Overview and Benchtop Testing of 2D Fiber Optic Bolometer Array*

A 2D fiber-optic bolometer (FOB) array is being developed for DIII-D as a plasma radiated power diagnostic for use in challenging spatial and electromagnetic (EM) noise situations. A prototype single-channel system also installed in DIII-D showed that the FOB is comparable to resistive bolometer performance and avoids EM interference by using a Fabry-Pérot resonator system to encode small temperature changes related to the incoming power. The 2D FOB array is designed to have high spatial resolution near the X-point and divertor to resolve highly localized emissions. The array consists of 8-by-8 sensors (64 sensors in total) with a tangential view into the DIII-D tokamak. Performance of the array design is evaluated using two forward-modeling tests using synthetic radiation profiles: sectional radiated power and radiation structure analyses. These tests show that the design will have spatial resolution of ~4 cm. In addition, a new technique, which adds a copper thermal sink to the sensor, is implemented to reduce the time-constant of the raw FOB measurements from ~6 seconds to ~150 ms. The diagnostic design and benchtop test results including calibrations of the FOB array will be presented.