Hiroshi Akatsuka

Spectroscopic measurement of electron temperature and density in argon plasmas based on collisional-radiative model

The present paper describes a spectroscopic method for determining the electron temperature Te and density Ne in argon plasmas on the basis of a collisional-radiative model of argon. We measured Te and Ne in a positive column of an argon dc discharge by the method developed, and compared them with those obtained by a Langmuir probe. The results for Te obtained by the spectroscopic method agreed roughly with those by the probe. However, a limitation of our method for obtaining Ne was found.

Spectroscopic study on the vibrational populations of N2 CΠ3 and BΠ3 states in a microwave nitrogen discharge

We measured the band spectra (first and second positive systems) of the nitrogen molecule to examine the vibrational and rotational temperatures of the CΠ3 and BΠ3 states by optical emission spectroscopy. We compared the experimentally measured and the calculated spectra to determine those temperatures of the generated plasma. We generated a microwave discharge nitrogen plasma in a cylindrical quartz tube (26mm inside diameter) with a discharge pressure of 0.5–1.0Torr. The microwave frequency was 2.45GHz and the output power was set at 600W. It was found that Tv≈0.5–0.7eV and Tr≈0.07–0.15eV at BΠ3 (v=7, 8, and 9), whereas Tv≈0.65–0.9eV and Tr≈0.06–0.16eV at CΠ3 (v=0 and 1). Both rotational temperatures obtained from first and second positive systems were in good agreement. We also compared the measured vibrational populations with theoretical calculations, in which vibrational distribution function at N2 X and electron energy distribution function are calculated self-consistently.

Spectroscopic Study on Vibrational Nonequilibrium of a Microwave Discharge Nitrogen Plasma

We generate a microwave discharge nitrogen plasma using a rectangular waveguide and a quartz tube (30 mm i.d.) inserted along the vector of the electric field, with an adjustable short-circuited plunger. The typical discharge conditions used are as follows: microwave frequency 2.45 GHz, input power 550 W, nitrogen (99.5%) gas flow rate 0.01–1.6 l/min, and discharge pressure p=0.5–10 Torr. Electron temperature Te, and density ne are measured using a double probe. Vibrational temperature Tv is obtained from the population density of the vibrational exited states of N2 C 3Πu by spectroscopic examination. Rotational temperature Tr is obtained from a comparison of the rovibronic spectra observed experimentally with the calculated ones. It is found that Te0.5–2 eV, Tv0.45–1 eV, and Tr0.06–0.1 eV under the present pressure conditions, whereas ne1011–1012 cm-3 at a low discharge pressure, and ne108–109 cm-3 at a high discharge pressure. We discuss the measured vibrational populations by theoretical calculations in which the variation in their number density is expressed in terms of molecular processes in the nitrogen plasma.

Scientific feasibility of incineration in scnes

Abstract We confirm the simultaneous realization of burning or transmutation of radioactive nuclides and of net energy generation. An investigation of the neutron balance in a reactor core is carried out. It is numerically shown that the neutrons can burn all the transuranium elements (TRUs) produced in the core as fuel in the SCNES reactor. It is numerically found that the fission products (FPs) whose half-lives are longer than one year can be contained and transmuted into harmless nuclides in the core without losing the neutron balance. It is shown that isotope separation of the FPs is required to realize the SCNES. As an example, we investigate the required energy for a scheme of the atomic vapor laser isotope separation (AVLIS) of FPs. It is shown that, in principle, the energy required for the isotope separation is much lower than the generated fission energy. The SCNES is scientifically realized in principle.

Experimental Study of Temperatures of Atmospheric-Pressure Nonequilibrium Ar/N2 Plasma Jets and Poly(ethylene terephtalate)-Surface Processing

To understand the mechanism of surface processing using atmospheric-pressure nonequilibrium plasma jets, we measured the vibrational and rotational temperatures in the plasmas by optical emission spectroscopy. Plasma was excited using a high-frequency pulsed power supply, using a gas mixture of Ar (20 L/min) and N2 (0.1 to 0.5 L/min) as the plasma gas, and changing the flow rate of N2 gas at an input power of 100 W and plasma frequencies of 5 and 10 kHz. The measured vibrational and rotational temperatures in plasma were approximately 0.18 to 0.26 eV and 0.21 to 0.28 eV, respectively. We also carried out a plasma surface processing of polyethylene terephtalate film to measure the changes in water contact angle before and after the processing. We found a monotonic decrease in the contact angle of the processed poly(ethylene terephtalate) (PET) film as plasma rotational temperature increased. It is concluded that the hydrophilicity of the PET surface increases with plasma rotational temperature.

Gas temperature and surface heating in plasma enhanced chemical-vapour-deposition

The gas temperature in plasma enhanced chemical-vapour-deposition is a key parameter to determine the properties of deposited films because it influences gas-phase reactions of radicals and surface reactions of precursors. In this paper, we report the measurement results of the gas temperature determined from optical emission spectroscopy of molecular spectra and discuss heating of the growing surface of the film. It is found that the gas temperature linearly increases with the plasma density and the surrounding wall temperature. The surface heating is dominated by collisions with high-temperature gas molecules in a plasma generated at a high gas pressure condition. The measurements are performed in a hydrogen diluted silane plasma generated by very-high-frequency discharge under a high-rate growth condition of hydrogenated micro-crystalline silicon for photovoltaic applications.

Carbon and Oxygen Isotope Separation by Plasma Chemical Reactions in Carbon Monoxide Glow Discharge

The separation of carbon and oxygen isotopes in CO glow discharge has been studied. The isotope enrichment in the products was measured by quadru-pole mass spectrometer. The reaction yield and empirical formula of solid phase products were determined by the gas-volumetric analysis. The stable products obtained in our experiment are CO2 and solid polymers formed on the discharge wall. The polymer consists of both carbon and oxygen and the oxygen/carbon mole ratio in the polymer is 0.35±0.05. The isotope enrichment coefficients show a strong negative dependence on discharge current though the relative reaction yields have an opposite tendency. Consequently, the maximum isotope enrichment coefficients for 13C in wall deposit of 2.31 and for 18O in CO2 of 1.37 are obtained when the discharge current and the reaction yields are minimum in our experimental range. The experimental results of isotope enrichment have been compared with theoretical values estimated by an analytical model of literature. The dilution mechanism of the isotope enrichment of stable products is inferred from the isotopic distributions of 13C and 18O in products and theoretical predictions for isotope enrichment.

Spectroscopic study on vibrational distribution of N2 C3π and B3π states in microwave nitrogen discharge

We examined the vibrational and rotational temperatures of the C3Π and B3Π states of N2 by optical emission spectroscopy. We measured the band spectra (first and second positive systems) of N2 compared the experimentally measured and the calculated spectra to determine the actual vibrational and rotational temperatures of the generated plasma. We generated a microwave discharge nitrogen plasma in a cylindrical quartz tube (26 mm i.d.) with a discharge pressure of 0.5–1.0 Torr. The microwave frequency was 2.45 GHz and the output power was set at 600 W. It was found that Tv≈0.5–0.7 eV and Tr≈0.07–0.15 eV at B3Π (v=7, 8 and 9), whereas Tv≈0.65–0.9 eV and Tr≈0.06–0.16 eV at C3Π (v=0 and 1). We also discussed the measured vibrational populations using theoretical calculations, in which the variation in the number density was expressed in terms of molecular processes.

Arc‐heated magnetically trapped expanding plasma jet generator

For the purpose of new applications of thermal and recombining plasma, an apparatus is developed which continuously produces ‘‘arc‐heated and magnetically trapped expanding plasma jet.’’ In this apparatus, arc‐heated thermal helium plasma of atmospheric pressure is spouted from a nozzle of 1.2 mm inner diameter into a rarefied gas wind tunnel of about 3–20 Pa with a parallel magnetic field of 0.025–0.16 T. Investigations about the plasma are carried out and stationary inverted populations are observed downstream along this plasma jet. The magnetic field establishes stable arc discharge. Electron temperature Te, ion temperature Ti, and electron density ne of the plasma are about 0.1–1, 0.1–0.8 eV, and 1×1012–2×1013 cm−3, respectively. Two examples of applications of this apparatus are discussed. One is a potential active laser medium, and the other is a cluster preparer.

Actinometry Measurement of Dissociation Degrees of Nitrogen and Oxygen in N2–O2 Microwave Discharge Plasma

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.