Laboratoire National Des Champs Magnetiques Research Articles

Design and Tests of the 100-T Triple Coil at LNCMI

The Laboratoire National des Champs Magnetiques Intenses (LNCMI) is a French host facility for experiments in high magnetic fields. Based on two sites, the LNCMI offers routinely static magnetic fields up to 36 T at its Grenoble site, and pulsed magnetic fields up to 90 T using nondestructive magnets and up to 180 T using single-turn magnets at its Toulouse site. Internal research is carried out in the lab and experiment time is allocated to external researchers. LNCMI is a founding member of the European Magnetic Field Laboratory with the Hochfeld-Magnetlabor in Dresden (HLD) and High Field Magnet Laboratory in Nijmegen. The LNCMI develops all the instrumentation required by experiments in high magnetic fields, in particular, the electromagnets that generates these high fields. The main difficulty in generating a very high magnetic field in a nondestructive way is to contain the huge stresses on the magnet conductors due to the Lorentz forces. We present here the design and first operation of a new type of pulsed magnet consisting of three nested coils energized with three independent capacitor banks. This triple coil, unique in the world and associated with the most powerful generators of the LNCMI, reached a peak field value of 98.8 T and permitted the LNCMI to break the European record for the nondestructive pulsed magnetic fields established at 95.6 T in October 2016 by HLD. The next objective is to go beyond the symbolic value of 100 T and the world record of 100.75 T held by the Los Alamos National Laboratory since June 2012. We will describe the next steps toward this goal and some ways to go beyond, keeping in mind that this magnet is above all else a tool for scientific research, in particular to explore the fundamental properties of the matter.

REBCO Performance at High Field With Low Incident Angle and Preliminary Tests for a 10-T Insert

New improvements in high-temperature superconductors (HTS) are encouraging for large-scale applications, particularly for high-field magnets. In this context, the “NOUGAT” project aims at designing and building a 10-T HTS insert operating inside a 20-T resistive magnet. The insert is foreseen as a stack of double pancakes wound with REBCO tapes. The combination of current and magnetic field generate large mechanical stresses. Moreover, as the conductor has strong anisotropic properties, its performances are affected by transverse magnetic fields. Therefore, they have to be studied under high magnetic field at a small disorientation, close to the longitudinal axis of the coil. The objective is to evaluate its limiting critical current. This paper reports critical current measurements on a 4-mm REBCO tape provided by SuperOx. They were performed on the tape full width under a high magnetic field of up to 23 T at 4.2 K at the Laboratoire National des Champs Magnetiques Intenses (LNCMI) at various field angles. The limiting critical current is found to be about 350 A, which represents a current margin of 57% on a basic model. Then, a preliminary test of a prototype double-pancake coil is reportedly tested at up to 16 T.

Performance Tests of Prototype High-Field HTS Coils in Grenoble

Longitudinal and transverse quench propagation tests were performed at the Laboratoire National des Champs Magnetiques Intenses (LNCMI) high-field test facility on instrumented double pancake coils fabricated by CEA-Saclay using co-wound high-temperature superconductor (HTS) tapes. Energy deposited on an embedded heater initiated a quench and its subsequent propagations. Following the resulting thermomechanical analysis, a conductor design with stacked HTS tapes co-wound with stabilizers was conceived. A ten-turn demonstrator racetrack coil has been fabricated from the stacked HTS conductor with an aim to investigate the operation margin of an HTS coil in a background magnetic field misaligned from the coil axis as expected for the operating condition of an accelerator magnet insert. A test setup with a high current capacity up to 3 kA and angular variability that utilizes a room-temperature 376-mm-bore 10-T resistive magnet at LNCMI in Grenoble has been built. The performances and operation margin of the racetrack coil were investigated.

Magnetic Field Effect on the Excitation Spectrum of a Neutral Exciton in a Single Quantum Dot

Magnetic Field E ect on the Excitation Spectrum of a Neutral Exciton in a Single Quantum Dot M.R. Molas, A.A.L. Nicolet, B. Pi¦tka, A. Babi«ski and M. Potemski Faculty of Physics, University of Warsaw, L. Pasteura 5, 02-093 Warszawa, Poland Laboratoire National des Champs Magnetiques Intenses, CNRS-UJF-UPS-INSA, 25, av. des Martyrs, 38042 Grenoble, France Excitation-energy-dependent magnetospectroscopic measurements of a single GaAlAs/AlAs quantum dot were performed. A signi cant e ect of the excitation energy on the photoluminescence spectra is reported. The photoluminescence excitation spectroscopy has been used to investigate the excitation spectrum of a single electron hole pair a neutral exciton in magnetic eld up to 14 T. The observed resonances exhibit diamagnetic shift characteristic of an s-shell related emission. In our opinion, the creation of excited complexes involving an excited hole and a ground electron is responsible for the process.

State of the art and developments of high field magnets at the “Laboratoire National des Champs Magnétiques Intenses”

The “Laboratoire National des Champs Magnétiques Intenses” (LNCMI) is the result of the merger of the “Laboratoire des Champs Magnétiques Intenses” in Grenoble specialised in the generation of DC magnetic fields and the “Laboratoire National des Champs Pulsés” in Toulouse specialised in the generation of pulsed magnet fields. DC fields of up to 35 T, pulsed fields up to 80 T and single-shot pulsed fields up to 170 T are provided to an international community of users. In the present paper we present the current state of our installations and the developments which are pursued in the context of an increasing international competition. Le Laboratoire national des champs magnétiques intenses (LNCMI) est issu de la fusion du Laboratoire des champs magnétiques intenses de Grenoble spécialisé dans la production de champs magnétiques continus et du Laboratoire national des champs pulsés de Toulouse spécialisé dans la production de champs magnétiques pulsés. Le LNCMI accueille une large communauté internationale de chercheurs pour la réalisation de projets scientifiques ou technologiques nécessitant lʼutilisation de champs magnétiques intenses. Des champs magnétiques de 35 T en continu, 80 T en pulsé et 170 T à lʼaide bobine explosive ont ainsi été développés au laboratoire et mis à disposition des chercheurs. Nous présentons dans cet article lʼétat de lʼart et les perspectives de développements en situant le laboratoire vis-à-vis dʼune compétition internationale de plus en plus acharnée.

The French High Magnetic Field Facility

The Laboratoire National des Champs Magnetiques Intenses (LNCMI) is a host laboratory for experiments in high magnetic fields. It was created on the 1st of January 2009 through the merger of the Laboratoire des Champs Magnetiques Intenses (Grenoble, specialized in DC fields) and the Laboratoire National des Champs Magnetiques Pulses (Toulouse, specialized in pulsed fields). The facility is open to a large community of users from all over Europe and the rest of the world. In this paper we report our efforts to offer the highest magnetic fields, ranging from 35 T DC, through 80 T non-destructive, up to 170 T semi-destructive, in the best conditions for our in-house and visiting scientists. We describe the installations and coils improvements. As an example of our activity we present some recent scientific results.

Special Coils Development at the National High Magnetic Field Laboratory in Toulouse

The Laboratoire National des Champs Magnetiques Intenses (LNCMI) develops different types of coils suited to specific experiments. We present some recent developments on magnet design. Several coils are dedicated to experiments in large scale facilities in France and Switzerland. A 30 T split-pair coil for X-rays diffraction and one 40 T coil for plasma physics at the LULI, two 30 T coils with axial access (one with an conical bore) for X-ray diffraction and absorption experiments. A 40 T wide angle conical access solenoid with a high duty-cycle for neutron scattering at the ILL is being constructed. For use at the installation in Toulouse we have developed, apart from our standard 60 and 70 T coils, several special coils: a coil with a long optical path with 30 T transverse magnetic field and a 90 T long pulse dual coil system.

DC High Field Magnets at the LNCMI

The Laboratoire National des Champs Magnetiques Intenses (LNCMI) is a French large scale facility enabling researchers to perform experiments in the highest possible magnetic field. DC magnetic fields up to 35 T are provided at the Grenoble site and pulsed fields up to 80 T at Toulouse. We focus in this paper on the latest developments of the polyhelix technologies which is used for the most constrained parts of the dc high field magnets. In November 2010, LNCMI has achieved the standardization of its three 24 MW magnets sites (which includes the site for the new 42 T+ hybrid magnet); longitudinally cooled polyhelix inserts are now systematically used as the innermost part of these magnets. The on-going developments aim at developing “hybrid” polyhelix inserts incorporating radially cooled helices in the center to decrease the thermal constraints and to reach higher magnetic fields with the maximal power presently available on the Grenoble site (24 MW). We give an overview of these developments which combine both numerical and experimental approaches.

Quantum vacuum magnetic birefringence

In this contribution to EXA2011 congress, we present the status of the BMV (Birefringence Magnetique du Vide) experiment which is based on the use of a state-of-the-art optical resonant cavity and high pulsed magnetic fields, and it is hosted by the Laboratoire National des Champs Magnetiques Intenses in Toulouse, France.

Rapid Cooling Methods for Pulsed Magnets

Pulsed magnets are generally evaluated and compared in terms of the magnetic field they can achieve in combination with a bore size. However, in practice another criterion is equally important: the waiting time for a researcher in between two consecutive shots. The cooling time of pulsed magnets can range from a few minutes up to several hours, depending on coil size and desired field. Using simulations and measurements several options to reduce the cool down time are compared in this paper. One of the discussed methods is now routinely in use at the Laboratoire National des champs magnetiques pulses (LNCMP) in Toulouse.

New Developments at the National Pulsed Field Laboratory in Toulouse

Pulsed-magnet users are requesting higher fields with longer pulse-times in larger bores. This request led logically to user facilities similar to facilities existing for continuous fields. The Laboratoire National des Champs Magnetiques Pulses (LNCMP) in Toulouse (FRANCE) has a user community from all over Europe. We report on current efforts in Toulouse to fulfill the request of users. We developed and tested coils up to 80 T and reduced the cool-down time. Moreover, we created special design installations: a transportable pulsed-field installation to be used at other large instruments and coils with optimized field profiles for optical experiments. We are currently investigating the sources of noise on our fields and have successfully tested a preliminary method to reduce this noise.

Upper Critical Fields Up to 60 T in Dirty Magnesium Diboride Thin Films

Upper critical fields of several magnesium diboride thin films were measured up to 28 T at the Grenoble High Magnetic Field Laboratory (GHMFL) in Grenoble and up to 60 T at the Laboratoire National des Champs Magnetiques Pulses (LNCMP) in Toulouse. The samples were prepared both by pulsed laser deposition (PLD) and hybrid physical chemical vapour deposition (HPCVD) technique; they have critical temperatures between 29 and 39 K and normal state resistivities between 5 and 250 μohmcm; one of them has been intentionally doped with carbon. The measured critical fields were exceptionally high; we obtained the record value of 52 T at 4.2 K in the parallel orientation. In contrast with the BCS predictions, no saturation in Hc2 at low temperature was observed. Furthermore, films with a wide range of resistivity values showed similar critical fields, suggesting that in a two band system resistivity and Hc2 are not trivially linked. The high Hc2 values seem to be related with the expanded c-axis. The structure of one of the samples was carefully investigated with X-ray diffraction at European Synchrotron Radiation Facility (ESRF) in Grenoble.