On August 6, 2015, we started to turn on the drift high voltage in the MicroBooNE detector for the very first time. We paused at 58 kV (this is about 1/2 of our design voltage) and immediately started to see tracks across the entire TPC. Below are some of our first images of cosmic rays and UV laser tracks (last picture) recorded by the TPC!
Collection plane images:
And here is one of the first images of a UV laser track in the TPC. You can tell which track is the laser by the large red cluster at the end of the track where the laser has crossed the cathode plane. You can also see that the laser track is more uniform (as expected) than the cosmic muon tracks in the picture.