Laser Thomson scattering (LTS) method has been applied to measure two dimensional distributions of electron density (n e ) and electron temperature (T e ) of a pulsed discharge in Ne gas at a pressure of 400 Torr. Such a discharge was produced with good reproducibility by using a set of electrodes composed of a needle and a hemisphere with a spacing gap of 0.5 mm. The values of n e and T e at t = 25 ns after the start of the discharge and at the center of the discharge were evaluated to be 4.6 × 10 22 m −3 and 1.0 eV, respectively. Based on the observed signal intensity and noise components, signal-to-noise ratios were examined and the way to apply present diagnostic system to the discharge plasma with an electron density as low as 10 18 m −3 was discussed.
A non-thermal plasma-water system using a microsecond pulsed high-voltage power supply was investigated with air, nitrogen, oxygen, and argon gas feedings individually. Optical emission spectroscopy (OES) was utilized to characterize the primary active species inside the plasmas generated by different gas feedings. The OES method was also employed to estimate the neutral gas and electron temperatures. The pH and the oxidation-reduction potential (ORP) of plasma-activated water (PAW) were measured in the liquid phase. An ion chromatography system (ICS) was employed to present the PAW activity, such as nitrite and nitrate species. Moreover, hydrogen peroxide as a secondary active species inside the activated water, generated by the gases mentioned above, was measured by potassium permanganate titration. It was found that the gas species have a noticeable effect on the pH level as well as the ORP of PAW. In the cases of argon and oxygen plasmas, the pH level of PAW does not change significantly. In contrast, the pH values of PAW generated by air and nitrogen plasmas decline sharply during the treatment time. Moreover, the gas species have a significant impact on the concentrations of nitrite, nitrate, and hydrogen peroxide generated in PAW. The activated water generated by oxygen plasma provides the highest level of hydrogen peroxide. Although the consumed power of argon plasmas was half of the other plasma sources, it provides relatively high hydrogen peroxide contents compared to the nitrogen and air plasmas.
Laser Thomson scattering was applied to an atmospheric-pressure plasma produced in a helium (He) gas flow for measuring the spatial profiles of electron density (n
e) and electron temperature (T
e). Aside from the He core flow, the shielding gas flow of N2 or synthesized air (
) surrounding the He flow was introduced to evaluate the effect of ambient gas components on the plasma parameters, eliminating the effect of ambient humidity. The n
e at the discharge center was 2.7 × 1021 m−3 for plasma generated with N2/O2 shielding gas, 50% higher than that generated with N2 shielding.
Proton radiography is a key diagnostics to measure and image the electric/magnetic field in laser-produced plasmas. A thin solid target is irradiated with an intense laser pulse to produce a proton beam. The accelerated proton can achieve higher energy with thinner target. In order to produce an extremely thin target, we have developed a large-area suspended graphene as a laser target for energetic ion sources. We describe the manufacturing process of the suspended graphene, and show the results of quality evaluations.
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