Abstract
The density and velocity distribution of neutral Fe atoms in the plasma-edge of the ISX-B tokamak have been measured by laser fluorescence spectroscopy. Fe neutrals were excited at 302 nm using a flashlamp-pumped dye laser. The fluorescence light was detected at 382 nm with an interference filter and photomultiplier system. The frequency-doubled laser output (700 W) and pulse length (500 ns) allowed saturation pumping of the Fe transition thereby enabling absolute measurement of densities. Insertion of an additional Fabry-Perot étalon into the laser cavity narrowed the laser bandwidth to 0.6 pm corresponding to a velocity resolution of 600 m/s (0.1 eV for Fe). Neutral densities were measured for two locations in the plasma-edge as a function of discharge time. Results show a detection sensitivity of 10 12 atoms/m 3 with a neutral Fe density of a few 10 12 atoms/m 3 in the first 20 ms of the discharge and 10 14 atoms/m 3 30 ms after the discharge. The velocity distribution of the neutral Fe at the end of the discharge is thermal (400–1000 K) while the smaller peak at the beginning of the discharge shows evidence of higher velocities.
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