First Look at Plasma Operation Data from 2D Fiber Optic Bolometer Array

A 2D fiber-optic bolometer (FOB) array has been developed, and initial results demonstrated in DIII-D as a plasma radiated power diagnostic for use in challenging electromagnetic (EM) noise situations. A prototype single-channel system, which was previously 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 was installed with a tangential view into the DIII-D Tokamak. The new array consists of 8-by-8 sensors viewing near X-point and divertor regions. Several channels were damaged during the installation and baking, leading to improvements in design and procedures for future use. Surviving channels successfully measured baking temperatures of up to 300°C at the sensors. Preliminary data from plasma operations showed an unexpected increase in the baseline measurements even after plasmas have ended. This posed a problem of distinguishing the measurements of the plasma radiation to the increased background temperature. Different methods were tested to overcome the problem and showed similar trends of measurements compared to resistive bolometers that were viewing the similar regions. Initial demonstration of a 2D FOB array has led to several important improvements and continues to show promise for application in fusion plasma.