Tomographic measurement of temperature in non-axisymmetric arc plasma by single camera multi-view imaging system.

In this paper, we introduce a method for dynamic and three-dimensional (3D) arc temperature measurement in non-axisymmetric arc plasma. Optical filters with narrow spectral bands are used to gain 696.5 nm line spectral information of a free-burning Argon (Ar) arc. A measuring system with a setup of mirrors allows a single camera chip to image multi-views of identical welding arc onto one monochromatic image. And based on the underlying characteristics of the arc plasma, we present a modified maximum likelihood expectation maximum (ML-EM) algorithm to reconstruct the emission coefficients from the line intensities. To verify the accuracy of our algorithm, two models of arc plasma have been established to simulate the reconstruction process. Simulation results demonstrated that the modified ML-EM can be utilized to improve the performance of 3D reconstruction compared to common ML-EM methods. To obtain the optimal scheme of the measuring system with limited view directions, the reconstruction quality with different directions is presented and discussed. In the experiment, asymmetric 3D plasma temperature distribution was determined at a direct current (DC) of 80 A and 100A. The results proved the feasibility of the 3D temperature measure method to characterize an asymmetric arc.