  We have wound a 157-turn, non-insulated pancake coil with an outer diameter
of 85 mm and we cooled it down to 77 K with a combination of conduction and gas
cooling. Using high-speed fluorescent thermal imaging in combination with
electrical measurements we have investigated the coil under load, including
various ramping tests and over-current experiments. We have found found that
the coil does not heat up measurably when being ramped to below its critical
current. Two over-current experiments are presented, where in one case the coil
recovered by itself and in another case a thermal runaway occurred. We have
recorded heating in the bulk of the windings due to local defects, however the
coil remained cryostable even during some over-critical conditions and heated
only to about 82-85 K at certain positions. A thermal runaway was observed at
the center, where the highest magnetic field and a resistive joint create a
natural defect. The maximum temperature, ~100 K, was reached only in the few
innermost windings around the coil former.
