A tangential Upper View Bolometer for DIII-D

Measuring total radiated power in tokamak divertors is important for understanding divertor performance, in particular how changes in the divertor impact power balance. A new tangential Upper View Bolometer (UVB) installed on DIII-D provides views into both the ceiling and Small Angle Slot (SAS) divertors. Tangential lines of sight into these two upper closed divertors fill in gaps in radiated power measurements from existing radial bolometer arrays. The SAS requires sub-cm alignment of 3-m-long viewchords; we used a light source on a robotic arm to confirm chord alignment and perform spatial calibrations. UVB measurements in the ceiling show the chord-integrated radiated power increase by a factor of 2-4 at detachment onset. The first power measurements in the SAS show an increase of 3-4 in chord-integrated radiated power at detachment onset, with similar radiation in shots with main-chamber vs in-slot gas puff fueling. These initial measurements with the new UVB foil detectors show a faster response time, with ELMs resolved, and higher signal-to-noise ratio than the radial foil bolometers. Upgrades in 2021 will add chords and increase the temperature limit during vessel bakes.