Influence of the shape of the current on AC losses in superconducting tube and coil
Résumé
The influence of the current waveform on the ac losses of a superconductor is studied in this paper. Three kinds of current waveforms (triangular, sinusoidal or square) having either the same rms value or the same maximum value are considered. Experimental tests are carried out for BSCCO superconducting tubes and the results are compared to theoretical calculations. Measurements on a BSCCO superconducting coil have also been performed. The losses are measured using an electrical method. The experimental bench is composed of a power amplifier which can deliver 50 A under 20 V controlled by an audio oscillator, a synchronous detection and the superconducting element. The experimental results show that the losses are higher in the case of a sinusoidal supply than in the case of a square wave current. In fact, the losses are only present during the current rise and down for the square wave whereas the continuous variation of the current makes the losses higher for the sinusoidal current waveform. These experimental results have been confirmed by the computed losses issued from finite element analyses. In large scale applications of superconductors, the presented results are of great importance in the design of their power supplies.