Hirotomo Itagaki

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.

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.

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.

A low-power nitriding technique utilizing a microwave-excited radical flow

We report a novel low-power nitriding technique by utilizing a 2.45 GHz microwave-excited nitrogen radical flow system. Nitrogen plasma was produced at the nozzle with dimensions of 50 × 0.5 mm2 and blown onto the surface of a target substrate. A titanium substrate has been used as a target plate since it is easy to visualize a nitriding effect. The titanium substrate was treated under the conditions of 60 W microwave power, 20 Torr of nitrogen gas pressure, and a plate temperature of ~800 °C. As a result, we have succeeded in nitriding of the titanium substrate in a quasi-atmospheric region of 20 Torr and of a very low power of 60 W with the hardness kept high, which is almost the same as the hardness processed by conventional nitriding methods.