expensive and comes from the technology developed for fusion. Rutherford superconducting cables, on the other hand, are based on technology developed for particle accelerators. To minimize losses due to inter-strand currents, a stainless steel core was inserted in the middle of the 19-strand Rutherford cable during the wiring operation subcontracted to the manufacturer Furukawa.
Fig. 1 : b) Focus on a Nb-Ti/Cu strand produced by Bruker EAS and composed of 6264 Nb-Ti filaments of 14 µm diameter stabilized by a copper matrix (Cu/Nb-Ti ratio = 1.24). The production of a single Nb-Ti/Cu strand requires more than fifty successive co-extrusion and drawing steps to reach the final diameter of 1.6 mm from an initial Nb-Ti/Cu conductor with the same filamentary distribution of several tens of centimetres in diameter, called a billet.
RCOCC Production Line
Contact : pierre.pugnat@lncmi.cnrs.fr
The Cu-Ag profile was produced using the Conform process thanks to a highly successful partnership with the Aurubis company in Olen, and required a dedicated R&D phase in order to guarantee the mechanical (Rp0.2% at 4.4 K = 290 MPa), electrical (RRR = 60-70), Ag content of the compound, mainly to increase the annealing temperature (0.05%), and sealing of the cooling channel, while guaranteeing geometric tolerances (± 0.04 mm) [3]. When it came to producing the RCOCC, no industrial company was willing to take on the role of manufacturer and to assume the risk of assembling this innovative superconducting conductor at a reasonable price. This operation therefore had to be entirely internalised at LNCMI-Grenoble, after a major R&D phase to develop the assembly line (Fig. 2 & 3), subcontracting parts of the equipment to Ravni Technologies [3]. The innovative concept for this production line is the strict control of the quantity of filler metal for the soft solder, the choice of compound for the latter [4] and the induction heating method, including its optimization.
Diagram of the production line for the RCOCC superconducting conductor specially developed for the Grenoble hybrid magnet and integrated at LNCMI-Grenoble for the production of 12 km of RCOCC segmented into 44 units of length wound into a single spool.
Views of the RCOOC production line installed at LNCMI-Grenoble a) Start of the line with unwinding reels, straightening rollers, assembly head, induction heating system and geometric sizing head.
Large-diameter winding system to limit shearing forces at the brazing point.
Development of HTS inserts for a 30-40 T superconducting magnet
Contact : xavier.chaud [a] lncmi.cnrs.fr
The magnetic field is a powerful thermodynamic parameter for influencing the state of matter, making it an exceptional experimental tool for physics, materials science, chemistry and beyond. Higher magnetic fields offer better resolution for materials analysis, more opportunities to discover new phases, properties or materials.
Currently, the fields that can be generated with commercial superconducting magnets are typically limited to 23 T. To go beyond this, very large infrastructures such as the LNCMI are required. Here, very high magnetic fields are generated by resistive magnets, with very high power consumption and cooling requirements (typically 30 MW), resulting in very high operating costs.
Used at very low temperatures, where their performance is exacerbated, high-temperature superconductors (HTS) become superconductors for intense magnetic fields. Our activity is to develop superconducting magnets generating more than 30 T, based on a traditional low-temperature superconducting (LTS) magnet into which an HTS insert is introduced.
The H2020-INFRADEV SuperEMFL project (2021-2024) has enabled a first phase in the design of all-superconducting magnets for the European community of users of intense magnetic fields, bringing together 11 academic and industrial partners from all over Europe. The PIA3 FASUM project follows on from this, with the aim of building a 40T superconducting magnet by combining a custom-designed in-house HTS insert with a commercial LTS magnet.
HTS magnets represent a huge advantage for facilities hosting users such as LNCMI. Not only do they enable a very significant reduction in electrical energy consumption (typically a factor of 5), and therefore in operating costs (also a factor of 5), but they also open up new experimental possibilities, such as very long-duration experiments (typically lasting several days instead of a few hours), or experiments requiring very low levels of electrical and mechanical noise, impossible to achieve with resistive magnets.
A unique testing platform
Contact : xavier.chaud [a] lncmi.cnrs.fr
Among facilities dedicated to high magnetic fields, the LNCMI-G not only produces intense magnetic fields, but also high magnetic fluxes. It is thus the only one to offer a range of configurations, from very intense fields in small diameters to medium fields in large diameters. The availability of this unique and original test platform is crucial for a thematic such as applied superconductivity.
It enables us to measure critical currents at low temperatures under intense magnetic fields on objects of varying dimensions, from wires or tapes to coils or sub-elements of superconducting magnets.
The most relevant configurations are :
30 T in a 50 mm room temperature bore for measuring 30 mm long wires or tapes for current transport measurement up to 1.2 kA at 4.2 K at different angles to the field;
20 T in a 170 mm RT bore for measuring 10 cm long ribbons or solenoids up to 120 mm outside diameter;
10 T in a 367 mm RT bore, for testing larger coils up to 290 mm (limited by the existing cryostat).
To meet the needs of applied superconductivity, LNCMI has developed several test benches adapted to each configuration. A test rig comprises a cryostat, a sample holder to be inserted into the cryostat, dedicated instrumentation (potential taps, temperature sensors, Hall probe, etc.), a power supply (the general objective being to study the current capacity of the ribbon, wire or coil under high field and low temperature conditions), and a data acquisition system. These test benches must be adapted to each experiment. Access to one of the facility’s configurations is based on a biannual call for projects. After examination of the proposal by an international scientific committee appointed by the EMFL, a time slot of one week, generally, is granted to the selected proposal, together with an energy budget in MWh.
Research in vortex physics at high magnetic fields
Superconducting critical current measurements in pulsed magnetic field up to 60T
Contact : maxime.leroux [a] lncmi.cnrs.fr
The recently demonstrated high field all-superconducting 32+ T magnets [1,2,3] require superconducting wires that retain significant current-carrying capacity (critical current, Jc) even at high magnetic fields. In these superconductors, the magnetic field permeates as superconducting vortices, which are nanoscopic tube of magnetic fields surrounded by rotating superconducting currents. These vortices are pinned to defects in the material until the applied current exceeds a critical value (Jc), causing the vortices to move and dissipate energy (Bardeen-Stephen theory), making the wire resistive and potentially burning the magnet.
At high magnetic fields, the critical current Jc is determined by the interactions between vortices and defects. The challenge increases with the magnetic field strength due to the higher number of vortices. RE-Ba2Cu3O7 superconductors have demonstrated high Jc values, enabling the 32 T magnets. Artificial pinning centers (APC) can further improve Jc in field, but the limits of vortex pinning above 40 T remain largely unexplored. With critical fields exceeding 150 T at 2 K, less than 20% of REBCO’s potential phase diagram has been studied. Current Jc measurements are limited to ~36 T in resistive coils and 45 T in hybrid coils [4], requiring pulsed magnetic fields to explore higher ranges [5]. We have set up a Jc measurement system to study vortex physics in pulsed fields up to 60 T in Toulouse.
[1] J Jaroszynski et al. 2020 Supercond. Sci. Technol. 33 080501
[2] Cavallucci L et al. IEEE Trans. Appl. Supercond. 29 4701605 (2019)
[3] P. Fazilleau, X. Chaud, et al., Cryogenics, Volume 106, 2020, 103053
[4] Abraimov, D. et al. Transport critical currents of modern ReBCO conductors in high magnetic fields up to 45T, ASC 2018, Seattle, Washington, United States, Oct.28- Nov. 3 (2018)
[5] Leroux M et al., Phys. Rev. Appl. 11, 054005 (2019)
Techniques
Contact Xavier CHAUD for this technique below :
xavier.chaud [a] lncmi.cnrs.fr
High-field and low-temperature characterization
Several test benches (sample holde
r, power supply, acquisition for Jc critical current measurement or coil test – field, stability, transition) for different field configurations:
- 30 T Ø50 mm RTB, Ø38 mm CB for sample holder (wire, ribbon or VAMAS coil) ;
- 20 T Ø170 mm RTB, Ø128 mm CB for sample holder (wire, ribbon, coil or coil sub-element) ;
- 10 T Ø376 mm RTB, Ø298 mm CB for sample holder (e.g. circuit coil).
The specificity of these characterizations is to measure µV at low temperature with currents greater than 500 A under very strong field (1200 A @ 20-30 T, 3000 A @ 10 T).
RTB for Room Temperature Bore (space available inside the magnet without cryostat) and CB for Cold Bore (space available for the samples in the cryostat inserted in the resistive magnet).
HTS windings
Thanks to support from LABEX Lanef, after a long search for a machine on the shelf, we finally built our own coiling machine. At the heart of our development work on high-field superconducting magnets, this winding machine is specially adapted for tapes from 4 to 12 mm wide and 30 to 150 microns thick, like the REBCO superconductor tapes we use. Equipped with three winding reels for coiling up to three tapes (superconducting, metallic or insulating tapes) together, with individual winding tension control, it enables a very smooth operation, avoiding jolts at start-up and shutdown, and the production of single and double coils up to 80 cm in diameter in a dust-protected environment. Thanks to this machine, we have been able to develop our own winding protocols and manufacture our own coils.
Contact Pierre PUGNAT for this technique below :
pierre.pugnat [a] lncmi.cnrs.fr
Development of new characterization methods
– Measurement of critical currents up to 1 kA at 4.4 K [5] in magnetic fields up to 20 T
These characterizations are based on the development of two specific pieces of equipment, a battery-powered low-noise current source up to 1 kA and a liquid He cryostat with liquid N2 guard equipped with an insert for testing up to 10 coils of 1600 mm long superconducting strand (Fig. 4).
Fig.4 : i) Cross-section of the cryostat with its tail (a) inserted into the 55 mm diameter hot hole of a resistive or superconducting magnet shown schematically (b). The cryostat is mounted on an elevator system to center each sample with regard to the center of the magnet when measuring its critical current. (ii) Geometry of the testable superconducting strand coils with a maximum length of 1600 mm, wound on a Derlin sample holder with an external diameter of 44 mm and a height of 38 mm, and assembled in pairs.
Characterization of heating of superconducting conductors during abrupt interruption of the magnetic field
It has been demonstrated experimentally that when a Rutherford Nb-Ti/Cu cable is subjected to the rapid magnetic field variation caused by accidental disconnection of the resistive magnet power supplies, a flux jump instability in the superconductor causes the latter to quench, even if it is not carrying any current [2]. This point illustrates one of the difficulties in producing hybrid electromagnets, and the need to control the inter-strand contact resistances of the RCOCC once it has been produced. This also implies developing an experimental approach to determining these contact resistances, and the choice fell on a thermometric approach. The specification for this contact resistance between adjacent strands Ra following soft soldering was established as being greater than 0.5 mW [3].
This value was one of the main inputs used to characterize the amount of soft solder filler metal required for RCOOC production. This specification was then verified by heating samples of RCOCC extracted from production, immersed in liquid helium and subjected to magnetic field variations. Remarkably, it was even possible to measure an increase in resistance of the order of +67% when the RCOCC sample was bent to the minimum winding radius of 550 mm.
Characterization of the mechanical brittleness of soldering filler metals at cryogenic temperatures
The other important feature for the production of RCOOC is its mechanical shear strength at cryogenic temperatures. The choice of brazing filler metal proved important, a fact that seems to have been somewhat overlooked [4]. Metallographic studies have been carried out on brazing alloys, as illustrated in Figure above.
The quantity of solder, the choice of pickling flux and the temperature cycle are the other parameters that have been optimized to meet the RCOCC technical specification with a mechanical shear strength in excess of 30 MPa.
Example of a sub-millimeter dendrite structure (diameter 0.4 mm) for one of the Sn-Pb alloys studied for soft soldering between superconducting conductors and for the RCOCC. Filler metals with good mechanical and electrical properties at cryogenic temperatures were selected.
References
[1] P. Fazilleau et al., “Role and Impact of the Eddy Current Shield in the LNCMI-G Hybrid Magnet”, IEEE Transactions on Applied Superconductivity, vol. 26, no. 4, pp. 1-5, June 2016, doi: 10.1109/TASC.2016.2525018
[2] P. Pugnat et al., “Study and Development of the Superconducting Conductor for the Grenoble Hybrid Magnet”, IEEE Transactions on Applied Superconductivity, vol. 22, no. 3, pp. 6001604-6001604, June 2012, doi: 10.1109/TASC.2011.2180882
[3] P. Pugnat et al., “In-House Industrial Production of the Superconducting Conductor for the 43 T Hybrid Magnet of LNCMI-Grenoble”, IEEE Transactions on Applied Superconductivity, vol. 28, no. 4, pp. 1-5, June 2018, doi: 10.1109/TASC.2018.2797548 ; Poster accessible depuis :
[4] R. Pfister and P. Pugnat, ” Tin Pest: A Forgotten Issue in the Field of Applied Superconductivity? “, https://arxiv.org/abs/1204.1443
[5] R. Pfister et al., “A New Test Station to Measure the Critical Current of Superconducting Strands”, IEEE Transactions on Applied Superconductivity, vol. 22, no. 3, pp. 9500504-9500504, June 2012, doi: 10.1109/TASC.2011.2178581
People involved
- Disparti1, P. Fazilleau2, F. P. Juster2, M. Kamke1, S. Krämer1, R. Pfister1,*, L. Ronayette1,**, J. M. Tudela1, E. Verney1, E. Yildiz1, et P. Pugnat1,***
Ex CDDs Projet1 : T. Boujet, P. Harnoux, W. Joss, C. Peroni, M. Pissard
1 LNCMI, EMFL, CNRS, Université Grenoble Alpes, 38042 Grenoble Cedex 9, France
2 CEA Paris-Saclay, IRFU, 91191 Gif-sur-Yvette Cedex, France
* Engineer in charge of projects
** Assistant Project Manager
*** Project Manager
Special thanks to the following people from industry who have contributed their expertise and support to this project beyond the purely contractual aspect :
Andre Aubele et Manfred Thoener, Bruker EAS
Peter Walmsley et Romain Hauselmann, Aurubis Olen (ex-SAM, Swiss Advanced Materials SA, Yverdon-les-bains)
Lionel et Alain Ravni, Ravni Technologies, 42230 Roche-la-Molière
Chabane Mokrani, A.T.C.I. 38170 Seyssinet-Pariset
Publications
Selected publications
Bottura et al., « Magnets for a Muon Collider—Needs and Plans », IEEE Transactions on Applied Superconductivity, vol. 34, no. 5, pp. 1-8, Aug. 2024, Art no. 4005708, doi: 10.1109/TASC.2024.3382069.
J.-B. Song, X. Chaud, F. Debray, S.Krämer, S. Bagnis, P. Fazilleau, T. Lécrevisse, « Metal-as-Insulation REBCO Insert: Simplified Protection Scheme and Investigation of Cooling Defect Under High-Field Operation », IEEE Transactions on Applied Superconductivity, vol. 34, no. 5, pp. 1-5, Aug. 2024, Art no. 4702405, doi: 10.1109/TASC.2024.3357474.
Muzet, C. Trophime, X. Chaud, C. PrudHomme and V. Chabannes, « 2D Axisymmetric Modeling of the HTS Insert Nougat in a Background Magnetic Field Generated by Resistive Magnet », IEEE Transactions on Applied Superconductivity, vol. 34, no. 5, pp. 1-5, Aug. 2024, Art no. 4903005, doi: 10.1109/TASC.2024.3362749.
Fazilleau, S. Bagnis, M. Durochat, T. Lécrevisse, C. Lorin, X. Chaud, A. Varney, S. Ball, R. Viznichenko and A. Twin, « Behavior during quenches of a 40 T magnet made of LTS and HTS parts », IEEE Transactions on Applied Superconductivity, vol. 34, no. 3, pp. 1-5, May 2024, Art no. 4704805, doi: 10.1109/TASC.2024.3370138.
J.-B. Song, X. Chaud, F. Debray, K. Paillot, P. Fazilleau, T. Lécrevisse, T. Herrmannsdörfer, C. Senatore, M. Dhallé, A. Smara, « Estimation of Physical and Electrical Properties of Various REBCO Tapes for Construction of Very-High-Field REBCO Magnet », IEEE Transactions on Applied Superconductivity, vol. 34, no. 5, Aug. 2024, Art no. 6600205, doi: 10.1109/TASC.2023.3340134.
Durochat, P. Fazilleau, X. Chaud and T. Lecrevisse, « Design of all-superconducting user magnets generating more than 40 T for the SuperEMFL project », IEEE Transactions on Applied Superconductivity, vol. 34, no. 5, pp. 1-5, Aug. 2024, Art no. 4904305, doi: 10.1109/TASC.2024.3368997.
Galstyan, J. Kadiyala, M. Paidpilli, C. Goel, J. Sai Sandra, V. Yerraguravagari, G. Majkic, R. Jain, S. Chen, Y. Li, R.Schmidt, J. Jaroszynski, G. Bradford, D. Abraimov, X. Chaud, J.-B. Song and V. Selvamanickam,“High critical current STAR® wires with REBCO tapes by advanced MOCVD”, Supercond. Sci. Technol., vol., no. 5, March 2023, 055007, doi: 10.1088/1361-6668/acc4ed
Lécrevisse, X. Chaud, P. Fazilleau, C.Genot and J.-B. Song, “Metal-as-insulation HTS coils“, Supercond. Sci. Technol., vol. 35, no. 7, May 2022, 074004, doi: 10.1088/1361-6668/ac49a5
J.-B. Song, X. Chaud, F. Debray, S. Krämer, P. Fazilleau and T. Lécrevisse, « Metal-as-Insulation HTS Insert for Very-High-Field Magnet: A Test Report After Repair », IEEE Transactions on Applied Superconductivity, vol. 32, no. 6, pp. 1-6, Sept. 2022, Art no. 4300206, doi: 10.1109/TASC.2022.3150622.
J.-B. Song, X. Chaud, B. Borgnic, F. Debray, P. Fazilleau and T. Lécrevisse, « Thermal and Electrical Behaviors of an MI HTS Insert Comprised of THEVA-SuperPower DP Coils Under High Background Magnetic Fields at 4.2 K”, IEEE Transactions on Applied Superconductivity, vol. 30, no. 4, pp. 1-6, June 2020, Art no. 4701806, doi: 10.1109/TASC.2020.2974854
Fazilleau, X. Chaud, F. Debray, T. Lécrevisse, J.-B. Song, “38 mm diameter cold bore metal-as-insulation HTS insert reached 32.5 T in a background magnetic field generated by a resistive magnet”, Cryogenics 106 (2020) 103053, doi: 10.1016/j.cryogenics.2020.103053. BEST PAPER AWARD 2020.
LNCMI thematic publications on HAL