Hartmut Schneidenbach

Basic concepts of temperature determination from self-reversed spectral lines

Complex high-pressure plasmas have become increasingly important in technical applications such as high-intensity discharge lamps. The knowledge of temperature distributions is of basic interest for the understanding of the physical mechanisms in these plasmas and for a selective manipulation of their properties. It is shown that self-reversed spectral lines provide a powerful diagnostic tool for temperature determination. The two most important approaches for the corresponding data analysis are reviewed and their limitations are discussed. On the basis of these approaches a new method is proposed which avoids the main limitations especially in the application to resonance lines. The temperature has been determined in a Hg/Ar and a Hg/Ar/TlI high-pressure discharge. Measured spectral radiances of the Hg 546.1 and 253.7 nm as well as Tl 377.6 nm lines are analysed and the potentials of the different methods are demonstrated.

Mercury-free high-intensity discharge with high luminous efficacy and good colour rendering index

A mercury-free high-pressure discharge in a quartz vessel is investigated which achieves a high luminous efficacy of more than 90?lm?W?1 and a good colour rendering index of more than 70. It is shown that the favourable properties are achieved by a combination of Xe and AlI3 as mercury is substituted with an admixture of TlI and TmI3. The molecular radiation of the mono-iodide TmI, which is present in large areas of the constricted temperature distribution of the plasma, dominates the spectral radiant flux.

Plasma diagnostics in Hg-free short-arc lamps for automotive lighting

In the context of developing a mercury-free lamp for automotive lighting an optimization of lamp design and plasma radiation was performed. In contrast to existing quartz lamps, a new lamp design was chosen consisting of a sapphire capillary combined with ceramic parts and pure tungsten electrodes. The lamps consist of metal halides and between 1 and 20 bar of xenon. They were operated with an electronic ballast at input powers between 20 and 40 W. Besides an optimization of the tube materials, thermography and plasma diagnostics were performed to understand the processes inside the lamp and to find optimal operation conditions. In addition to experimental diagnostics, a simulation of self-reversed sodium spectral lines was performed to verify plasma parameters, particularly the xenon pressure which could not be determined from the experiment. Additionally, tendencies of the influence of single components could be estimated by modelling.

Dimming Characteristics of Metal-Halide Plasma Lamps

The dimming of metal-halide plasma lamps means leaving the optimized technical lamp performance. As a consequence, the discharge behavior changes, which affects the photometric properties, the efficiency, and the lifetime of the lamps. In order to understand the plasma physical mechanisms of the dimming process, a simplified lamp system was studied, providing good comparability between the experiment and the model.

Temperature profiles of an ablation controlled arc in PTFE: II. Simulation of side-on radiances

The temperature determination by spectroscopic measurements in high-current high-pressure arcs in a polytetrafluoroethylene (PTFE) nozzle under the assumption of an optically thin plasma has been investigated. Assuming local thermodynamic equilibrium the radial temperature distributions as well as the plasma pressures have been determined by fitting a model to measured spectral radiances considering line and continuum absorption. It is shown that absorption has to be included in the error estimate of the experimental results. The different effects, which cause deviations from the optically thin case, have been analysed numerically and by using a simplified analytical model. The theoretically estimated pressures sensitively depend on the Stark broadening. In the studied plasmas the calculated large electron densities indicate a marked reduction of the Stark widths by nonideality effects. The applicability of the experimental method has been proved for suitably chosen lines.

Experimental determination of parameters for molecular continuum radiation of rare-earth iodides

The molecular continuum radiation of high intensity discharges (HID) containing the rare-earth iodides TmI3, HoI3 and DyI3 in quartz burners have been investigated. For the case of TmI3 a more detailed analysis has been performed. Two main molecular emission contributions have been identified, being located in the arc core and in the mantle region. These molecular emissions turned out to deliver half of the total emission of this type of discharge. The mantle emission was identified as originating from the diatomic TmI. Two distinct upper energy levels at about 4 eV have been determined, being separated about 0.4 eV from each other. A pragmatic approach has been chosen to describe the spectral molecular emission coefficient as a sum of three Gaussian profiles.The proposed method allows one to take into consideration molecular emission for modelling of HID containing rare-earth iodides.

Diagnostic Challenges of Asymmetrically Burning Arcs

Asymmetric arcs may cause some complications in the evaluation of optical emission spectroscopy for optically thin plasmas. Even a slight asymmetry can result in increased experimental uncertainties or erroneous conclusions.