Electron-density dependence of line intensities of Cu ilike Sm33+ to Yb41+ emitted from tokamak and laser-produced plasmas

The density dependence of n=0 (4-4) transitions for rare-earth-metal ions isoelectronic with Cu i has been studied over a large density domain 10131021 cm-3 by measuring the spectral emissions from these ions in tokamak and laser-produced plasmas and comparing them with theoretical models. The computational techniques used for the atomic parameters in the collisional radiative model of the level populations were checked in the low-density range 1013 cm-3 by analyzing the spectra of Eu34+ and Yb41+ emitted from a tokamak plasma. Then laser-produced spectra of Sm33+ and Yb41+ were analyzed using similar models for the density dependence of the line ratios in the high-density region 10191020 cm-3. The theoretical models included the effect of cascading from n=5 states on the population of the n=4 levels. In addition, optical depth effects on the line intensities were considered for the high-density laser-produced plasmas. The present work demonstrates the potential of highly ionized rare-earth-metal atoms as electron-density diagnostics in high-density plasmas. In particular, all along the isoelectronic sequence from Z=59 to Z=70 the two density-sensitive transitions 4d D5/224f F7/22 and 4p P3/224d D5/22 remain close to each other and are unblended with other lines, and thus their ratios represent particularly attractive density diagnostics.