Assessment of cryogenic thermography system using commercial fluorescent paints on their applicability to visualization of normal-zone propagation in YBCO coated conductor

To establish a stability criterion for YBCO coated conductors, it is required to clarify their transient thermal characteristics. In this study, we adopt a method for visualization of temperature distribution using fluorescent paints whose color changes depending on the temperature. In the visualization method, firstly, commercial fluorescent paints are coated on the surface of sample strips. And then, the sample is irradiated by a black light or UV-LEDs, and the image of the fluorescence is observed by a CCD camera. These captured images are manipulated image processing by a computer, and show the temperature distribution. This system can be applied to cryogenic and high magnetic field circumstances. By adopting this visualization method to the investigation of transient thermal characteristics of YBCO tapes, local heat generation in the YBCO tapes can be observed by higher resolution, and it is expected to identify the uniformity of critical current density of YBCO tapes. In this paper, we describe the developed thermal visualization system and the preliminary experimental results on visualization of normal-zone initiation and propagation in YBCO sample strip fabricated with IBAD/PLD method.