Performance Test of a Metal Insulated HTS Magnet with Conduction Cooling

Abstract

Abstract. In the fabrication and operation of an HTS magnet, ensuring thermal stability against uneven quench is the most important factor. A sample HTS magnet was designed and fabricated with the metal insulation (MI) method and its fundamental characteristic analysis was conducted under the liquid nitrogen cooling system. On the basis of the electromagnetic analysis results, the thermal and mechanical structural design and detailed experimental analysis of the MI HTS magnet under the conduction cooling condition were performed in this paper. The conduction cooling condition was achieved using the 1st stage GM cryo-cooler. The characteristic resistances and the charging and discharging times of the magnet were measured according to the operating temperature of 32 K of the HTS magnet. The long-term current flowing test was conducted by monitoring the coil temperatures. In addition, the thermal stability of the HTS magnet was analyzed when the over current flowed into the magnet. The test results will be applied to the large size HTS MI magnet. IntroductionIn the fabrication and operation of an HTS magnet, ensuring thermal stability against uneven quench is the most important factor. The no insulation (NI) winding method allows the HTS magnet to maintain the best thermal stability by distributing the quench energy evenly [1][2][3][4]. The NI HTS magnet has the characteristic resistance connected to the inductance of the magnet in parallel. The charging and discharging time are dependent on the characteristic resistance. In the case of, however, the characteristic resistance of the NI HTS magnet is too small, the charging and discharging time takes too long to generate the desired magnetic field.In 2013, our research team had developed and tested a NI HTS magnet for a 10kW-class prototype DC induction heater. In the previous research, the characteristic resistance was measured to be 98 μΩ, and it required 2,300 s to charge the current of the magnet of 230 mH with the maximum magnetic flux density [5][6][7]. Thus, we employed the winding method of metal insulation (MI) using stainless steel to reduce the long charging and discharging time. A sample HTS magnet was designed and fabricated with the MI method and its fundamental characteristic analysis was conducted under the liquid nitrogen cooling system. The characteristic resistance was measured to be 2.9 mΩ and the charging and time constant of the discharging mode was calculated to be 2.5 s. For the higher than critical current flowed to the sample magnet, detailed investigations through voltage and temperature characteristic analysis were conducted [8].On the basis of the electromagnetic analysis results, the thermal and mechanical structural design of the MI HTS magnet under the conduction cooling condition were performed and the detailed experimental analysis results were presented in this paper. The minimum cooling temperature of the 1