2 March 2017, 16h31
The main difficulty to generate a very high magnetic field is to contain the huge forces that are applied on the materials constituting the electromagnets. These latter are windings of high conductivity metals, copper based alloys or composites, some of them are elaborated in the laboratory, reinforced with Zylon® fibers. All these materials with extremely high mechanical performances are implemented with the utmost care in the LNCMI workshops where the coils are built. After cooling in liquid nitrogen down to -196 °C, they are connected to pulsed generators consisting in capacitor banks charged to voltage up to 24 kilovolts generating current of several tens of kilo-amps during a fraction of a second. These electromagnets must resist to the extreme mechanical stress imposed by the magnetic field they produced.
With a peak value of 98.8 T (Fig. 1) (click on picture to zoom ) , obtained in Toulouse, the LNCMI gets the European record of non destructive pulsed magnetic field. The previous record, 95.6 T, was established in October 2016 by the Hochfeld-Magnetlabor in Dresden (HLD) otherwise partner of the LNCMI inside the European Magnetic Field Laboratory (EMFL). To obtain this result it has been necessary to associate three concentric coils energized with the three most powerful generator of the laboratory.
Temporal profile of the magnetic pulse. Only 400 ms are represented, the field decay still continues during one second. The insert represent a zoom on the fast impulsion of the inner coil that will be the limiting one when this system will be used for experiment.
This construction, unique in the world and represented on (Fig. 2) (click on picture to zoom ) , permits to surpass the dual-coil system as those developed in Dresden or in Wuhan in China reaching respectively 95.6 on 90.6 T.
Picture of the magnet before installation in its nitrogen cryostat. It measures around 70 centimeter in diameter and weights near 600 kilograms while the zone where the maximum magnetic is generated is only few cubic centimeter. The magnetic energy stored during a pulse is equivalent to the one contained in several kilograms of TNT. The magnet is installed in cells that can resist in case of mechanical failure due to magnetic forces.
The objective is to go beyond the symbolic limit of 100 T and the world record of 100.75 T kept by the Los Alamos National Laboratory since June 2012. LNCMI engineers are now working to obtain this record later this year.
This magnet is before everything else a tool for scientific research, in particular to explore the fundamental properties of the matter. The pulse duration of the LNCMI last born magnet is above those offered by the other laboratory around the world, as shown in (Fig. 3) (click on picture to zoom ) , making easier the experiments that will be performed. © J. BEARD 20170301
Time during which the magnetic field value is above 80 T as a function of the maximum magnetic field reached by the major laboratory around the world. Beyond the intensity of the magnetic field, long pulse durations permit high quality measurements.