Takeshi Sakamoto

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.

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.

Evaluation of Electron Energy Distribution Function in Microwave Discharge Plasmas by Spectroscopic Diagnostics with Collisional Radiative Model

The effect of the electron energy distribution function (EEDF) on the population distribution of excited states is investigated in He and Ar plasmas sustained by a 2.45 GHz microwave at a discharge pressure of 1–5 Torr. The EEDF is measured with a Langmuir probe by Druyvesteyns method and used as the input parameter of the collisional-radiative (CR) model calculation. The calculated population density of the excited states is compared with the results of optical emission spectroscopic measurement. Reasonable agreement is found between them. It is also confirmed that the measured EEDFs was depleted at energies above the first excitation potential of the discharge gas atoms. When we assume a Maxwellian EEDF and calculate the population distribution of excited states of the argon plasma, we find a marked discrepancy between the populations of excited states observed experimentally and those calculated by the CR model, while a discrepancy for the helium plasma is also found but is less marked.

Experimental study of effect of rare gas admixture on temperatures of microwave-excited oxygen discharge plasma

We examined the effect of a rare gas admixture with oxygen discharge on the vibrational and rotational temperatures of the OH radical by optical emission spectroscopy (OES). We chose helium, neon, argon, krypton and xenon as admixture components with oxygen. We generated a microwave discharge oxygen plasma in a cylindrical quartz tube (26 mm i.d.) with a discharge pressure of about 1.0 Torr. The microwave frequency was 2.45 GHz and the output power was set at 600 W. To obtain the rotational temperature, we measured the band spectrum of the radiative transition A2Σ+→X2Πi of an OH radical. We compared the experimentally measured and calculated spectra to determine the actual vibrational and rotational temperatures of the generated plasma. When the mixture ratio was larger than about 80%, the vibrational and rotational temperatures markedly changed, with depended on the mixed rare gas species. The difference in temperature change is discussed from several physical viewpoints.

Experimental Study on the Effect of Different Noble Gas Admixtures on the Gas Temperature of Oxygen Plasma

Abstract We measured rotational temperature of oxygen plasma by optical emission spectroscopy (OES) in order to examine approximate value of its gas temperature. We generated microwave discharge oxygen plasma in a cylindrical quartz tube whose inner diameter 26 mm with its discharge pressure 0.5 - 2.0 Torr. We measured the band spectrum of radiative transition A 2Σ+ → X 2∏i , of OH radical to obtain rotational temperature in the present study. In order to obtain the rotational temperature, first we calculate the above OH band spectrum with the change in vibrational quantum number Δv = 0, for given vibrational and rotational temperatures. After that, we compare the experimentally measured spectrum with the calculated one to determine the real rotational and vibrational temperatures of the generated plasma. The rotational temperature observed ranges between 0.08 - 0.18 eV. Consequently, it is found that the rotational temperature in the oxygen plasma gradually decreases as the plasma flows to the downstream region of the discharge tube, and that higher discharge pressure makes the rotational temperature lower. We also examine the effect of admixture of noble gases with the oxygen discharge on its rotational temperature. It becomes remarkably lower when neon or argon is mixed more than 80% in the volumetric ratio. On the other hand, it becomes higher when krypton is mixed. The difference in the temperature change is discussed from several physical viewpoints.

Probe and Optical Emission Spectroscopy Measurement of Slotted Antenna-Excited Nitrogen Discharge Plasma

We generated and diagnosed a large-area planar surface wave nitrogen plasma excited by a slotted antenna applicator, which has four slots with an inclination angle of 75° with respect to the wall centerline. When the 2.45 GHz microwave power applied was larger than 500 W, a stable nitrogen plasma was generated as a large-area surface wave discharge. We carried out the optical emission spectroscopy measurement of the generated plasma and observed the intensity of the second positive system of nitrogen molecules. It was found that the vibrational temperature of the C state of nitrogen molecules is about 0.67–0.86 eV at the discharge pressures of 0.3–1.0 Torr and decreases with discharge pressure. The rotational temperature was found to be 0.13–0.14 eV, which is almost independent of discharge pressure. Probe measurement showed that the electron temperature and density are about 2.0–4.0 eV and in the order of 1011 cm-3, respectively. When the microwave power was as low as 400 W, a transition to a volume wave-excited plasma was observed, in which the electron density is less than the critical density for the 2.45 GHz microwave.

Acceleration Phenomenon Of Helium Arc Jet Through A Magnetic Nozzle

We measured basic plasma parameters of a supersonic helium arc jet accelerated through a magnetic nozzle from a uniform magnetic channel. The arc jet is generated by a normal arc discharge under atmospheric pressure, and ejected into a rarefied gas wind tunnel with a uniform longitudinal magnetic field of 0.16 T. After passing through a uniform magnetic channel, it expands from the end of the magnetic coil, which is a magnetic nozzle. The strength of the magnetic field decreases from 0.16 T to 0.01 T at 20 cm down from the end of the coils. We observed plasma potential drop at upper flow region than that of magnetic field. The longitudinal velocity of the plasma jet was measured by Mach probe. At the maximum gradient of the magnetic field, the potential drop saturated and the peak of ion Mach number 3.1 was observed. After the Mach number maximum, the Mach number decreased and electron temperature increased from 0.1 eV to 0.5 eV. Meanwhile the electron density decreased gradually. When the plasma came jus...

Actinometry Measurement of Oxygen Dissociation Degree in a Microwave Discharge Plasma and Effect of Electron Energy Distribution Function

Abstract We measured the dissociation degree of oxygen molecule in a microwave discharge oxygen plasma by optical emission spectroscopy measurement based on actinometry method. We generated an oxygen plasma in a cylindrical quartz tube (26 mm i.d.) with a discharge pressure 0.5 - 3.0 Torr. The microwave frequency was 2.45 GHz and the output power was set at 600 W. We monitored the oxygen atom density by actinometry using the 844.6 nm line of oxygen atom and the 811.5 nm line of argon. The dissociation degree was estimated at about a few percent. To discuss the validity of the measured dissociation degree, we calculated the population balance equations of the active spices and EEDF (electron energy distribution function) self-consistently. The theoretical calculations were in agreement with the experimental results. We discussed the validity of the dissociation degree of oxygen molecule and some reactions, which play an important role in the microwave discharge oxygen plasma.

Acceleration of the oxygen reaction in CuA-deficient Nitrosomonas europaea cytochrome c oxidase as revealed by the flow-flash measurement

The oxygen reaction of Nitrosomonas europaea cytochrome c oxidase containing either 2Cu or 1Cu per two heme a molecules was investigated by the flow-flash technique at 20 degrees C. The reaction profiles of the bacterial enzyme were essentially the same as those of bovine heart cytochrome c oxidase, although the rate of the primary oxygen compound formation was much slower. The 1Cu enzyme exhibited higher rates for both primary oxygen compound formation and intramolecular electron transfer than the 2Cu enzyme. This result clearly indicates that CuA is not essential functionally for the oxidation of ferrous heme a moieties, and suggests its structural importance in maintaining the molecular integrity of N. europaea cytochrome oxidase.