Spectroscopic measurements were made of lithiumlike Al emission lines from laser-produced plasmas. Flat targets, consisting of thin layers of Al coated on a Mylar backing, were irradiated with up to eight beams of the OMEGA laser system employing a line-focus configuration. The 0 Al xt 4f 3d line-at 154.7 A exhibited a gain coefficient of 4.1+1. 2 cm ' from comparisons of line in-0 tensities from 3and 6-mm-long plasmas. Similarly, the 4d-3p line at 150.7 A and the 5f 3d line at-105.7 A had gain coefficients of 4.521.3 and 3.5+0.8 cm, respectively. The linewidth of the 5f 3d-0 line was measured to be 0.35 A, which is much larger than the expected Doppler and instrumental width and can be attributed to Stark broadening. This Stark broadening corresponds to an electron density of 3X10' cm Laser-produced plasmas have been extensively studied as a medium for producing xuv and x-ray laser systems. Using three-body recombination in a dense plasma to produce an x-ray laser was first proposed by Gudzenko and Shelepin. ' In order for this method to work, the plasma must be ionized past the ionization stage where inversion occurs. Then as the plasma cools and recombines, higher n (quantum-number) levels become populated preferentially, leading to population in versions. Much progress has been made in using the recombination phase of a plasma to create a population inversion in selected ions. Early experimental work showed population inversion in C vI. ' Suckewer et al. used a recombining, cylindrical plasma to demonstrate amplification and gain (G=6.5 cm ') in the 182-A line of Cvt. A great deal of computational modeling of a plasma with recombination into hydrogenlike ions has been developed by Pert. 'In Li-like ions, the 4f 3d and 5 f 3d li-nes have both ex-hibited gain in various experiments. An early experiment using a Nd:glass laser of intensity (1 -2) X 10' W/cm indicated inversion of the n =4 and 5 levels of Alxr relative to the n =3 level. The populations were deduced from measurements of the nd-2p transitions allowing for self-absorption.Extensive study of the 5f 3d line of-Al xI at 105.7 A has been performed by Jaegle et al. using a line-focused Nd:glass laser irradiating a slab target. ' Amplification of this line with a gain-length product of 2 -2.5 was observed. Suckewer et al. , using a CO2 laser, showed evidence for population inversion in the 4f 3d lines of Ovl and Ne-VIII. 'o In later experiments, also using a CO& laser, the Al XI and Si x11 4f 3d transi-tions exhibited population inversion and gain. "In our experiment we have recorded high-resolution, time-integrated spectra of highly ionized, cylindrical Al plasmas. The 4f 3d (154.7-A), 4d 3d -(150.7-A), an-d the 5f-3d (105.7-A) lines of Li-like Al exhibited gain upon increasing the length of the plasma column. Measurements of spectral linewidths of these transitions will also be discussed.Cylindrical plasmas were produced for these measurements by using up to eight line-focused beams from the OMEGA Nd:glass laser system at a wavelength of 351 nm. A sche...

Experiments are underway on the Alcator C Tokamak with over 1 MW of RF power injected into the plasma at a frequency of 4.6 GHz to study both heating and current drive effects. During these studies, impurity generation from limiter structures has been observed.The RF induced impurity influx is a strongly nonlinear function of net injected power. For Prf < 500 kW, only small effects are seen.As Prf approaches 1 MW, however, sharp increases in impurity influxes and Zeff are observed. Three different limiter materials have been used during these studies: molybdenum, graphite, and silicon-carbide coated graphite.In each case, the materials of the limiter structure are seen to dominate the increased impurity influx. In a typical case, with Prf =

Densities of C, 0, and Si during the steady state portion of Alcator C discharges have been computed from spectroscopic measurements of the absolute brightnesses of visible and UV emission lines in combination with with a 1-D transport calculation which models the charge state and emissivity profiles. Profiles of all the charge states of a particular impurity were calculated by utilizing independent measurements of plasma density and temperature and solving the coupled system of transport and rate equations connecting the ionization states. These profiles were then used to calculate emissivity profiles by solving the matrix equation relating the level populations through collisional excitation, collisional de-excitation, spontaneous emission, innershell ionization and cascades from upper levels. Three different types of limiters, molybdenum, graphite and SiC coated graphite, have been used on Alcator C. It was observed that the principal impurities in the plasma, under most conditions, were determined by the type of limiter material being used.However, the source of the impurities could be either the wall or the limiters, since it has been shown that the wall becomes coated with limiter material. A significant influx of impurities directly from the limiters was often seen during the application of lower hybrid RF power to the plasma.