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.

Population Kinetics Modeling of Low-Temperature Argon Plasma

Optical emission spectroscopy has been widely used in low-temperature argon plasma diagnostics. A coronal model is usually used to analyze the measured line ratios for diagnostics with a single temperature and density. However, many plasma processing conditions deviate from single temperature and density, optically thin conditions, or even coronal plasma conditions due to cascades from high-lying states. In this paper, we present a collisional-radiative model to investigate the validity of coronal approximations over a range of plasma conditions of Te = 1–4 eV and Ne = 108–1013 cm−3. The commonly used line ratios are found to change from a coronal limit where they are independent of Ne to a collisional-radiative regime where they are not. The effects of multiple-temperature plasma, radiation trapping, wall neutralization, and quenching on the line ratios are investigated to identify the plasma conditions under which these effects are significant. This study demonstrates the importance of the completeness of atomic datasets in applying a collisional-radiative model to low-temperature plasma diagnostics.

Determination of positive anode sheath in anodic carbon arc for synthesis of nanomaterials

. In the atmospheric pressure anodic carbon arc, ablation of the anode serves as a feedstock of carbon for production of nanomaterials. It is known that the ablation of the graphite anode in this arc can have two distinctive modes with low and high ablation rates. The transition between these modes is governed by the power deposition at the arc attachment to the anode and depends on the gap between the anode and the cathode electrodes. Probe measurements combined with optical emission spectroscopy (OES) are used to analyze the voltage drop between the arc electrodes. These measurements corroborated previous predictions of a positive anode sheath (i.e. electron attracting sheath) in this arc, which appears in both low and high ablation modes. However, the positive anode sheath was determined to be ~3-8 V, significantly larger than ~0.5 V predicted by previous models. Thus, there are apparently other physical mechanisms not considered by these models that force the anode sheath to be electron attracting in both ablation regimes. Another key result is a relatively low electron temperature (~ 0.6 eV) obtained from OES using a collisional radiative model. This result partially explains a higher arc voltage (~ 20 V) required to sustain the arc current of 50-70 A than predicted by existing simulations of this discharge.

Development of a Plasma Chemistry Model for Helicon Plasma Thruster analysis

The present work is part of a wider project aimed at improving the description of the plasma dynamics during the production phase of a Helicon Plasma Thruster. In particular, the work was focused on the development of a chemical model for Argon- and Xenon-based plasma. The developed model consists of a collisional radiative model suitable to describe the dynamics of the 1s and 2p excited levels. The model is meant to be complementary to 3D-VIRTUS, a numerical tool which enforces a fluid description of plasma, developed by the University of Padova to analyse helicon discharges. Once identified, the significant reactions for both propellants, the reaction rate coefficients, have been integrated exploiting cross sections from literature and assuming a Maxwellian velocity distribution function for all the species. These coefficients have been validated against experimental measurements of an Argon Inductively Coupled Plasma and compared with a well-established code. For Argon, the selected reactions have been reduced through a proposed lumping methodology. In this way, it was possible to reduce the number of equations of the system to solve, and implement them into 3D-VIRTUS. A validation against an experimental case taken from literature was performed, showing good agreement of the results. Regarding the Xenon model, only a verification has been performed against the results of another collisional-radiative model in literature. Finally, a predictive analysis of the propulsive performances of a Helicon Plasma Thruster for both Argon and Xenon is presented.

Numerical Validation of the Radiative Model for the Solar Cadaster Developed for Greater Geneva

The achievement of the targets for reducing greenhouse gas emissions set by the Paris Agreements and the Swiss federal law on the reduction of greenhouse gas emissions (CO2 law) requires massive use of renewable energies, which cannot be achieved without their adoption by the general public. The solar cadaster developed as part of the INTERREG G2 Solar project is intended to assess the solar potential of buildings at the scale of Greater Geneva—for both industrial buildings and for individual residential buildings—at a resolution of 1 m. The new version of the solar cadaster is intended to assess the solar potential of roofs, as well as that of vertical facades. The study presented here aims to validate this new version through a comparison with results obtained with two other simulation tools that are widely used and validated by the scientific community. The good accordance with the results obtained with ENVI-met and DIVA-for-Rhino demonstrates the capability of the radiative model developed for the solar cadaster of Greater Geneva to accurately predict the radiation levels of building facades in configurations with randomly distributed buildings (horizontally or vertically).

Assessment of the spectral downward irradiance at the surface of the Mediterranean Sea using the radiative Ocean-Atmosphere Spectral Irradiance Model (OASIM)

A multiplatform assessment of the Ocean–Atmosphere Spectral Irradiance Model (OASIM) radiative model focussed on the Mediterranean Sea for the period 2004–2017 is presented. The BOUée pour l'acquiSition d'une Série Optique à Long termE (BOUSSOLE) mooring and biogeochemical Argo (BGC-Argo) float optical sensor observations are combined with model outputs to analyse the spatial and temporal variabilities in the downward planar irradiance at the ocean–atmosphere interface. The correlations between the data and model are always higher than 0.6. With the exception of downward photosynthetic active radiation and the 670 nm channel, correlation values are always higher than 0.8 and, when removing the inter-daily variability, they are higher than 0.9. At the scale of the BOUSSOLE sampling (15 min temporal resolution), the root mean square difference oscillates at approximately 30 %–40 % of the averaged model output and is reduced to approximately 10 % when the variability between days is filtered out. Both BOUSSOLE and BGC-Argo indicate that bias is up to 20 % for the irradiance at 380 and 412 nm and for wavelengths above 670 nm, whereas it decreases to less than 5 % at the other wavelengths. Analysis of atmospheric input data indicates that the model skill is strongly affected by cloud dynamics. High skills are observed during summer when the cloud cover is low.