### Session GW1: Lighting Plasmas

Chair: John Curry, NIST
Room: Doubletree Crystal City Crystal Ballroom A

 Wednesday, October 3, 2007 8:00AM - 8:15AM GW1.00001: Propagator Description of Radiation Transport, Applied to Lighting Discharges Chonlarat Wichaidit , William N.G. Hitchon , James E. Lawler , Graeme G. Lister Radiation transport calculations based on the use of propagators (or Green's functions) to describe photon transport are presented for the Hg I resonance at 254 nm in the Complete Frequency Redistribution (CFR) regime. This Hg I resonance dominates the power balance of fluorescent lamp discharges. Recent studies have suggested that transport modes above the fundamental are important in some lamp discharges. The probabilities of photons traveling from one cell of the simulation to another are found by integrating the fluxes due to a point source over the boundaries of each cell volume. Complete hyperfine and isotopic patterns with a Voigt profile for each component are used in our simulations. The Holstein transmittance function T(R) is determined at low opacity using numerical integration across the line profile, and at high opacity using an analytic approximation. ~A power series expansion of T(R) is then used in geometrical integrals needed to evaluate propagator matrix elements. A time dependent radiation transport equation is solved in a cylindrical geometry and compared to very detailed Monte Carlo simulations of radiation transport in a fluorescent lamp. Wednesday, October 3, 2007 8:15AM - 8:30AM GW1.00002: Determination of gas-phase emitter effect in ac operated ceramic metal halide lamps Michael Westermeier , Oliver Langenscheidt , Jens Reinelt , Juergen Mentel , Peter Awakowicz Dy-densities and the corresponding electrode tip temperature have been determined by spatially and temporally resolved spectroscopy at and in front of electrodes operated with an ac-current in metal halide lamps. The lamps, made of transparent YAG arc tubes and containing Hg+NaTlDy iodides, were installed in the Bochum model lamp as an outer sleeve. It allows salt pressure depending measurements of the electrode temperature profiles, yielding a global tip temperature and an electrode loss power, and spectroscopic measurements of absolute line intensities to determine the Dy-densities in front of the electrode. It is found that Dy atoms in the gas phase generate a strong gas-phase emitter effect characterized by a clear reduction of the work function. It reduces the electrode temperature, the input power and influences the type of arc attachment. To distinguish between cathodic and anodic effects, phase resolved measurements of the electrode tip temperature will be presented. Wednesday, October 3, 2007 8:30AM - 8:45AM GW1.00003: Investigations of HID Lamp Electrodes under HF Operation Jens Reinelt , Oliver Langenscheidt , Michael Westermeier , Juergen Mentel , Peter Awakowicz Low pressure lamps are operated many years at high frequencies to improve the efficiency of these lamps and drivers. For high pressure discharge lamps this operation mode has not been installed yet. Generally it can be assumed that there are changes in the electrode physics which may lead to an undesired lamp behavior if HID lamps are operated at a high frequency. To gain insights into these fundamental changes the so called Bochum Model Lamp is used. It is an easy system which allows a fundamental research on HID electrode behavior and the near electrode region without the occurrence of acoustic resonances. For the investigation phase resolved photography, pyrometry and spectrometry is used. The presented results describe changes in the electrode temperature and changes in the kind of arc attachment on the electrodes (diffuse and spot mode) depending on frequency. Also measurements of the Electrode-Sheath-Voltage (ESV), depending on frequency, are presented. Wednesday, October 3, 2007 8:45AM - 9:00AM GW1.00004: Preventing transient spots on thermionic cathodes Mikhail Benilov , Pedro Almeida , Mario Cunha Transitions between diffuse and spot modes of attachment of a high-pressure arc to a thermionic cathode, provoked by a current jump, are studied by means of a numerical and physical experiment. The numerical simulation is based on the model of nonlinear surface heating, which has become during the last decade a universally accepted tool for modeling arc-cathode interaction. Experiments were performed on COST-529 standard lamps, which are HID lamps with quartz walls and a quartz envelope. The lamps had pure tungsten cylindrical electrodes and operated at pressures of about 4 bar. The power supply to the lamps was provided by a voltage driven power amplifier FM 1295 DCU/I 750, which functioned as a current source and was controlled by an arbitrary waveform generator Agilent 33220A or by an analogue function generator Leader LFG--1300S. A good agreement between the numerical modeling and experimental results was found. A possibility of prevention of formation of transient spots is demonstrated both numerically and experimentally. Wednesday, October 3, 2007 9:00AM - 9:15AM GW1.00005: Mercury-free alternatives for HID lamps Ralf Methling , Steffen Franke , Helmut Hess , Hartmut Schneidenbach , Heinz Sch\"opp , Lothar Hitzschke , Marko K\"aning , Bernhard Schalk Lighting consumes about 20\% of the world-wide electrical energy. The development of energy-efficient environmentally friendly lamps proves to be a major task of sustainability research. Up to now most of the highly efficient plasma lamps depend on the unique properties of mercury, which are the high vapor pressure and the large electron momentum-transfer cross section. The replacement of mercury became a challenge and motivation for the development of new high-intensity discharge lamps (HID lamps) in recent years. We introduce a mercury-free high-pressure discharge lamp in quartz technology and compare it with a corresponding mercury-containing lamp. It will be shown that the favorable properties of mercury are provided in a large extent by a combination of Xe and AlI$_{3}$. The atomic and molecular radiation caused by the admixture of TlI and TmI$_{3}$ dominates the spectral radiance. For this mercury-free high-pressure discharge a high luminous efficacy of more than 90~lm/W and a good color rendering index of more than 75 are achieved. Wednesday, October 3, 2007 9:15AM - 9:30AM GW1.00006: Modeling of dielectric barrier discharge excimer lamp excited by mono polar voltage pulses Haruaki Akashi , Akinori Oda , Yosuke Sakai Filametal discharges in Dielectric Barrier Discharge (DBD) excimer lamp excited by mono polar voltage pulses has been simulated using two dimensional fluid model. And the differences of the filament discharges formations between mono polar case and bipolar case [1] have been examined. Xe gas was used and its pressure is 300Torr. Simulated region is 1cm (gap length) x 3cm (radial length). Periodical boundary conditions are assumed for the radial direction boundaries. The both electrodes are covered with dielectrics and their thickness is 0.2cm. Applied voltage is 5kV trapezoid shape with 50\% duty ratio waveform and its repetition rate is 200kpps. First a small amount of electron-ion pair is provided in the middle of the gap for initial condition. Then the voltage starts to apply. In the case of bipolar excitation, the discharge starts from one filament (streamer discharge), and finally, 5 filaments are obtained self-consistently. In the case of mono polar case, as first, similar to bipolar case, the discharge starts from one filament, however, only 3 filaments have been obtained. This result is similar to that of 100kHz bipolar voltage case. \newline [1] H. Akashi et al, IEEE Trans. Plasma Science, Vol.33, No.2 (2005) pp.308-309