AC loss measurements on Cable in Conduit Conductor with random-changing magnetic fields

摘要

Beside the generation of the poloidal component of the field, the main function of the poloidal field coils in a tokamak is the control of the shape and the position of the plasma, according to the chosen plasma scenario. A plasma scenario, namely a sequence of plasma shapes, is obtained and controlled by varying the current in the PF coils. The control currents create magnetic fields having complex trends, being almost random waveforms with frequencies in the range between 0.1 and 10 Hz. As a consequence, AC loss is generated in the superconducting coils exposed to those signals, and the feasibility of a plasma scenario is strictly related to the ability to withstand and remove the heat coming from the AC loss.rnIn order to study what the behavior of the loss is in random magnetic fields, namely similar to the control fields, a SULTAN sample is tested under two kinds of random field signals. The first signal is obtained by summing several harmonic frequency components, in the range between 0.2 and 6 Hz, having random amplitude. The second waveform is generated by a random function generator and it has a much broader spectrum of frequencies. The tests are carried out by varying also the maximum amplitude of the signals. The results are here discussed and compared to the results of the single frequency AC loss tests, and a correlation between them is studied.