A new ac technique for fast and continuous characterization of coated conductor tapes

A new ac technique for high-speed characterization of long coated conductor tapes is proposed and demonstrated. The technique utilizes an excitation coil and a small pick-up coil and continuously measures the ac susceptibility of a traveling superconducting tape. The pick-up coil signal is phase-sensitively detected by a digital lock-in amplifier and the ratio between the real and imaginary components is converted into the critical current density of the superconducting tape relying on a simple critical state assumption. An advantage of the technique is that precise information about the size and the location of coils is not necessary because the ratio is not sensitive to them. The technique is also useful for the characterization of striated tapes, for which the conventional Hall sensor array technique does not give useful information. (paper)