Effect of gas temperature on CO2+ ion transport in CO2

The effect of gas temperature on the transport of the CO2+ ion in its parent gas CO2 is studied. For this purpose, a Monte Carlo (MC) solution technique of the ion transport equation developed in the past by the authors, which was formally proven to provide the exact solution of the transport equation, is used. The study is performed first by benchmarking against experimental data and another MC code, using cross sections from literature and then changing the gas temperature. The solution is characterized through its moments such as reduced mobility, coefficients of its expansion in Legendre polynomials and three-dimensional ion velocity distribution function. It is shown that the gas temperature has a significant effect on all these quantities. This finding has important consequences for plasma modeling which are discussed.</p

Benchmarking of Monte Carlo Flux simulations of electrons in CO2

Electron velocity distribution functions (EVDFs) in CO2 obtained by means of the Monte Carlo Flux (MCF) method are compared with results from two-term and multi-term Boltzmann solvers. The MCF method provides detailed calculations of the EVDF through a highly efficient variance reduction technique. Benchmark calculations of Legendre polynomial coefficients of the EVDF expansion are reported for a wide range of reduced electric fields (E/N), showing excellent agreement with multi-term solutions. Rate coefficients of inelastic processes calculated from two-term Boltzmann solvers differ significantly, up to 70%, from MCF and multi-term solutions, due to the anisotropy of the EVDF. An extension of the method to consider the thermal distribution of the background gas is also presented. This extension, together with an accurate description of the population of rotationally and vibrationally excited states, provides excellent agreement with measured transport coefficients at low E/N. A good agreement is obtained at moderate E/N between experimental values of dissociation rate coefficients and MCF calculations after careful consideration and analysis of several cross sections data sets.</p

Benchmark calculations for electron velocity distribution function obtained with Monte Carlo Flux simulations

Modern, multi-modular plasma modeling requires accurate and versatile methods for the determination of the electron velocity distribution function from which rate coefficients of electron impact processes as well as electron transport quantities are determined. In this paper we propose as a solution a modified version of a strongly overlooked method developed in the early 90\u27s, namely, Monte Carlo Flux (MCF). The improvement lies in a criterion for the otherwise somewhat empirical selection of the time-step used in the method. We show that an MCF based code highlights and overcomes the limitations of two-terms codes such as BOLSIG+ and it is much faster than a conventional Monte Carlo. Moreover, MCF is in excellent agreement with the multi-term method for a wide range of reduced electric fields, being at the same time much simpler to implement and to extend to more general cases than the latter. Explicit illustrations of the Markov matrices representing short-time kinetics are presented to gain insight into the method. The two-dimensional velocity distribution and its expansion into Legendre polynomials are discussed for electrons in argon.</p

Benchmarking of Monte Carlo flux simulations of electrons in CO2

Electron velocity distribution functions (EVDFs) in CO2 obtained by means of the Monte Carlo flux (MCF) method are compared with results from two-term and multi-term Boltzmann solvers. The MCF method provides detailed calculations of the EVDF through a highly efficient variance reduction technique. Benchmark calculations of Legendre polynomial coefficients of the EVDF expansion are reported for a wide range of reduced electric fields (E/N), showing excellent agreement with multi-term solutions. Rate coefficients of inelastic processes calculated from two-term Boltzmann solvers differ significantly, up to 70%, from MCF and multi-term solutions, due to the anisotropy of the EVDF. An extension of the method to consider the thermal distribution of the background gas is also presented. This extension, together with an accurate description of the population of rotationally and vibrationally excited states, provides excellent agreement with measured transport coefficients at low E/N. A good agreement is obtained at moderate E/N between experimental values of dissociation rate coefficients and MCF calculations after careful consideration and analysis of several cross sections data sets

Validation of the Fokker-Planck Approach to Vibrational Kinetics in CO2 Plasma

The Fokker-Planck (FP) approach to describe vibrational kinetics numerically is validated in this work. This approach is shown to be around 1000 times faster than the usual state-to-state (STS) method to calculate a vibrational distribution function (VDF) in stationary conditions. Weakly ionized, nonequilibrium CO2 plasma is the test case for this demonstration, in view of its importance for the production of carbon-neutral fuels. VDFs obtained through the resolution of an FP equation and through the usual STS approach are compared in the same conditions, considering the same kinetic data. The demonstration is shown for chemical networks of increasing generality in vibrational kinetics of polyatomic molecules, including V-V exchanges, V-T relaxation, intermode V-V\u27 reactions, and excitation through e-V collisions. The FP method is shown to be accurate to describe the vibrational kinetics of the CO2 asymmetric stretching mode, while being much faster than the STS approach. In this way, the quantitative validity of the FP approach in vibrational kinetics is assessed, making it a fully viable alternative to STS solvers, that can be used with other processes, molecules, and physical conditions.</p

Review of the ELI-NP-GBS low level rf and synchronization systems

The Gamma Beam System (GBS) of ELI-NP is a linac based gamma-source in construction at Magurele (RO) by the European consortium EuroGammaS led by INFN. Photons with tunable energy and with intensity and brilliance well beyond the state of the art will be produced by Compton back-scattering between a high quality electron beam (up to 740 MeV) and a 515 nm intense laser pulse. Production of very intense photon flux with narrow bandwidth requires multi-bunch operation at 100 Hz repetition rate. A total of 13 klystrons, 3 S-band (2856 MHz) and 10 C-band (5712 MHz) will power a total of 14 Travelling Wave accelerating sections (2 S-band and 12 C-band) plus 3 S-band Standing Wave cavities (a 1.6 cell RF gun and 2 RF deflectors). Each klystron is individually driven by a temperature stabilized LLRF module, for a maximum flexibility in terms of accelerating gradient, arbitrary pulse shaping (e.g. to compensate beam loading effects in multi-bunch regime) and compensation of long-term thermal drifts. In this paper, the whole LLRF system architecture and bench test results, the RF reference generation and distribution together with an overview of the synchronization system will be described