X-ray absorption measurements to determine the gas temperature

摘要

For understanding the plasma transport processes and energy balance inside high intensity discharge (HID) lamps, the gas temperature profile is an important parameter. Therefore a good diagnostic method is needed to determine the gas temperature profile accurately. In many Hg containing HID lamps, due to the fact that mercury is the majority species in the plasma and the pressure is constant, the gas temperature is the inverse of Hg density profile. By measuring the Hg density, we can thus determine the relative temperature profile. If we combine this with an absolute measurement of wall temperature, we can get the absolute temperature field inside the lamp. This is the principle of the X-ray absorption technique that has been applied to measure Hg densities in HID lamps [1][2][3][4]. This X-ray absorption method is more attractive than other diagnostic tools based on the emission of line or continuum radiation for the following reasons. 1. X-rays can penetrate all regions of the lamp, especially without refractive of scattering effects, which makes this method especially interesting for polycrystalline alumina (PCA) burners. 2. The X-ray absorption cross-section depends only weakly on the electronic or chemical state of the atom. 3. X-ray absorption measurements only depend on the absolute density of the detected atoms. Other plasma parameters such as electron density, electron temperature, do not influence the absorption directly.