SULTAN MAGNET SYSTEM

The background field of SULTAN is generated by three pairs of concentric split coils placed in a vacuum tank and cooled directly by forced flow of supercritical helium. To withstand the axial compressive forces during operation, a set of concentric flanges and two semicircular spacers separate the coils, i.e. leaving a vertical shaft of 94 x 144 mm² for the sample unit. Besides the radial access for straight 'short' samples, the magnet system allows in its 0.6 m bore, horizontal access for coiled specimens when experiments on long conductor lengths are performed. The magnet array together with the vertical and the horizontal insertion spaces are visible.

In the present configuration (split solenoid), SULTAN has no warm bore access, just two cryogenic vacuum chambers: the main one for the coils and the small one, "test well", for the sample. The field is 11 T in the test well and 12 T on the SULTAN windings. Including the self field of the sample, the actual test field is up to 11.5 T (depending on the sample current and geometry). There are iron cores to increase the field by 1 T if necessary. The inner radius of the split solenoid is 600 mm, the gap between the solenoid is 100 mm. The outer coil pair, supplied by ENEA, is based on the ductile NbTi superconductor while the middle and inner coil pairs are made of brittle Nb3Sn and were developed at CRPP. Due to their contribution to the total field, the outer, middle and inner sections are also called 6T, 9T and 12T coils respectively.

Conductors and coils

The superconductor of the 6T coils is made of 33 NbTi composite strands cabled and soldered onto a squared copper tube. The selected concept for the superconductor used in the 9T and 12T coils is a flat cable of Nb3Sn strands. The flat cable geometry is a direct consequence of the "react-and-wind" technique adopted for coil fabrication. By choosing a flat cable configuration, where the brittle Nb3Sn filaments lie close to the neutral axis, the bending strain degradation of the critical current has been minimized. Each coil of the outer 6T section consists of 20 double pancakes, electrically in series and hydraulically in parallel for cooling. The pancakes are epoxy impregnated and clamped together by two stainless steel flanges tightened by bolts against the outermost pancakes. To minimize possible interference between the middle and outer coil sections, stainless steel cylinders are inserted between the 9T and 6T coil sections. On the other hand, all four coils of the 9T and 12T sections are layer-wound and each of them is manufactured from a single length of Nb3Sn based conductor.

Photos

Literature

• Pasztor G., Jakob B., Horvath I., Ming P., Vecsey G., Weymuth P., "Successful operation of the Nb3Sn Swiss insert coil for the 12T SULTAN Test Facility", IEEE Trans. Magn., MAG-24, 1086, 1988
• Jakob B., Pasztor G., Schindler R.G., "Fabrication of high current Nb3Sn forced flow conductors and coils for the SULTAN III Test facility", Fusion Technology, North Holland, Vol. 1, 872, 1993
• Blau B., ..., Pasztor G. et al., "First performance tests of the 12T split coil Test facility SULTAN III", IEEE Trans. Appl. Superconductivity, 3, 361, 1993.

CRPP-Superconductivity
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