Kohki Satoh

A complete and consistent set of electron collision cross sections of molecular oxygen (O₂) is constructed. The present cross section set consists of the following cross sections: one elastic momentum transfer cross section, 15 rotational excitation cross sections, 15 rotational de-excitation cross sections, one dissociative electron attachment cross section, one three-body attachment cross section, four vibrational excitation cross sections, 11 electronic excitation cross sections, two neutral dissociation cross sections, one cross section for ion-pair formation, and six ionization cross sections. Electron transport coefficients in O₂ and O₂-Ar mixtures are calculated from the present cross section set and previously reported cross section sets, some of which are available on LXCat. The calculations are performed using the Monte Carlo method. The consistency of the cross section sets is assessed by comparing the calculated electron transport and reaction rate coefficients with measured data over a wide range of reduced electric fields. The branching ratio for the quenching of O(¹D) by O₂ and that for the Herzberg states of O₂ to neutral dissociation are examined by comparing the calculated and measured excitation coefficients of O₂(b ¹Σ_g ⁺). In addition, the effect of considering anisotropic electron scattering on the calculated electron transport coefficients is evaluated. The present cross section set of O₂ will be available in MuroranIT database on LXCat.

In this study, we develop a novel method for determining electron transport coefficients from electron swarm maps measured by a scanning drift-tube experiment. In our method, two types of electron continuity equations that describe either the spatial or the temporal evolution of an electron swarm are discovered in the electron swarm map. The electron transport coefficients can be determined from the coefficients in the discovered equations. Therefore, we can determine the Townsend ionization coefficient, ionization rate coefficient, center-of-mass drift velocity, mean arrival-time drift velocity, longitudinal diffusion coefficient, and longitudinal third-order transport coefficient. These transport coefficients in argon are determined over a wide range of reduced electric fields, E/N, from 29.7 to 1351.6 Td (1 Td = 10⁻²¹ Vm²) using our method. We establish that the consideration of high-order transport coefficients, which have been systematically ignored so far, is important for the proper determination of low-order transport coefficients, specifically the electron drift velocity and longitudinal diffusion coefficient, in the presence of ionization growth.

Positive pulsed discharge plasma is generated above a test liquid containing NaCl in Ar atmosphere, and H ⁺ distribution and a temperature variation in the liquid are, respectively, visualized by colorimetric methods using methyl red (MR) and microencapsulated thermotropic liquid crystals (MTLCs). The discharges generated above the liquid containing MR and MTLCs have almost the same characteristics in the waveforms of discharge voltage and current, and the appearance of discharges. The generation of H ⁺ and the temperature increase in the liquid are induced below the discharge area, and H ⁺ distribution and temperature-increased area expand similarly, by the plasma exposure. The spatiotemporal measurement of temperature distribution in the liquid is also observed with MTLCs using a sheet laser. It is found that temperature increase is measured just below the extremity of the discharge and distributes in a torus form and that no temperature increase occurs below the middle of the discharge area. Since good similarity is observed between the H ⁺ distribution and the temperature increase in the test liquid, H ⁺ distribution probably expands in a concentric configuration from the generation area with the plasma exposure time.

Positive and negative pulsed discharge plasma is generated above test liquid containing NaCl in Ar atmosphere, and the spatiotemporal variation of pH value in the liquid is visualized by a colorimetric method using bromothymol blue. Furthermore, polarity effects on H₂O₂ generation are examined by electrochemical calculation and a colorimetric method using titanium sulfate. When the positive pulsed discharge plasma is generated, the pH value of the liquid is decreased by H⁺ generation through the dissociation of H₂O⁺, formed by the charge exchange reaction between Ar⁺ and H₂O, while the pH value of the vicinity of an earthed electrode is increased by OH⁻ generation through the electrolysis of water. When the negative pulsed discharge plasma is generated, the pH value of the liquid is increased by OH⁻ generation and H⁺ reduction, respectively, through the reaction of hydrated electrons with H₂O and H⁺, while the pH value in the vicinity of the earthed electrode is decreased by H⁺ generation through the electrolysis of water. The generation of H₂O₂ is found to be promoted when the positive pulsed discharge plasma is generated, and this increase rate of H₂O₂ is in approximate agreement with the calculated generation rate of H₂O₂, which is produced from OH generated by electrolysis.

The relation between the longitudinal third-order transport coefficient ω ₃ contained in the continuity equation for electrons and α parameters defined by arrival-time spectra of an electron swarm is deduced. Values of ω ₃ and the α parameters in CH ₄ gas and SF ₆ gas are calculated by Monte Carlo simulation, and then the values of ω ₃ are compared with those of the longitudinal third-order transport coefficient ω ′ ₃ which are calculated from the α parameters to examine the validity of the deduced relation. The values of ω ′ ₃ are found to excellently agree with those of ω ₃ below 500 Td in CH ₄ gas and from 150 Td to 700 Td in SF ₆ gas, where the values of the effective ionisation coefficient are nought or quite small. The results suggest that values of ω ₃ can be obtained experimentally from arrival-time spectra measured by a double-shutter drift tube.

SUMMARY: An artificial underground coal gasification (UCG) gas is generated by heating crushed coal, the artificial UCG gas is reformed by a packed‐bed dielectric barrier discharge (PB‐DBD), and then the reforming characteristics of the UCG gas are investigated. H₂S, H₂, CH₄, CO, CO₂, N₂, and O₂, which have been known as typical UCG gas components, are found to be contained in the gas, and alkanes (C_nH_2n+2), alkenes (C_nH_2n), and so on are also detected. When the UCG gas containing H₂S of 400 ppm is reformed at an input power of 40W and a flow rate of 0.1 L/min, it is found that the decomposition rate and the decomposition efficiency of H₂S are approximately 80% and 1.94 mmol/kWh, respectively, and that the production amount of H₂ increases by approximately 14−40% and the production efficiency of H₂ is 81.4 mmol/kWh. It is also found that the concentration of alkenes decreases obviously, while the concentration of alkanes is not affected significantly by discharge plasma reforming. This indicates that H₂ may be produced from alkenes contained in the UCG gas by discharge plasma reforming. This leads that desulfurization and H₂ production can be done simultaneously in a single reactor.

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Reliable and detailed sets of electron collision cross sections for tetramethylsilane [TMS, Si(CH ₃ ) ₄ ] and tetraethoxysilane [TEOS, Si(OC ₂ H ₅ ) ₄ ] vapours are proposed. The cross section sets of TMS and TEOS vapours include 16 and 20 kinds of partial ionization cross sections, respectively. Electron transport coefficients, such as electron drift velocity, ionization coefficient, and longitudinal diffusion coefficient, in those vapours are calculated by Monte Carlo simulations using the proposed cross section sets, and the validity of the sets is confirmed by comparing the calculated values of those transport coefficients with measured data. Furthermore, the calculated values of the ionization coefficient in TEOS/O ₂ mixtures are compared with measured data to confirm the validity of the proposed cross section set.

Beyond on remarkable progresses in a technology of high-voltage pulse, it is considered to apply the high-voltage pulsed electric field to an inactivation of a microorganism. In particular, the method of the high-voltage pulse has advantage in the inactivation of bacteria in foods, since conventional methods such as heat disinfectant, X-ray or gamma-ray are expected to induce negative secondary effects, changes of flavor, taste, texture of the foods, and so on. In the treatment of the microorganism by the high-voltage pulse, the microorganism is destroyed by pure mechanical stress force created by externally applied electric field, and therefore there are no negative secondary effects. However, it should be carefully evaluated how much strong stress force can be produced by reasonable voltage and pulse duration of the high-voltage pulse for the inactivation of the microorganism. Then, evaluation of the stress force for cases of complete sphere and axis-symmetric shapes of the microorganism were presented by using an analytical formula or 2-D FEM. In this paper, an electrostatic field analysis by using 3-D BEM with a thin layer approximation for a membrane of the microorganism is presented to aim to evaluate the stress force for arbitrary shape microorganism.