Speaker
Davide Uglietti
(EPFL)
Description
An insert coil was constructed using coated conductor tape without electrical insulation. The coil inner diameter, outer diameter and height are 43 mm, 56 mm and 120 mm respectively; the coil constant is 16.7 mT/A. The coil is composed of 13 double pancakes (270 m of tape in total) with insulating disks placed in between the pancakes; the coil was impregnated with beeswax. The reason for choosing a coil without turn to turn insulation is to obtain a better tolerance to over-current. Indeed, at 77 K it was possible to apply twice the critical current, without any thermal run-away, because of the current sharing between tapes in adjacent turns; of course at such high currents the magnetic field generated in coil centre is lower than the expected value, the current flowing radially instead that azimutally (along the superconducting ceramic). The quench protection is a simple circuit which switches the power supply off when the voltage exceeds a threshold value that can be set between 50 mV and 200 mV. After the power supply is switched off the energy stored in the coil is dissipated in the coli itself, with the contact resistance between turns replacing the dump resistor usually found in standard insulated coils. Quench tests at 4.2 K in self field and in background field (up to 12 T) were also carried out.
Primary author
Davide Uglietti
(EPFL)
Co-authors
Pierluigi Bruzzone
(EPFL-CRPP)
Rainer Wesche
(Ecole Polytechnique Fédérale de Lausanne (EPFL))
