Abstract
A laser system for impurity diagnostics in the edge region of plasma devices is described. It consists of a scanning, single mode, cw dye laser followed by a 3-stage, fast flow dye cell amplifier, pumped by a high repetition rate excimer laser (60 mJ/pulse at 130 Hz, for 308 nm output). Substantial improvements are achieved over previous systems in scan speed (30 GHz/100 ms) and velocity resolution (now small relative to the widths of thermal distributions). The usefulness of high resolution is demonstrated by a model calculation for Fe velocity spectra involving the presence of thermal and sputtered flux, and spatial averaging. The high output pulse power (0.8 MW at 604 nm, 80 kW at 302 nm) allows efficient frequency doubling and can be used to vary the effective bandwidth by power broadening. Broadband operation (50 GHz FWHM) is also possible, for saturated measurements of atomic density. Laboratory velocity spectra for Fe atoms sputtered in the ground state demonstrate the capability for such measurements in a single Tokamak discharge at estimated densities of 108 atoms/cm3.
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