Presentation on theme: "ION BROADENING OF SODIUM nS - 3P TRANSITIONS Z. Miokovic 1 and D. Veza Physics Department, Faculty of Science, Uni-Zagreb, Bijenicka 32, HR-10002 Zagreb,"— Presentation transcript:
ION BROADENING OF SODIUM nS - 3P TRANSITIONS Z. Miokovic 1 and D. Veza Physics Department, Faculty of Science, Uni-Zagreb, Bijenicka 32, HR Zagreb, Croatia 1 Faculty of Electrical Engineering, Uni-Osijek, K. Trpimira 2B, Osijek, Croatia MOTIVATION Better understanding of the physics and chemistry of high-pressure discharges (sodium-mercury /cadmium and metal-halide discharges) Importance of atomic plasma parameters for modeling high-pressure discharges and optimization of metal-halide and alkali lamps The line shift and the line broadening of n D – 3P ( n > 4) series and n S – 3P ( n = 5, 6, 7) series are rarely investigated To find out mechanisms leading to the formation of n S-3P ( n = 5, 6, 7) sodium atomic lines and to determine the corresponding interaction constants Sodium n S-3P ( n = 5, 6, 7) atomic lines emitted from high-pressure sodium discharges [1, 2, 3] show a systematic red asymmetry EXPERIMENT EXPERIMENT Fig.1. Experimental arrangement Experimental arrangement: LPL- low pressure lamp; HPL-high pressure lamp; R- folding mirror; L-lens; F-cut of filter; M- monochromator; PMT-photomultiplier; A/D-analog-to-digital converter; PC-personal computer. Fig. 2. The external- or the line triggering for the time resolved measurements is used, provided by boxcar averager. All measurements were performed at the maximum value of the AC driving current. Fig. 3. The 5 2 D 3/2, 5/2 3 2 P 1/2;3/2 atomic lines measured from the HP 400W Na-Cd discharge at the current of 3.4 A (hollow circles). The solid red line represents the best fit of Lorentzian profiles to the experimental data measured from the HP discharge. The lower part shows the same atomic lines measured from the low-pressure sodium spectral lamp (reference source, unshifted lines). RESULTS RESULTS Fig. 5.: The 7 2 S 1/2 3 2 P 1/2;3/2 atomic line measured from the 400W Na-Cd discharge at the current of 4.0 A (circles). The theoretical profiles (full and dotted lines, representing the best fit to the experimental data), calculated using the Bartels’ method  with the following plasma parameters: N Na = 2 m -3, N Cd = 20 m -3, N e = 7.58 m -3, d e = nm, d i = nm, w e = nm, w i = nm and T e = 3850 K. The dotted line represents the analytical line profile calculated according to Stormberg . This calculation takes into account the line broadening by electrons and the van der Waals broadening by Cd (or Hg) atoms. The full line represents a profile calculated by numerical convolution  of the reduced Stark profile accounting for the quasistatic approximation for ions and the impact approximation for electrons, and also the van der Waals broadening by Cd (or Hg) atoms. The lower part shows the difference between experimental and theoretical profiles. CONCLUSIONS We measured the Stark-shift, -width and shape of neutral sodium spectral lines corresponding to the n 2 S 1/ P 1/2, 3/2 (n = 5, 6, 7) transitions, measuring the side-on emission from a high-presssure sodium discharge Electron density determined measuring the shift of the sodium 7 2 S 1/2 3 2 P 1/2;3/2 spectral line Electron temperature determined by Bartels’ method (fitting the calculated to the experimentally measured line shapes) The dominant shift and broadening mechanism is the Stark broadening Line-shifts and widths of the sodium n S - 3P ( n =5, 6, 7) transitions show a linear dependence on the electron density The red asymmetry of sodium atomic lines can be explained by a combined effect of ion broadening (the dominant one) and foreign gas (Cd or Hg) broadening. References  Z. Miokovic, D. Balkovic, D. Veza, Proceedings of the 34 th EGAS, pp P2: (Sofia, 9-12 July 2002). Z. Miokovic,and D. Veza, FIZIKA A10, 129 (2001). Z. Miokovic, D. Balkovic, D. Veza, submitted for publication. H. P. Stormberg, J. Appl. Phys. 51, 1963 (1980). W. H. Press, S. A. Teukolsky, W. T. Vetterling, Numerical Recipes in C, Cambridge UP, New York (1992). M. S. Dimitrijevic, S. Sahal-Bréchot, J. Quant. Rad. Trans., 34, No. 2, 149 (1985) H. R. Griem, Plasma Spectroscopy, McGraw-Hill, New York (1964). H. Bartels, Z. Phys. 128, 546 (1950). Fig. 4.: The comparison of our measured Stark shift d e of sodium 7 2 S 1/ P 1/2,3/2 line at 475 nm, radiated from HP 400 W Na-Cd ( ) and Na - Hg ( ) discharges, and Stark (electron-impact) half widths w e determined by fitting the simulated line shapes calculated within Bartels’ method with calculations by Griem (1964., full line) and Dimitrijevic et. al (1985., dotted line). The 7 2 S 1/ P 1/2,3/2 line was used as the calibrant line, used to deliver values of N e at different currents through the discharges. Table 1.: The electron broadening caused shift and width data (d e,w e ) and ion broadening data (d i, w i ) of the sodium n 2 S 1/2 3 2 P 1/2;3/2 (n=5, 6, 7) atomic lines radiated from high-pressure Na-Cd discharge are tabulated for given electron density and temperatures. The Stark-broadened line-width ( 1/2 ) S and line-shift ( 1/2 ) S are given by  ( 1/2 ) S = [ A ( r) ] w, ( 1/2 ) S = [ d/w + 2 A ( r) ] w, where is w = 2 w e N e / The appropriate values of the quasi-static ion broadening parameter A and the Debye shielding parameter r : < A < 0.151, < r < 0.65.