TIME CONSTANTS AND AC LOSSES OF FLAT SUPERCONDUCTING CABLES IN MAGNETIC-FIELDS CHANGING ALONG THE CABLE

The induced currents in flat cables exposed to AC magnetic fields acti ng on some part of the cable are calculated from the flux diffusion eq uation including the inductance of these currents. At low frequencies, the corresponding coupling losses inside the field region are enhance d due to currents induced outside this region, whereas the losses are negligible in field-free regions. At high frequencies, these contribut ions to losses are approximately the same, being of the same type as i n normal conductors (skin effect). The time constant for decaying the induced currents is proportional to the cable length and can be much l arger than calculated for spatially homogeneous AC fields. This could explain the existence of long-living oscillatory currents (or 'super c oupling currents') in some cables for accelerator magnets, as well as in some model cables. (C) 1996 Elsevier Science Limited