Akitoshi Okino

Development and characterization of a low current capillary discharge for X-ray laser studies

Capillary discharge experiments were carried out for soft X-ray laser studies. A ceramic capillary, which has an inner diameter of 3 mm and a length of 150 mm, has been used for the end-on X-ray diode observation, and a Pyrex capillary has been used for side-view observation. Spike output has been observed, when operating the device with a predischarge current of 5 to 15 A, a current of 9 to 35 kA with a rise time of 55 ns in an argon gas pressure range from 100 to 800 mtorr. It is found that without a predischarge current, spike output has been hardly observed. Observation of spike output at a low discharge current of 9 kA provides us a possibility for design of a compact soft X-ray laser device. When the predischarge is turned off, the side-view observation of the capillary discharge clearly shows the growth of instabilities during the pinch process. This suggests that the predischarge is indispensable for achieving a uniform plasma, which is required by the soft X-ray lasing in a capillary discharge.

Observation of multi-pulse soft x-ray lasing in a fast capillary discharge

We have designed, fabricated and tested a soft x-ray device, which uses a capillary discharge to achieve neon-like argon lasing. The ceramic capillary has an inner diameter of 3 mm and a length of 150 mm. When operating the device with a current of 16 kA and dI/dt of 517.8 A ns-1 at gas pressure of 26.7 Pa, lasing has been confirmed. Multi-pulse laser output has also been observed with a slightly higher current of 17.5 kA, and this indicates that there exist several configurations suitable for the Ne-like Ar lasing during one pinch process. This is the first observation of multi-pulse laser output.

Investigation of reactive species using various gas plasmas

In this study, atmospheric nonequilibrium plasmas were generated with six gas species using a multi-gas plasma jet. Singlet oxygen, OH radicals, H radicals, and NO radicals, in reaction with a solution interface, were measured using electron spin resonance. Carbon dioxide plasma generated the largest amount (90 μM) of singlet oxygen at 30 s, and argon-containing vapor gas plasma generated the largest amount (210 μM) of OH radicals. Among the homo-atomic gas species, nitrogen plasma generated the largest amount (130 μM) of OH radicals. In addition, H radicals were generated with argon, helium, and nitrogen plasmas. NO radicals were generated with nitrogen–oxygen plasma, and the largest amount of NO radicals was generated at a 1 : 1 volume ratio. These measurement results of the reactive species generated by individual gas plasmas permit identification of the production processes of reactive species.

Sample introduction of single selenized yeast cells (Saccharomyces cerevisiae) by micro droplet generation into an ICP-sector field mass spectrometer for label-free detection of trace elements

We have applied a micro droplet generator (μDG) for sample introduction of single selenized yeast cells into a sector field ICP-MS, which was operated in a fast scanning mode with sampling rates of up to 10 kHz, to measure single cells time resolved with 100 μs integration time. Selenized yeast cells have been used as a model system for preliminary investigation. The single cells to be measured have been embedded into droplets and it will be shown that the time duration of a single cell event always is about 400 to 500 μs, and thus comparable to the time duration of a droplet without a cell. A fixed droplet generation rate of 50 Hz produced equidistant signals in time of each droplet event and was advantageous to separate contribution from background and blank from the analytical signal. Open vessel digestion and a multielement analysis were performed with washed yeast cells and absolute amounts per single cell were determined for Na (0.91 fg), Mg (9.4 fg), Fe (5.9 fg), Cu (0.54 fg), Zn (1.2 fg) and Se (72 fg). Signal intensities from single cells have been measured for the elements Cu, Zn and Se, and histograms were calculated for about 1000 cell events. The mean elemental sensitivities measured here range from 0.7 counts per ag (Se) to 10 counts per ag (Zn) with RSDs from 49% (Zn) to 69% (Se) for about 1000 cell events.

Application of a micro-droplet generator for an ICP-sector field mass spectrometer – optimization and analytical characterization

A micro-droplet generator (μDG) sample introduction system was coupled to a sector field ICP-MS instrument to investigate the analytical figures of merit with respect to single cell analysis. The sector field instrument was operated for the first time in a fast scanning mode (E-scan) with the shortest time resolution of 100 μs to measure the single droplet time resolved and using the original detector in a pulse counting mode without modification of the existing electronics. For reduction of the droplet diameter a triple pulse mode of the droplet generator was applied and a droplet diameter down to 23 μm has been achieved for this investigation with a 100% transport efficiency of droplets. Signal duration times of single droplets of less than 500 μs have been measured. Overall detection efficiencies in the range of 10−3 counts per atom have been achieved and absolute limits of detection range between 120 ag for Fe and 1.1 ag for Mg as a mean value from 1000 droplet events.

Surface Hydrophilization of Polyimide Films Using Atmospheric Damage-Free Multigas Plasma Jet Source

Atmospheric-pressure plasma jet sources have proven useful for surface treatments; however, conventional plasma and near-plasma sources have limitations in the number of different plasma gas species that they can handle. We previously developed a damage-free multigas plasma jet source that can generate stable atmospheric-pressure plasma using various gas species without thermal/electrical discharge damage. Herein, we investigate the fundamental characteristics of the generated plasma such as gas temperature (<;57°C) and emission properties. In addition, we evaluate the industrial potential of the jet source by using it with various gas species to induce surface hydrophilization in a polyimide film. The jet source proved useful, and carbon dioxide proved the most effective of the studied gas species for the purpose with the hydrophilized surface maintaining a contact angle of about 30° for over 32 days after plasma irradiation.

Performance of pulsed power generator using high-voltage static induction thyristor

In present pulsed power generator systems using semiconductor switches, saturable magnetic switches are usually connected in series to compress the output pulse because the current rise time of semiconductor switches are generally not short enough. However, these magnetic switches are heavy and they reduce the energy transfer efficiency. Here, the authors propose a pulsed power generator system using 5500 V static induction thyristor (SI-Thy) and a Blumlein line for pulse formation, and its fundamental characteristics are evaluated. From experiments using only one SI-Thy, they obtained a turn-on time of several tens of nanoseconds and a maximum rise rate of the output voltage of 96 kV//spl mu/s. It is confirmed that SI-Thy will have sufficient performance as the main switch of the pulsed power generator for flue gas treatment and decomposition of hazardous gases if several devices are connected in series.

Fundamental properties of a non-destructive atmospheric-pressure plasma jet in argon or helium and its first application as an ambient desorption/ionization source for high-resolution mass spectrometry

Various plasma sources were used as ionization sources for ambient desorption/ionization mass spectrometry (ADI-MS) in the past. In the present study, a plasma jet, termed an atmospheric-pressure damage-free multi-gas plasma jet, which can generate a stable atmospheric low-temperature plasma with various gas species, was investigated and used as an ionization source for ambient MS. First, the OH rotational temperature and electron number density of the plasma were determined spectroscopically. It was found that a relatively low temperature (<350 K) and high-density (1014 cm−3) plasma can be generated in helium and argon. Second, the amount of reactive species in the glow-like discharge was indirectly compared to those typically found in a dielectric barrier discharge jet by means of differences in hydrophilization efficiencies of polyimide films. It was found that the plasma jet was more reactive when the plasma exit was positioned close to the sample (<3 mm). Third, the plasma source was coupled to a high-resolution molecular mass spectrometer (Exactive with Orbitrap mass analyzer) and used for direct solid sample analyses. Commercially available acetaminophen, loratadine, and aspirin tablets were successfully analyzed without any sample pre-treatment. The plasma source was also used for direct solution analysis of model compounds to demonstrate the analytical capacity. Calibration curves were obtained with correlation coefficients of ≧0.9975, and limits of detection were in the picogram to nanogram range for acetaminophen, loratadine, and aspirin.

Pulsed Operation of a Compact Fusion Neutron Source Using a High-Voltage Pulse Generator Developed for Landmine Detection

Abstract Preliminary experimental results of pulsed neutron source based on a discharge-type beam fusion called Inertial Electrostatic Confinement Fusion (IECF) for landmine detection are presented. In Japan, a research and development project for constructing an advanced anti-personnel landmine detection system by using IECF, which is effective not only for metal landmines but also for plastic ones, is now in progress. This project consists of some R&D topics, and one of them is R&D of a high-voltage pulse generator system specialized for landmine detection, which can be used in the severe environment such as that in the field in Afghanistan. Thus a prototype of the system for landmine detection was designed and fabricated in consideration of compactness, lightness, cooling performance, dustproof and robustness. By using this prototype pulse generator system, a conventional IECF device was operated as a preliminary experiment. As a result, it was confirmed that the suggested pulse generator system is suitable for landmine detection system, and the results follow the empirical law obtained by the previous experiments. The maximum neutron production rate of 2.0×108 n/s was obtained at a pulsed discharge of -51 kV, 7.3 A.

Fundamental properties of a touchable high‐power pulsed microplasma jet and its application as a desorption/ionization source for ambient mass spectrometry

Plasma-based ambient desorption/ionization mass spectrometry (ADI-MS) has attracted considerable attention in many fields because of its capacity for direct sample analyses. In this study, a high-power pulsed microplasma jet (HPPMJ) was developed and investigated as a new plasma desorption/ionization source. In an HPPMJ, a microhollow cathode discharge is generated in a small hole (500 µm in diameter) using a pulsed high-power supply. This system can realize a maximum power density of 5 × 10(8) W/cm(3). The measured electron number density, excitation temperature and afterglow gas temperature of the HPPMJ were 3.7 × 10(15) cm(-3), 7000 K at maximum and less than 60 °C, respectively, which demonstrate that the HPPMJ is a high-energy, high-density plasma source that is comparable with an argon inductively coupled plasma while maintaining a low gas temperature. The HPPMJ causes no observable damage to the target because of its low gas temperature and electrode configuration; thus, we can apply it directly to human skin. To demonstrate the analytical capacity of ADI-MS using an HPPMJ, the plasma was applied to direct solid sample analysis of the active ingredients in pharmaceutical tablets. Caffeine, acetaminophen, ethenzamide, isopropylantipyrine and ibuprofen were successfully detected. Application to living tissue was also demonstrated, and isopropylantipyrine on a finger was successfully analyzed without damaging the skin. The limits of detection (LODs) for caffeine, isopropylantipyrine and ethenzamide were calculated, and LODs at the picogram level were achieved. These results indicate the applicability of the HPPMJ for high-sensitivity analysis of materials on a heat-sensitive surface.