Date of Award
Doctor of Philosophy
David C. Donovan
David Donovan, Jamie Coble, Matthew Reinke, Morgan Shafer
The fiber optic bolometer (FOB) was demonstrated observing a fusion plasma for the first time, and 2D fiber optic bolometer was developed and demonstrated to have high spatial resolution. The FOB is a novel type of a bolometer that is theoretically immune to EMI. A bolometer that is a sensor that measure the power of the incoming electromagnetic radiation. The most common bolometer used in fusion research is a resistive bolometer that utilize resistors in an electrical circuit. Due to high electromagnetic interferences (EMI) in fusion environment, noise can be a serious problem in determining accurate plasma radiation. The demonstration at DIII-D tokamak utilized a single-channel system having a measurement FOB and a reference FOB, which was blocked of incoming radiation. The demonstration showed negligible increase in noise in fusion environment and acceptable absolute-value comparisons with the resistive bolometers. Plasma radiations contain information relating to plasma phenomena, and the structures are unique depending on plasma conditions. 2D FOB array was designed to investigate plasma radiations near the divertor with higher resolutions more rigorously for DIII-D. The design parameters were optimized using the machine learning technique called Bayesian global optimization, which was efficient for the multivariate non-linear problem. A physics-based regularization was developed using a magnetic reconstruction profile for the DIII-D implementation with an iterative inversion method. Neural network inversion methods were developed to not depend on an arbitrary regularization strength and to do between-plasma-shot inversions, which could not overcome the problem of biasing on input data A new method of raw spectra data processing that used Fourier transform was developed for real time analysis. The design from the optimization was validated with several analysis methods to characterize the performance. The forward-modelled radiated power divided into different sections compared to the values from the original synthetic radiation profiles. The central location and shape of various radiation profiles were analyzed and compared to the original values using a computer vision library. The regularized iterative methods worked well. The results demonstrated that the optimized 2D FOB array system will be able to answer important questions relating plasma radiation structures.
Lee, Seungsup, "First Development and Demonstration of Fiber Optic Bolometer. " PhD diss., University of Tennessee, 2022.