Recent development of superconducting cryomagnets by Spark plasma Sintering
Résumé
We report on our progress in the preparation of MgB2 and YBa2Cu3O7 (YBCO) superconducting cryomagnets consolidated by the unconventional sintering process called Spark Plasma Sintering (SPS). SPS is a promising rapid consolidation method that results in a better understanding and control of the sintering kinetics than other techniques.
Three main experimental processes are reported here:
(i)Preparation of intermetallic MgB2 using conventional graphite moulds at 1000°C, 50 MPa under vacuum.
(ii)Preparation of intermetallic MgB2 at high pressure (600MPa) using tungsten carbide moulds (WC) at 800°C under vacuum.
(iii)Preparation of oxide YBCO in air using WC moulds at quite low temperature (500-650°C) and high pressure (600MPa).
The obtained YBCO and MgB2 pellets show 99% relative density. For the MgB2 compounds, a Tc onset of 38 K was obtained. At 20K, the critical current density was measured and found equal to Jc = 2.8x105 A/cm2, while the trapped field measured at the surface of a 20 mm diameter disk was equal to 3.9 T. Levitation force measurements were carried out on a MgB2 ring and a MgB2 disk with the same thickness and external diameter as a function of the temperature. The levitation force took the same values from 17 to 32 K for the disc and the ring samples, supporting the claim by E.H. Brandt [1] that the screening current in disks flow at first along the outside edge of the samples. Otherwise, the Tc determined from these measurements was equal to 38 K, in good agreement with the result of other techniques. Overall these results suggest that bulk MgB2 superconductors could be a viable variant for magnetic levitation applications.
The measurement of the properties of single phase YBCO bulks consolidated using SPS is in progress and will be also discussed.
[1] E.H.Brandt, Phys.Rev.58, 6506 (1998)