Vibrational kinetics, electron dynamics and elementary processes in H₂and D₂plasmas for negative ion production: modelling aspects

Abstract

Old and new problems in the physics of multicusp magnetic sources for the production of negative H -/Dions are presented and discussed. We emphasize particularly, in this kind of plasmas, both the vibrational and electron non equilibrium energy distributions, the role of Rydberg states in enhancing the negative ion production, the production of vibrationally excited states by the Eley-Rideal mechanism, and the enhancement of negative ion concentrations in pulsed discharges. In appendix I recent cross sections calculations for elementary processes and the theoretical determination of hydrogen recombination probability on graphite surface are illustrated. In appendix II two types of sources are modeled: the first one is a classical negative ion source in which the plasma is generated by thermoemitted electrons; in the second one, electrons already present in the mixture are accelerated by an RF field to sufficiently high energy to ionize the gas molecules.

MONTE CARLO CALCULATION OF THE TRANSLATIONAL RELAXATION OF SUPERTHERMAL H ATOMS IN THERMAL H2GAS

“…Examples of reactions that may be reconsidered in this light are the radiative association reactions of H with C + (Barinovs & van Hemert 2006) and H + (Stancil et al 1993), which are of importance for the ISM and for the early universe chemistry, respectively. Superthermal atoms can also affect the cooling function of the gas due to the strong energy dependence of the collisional de-excitation coefficients, i.e., the rate constants of the reactions H+H 2 (v, j ) → H+H 2 (v , j ) (Capitelli et al 2006). The complex thermalization of H atoms will also affect preheating in strong shocks in hydrogen and the cooling function, e.g., for early universe models (Coppola et al 2012).…”

Elementary Processes and Kinetic Modeling for Hydrogen and Helium Plasmas

“…The theoretical investigation on hydrogen and hydrogen/helium plasmas is of great interest for many different technological applications, from fusion [1,2] to astrophysical [3] and aerospace [4] research. These plasmo-chemical systems, though characterized by widely different conditions, share a fundamental feature that governs their behavior and dictates the level of knowledge required in the dynamical information for elementary processes.…”

“…The complete set of rate coefficients for the VT energy transfer and dissociation channels in H 2 -He collisions is presented in Section 3, demonstrating the reliability of the adopted quasi-classical trajectory (QCT) approach and briefly discussing its complementarity with the quantum method [10]. The recombination, through the Eley-Rideal mechanism, of atomic hydrogen on tungsten and graphite surface, relevant to the kinetic simulation of wall effects in negative ion sources and the divertor region of the TOKAMAK fusion reactor [2,11,12], has been investigated in Section 4, shedding light on the role of the chemical nature of the surface in affecting the dynamics. Section 5, though not yet including all of the recently calculated processes discussed in the previous sections, shows the fundamental role of these advanced chemical-physical models in a state-to-state kinetic code, allowing the description of the temporal evolution of the plasma as determined by the collisional and reaction dynamics occurring at a microscopic level.…”

From cold to fusion plasmas: spectroscopy, molecular dynamics and kinetic considerations

“…Non equilibrium vibrational distributions are controlled not only by electron molecule impact collisions i.e. the so called e-V and E-V pumping processes [1,2,3] but also by quenching processes involving atomic species, in particular the process H + H 2 (ν, j) ↔ H + H 2 (ν , j )…”