Collisional radiative model for the evaluation of the Thermal Helium Beam diagnostic at ASDEX Upgrade

The thermal helium beam diagnostic at ASDEX Upgrade is used to infer the electron density ne and temperature Te in the scrape-off layer and the pedestal region from the emission of visible lines of the locally injected helium. The link between ne and Te and the emission is provided by a collisional radiative model, which delivers the evolution of the populations of the relevant excited states as the He atoms travel through the plasma. A computationally efficient method with just three effective states is shown to provide a good approximation of the population dynamics. It removes an artificial rise of Te at the plasma edge when using a simple static model. Furthermore, the re-absorption of the vacuum ultra-violet resonance lines has been introduced as additional excitation mechanism being mainly important in the region close to the injection point. This extra excitation leads to a much better fit of the measured line ratios in this region for larger puff rates.

The rise of an exciton in solid ammonia

An exciton gives rise to an absorption peak in vacuum ultra-violet spectroscopy of solid ammonia, with time-resolved evolution of the peak revealing the rate of nucleation and phase change.

Luminescence Quenching Behavior of Hydrothermally Grown YVO4:Eu3+ Nanophosphor Excited under Low Temperature and Vacuum Ultra Violet Discharge

The luminescence quenching behavior and energy transfer process in hydrothermally grown Eu3+-doped YVO4 nanophosphors were studied using low temperature photoluminescence spectroscopy. The luminescence efficiency of nanophosphor is dependent on the acidity of its solution media and the post annealing condition after hydrothermal processing. The overall results suggest that the abnormal luminescence behavior of Eu3+-doped nanocrystalline YVO4 under low temperature photoexcitation is due to the incorporated non-radiative hydroxyl groups often encountered in hydrothermal synthesis as well as to the inefficient energy transfer to luminescent ions from vanadate groups.

Laboratory studies of Vacuum Ultra-Violet (VUV) emission spectra of heavy element ions

Reliable spectroscopic data are needed for interpretation and modeling of observed astrophysical plasmas. For heavy element ions, which have complex spectra, experimental data are rather incomplete. To provide valuable fundamental quantities, such as precise wavelengths, level energies and semi-empirical transition probabilities, we are carrying out laboratory studies of high-resolution VUV emission spectra of moderately charged ions of transition metals and rare earth elements. Experimental and theoretical methods are summarized. Examples of studies are described.