Masanori Fujiwara

Spectroscopy of reactive species produced by low-energy atmospheric-pressure plasma on conductive target material surface

A method for blood coagulation using low-energy atmospheric-pressure plasma (LEAPP) is confirmed as an alternative procedure to reduce tissue damage caused by heat. Blood coagulation using LEAPP behaves differently depending on working gas species; helium is more effective than argon in promoting fast coagulation. To analyse the difference in reactive species produced by helium and argon plasma, spectroscopic measurements were conducted without and with a target material. To compare emissions, blood coagulation experiments using LEAPP for both plasmas were performed under almost identical conditions. Although many kinds of reactive species such as hydroxyl radicals and excited nitrogen molecules were observed with similar intensity in both plasmas, intensities of nitrogen ion molecules and nitric oxide molecules were extremely strong in the helium plasma. It is considered that nitrogen ion molecules were mainly produced by penning ionization by helium metastable. Near the target, a significant increase in the emissions of reactive species is observed. There is a possibility that electron acceleration was induced in a local electric field formed on the surface. However, in argon plasma, emissions from nitrogen ion were not measured even near the target surface. These differences between the two plasmas may be producing the difference in blood coagulation behaviour. To control the surrounding gas of the plasma, a gas-component-controllable chamber was assembled. Filling the chamber with O2/He or N2/He gas mixtures selectively produces either reactive oxygen species or reactive nitrogen species. Through selective treatments, this chamber would be useful in studying the effects of specific reactive species on blood coagulation.

Investigation on luminescence and NOx removal by pulse corona discharges

Abstract In a streamer dominated pulse corona the energetic electrons can interact with the gas molecules and produce radicals. Emission of second positive band (SPB) of the nitrogen, which was considered to correspond to local yield of N radical, was monitored in this study for analyzing N radical effect on removal of nitrogen oxides (NO x ) from exhaust gases. It was found that the length of high luminous region (HLR) is related to energy efficiency of NO x removal. It was also testified that total emission intensity of SPB is linearly proportional with NO x removal in NO/N 2 mixture gas. Analysis of experimental data shows that the NO x removal energy efficiency is smaller when pulse width is longer. The energy efficiency also decreases with the increase of injected power and length of HLR, respectively. It was assumed that the local concentrated production of N radical in HLR is not effectively used for NO removal in the condition of low initial NO x concentration. It is concluded that the luminescence analysis provides a good method to understand NO x removal process in pulse discharge corona.

Observations of multiple stationary striation phenomena in an atmospheric pressure neon plasma jet

The formation of multiple stationary striations between a nozzle exit and a conductive target plate was clearly observed at regular intervals using a digital camera along an atmospheric pressure plasma jet of dielectric barrier discharge using a neon gas into ambient air. From the results of measuring using a high-speed camera during the positive current phase, the emission initially started in the middle between the nozzle and the target, and striations progressed in both upward and downward directions. During the negative current phase, the emission initially started in a region near the target, and the striations rapidly progressed to the nozzle.

Production and Removal Mechanisms of Discharge NOx Treatment in N2/O2 Gas Mixture

We investigated removal reactions of NOx in flue gas using streamer discharge, both experimentally and analytically. We clarified the reaction mechanism that can satisfy the experimental results in the N2/O2/NOx gas mixture. In a gas mixture including N2, NO, and 5% O2, the NOx removal amount decreases markedly, and NOx molecules are produced with a low initial NO concentration. Based on simulation focused on the streamer head, we evaluated dominant factors in the NOx removal reactions. The primary factor affecting the marked decrease in NOx removal is the effect of excited N radicals which react rapidly with O2 to produce NO. Another factor that causes the NOx production is the reaction of N+NO2, in which NO2 molecules are produced by O3. Based on the reaction mechanism, we estimated the reduced electric field E/n and the N radical production that fit the experimental results.

Bending and turbulent enhancement phenomena of neutral gas flow containing an atmospheric pressure plasma by applying external electric fields measured by schlieren optical method

To understand the mechanism of turbulent enhancement phenomena of a neutral gas flow containing plasma ejected from the nozzle of plasma equipment, the schlieren optical method was performed to visualize the neutral gas behavior. It was confirmed that the turbulent starting point became closer to the nozzle exit, as the amplitude of discharge voltage (electric field) increased. To study the effect of electric field on turbulent enhancement, two sets of external electrodes were arranged in parallel, and the gas from the nozzle was allowed to flow between the upper and lower electrodes. It was found that the neutral gas flow was bent, and the bending angle increased as the amplitude of the external electric field increased. The results obtained using a simple model analysis roughly coincide with experimental data. These results indicate that momentum transport from drifted ions induced by the electric field to neutral particles is an important factor that enhances turbulence.

Short-Pulse Discharge for Simultaneous Pursuit of Energy and Volume-Efficient NOx Removal

Concerning NOx removal (deNOx) by pulsed corona discharge, the methods of decreasing pulse width and peak voltage are effective in improving the energy efficiency. Since the latter has no technical barrier, the former should be more effective for practical application. In this study, an experimental comparison between the effects of these methods is presented. As a result, decreasing pulse width has an equal or greater effect than decreasing peak voltage on energy cost of deNOx. Therefore, it is possible to improve energy efficiency by decreasing pulse width while maintaining the processing amount per reactor volume by increasing peak voltage.