Diagnosis of Winding Conditions in High Temperature Superconducting Coils by Applying Poynting´s Vector Method

We have proposed a new method for detecting unusual local conditions in a high-temperature superconducting coil. In this method, two kinds of pick up coils for measuring electric fields and magnetic fields are used to obtain Poynting´s vectors around the coil. This is a noncontact method using pick-up coils around the vessel for cooling the coil. The method has the following benefits: safe detection, easy handling, high sensitivity, and high usability. The purpose of this paper is to clarify the relation of measured signals to the conditions of the windings. When a temperature rise has been produced locally in the Bi-2223 solenoidal coil, Poynting´s vectors around the coil and the temperature of windings were measured. It was found that the measured signals rapidly decrease as the temperature of the winding achieved a critical level, making this a reliable method to estimate the conditions in the windings.