Measurement of incandescent microparticle acceleration using stereoscopic imaging.

Microparticles ranging from sub-microns to millimeter in size are a common form of matter in magnetic fusion environment, and they are highly mobile due to their small mass. Different forces in addition to gravity can affect their motion both inside and outside the plasmas. Several recent advances open up new diagnostic possibilities to characterize the particles' motion and their forces: high-speed imaging camera technology, microparticle injection techniques developed for fusion, and image processing software. Extending our earlier work on high-temperature 4D microparticle tracking using exploding wires [Z. Wang et al. Rev. Sci. Instrum. 87, 11D601 (2016)], we report here the latest results on time-resolved microparticle acceleration measurement. New particle tracking algorithm is found to be effective in particle tracking even when there are a large number of particles close to each other. Epipolar constraint is used for track-pairing from two-camera views. The error field based on an epi-geometry model is characterized on the basis of a large set of 2D track data and 3D track reconstructions. Accelerations based on individual reconstructed 3D tracks are obtained. Force sensitivity in the order of ten gravitational acceleration has been achieved. High-speed imaging is a useful diagnostic tool for microparticle physics, computer model validation, and mass injection technology development for magnetic fusion.