EXPERIMENTAL CHARACTERISATION OF THE HIGH-PRESSURE METAL-HALIDE Na-Sc-Hg DISCHARGE

1. EXPERIMENTAL CHARACTERISATION OF THE HIGH-PRESSURE METAL-HALIDE Na-Sc-Hg DISCHARGE Z. Miokovic1and D. Veza Physics Department, Faculty of Science, Uni-Zagreb, Bijenicka 32, HR-10002 Zagreb, Croatia (veza@phy.hr) 1Faculty of Electrical Engineering, Uni-Osijek, K. Trpimira 2B, 31000 Osijek, Croatia (zeljka@etfos.hr) • MOTIVATION • Better and more complete understanding of physics and chemistry of metal-halide discharge • Metal-halide high intensity discharges play an increasing role as light sources • Importance of atomic plasma parameters for modeling high-pressure discharges and optimization of metal-halide and alkali lamps • An increasing interest for the plasma broadening of isolated non-hydrogenic lines of neutral atoms EXPERIMENT Abel’s inversion Fig. 2. Emission spectroscopy technique was used to measure the discharge temperature and densities of radiating atoms [3, 4]. The lateral intensity distribution, emitted by axially symmetrical plasma source, is measured. The radial intensity distribution is calculated using Abel inversion technique. The calibration of the system response has been made using a tungsten ribbon lamp. Fig. 4.: The sodium 52S1/2 32P1/2,3/2 atomic lines measured from the HP 400W metal-halide Na-Sc-Hg discharge at the current of 3.4A. The upper part shows the sodium atomic lines measured from the low-pressure (LP) sodium spectral lamps (reference source, unshifted lines). The lower part represents the recorded spectral lines mesured, simultaneously, from the HP discharge and LP discharge. Fig. 1. Experimental arangement : LPL-low pressure lamp;HPL-high pressurelamp; R-folding mirror; L-lens; F-cut of filter; T-translator; SM-spherical mirror; M-monochromator; PMT-photomultiplier;A/D - analog-to-digital converter; PC-personal computer Fig. 3. To determine the discharge temperature optically thin spectral lines wereused. The self-absorption test for spectral lines has been made by placing a concave spherical mirror behind the discharge to double the optical path length (Fig.1.). The correction for self-absorption is calculated by [5]. The solid line represents the measured line profile I1() with single plasma length, and the dotted line represents the measured line profile I2() with double plasma length. To obtain the line profile for optically thin case the measured profile I1() is multiplied by the correction factor K. The dashed line is the corrected line profile I1C(). RESULTS Fig. 5. The emission coefficients for the center of the discharge, of optically thin scandium spectral lines, were introduced into the Boltzmann’s plot. From the slope of the regression line the electron temperature was deduced ( full line ). Dotted line - the interval of confidence according to statistical analysis. Fig.6.: The comparison of our measured Stark shift de of sodium 52S1/2 32P1/2,3/2 line at 615 nm, radiated from HP 400W metal-halide Na-Sc-Hg discharge with calculations by Griem. The 52S1/2 32P1/2,3/2 line was used as the calibration line to deliver values of electron densities Ne at different currents through the discharge. • -experiment, full line - theory (Griem, 1964) • CONCLUSIONS • Electron temperature is determined by Boltzmann plot method. Depending on discharge load and on the location in the discharge, the temperature is in the range of 6000 K - 8000 K. • Electron density is determined by measuring the Stark shift of the sodium 5 2S1/2 3 2P1/2, 3/2 spectral line. Electron densities are in the range of 7·1015 - 1.5 ·1016 cm-3. • Line-shifts of the sodium 5 2S1/2  3 2P1/2, 3/2 transition show an almost linear dependence on the electron density. Fig. 6. The electron densities are shown as a function of the current through the discharge. The electron densities show approximately a linear dependence on the discharge current. • References • [1] G. H. Reiling, JOSA 54, 532 (1964) • [2] J. T. Dakin, T. H. Rautenberg, Jr. and E. M. Goldfield, J. Appl. Phys. 66 (9), 4074 (1989) • [3] J. F. Waymounth, Electric Discharge Lamps (MIT, Cambridge, 1971) • [4] H. Ywicker, in Plasma Diagnostics, p.214, ed. By W. Lochte-Holtgreven(Wiley, NY 1968) • [5] W. L. Wiese, R. H. Huddleston, S. L. Leonard (Eds.), Plasma Diagnostics Techniques, Academic Press, NY, (1965) • [6] H. R. Griem, Plasma Spectreoscopy, McGraw-Hill, New York (1964)