  Fluorescent Microthermographic Imaging, a method using rare-earth fluorescent
coatings with temperature-dependent light emission, was used for quench
investigation in high temperature superconductors (HTS). A fluorophore was
embedded in a polymer matrix and used as a coating on top of an HTS tape, while
being excited with UV light and recorded with a high-speed camera.
Simultaneously, the tape was pulsed with high amplitude, short duration DC
current, and brought to quench with the help of a localized defect. The joule
heating during a quench influences the fluorescent light intensity emitted from
the coating, and by recording the local variations in this intensity over time,
the heating of the tape can be visualized and the developed temperatures can be
calculated. In this paper, the fluorophore Europium
tris[3-(trifluoromethylhydroxymethylene)- (+)-camphorate] (EuTFC) provided
sufficient temperature sensitivity and a usable temperature range from 77 K to
260 K. With the help of high-speed recordings, the normal zone development was
imaged in a 20 \mu m copper stabilized HTS tape held in a liquid nitrogen bath,
and using a calibration curve, the temperatures reached during the quench have
been calculated.
