Volume 93, Issue 5, 01 March 2003
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
93(2003); http://dx.doi.org/10.1063/1.1534623View Description Hide Description
The use of x-ray induced fluorescence to measure elemental densities in a metal–halide lighting arc is described. High-energy synchrotron radiation generated on the Sector 1 Insertion Device beam line at the Advanced PhotonSource induces K-shell fluorescence in a high-pressure plasma arc. The detected fluorescence is spectrally resolved, so that multiple elemental species are observed simultaneously. Absolute calibration of the measured densities is straightforward and robust. The penetrating nature of high-energy photons allows these measurements to be made in situ, with the arc contained by an optically translucent polycrystalline alumina arc tube and a glass vacuum jacket. Spatial distributions extending from one end of the arc tube to the other and from the arc core all the way to the wall have been obtained for all the principal elements in the arc. A volume element measuring 1 mm × 1 mm × 1 mm is resolved in the present work, with significantly better spatial resolution possible. Densities as low as have been observed. X-ray induced fluorescence is useful for the observation of many important high-pressure plasmalighting chemistries including those containing Hg, Tl, Dy, Tm, Ho, Cs, Sn, I, and Xe.
Particle-in-cell/Monte Carlo simulation of a capacitively coupled radio frequency discharge: Effect of gas composition93(2003); http://dx.doi.org/10.1063/1.1542920View Description Hide Description
A one-dimensional particle-in-cell/Monte Carlo model is developed to study a capacitively coupled radio frequency discharge in a gas mixture of argon and The simulation takes into account the following charged particles: electrons, two kinds of positive ions and two kinds of negative ions The model considers electron–Ar collisions,collisions, various kinds of collisions of or with Ar or and positive–negative ion recombination. The probability for the positive–negative ion recombination is determined from a recombination rate constant. The ion–neutral elastic and reactive collisions are simulated by an ion–molecule collision model for endothermic reactions. The typical results of this model are electron and ion densities, fluxes and energy distributions, collision rates, and electric field and potential distributions. The simulation is performed for 0.1/0.9, 0.5/0.5, and 0.9/0.1 ratios of a mixture, as well as for pure Ar and pure discharges at a pressure of 200 mTorr. It is observed that at high concentration the discharge behaves as a typical electronegative discharge and that is the major positive ion. At low concentration, keeping the other operating parameters the same, the double layer structure and the electron density maxima at the bulk–sheath interface, which are representative for an electronegative discharge, disappear and the density exceeds the density by more than 1 order of magnitude. The results show that the ions are the dominant negatively charged species for all ratios investigated.
93(2003); http://dx.doi.org/10.1063/1.1544070View Description Hide Description
The effect of ambient gas on the expansiondynamics of the plasma generated by laser ablation of an aluminum target has been investigated using frequency doubled radiation from a Q-switched Nd:YAG laser. The diagnostic tools include fast photography of overall visible plume emission using a 2 ns gated intensified charged coupled device and space and time resolvedemission spectroscopy using a 50 cm monochromator/spectrograph and photomultiplier tube. The expansion behavior of the plasma was studied with ambient air pressure ranging from to 100 Torr. Free expansion, plume splitting and sharpening, hydrodynamic instability, and stagnation of the plume were observed at different pressure levels. Space and time resolved emission spectroscopic studies showed a twin peak distribution for Al and species at farther distances illustrating plume splitting at pressures higher than 100 mTorr. Combining imaging together with time resolved emission diagnostics, a triple structure of the plume was observed. The expansion of the plume front was compared with various expansion models and found to be generally in good agreement.