Telecentric viewing system for light collection from a z-pinch plasma

Abstract

As part of a Doppler spectroscopy system to measure the radial variation of ion flow and temperature, a pair of telecentric viewing telescopes has been installed on the ZaP z-pinch plasma device. Each telescope simultaneously collects 20 chords of light (200–1200 nm) emitted by impurities in the plasma, and images the chords on a fiber optic bundle for transport to a spectrometer. The center-to-center spacing of adjacent chords in the plasma is 1.24 mm, thus radial variation across the r=10–15 mm ZaP plasma is completely recorded. In this telecentric imaging system, all object chords and image points, including those laterally displaced from the optical axis, are formed by ray bundles whose chief ray is parallel to the optical axis. Thus all 20 light collection chords passing through the ZaP plasma are parallel, and all 20 image points fill the optical fibers with an identical cone. This maximizes system efficiency and measurement precision, and simplifies calibration and data analysis.