R. Methling

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.

Overview spectra and axial distribution of spectral line intensities in a high-current vacuum arc with CuCr electrodes

Spectroscopic investigations of free-burning vacuum arcs in diffuse mode with CuCr electrodes are presented. The experimental conditions of the investigated arc correspond to the typical system for vacuum circuit breakers. Spectra of six species Cu I, Cu II, Cu III, Cr I, Cr II, and Cr III have been analyzed in the wavelength range 350–810 nm. The axial intensity distributions were found to be strongly dependent on the ionization stage of radiating species. Emission distributions of Cr II and Cu II can be distinguished as well as the distributions of Cr III and Cu III. Information on the axial distribution was used to identify the spectra and for identification of overlapping spectral lines. The overview spectra and some spectral windows recorded with high resolution are presented. Analysis of axial distributions of emitted light, which originates from different ionization states, is presented and discussed.

Mercury-Free High Pressure Discharge Lamps Dominated by Molecular Radiation

High intensity discharge (HID) lamps dominated by molecular radiation offer a very promising alternative for use in future light sources. They are able to deliver competitive efficacies of about 110?lm?W?1 and higher, excellent colour rendering index above 90 and a correlated colour temperature in the 3000?4000?K region at the operating point near the Planckian locus. Moreover, these lamps are opening up the possibility of dimming. Due to the fact that they are able to omit mercury they are environmentally friendly.The emission spectra generated by these HID lamps differ significantly from those of conventional lamps. The reason for this is the dominance of molecular radiation processes. In comparison with conventional HID lamps atomic contributions are usually rather small. In the present case they amount to less than about 10% of the total intensity in the visible range.

Electrical Arc Model Based on Physical Parameters and Power Calculation

This paper presents an electrical arc model based on physical parameters of the arc including temperature, enthalpy, pressure, and also arc geometry. In this model, different mass flows and power losses are considered. The different powers including radiative and turbulent power as well as power gain and loss carried by axial and radial mass flows are calculated and simulated as a function of physical parameters. Moreover, the different arc diameter expressions and their influence on power losses are examined by arc experiments with high-speed imaging and arc dynamic behavior analysis. This model can provide the dynamic behavior of the arc easier in contrast to more complex physical models. The comparison with conventional arc models, such as Schwamaker, Habedank, Kema, and Schwarz, illustrates that the new arc model can better reproduce electrical measurements.

Time-resolved spectroscopy on cathode spots of a vacuum discharge

Cathode spots show a very dynamic behaviour. Thanks to great improvements in experimental techniques, our knowledge on vacuum spots could be remarkably enlarged in the last one or two decades, e.g. by the application of fast intensified CCD cameras. Two-dimensional imaging techniques with high time resolution yield a wealth of information on the spot (sub-) structures, their dynamics and lifetimes. Ultra-high time resolution in the sub-ns range with long measuring intervals can be achieved in one dimensional streak imaging. Here, we are interested in the optical emission of the cathode spots. Therefore, we combined a 0.5 m spectrograph with a streak camera enabling a time resolution in the nanosecond range. Limits concerning wavelength and time resolution as well as the emission intensity will be discussed. The investigations were carried out under UHV conditions using a liquid metal cathode of GaIn alloy. We present first results in which spectral lines of the atom and single as well as double charged ions of the cathode spot plasma could be observed simultaneously. At the beginning of the discharge, the emission spectra are dominated by ionic lines. With a delay in the range of hundreds of nanoseconds atomic lines appear. The intensity of atomic lines is much higher than that of the ionic ones and increases the brightness of the spot in this stage.

Time and space resolved video spectroscopy of the vacuum arc during the formation of high-current anode modes

This paper presents the results of time and space resolved optical investigations of high-current vacuum arcs by means of video spectroscopy. Especially, the transition from the diffuse mode to constricted modes (footpoint, intense or spot mode) has been studied in dependency on the arc current and instantaneous electrode distance. The driving current pulse from a high-current generator which corresponds to the pulsed DC 10 ms was applied. Spectral lines of Cu I, Cu II, and Cu III have been analyzed for various anode modes using a combination of spectrograph and high-speed camera.

Comparison of methods of electrode temperature determination in high-current vacuum arcs

The present contribution reports on investigations of electrode temperatures for Cu-Cr butt electrodes exposed to vacuum arcs with sinusoidal currents of 10-20 kA. Near infrared spectroscopy was carried out by means of a fiber optics spectrometer working in the wavelength range from 900 to 1700 nm with a temporal resolution of 1-2 ms. Electrode surface temperatures after current zero were obtained from the relative shape of the spectrum using a Planck curve fitting procedure. Furthermore, electrode emissivities were derived after performing absolute calibration of the spectra. Pyrometric measurements were performed in the spectral range around 2 μm with high temporal but without spatial resolution.

Interaction of a free burning arc with regenerative protective layers

The possible use of protective layers made of ceramic powders for walls in thermal plasma applications is studied. A stable free burning arc of currents up to 5 kA between copper- tungsten electrodes is used to analyse the arc interaction with samples coated by mixtures of CaCO3, MgCO3, and Mg(OH)2 with plaster. By means of optical emission spectroscopy the maximum arc temperature and the radiation impact on the surfaces are estimated to be around 15000 K and 20 MWm−2, respectively. Thermographic measurements confirm the efficient protection of substrates by all layer materials. Layers containing CaCO3 lead to the lowest heating of ceramic samples which may be caused by a strong evaporation of the layer material.

Spectroscopy of single vacuum arc cathode spots with improved sensitivity

Recently, we reported on the optical emission of vacuum arc discharges with a single cathode spot. The discharges were initiated by rectangular voltage pulses of 100-ns length produced by a cable generator. In combination with the application of a liquid Ga-In alloy cathode and ultrahigh vacuum conditions, a high reproducibility was obtained. An improvement of the sensitivity and the signal-to-noise ratio was achieved by the replacement of the streak camera by an intensified charge-coupled device camera. Thus, the accumulation of calibrated spectra with high temporal, spatial, and wavelength resolution was possible. Distinct differences in the temporal development of the atomic and ionic line intensities were found depending on the spatial position, that is, comparing the spot core and the spot surrounding.

X-Ray Computer Tomography in End-of-Life Investigations of HID Lamps

Abstract X-ray computer tomography gained increasing interest last years, when it became affordable not only for medical applications. The diagnostic opportunities provided by X-ray computer tomography in end-of-life investigation of HID lamps are presented here. Limitations of this technique are discussed.