Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session RR2: Lighting Plasmas |
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Chair: D. Leonhardt, Fusion UV Systems, Inc. Room: Salon A-D |
Thursday, October 16, 2008 1:30PM - 1:45PM |
RR2.00001: Phase resolved investigation of the power balance of HID lamp electrodes from low to RF frequency operation Jens Reinelt, Michael Westermeier, Juergen Mentel, Peter Awakowicz For HID lamps the electrode temperature is a very important parameter since it has a strong influence on the whole discharge. Also the power balance of the lamp is strongly depending on the electrode temperature. For the efficiency of the lamp it is very important to minimize the part of the input power P$_{in}$ which is not transformed into visible light. This part mainly consists of the power input into the electrode plasma sheaths P$_{sheath}$ which is in part dissipated by thermal radiation of the electrodes and in part by heat conduction to the lamp bulb. For dc operation an extensive investigation of these parameters can be found in literature. For ac operation these parameters change since now the heat capacity and the change of the polarity of the electrodes have to be considered. Shown are phase resolved measurements and calculations for various frequencies at the Bochum model lamp of the electrode temperature, the input power, the power loss of the electrodes and the electrode sheath voltage (ESV). Furthermore calculations of the cathode and anode fall voltage U$_{c}$ and U$_{a}$ are presented. [Preview Abstract] |
Thursday, October 16, 2008 1:45PM - 2:00PM |
RR2.00002: Barium transport in fluorescent lamps F. Sigeneger, K. Rackow, D. Uhrlandt, J. Ehlbeck, G. Lieder The transport of barium atoms and ions in the cathode region of fluorescent lamps driven at 25\,kHz is studied experimentally and theoretically. The density of Ba atoms and ions have been measured time-resolved by laserinduced fluorescence at different distances from the spot center. Furthermore, the time-dependent cathode fall voltage was approximately determined using an improved band method. The model comprises the solution of the time-dependent particle balance equations of Ba and Ba$^+$ which include the Ba ionization as gain and loss terms, respectively. The ionization rate coefficient of Ba and the electron density are determined by solving the space-dependent electron Boltzmann equation in spherical geometry using the measured cathode fall voltage and the discharge current as input. Good agreement between the measured and calculated density profiles of barium atoms has been obtained. The results demonstrate the sensitive dependence of the Ba density profiles on the ionization which leads to a strong depletion of the Ba density in the cathode phase of the investigated electrode. The model yields the Ba flux from the cathode which limits the lifetime of the lamp. [Preview Abstract] |
Thursday, October 16, 2008 2:00PM - 2:30PM |
RR2.00003: Continuum Processes in High and Ultra High Pressure Lamps Invited Speaker: The growing use of Ultra High Pressure (UHP) lamps for projection applications has motivated studies of thermal or LTE Hg plasmas in a peculiar region of parameter space. These UHP lamps, which are now commonly found in conference room projectors and large screen TVs, operate with Hg pressures $>$ 200 bar, electron densities $\sim $1.0E18 / cc, and power densities $>$ 1.0E5 W/cc. Such lamps were developed to couple the maximum amount of light into small etendue LCD projection systems. Unlike most other plasmas in similar parts of parameter space, the plasmas in UHP lamps are steady-state. A greater variety of diagnostic techniques and more accurate measurements are possible in UHP lamp plasmas. Continuum processes are much more important in both the opacity and power balance of UHP lamps than they are in typical ($<$ 20 bar) High Intensity Discharge (HID) lamps. Electron + Hg atom bremstrahlung dominates ($\sim $90{\%}) the near IR emission from UHP lamps [1]. Quasi-molecular absorption at $>$ 200 bar yields substantial opacity and results in minimal UV emission from UHP lamps [2, 3]. There are additional physics issues in the 200 bar to 1 kbar range: e.g. (1) spectral line broadening of the few remaining Hg transitions including the breakdown of the single perturber approximation of line broadening theory, (2) free electron continuum processes including the breakdown of the binary collision approximation, and (3) the effect of strong coupling of the plasma on radiative processes. A more quantitative understanding of electron + Hg atom bremsstrahlung in UHP lamps has resulted in a better understanding of near IR losses from widely used, lower pressure metal-halide HID lamps. \newline [1] Lawler JE, Koerber A, and Weichmann U 2005 J. Phys. D: Appl. Phys. 38, 3071. \newline [2] Wharmby D 2008 J. Phys. D: Appl. Phys. in press. \newline [3] Kato M, Kane J, and Lawler JE 2008 J. Phys. D: Appl. Phys. submitted. [Preview Abstract] |
Thursday, October 16, 2008 2:30PM - 2:45PM |
RR2.00004: Generation of Transition Probability Data: Can quantity and quality be balanced? J.J. Curry, C. Froese Fisher The possibility of truly predictive plasma modeling rests on the availability of large quantities of accurate atomic and molecular data. These include a variety of collision cross-sections and radiative transition data. An example of current interest concerns radiative transition probabilities for neutral Ce, an additive in highly-efficient metal-halide lamps. Transition probabilities have been measured for several hundred lines (Bisson et al., JOSA B {\bf 12}, 193, 1995 and Lawler et al., unpublished), but the number of observed and classified transitions in the range of 340 nm to 1 $\mu$m is in excess of 21,000 (Martin, unpublished). Since the prospect for measuring more than a thousand or so of these transitions is rather low, an important question is whether calculation can adequately fill the void. In this case, we are interested only in electric dipole transitions. Furthermore, we require only that the transition probabilities have an average accuracy of $\sim$20\%. We will discuss our efforts to calculate a comprehensive set of transition probabilities for neutral Ce using the Cowan ({\it The Theory of Atomic Structure and Spectra}, 1981) and GRASP (J\"onsson et al. Comput. Phys. Commun. {\bf 176}, 559-579, 2007) codes. We will also discuss our efforts to quantify the accuracy of the results. [Preview Abstract] |
Thursday, October 16, 2008 2:45PM - 3:00PM |
RR2.00005: Arguments for increased efficiency of Xe excimer DBDs by pulsed instead of sinusoidal excitation Mark Paravia, Klaus E. Trampert, Michael Meisser, Wolfgang Heering Xenon excimer dielectric barrier discharges are used as VUV sources or as plane light sources with phosphor coating. The plasma efficiency of up to 65{\%} [1] depends on the excitation waveform and rises by pulsed operation compared to sinusoidal excitation. However, loss processes and efficiency gain are not completely known. This is caused by the dielectric barrier prohibiting direct measurement of the plasma power. Here internal plasma power measurements, based on an analog method, are presented for sinusoidal and pulsed excitation. The plasma power can be separated into ignition power during ignition phase and glow phase after ignition. It can be shown that ignition power correlates with the VUV radiation. A comparison of ignition power and glow phase power shows that during ignition the generation of exited Xe atoms is very efficient whereas the glow phase is inefficient in production VUV radiation. Time resolved optical measurements of NIR line radiation of excited xenon atoms show that the discharge is supported during glow phase. Comparing sinusoidal and pulsed excitation, the efficiency gain can be explained by reduced glow phase losses. This is shown and explained experimentally using pulse excitation down to a pulse length of a few hundred ns. [1] Vollkommer, F.; Hitzschke L., WO94/23442, 1994 [Preview Abstract] |
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