Electromagnetic Emissions from a Laser-Heated Z-Pinch Plasma (Molecular Helium).

The soft X-ray and visible electromagnetic emissions from a dense helium Z-pinch plasma were investigated with and without heating by a high power CO(,2) laser. In the case of the unheated plasma, soft X-ray emission measurements were consistent with a thermalized plasma at a temperature of 30 eV. These measurements were performed by a foil-filtered photomultiplier tube which measured the frequency integrated soft X-ray emissions. Time resolved visible spectroscopic measurements were performed with a gated optical multichannel analyzer. During the pinch, the visible emissions were dominated by a strongly Stark broadened He II line at 468.6 nm. The width of that line corresponded to an electron density of 10('19) electrons/cm('-3), which agreed well with results from holographic interferometry. Line to continuum measurements for the He II 468.6 nm line also resulted in a electron temperature of between 20 and 30 eV. In the afterglow of the discharge, radial spectra exhibited many molecular helium emission lines. Axial spectra were dominated by a bright continuum with many absorption b and s. The absorption b and s cannot be identified with helium, molecular helium nor impurities. The temporal behavior of several of these b and s followed the intensity of the helium molecular b and s and may be the first experimental evidence for helium molecular ion spectra. In the case of the high power laser heating of the pinch plasma, the frequency integrated soft X-ray emissions were consistent with an inverse bremsstrahlung modified electron distribution, rather than a bi-Maxwellian distribution. The results of the soft X-ray measurements for the laser heated plasma indicated that the temperature was approximately 60-100 eV.PhDPlasma physicsUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161042/1/8612641.pd