Abstract
A 16 chord optical tomography system has been developed and implemented in the flux coil generated-field reversed configuration (FRC). The chords are arranged in two fans of eight, which cover ~35% of the vessel area at the midplane. Each illuminate separate photomultiplier tubes (PMTs) which are fitted with narrow band-pass filters. In this case, filters are centered at 434.8 nm to measure emission from singly ionized argon. PMT crosstalk is negligible. Background noise due to electron radiation and H(γ) line radiation is <10% of argon emission. The spatial resolution of the reconstruction is 1.5 cm. Argon is introduced using a puff valve and tube designed to impart the gas into the system as the FRC is forming. Reconstruction of experimental data results in time-dependent, 2D emissivity profiles of the impurity ions. Analysis of these data show radial, cross-field diffusion to be in the range of 10-10(3) m(2)∕s during FRC equilibrium.
Highlights
Complete understanding of transport processes occurring in a field-reversed configuration (FRC) is essential for long timescale confinement
Injection of impurity species into plasma can lead to measurement of localized particle flux/diffusion through line emission observation
Analysis of profiles provides direct measurement of D⊥ of the impurity species, which contributes to overall understanding of plasma transport processes
Summary
Complete understanding of transport processes occurring in a field-reversed configuration (FRC) is essential for long timescale confinement. Injection of impurity species into plasma can lead to measurement of localized particle flux/diffusion through line emission observation. Complete understanding of transport processes occurring in a field-reversed configuration (FRC) is essential for long timescale confinement.. Injection of impurity species into plasma can lead to measurement of localized particle flux/diffusion through line emission observation. Reconstruction of these data gives 2D, time evolved emissivity profiles. Analysis of profiles provides direct measurement of D⊥ of the impurity species, which contributes to overall understanding of plasma transport processes. These values can be compared to theoretical predictions, which, until now, have had to rely on inferential measurements in hydrogen FRCs
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