The dissociation degrees of N2 and O2 are examined in a nitrogen–oxygen mixed microwave discharge plasma in a cylindrical quartz tube of 26 mm inner diameter with a discharge pressure of 0.5–1.0 Torr and a microwave power of 600 W by the actinometry method. We measured the electron temperature and density with a Langmuir double probe, while the vibrational and rotational temperatures of the first and second positive bands of N2 were measured by optical emission spectroscopy. Even when the line intensity of atomic nitrogen was weak and partly coincided with the high-intensity band spectrum of the first positive system due to its small dissociation degree, the actinometry method was found to be feasible when the first positive band spectrum, calculated as a function of the rotational and vibrational temperatures, was subtracted from that observed experimentally. It was found that the dissociation degrees of both N2 and O2 increase with the molar ratio of nitrogen in the mixed N2–O2 discharge gas for the same total discharge pressure. The experimental results are discussed by comparison with a simple numerical model based on chemical kinetics in the plasma. It was found that the dissociation of oxygen molecules is enhanced by the collision with excited nitrogen molecules, particularly those with metastable states, whereas that of nitrogen is suppressed by an admixture of oxygen molecules due to the chemical quenching processes of nitrogen atoms.

The electron temperature T e and density N e of atmospheric-pressure non-equilibrium dielectric barrier discharge argon (Ar) plasma are measured with optical emission spectroscopy. Continuum emission due to bremsstrahlung is applied to the analysis of the electron temperature and density with the spectrometric system in the visible wavelength range calibrated absolutely. The assumption of the Maxwellian electron energy distribution function (EEDF) results in T e ≃ 0.29 eV and N e ≃ 1.1 × 1016 cm−3, whereas the Druyvesteyn EEDF leads to the result T e ≃ 0.79 eV and N e ≃ 1.4 × 1014 cm−3. To confirm the validity of these values, several line intensities of the excited states of the Ar atom are observed experimentally and compared with the theoretical population densities calculated by the Ar collisional–radiative (CR) model that includes atomic collisional processes. It is confirmed that the order of the observed excited-state number densities agrees well with that calculated numerically by the CR model with the Druyvesteyn EEDF, while the Maxwellian EEDF gives poor results.

This article focuses on the speciation of molten fluoride mixtures based on ThF 4 and UF 4 actinides used in molten salt reactors. The local structure of molten AF-MF 4 systems (A=Li + , Na + , K + ; M= Th 4+ , U 4+ ) was studied in situ by combining measurements by high temperature X-ray absorption spectroscopy and molecular dynamics simulations. In the molten state, 20°C higher than the melting temperature, these mixtures are composed of free fluorine and anionic species [MF 7 ] 3-, [MF 8 ] 4and [MF 9 ] 5whose distribution varies with the amount of MF 4 (M= Th 4+ , U 4+ ). Regardless of the cation, these complexes consist of an average of 8 Fneighbors for MF 4 content is less than 35 mol. %. This value decreases to 7 as the size of the alkaline ion A (A=Li + , Na + , K + ) increases. The [MF x ] 4-x species are linked together by bridging fluorine ions to form long chains [M x F Y ] 4x-y . The addition of a few percent UF 4 to the eutectic LiF-ThF 4 composition (77.5 mol% -22.5 mol. %) at 700°C leads to a slight increase in the population of free fluorine ions due to the breakdown of the Th-F links to form complexes [UF x ] 4-x isolated or connected to the (Th x F y ) 4x-y chains. This change in the structure of the liquid results in a slight decrease in viscosity when a few mol. % of UF 4 is added.

We experimentally study plasma parameters including ion acoustic Mach number of expanding cold helium plasma jet with an electron temperature of less than 1 eV flowing along open field lines. It is experimentally found that the ion Mach number increases from 1 to 3, and that the plasma potential decreases by about 1 V. We discuss the experimental results based on a quasi one‐dimensional flow model in which the plasma is assumed to be quasi‐neutral and in a state of thermodynamic equilibrium. Our model describes the ion acceleration, the axial profiles of the potential drop, and the electron temperature/density. The model also shows that the helium ions are accelerated both by the electric field and by the increasing cross‐sectional area of the transonic flow. After the ion acceleration, the ion Mach number decreases and the electron temperature increases. These phenomena are discussed in terms of a shock wave. It is noted that the electron density decreases even in the shock wave. This is discussed in terms of rapid recombination because of the low electron temperature. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

This work is focused on diagnostics of electron temperature (1.0 eV–3.8 eV) and electron density (1.0 × 109 cm−3–5.0 × 1012 cm−3) of low-pressure (133 Pa) discharge argon plasma by optical emission spectroscopic (OES) measurement. The diagnostic method using multi-emission lines was analyzed. First, the excitation-kinetic models were obtained by extracting dominant kinetic processes based on the collisional-radiative model. Then, the diagnostic equations for wide range of electron temperature and density were proposed to describe the approximate excitation kinetic balance of several excited levels. 15 optical emission lines (wavelength range: 340.7 nm–912.3 nm) were selected for OES measurement. RMS of the theoretical relative error was found to be 5.96% for electron temperature, while 32.6% for electron density. The diagnostics of 2.45 GHz microwave plasma was demonstrated by the proposed method and by the probe method. The electron density results by the proposed method were in good agreement with the probe method.

The arbitrary electron energy distribution function (EEDF) of a cold atmospheric-pressure plasma is determined from optical emission spectroscopy measurement. Using the electron-neutral bremsstrahlung-dominated continuum spectrum and relevant cross section data, a partial arbitrary EEDF can be reconstructed through the reinforcement learning-based visible bremsstrahlung inversion (VBI) method. From an atmospheric-pressure argon dielectric barrier discharge plasma emission spectrum (440-900 nm), a partial arbitrary EEDF can be determined with a resolution of 0.2 eV. Resemblance between the obtained arbitrary EEPF and a two-temperature Maxwellian was found with T_e = 0.26 and 2.2 eV. The EEDF range is mostly constrained by the spectrum wavelength range.

We study supersonic flow of rarefied weakly ionized plasma at diverging magnetic field. While the flows of ions and neutral are treated by particle-based direct simulation Monte Carlo method, the electron is treated as a fluid, i.e., we carried out hybrid simulation. We calculate number density, velocity, temperature, and electric potential of charged particles and neutrals when the arc plasma flows out of the uniform magnetic field into lower pressure region in a steady state. We find the velocity increase just after passing the open magnetic field line, followed by deceleration due to collisions with residual molecules. We also find the temperature increase during the deceleration. In this acceleration/deceleration phenomena, the velocity difference between the neutrals and charged species are found, which also changes the electric potential. We discuss the mechanisms of potential formation along the plasma flow mainly by the pressure difference and the friction force between the charged particles and neutral species. The numerical results are, at least qualitatively, consistent with our previous experimental results.Index Terms-Diverging magnetic field, hybrid simulation, ion slip, potential drop, rarefied flow, supersonic plasma flow, weakly ionized plasma.

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