Measurement of Ba-densities close to the electrode in an HPS-lamp by broadband absorption spectroscopy with a UHP-lamp

Abstract

Within this work, the emitter-effect of barium is investigated in a high-pressure-sodium (HPS) lamp. The emitter-effect reduces the thermal stress of the lamp electrode by a reduction in the effective work-function of the tungsten material. The investigated HPS-lamp has a special design of the Ba-emitter storage: it is deposited during lamp production in a tungsten coil around the electrode rod with a certain distance to the electrode tip. During lamp operation the Ba-emitter diffuses along the electrode surface to the electrode tip.To optimize the Ba-diffusion along the electrode, a measurement of the Ba-vapour density close to the electrode is executed by means of a broadband absorption spectroscopy (BBAS) at a Ba resonance line. An ultra-high-pressure (UHP) lamp is used as an absorption backlight source. It provides a high radiance at the measuring wavelength and operates very stably over time. An approximately linear decrease in the Ba-vapour density close to the electrode rod from 1.5 × 1012 to 0.5 × 1012 cm−3 is measured between the coil and the tip. The UHP-broadband absorption measurement at the Ba resonance line yields results which are independent of the plasma temperature. It can be applied to any arbitrary position within the HPS-lamp. Thus, the presented BBAS by means of a UHP-lamp is a very flexible but simple alternative to laser-absorption spectroscopy or to emission spectroscopy.

Investigating the gas phase emitter effect of caesium and cerium in ceramic metal halide lamps in dependence on the operating frequency

“…Its formation becomes obvious by comparing the electrode tip temperatures T tip (ϕ) in figure 5 and figure 1(a) of [26]. Furthermore, the missing formation of an emitter spot within the cathodic phase is an indication for a moderate Cs ion current density in front of the cathode [20,24]. The decrease of N a,Cs (ϕ) and N i,Cs (ϕ) in the anodic phase is caused by the reversal of the Cs ion current.…”

“…To measure particle densities by absorption spectroscopy the set up for emission spectroscopy is extended by a back light source being positioned behind the YAG lamp on the elongation of the optical axis [20,21,31]. A powerful broadband light source with a high radiance within the visible spectral range and a temporarily very stable emission is realized with an ultra high pressure (UHP) lamp [34].…”

“…A first discussion of the broadband absorption spectroscopy with an UHP lamp is given in [20,31] while first results by means of this method are presented for YAG lamps seeded with DyI 3 in [21,31] and with CeI 3 in [31,40].…”

“…When the electrode is heated up the emitter material, e.g. barium, diffuses along the electrode surface to the tip [20,21].…”

“…The Ce atom density is determined by absorption spectroscopy. For this purpose the measuring system for emission spectroscopy is supplemented by an intense back light, realized by an UHP lamp [20,21,31].…”