Improved poynting's vector method: Ac loss measurement of HTS tapes formed into a short straight or a solenoidal coil

Improved Poynting's vector method without movements was proposed to measure ac losses of HTS tapes, formed into a short straight or a solenoidal coil, which were carrying ac transport currents under transverse ac magnetic fields. In the previous Poynting's vector methods, for a short straight case two sets of both potential lead pairs and pickup coils were rotated around tapes in order to measure local energy flow densities, i.e., the distribution of Poynting's vector; for a solenoidal coil case two sets of both potential lead coils and spiral pickup coils were shifted to the coil axis direction by one winding pitch of the solenoidal coil. During moving these sets at low temperature, the data acquisition system was working and the value of ac losses was finally obtained. These previous methods, therefore, have inconveniences such as much time to get the value, much space needed for moving sets, or frequent troubles of movements due to low temperature deformation. The present method based on the following idea can resolve them: As for pillar parts of potential lead lines which are standing on the tape surface, only one plays a substitute role for all as long as all lines are connected together. As a result, immovable arrays of sets can be rigidly arranged, so that the signal measured at each position can be simultaneously. Moreover, information enough to clarify the electromagnetic behavior inside the tape can be obtained, because the sets can put more closely to the tape surface. The validity of the present method was confirmed by preliminary experiments using Bi-2223 multifilamentary tapes in liquid nitrogen.