Evaluation of emission contributions from charge-exchange between the excited states of deuterium with He+ during diagnostic of thermal helium gas beam injection and laser-induced fluorescence

Abstract

Emission contributions from charge-exchange of excited deuterium (n = 2, 3) with He + are evaluated in a 1-D kinetic collisional radiative model (CRM) in order to analyze their effects on the Thermal Helium Beam (THB) line-ratio diagnostic on ASDEX Upgrade (AUG), and Laser Induced Fluorescence (LIF) He I density measurements in ITER. Recent charge-exchange calculations show that cross-sections from excited deuterium (n = 2, 3) with He + are over 4-orders of magnitude higher than those from the ground state (n = 1), and occur at very low energies where they are more likely to interact with the thermal He + ions introduced by ionization of the diagnostic helium gas-puff injection. Higher densities of excited deuterium are typically present in the Scrape-Off Layer (SOL), Divertor, and Edge regions of Tokamaks, where the LIF and THB helium diagnostic are typically used for n HeI and simultaneous determination of electron temperatures and densities, and where contributions from charge-exchange emission may offset these values if not taken into account. The analysis presented in this work shows that due to the higher density of deuterium in the ground rather than in excited states, and the divergent behavior of deuterium and He + density profiles along the SOL and Edge regions, the deuterium-He + charge-exchange contributions to the helium puff emission are 3-orders of magnitude lower than those from electron-impact excitation. Similar plasma conditions are expected in the ITER divertor, with the exception that in the area near the strike-points and targets the electron temperature is not high enough to excite from the ground state but, deuterium, electron, and He + densities are high enough to dominate the emission from charge-exchange and recombination. These findings strengthen the assumption made in the present line-ratio model that helium emission from gas-puff into plasma is mainly dominated byelectron-excitation. It is also shown that in general, charge-exchange helium emission is 2-orders of magnitude higher than emission due to recombination. These findings suggest the importance of including charge-exchange processes as a source of neutrals in ionic fractional abundance calculations in plasmas, and helium-ash transport modeling in fusion reactors.

Charge-Transfer-Induced Predissociation in Rydberg States of Molecular Cations: MgAr+

“…At the same time, Rydberg states of molecular cations are known to play an important role as transient resonances in ion-neutral collisions 1 − 4 and in plasmas. 5 − 9 Now that photoionization studies of molecular cations are becoming feasible at synchrotron and free-electron-laser facilities, the prospects of systematic studies of Rydberg states of molecular cations are excellent. 10 − 12 Rydberg electrons are primarily located outside the ionic core, so that, in first approximation, Rydberg states have potential-energy functions that closely resemble those of the ion-core electronic states to which the Rydberg series converge.…”

“…High-resolution spectroscopic data on the electronically excited states of molecular cations are scarce, particularly on their Rydberg states. At the same time, Rydberg states of molecular cations are known to play an important role as transient resonances in ion-neutral collisions − and in plasmas. − Now that photoionization studies of molecular cations are becoming feasible at synchrotron and free-electron-laser facilities, the prospects of systematic studies of Rydberg states of molecular cations are excellent. − Rydberg electrons are primarily located outside the ionic core, so that, in first approximation, Rydberg states have potential-energy functions that closely resemble those of the ion-core electronic states to which the Rydberg series converge. − In the case of molecular cations M + = F 1 F 2 + , the ionic core (M 2+ ) is doubly charged and prone to dissociation into two charged atomic or molecular fragments F 1 + + F 2 + on a repulsive Coulomb potential (see Figure a). This situation does not favor the observation of discrete structures associated with Rydberg states (principal quantum number n ) in the spectra of molecular cations, except those associated with shallow potential wells at long-range resulting from charge–induced-dipole interactions between F i + and F j ( n ) ( i , j = 1, 2).…”

Kinetics of dense plasma in the field of short laser pulses: A generalized approach

“…Let us use the formulas obtained above to describe the influence of the optical depth of the plasma and the pulse parameters on the time dependence of the excitation probability given by ( 25) and ( 26). As indicated by (12), this probability is equal to the population of the upper level in the framework of perturbation theory and for a long relaxation time T 1 .…”

Near- and far scrape-off layer transport studies in detached, small-ELM ASDEX Upgrade discharges by means of EMC3-EIRENE

“…Furthermore, the data is strongly perturbed by the neutral gas recycled at the limiter as well as due to the seeded nitrogen, so that the data is not shown here. The recently installed He-beam diagnostics [35,36] measuring n e and T e simultaneously, however, covers the near-SOL up to the separatrix. Since it relies on a line-ratio-instead of an attenuation measurement it is less affected by the neutral gas.…”