Yoshihiko Uesugi

Evaluation of extra- and intracellular OH radical generation, cancer cell injury, and apoptosis induced by a non-thermal atmospheric-pressure plasma jet

In this study, we investigated the effects of a non-thermal atmospheric-pressure plasma jet inducing extracellular and intracellular OH radical generation as well as cell injury and apoptosis for the cultured human breast cancer cells. Increased OH radical generation in the extracellular culture medium (liquid phase) was observed with increased irradiation time, distance to the liquid surface, and voltage. From the voltage‐response relationships for two breast cancer cell lines (invasive MDA-MB-231 cells and non-invasive MCF-7 cells) and normal breast cells (HMEC), the half-maximal effective peak-to-peak voltage (EV50) values were 16.7 ± 0.3kV, 15.0 ± 0.4kV and 11.2 ± 0.7kV for MDA-MB-231, MCF-7 and HMEC cells, respectively. This indicated that there was almost no selective cancer cell injury induced by plasma jet irradiation under these conditions. Compared with control condition without a plasma jet, intracellular OH radical accumulation and apoptotic cells were observed with a plasma jet using conditions that induced injury to 50% of cells irrespective of the cancer cell line. (Some figures may appear in colour only in the online journal)

Hydrodynamic chemical non-equilibrium model of a pulsed arc discharge in dry air at atmospheric pressure

We developed a time-dependent hydrodynamic chemical non-equilibrium model to simulate the transient behaviour of a pulsed arc discharge in dry air at atmospheric pressure. This model simultaneously solves the momentum and energy conservation equations and the mass conservation equation of each species, combining Ohms and Amperes laws and the state equation. Seventy-six elementary reactions in dry-air plasmas were considered in this study. These calculations introduced the influence of chemical non-equilibrium composition on thermodynamic and transport properties of dry-air plasmas. Time evolutions in the radial distributions of the number density, the temperature and the pressure in the discharge were derived. Calculation results indicated good agreement with experimental ones in terms of the number density distribution, the expanding velocity of the shock-wave front and the pressure evolution.

Modeling of dust-particle behavior for different materials in plasmas

The behavior of dust particles made of different fusion-related materials (Li, Be, B, C, Fe, Mo, or W) in tokamak plasmas is simulated using the dust transport code DUSTT [A. Pigarov et al., Phys. Plasmas 12, 122508 (2005)]. The dependencies of the characteristic lifetime of dust particles on plasma parameters are compared for the different dust materials. The dynamics of dust particles in the tokamak edge plasma is studied and the effects of dust material on the acceleration, heating, and evaporation/sublimation of particles are analyzed.

Nanoparticle synthesis using high-powered pulse-modulated induction thermal plasma

Nanoparticle synthesis was performed using the high-powered pulse-modulated induction thermal plasma (PMITP) technique to study the effect of coil current modulation on synthesized nanoparticles. This is the first paper to present a summary of results of TiO2 nanoparticle synthesis using high-power Ar–O2 PMITP at 20 kW. The synthesized particles were analysed using field emission scanning electron microscopy and x-ray diffractometry. In addition, optical emission spectroscopy was used during nanoparticle synthesis experiments to measure TiO spectra and to determine the time-averaged vibrational and rotational temperatures of TiO in the reaction chamber. The results showed that the PMITP produced smaller nanoparticles and a narrower size distribution of particles. Moreover, PMITP provided a lower temperature region in the reaction chamber downstream of the plasma torch than such regions in non-modulated thermal plasmas.

Simultaneous control of numerical enhancement of N atoms and decrease in heat flux into reaction chamber using Ar-N2 pulse-modulated induction thermal plasmas

A numerical enhancement of nitrogen atoms and a simultaneous decrease in heat flux flowing into the reaction chamber were found using a high-power Ar–N2 pulse-modulated induction thermal plasma. Optical emission spectroscopy was carried out to estimate the relative number of excited nitrogen atoms flowing into the reaction chamber. The relative heat flux into the reaction chamber was evaluated from surface temperature measurement of a metal specimen installed at the downstream portion of the plasma torch. Results showed that decreasing the shimmer current level, which means the modulation degree of the coil current, increases the number of excited nitrogen atoms, while the heat flux can be reduced compared to a conventional steady state induction thermal plasma.

Statistical analysis of fluctuation characteristics at high- and low-field sides in L-mode SOL plasmas of JT-60U

For the first time, fluctuation characteristics at the high-field side (HFS) and low-field side (LFS) scrape-off-layers (SOLs) in L-mode plasmas of the JT-60U tokamak are compared in detail; the plasma transport is studied using reciprocating Langmuir probes. A statistical analysis based on probability density functions (PDFs) is employed to describe intermittent (nondiffusive) transport in SOL plasma fluctuations. It is found that positive bursty events associated with blobby plasma transport appear frequently at the LFS midplane. Further, the PDF at the LFS midplane is strongly positively skewed, while the PDF at the HFS SOL is close to a Gaussian distribution. The conventional conditional averaging method is improved by using the variable-interval time-averaging method along with it, which enables the precise reconstruction of the burst profile exhibiting a rapid increase and a slow decay. The radial evolution of plasma blobs is analysed by using an autocorrelation function, the short-time Fourier transform and wavelet analysis.

Numerical and experimental investigations on thermal interaction between thermal plasma and solid polymer powders using induction thermal plasma technique

The interaction between thermal plasma and polymer solid powders was investigated using the inductively coupled thermal plasma (ICTP) technique. Interaction between thermal plasmas and polymers is extremely important, for example, for design of down-sized circuit breakers, because it fundamentally affects the interruption capability of the circuit breakers. The ICTP technique was used in this work because it presents the advantages of no contamination and good repeatability. Polytetrafluoroethylene (PTFE), polymethylmethacrylate (PMMA), polyethylene (PE), and polyoxymethylene (POM) were treated as polymer materials. Numerical modelling for injection of polymer solid powders into Ar thermal plasma was also made including thermal interactions between thermal plasmas and polymer powders. Results showed that PMMA-ablated vapour has a higher plasma-quenching efficiency than others; the polymer solid properties affect the plasma-quenching ability indirectly. Comparison of the calculated results with experimental results showed good agreement from the viewpoints of the spatial distribution of ablated vapour concentration and the average solid particle velocity.

Control of Nitrogen Atomic Density and Enthalpy Flow Into Reaction Chamber in

Simultaneous control of the nitrogen atomic density and the enthalpy flow onto the specimen installed downstream of the plasma torch was accomplished using Ar/N2 pulse-modulated induction thermal plasmas (PMITPs). Such simultaneous control was difficult to realize because the increasing input power into conventional nonmodulation thermal plasmas increases the number density of the nitrogen atoms, but it also increases the enthalpy flow onto the specimen. The behavior of the excited nitrogen atoms was measured through spectroscopic observation. The specimens surface temperature was measured using a radiation thermometer. Then, the net enthalpy flow onto the specimen was estimated. Results showed that the modulation of coil current increases the time-averaged nitrogen atomic density and decreases the time-averaged enthalpy flow during the modulation cycle onto the specimen irradiated by the Ar/N2 PMITP. This result was confirmed by results from the developed 2-D two-temperature chemical nonequilibrium model of the Ar/N2 PMITP

\hbox{Ar/N}_{2}

It is well known that the coating quality of plasma spraying is strongly influenced by the instability of jets in the plasma spray, which is due to arc root fluctuation. Three dimensional (3D) unsteady-state modeling was employed in this research to analyze the arc root fluctuation in a DC non-transferred plasma torch. Numerical calculations on the distributions of gas temperature and velocity in the plasma torch were carried out using argon as the plasma gas. The electrical current density and potential were also discussed. The results indicate that the fluctuation of arc inside the plasma torch is mainly induced by the movement of the arc root on the anode surface. The arc root moves downstream with the flow of gas, and simultaneously the arc is bent by electromagnetic force. When the arc bends close enough to the anode boundary, a new arc root is formed somewhere upstream of the current attachment. In this paper the nature of the arc root fluctuation is presented, and also it is demonstrated that the voltage-drop calculated is larger than that measured experimentally because the plasma inside the torch has some deviation from the local thermodynamic equilibrium state hypothesis used in the current study.

Pulse-Modulated Induction Thermal Plasmas

An arbitrary-wave-form modulated induction thermal plasma (AMITP) system was developed using a high-power semiconductor high-frequency power supply. The modulated high-power plasma is a breakthrough technique for controlling the temperature and the radical density in high-density plasmas. The arbitrary-wave-form modulation of the coil current enables more detailed control of the temperature of the high-density plasmas than the pulse-amplitude modulation that has already been developed. The Ar AMITP with intentionally modulated coil current could be generated at a power of 10–15kW. Results showed that the Ar excitation temperature between the specified excitation levels was changed intentionally according to the modulation control signal.