研究者データベース

白井 直機(シライ ナオキ)
工学研究院 応用量子科学部門 物質量子工学
准教授

基本情報

所属

  • 工学研究院 応用量子科学部門 物質量子工学

職名

  • 准教授

学位

  • 博士(工学)(東京工業大学)

ホームページURL

科研費研究者番号

  • 80552281

J-Global ID

プロフィール

  • 1980年生まれ。福島県会津若松市出身。2008年3月東京工業大学大学院理工学研究科電気電子工学専攻博士後期課程修了。日本学術振興会特別研究員(DC2-PD)を経て,2009年4月より首都大学東京助教,2016年4月より北海道大学准教授,現在に至る。主として液体の介在した大気圧プラズマの研究に従事。博士(工学)、電気学会、応用物理学会、プラズマ核融合学会、物理学会。

研究キーワード

  • 大気圧グロー放電   液体電極   パルス放電   大気圧プラズマ   プラズマ気液界面現象   分子動力学   非熱平衡大気圧プラズマ   流体シミュレーション   プラズマシミュレーション   電解反応   

研究分野

  • エネルギー / プラズマ科学
  • エネルギー / プラズマ応用科学

職歴

  • 2016年04月 - 現在 北海道大学 工学研究院量子理工学部門 准教授
  • 2009年04月 - 2016年03月 首都大学東京 大学院 理工学研究科電気電子工学専攻 助教
  • 2007年04月 - 2009年03月 日本学術振興会 特別研究員

学歴

  • 2003年04月 - 2008年03月   東京工業大学   大学院 理工学研究科   電気電子工学専攻
  • 1999年04月 - 2003年03月   東京工業大学   工学部   電気電子工学科

所属学協会

  • プラズマ核融合学会   物理学会   応用物理学会   電気学会   

研究活動情報

論文

  • Naoki Shirai, Takuma Kaneko, Yuto Takamura, Koichi Sasaki
    Journal of Physics D: Applied Physics 2022年01月06日 [査読有り]
  • Naoki Shirai, Hiroki Owada, Koichi Sasaki
    Plasma Sources Science and Technology 2021年12月01日 [査読有り]
  • ルミノール化学発光を用いた気液界面プラズマによって誘起される短寿命活性種の検出
    白井直機, 佐々木浩一
    静電気学会誌 45 4 144 - 149 2021年07月 [査読有り]
  • 大気圧DCグロー放電により誘起されるプラズマ-液体間の界面反応
    白井直機
    97 7 381 - 387 2021年07月
  • J. Liu, N. Shirai, K. Sasaki
    Journal of Physics D: Applied Physics 54 10 105201 - 105201 2020年11月 [査読有り]
  • Koichi Sasaki, Ryohei Hosoda, Naoki Shirai
    Plasma Sources Science and Technology 29 085012  2020年07月16日 [査読有り][通常論文]
  • Koichi Sasaki, Shusuke Nishiyama, Naoki Shirai
    Contributions to Plasma Physics e202000061 - e202000061 2020年07月07日 [査読有り][通常論文]
  • T. Akiyama, M.A. Van Zeeland, T.N. Carlstrom, R.L. Boivin, K.J. Brunner, J. Knauer, R. Yasuhara, K. Tanaka, H.Q. Liu, Y. Zhou, N. Oyama, A. Sirinelli, K. Urabe, N. Shirai
    Journal of Instrumentation 15 1 C01004  2020年01月 [査読有り][通常論文]
     
    © 2020 IOP Publishing Ltd and Sissa Medialab. A dispersion interferometer (DI) is known to be less sensitive to mechanical vibrations, which is one of the main sources of error for conventional interferometers. A simple optical configuration is also one of the advantages of the DI approach. Since the first application of a homodyne DI on a nuclear fusion plasma device in the 1990s, several interferometer techniques have improved the operation of the DI. Improvements in nonlinear crystals have also improved the performance and availability of the DI. Immunity to neutral gas density changes, which is needed for low-temperature plasma measurements, is also found. A remaining challenge is the suppression of the offset drifts, which can be significant. Recent studies confirmed that they are caused by ambient humidity changes.
  • Naoki Shirai, Goju Suga, Koichi Sasaki
    Plasma Sources Science and Technology 29 2 025007 - 025007 2020年01月 [査読有り][通常論文]
  • Naoki Shirai, Goju Suga, Koichi Sasaki
    Journal of Physics D: Applied Physics 52 39LT02  2019年08月 [査読有り][通常論文]
  • Yuya Yamazaki, Naoki Shirai, Yusuke Nakagawa, Satoshi Uchida, Fumiyoshi Tochikubo
    Japanese Journal of Applied Physics 57 9 096203  2018年09月 [査読有り][通常論文]
     
    © 2018 The Japan Society of Applied Physics. We investigated the reaction process in magnetite nanoparticle (MNP) synthesis by glow-discharge electrolysis in atmospheric air combined with iron electrolysis using NaCl aqueous solution as electrolyte. The iron electrolysis supplies Fe2+ in the solution, and electrons from the glow discharge induce liquid-phase reactions. We found experimentally that the concentration of dissolved oxygen (DO) in the solution is a key parameter in MNP synthesis. The excess oxidation of ferrous iron species at a high DO concentration causes the generation of hematite nanoparticles, while MNPs are mainly synthesized at a low DO concentration. Simple rate equations were solved to investigate the liquid-phase reaction process. The calculated results showed that the DO concentration reasonably changed the ratio between ferrous and ferric iron species, which will be important for the chemical composition of synthesized nanoparticles. The solution pH, which is locally increased by the glow discharge, affects the liquid-phase reaction process, especially through the hydroxylation of ferrous iron species.
  • Naoki Shirai, Yutaka Matsuda, Koichi Sasaki
    Applied Physics Express 11 2 026201 - 026201 2018年02月01日 [査読有り][通常論文]
     
    Blue chemiluminescence was observed just below the plasma-liquid interface when an atmospheric-pressure plasma was in contact with an alkaline solution in which luminol was dissolved. The shape of the chemiluminescent area was that of a thin disk. The diameter of the disk was approximately the same as that of the plasma column, and the thickness was roughly estimated to be less than 0.1 mm. The chemiluminescence is considered to originate from the oxidation reaction of luminol by O2 - and/or OH. The experimental results reveal that the chemiluminescence of luminol is useful for real-time visualization of plasma-induced short-lived species in liquids.
  • T. Akiyama, S. Yoshimura, K. Tomita, N. Shirai, T. Murakami, K. Urabe
    JOURNAL OF INSTRUMENTATION 12 C12028  2017年12月 [査読有り][通常論文]
     
    When the electron density of a plasma generated in high pressure environment is measured by a conventional interferometer, the phase shifts due to changes of the neutral gas density cause significant measurement errors. A dispersion interferometer, which measures the phase shift that arises from dispersion of medium between the fundamental and the second harmonic wavelengths of laser light, can suppress the measured phase shift due to the variations of neutral gas density. In recent years, the CO2 laser dispersion interferometer has been applied to the atmospheric pressure plasmas and its feasibility has been demonstrated. By combining a low power laser and a high efficiency nonlinear crystal for the second harmonic component generation, a compact dispersion interferometer can be designed. The optical design and preliminary experiments are conducted.
  • Naoki Shirai, Taketo Yoshida, Satoshi Uchida, Fumiyoshi Tochikubo
    JAPANESE JOURNAL OF APPLIED PHYSICS 56 7 1 - 7 2017年07月 [査読有り][通常論文]
     
    For the synthesis of magnetic nanoparticles (NPs), we used plasma-assisted electrolysis in which atmospheric-pressure DC glow discharge using a liquid electrode is combined with electrolysis. The solution surface is exposed to positive ions or electrons in plasma. To synthesize magnetic NPs, aqueous solutions of FeCl2 or an iron electrode immersed in liquid was used to supply iron ions in the liquid. Magnetic NPs were synthesized at the plasma-liquid interface upon the electron irradiation of the liquid surface. In the case of using aqueous solutions of FeCl2, the condition of magnetic NP synthesis depended on the gas species of plasma and the chemical agent in the liquid for controlling oxidization. The amount of magnetic NPs synthesized using plasma is not very large. On the other hand, in the case of using an iron electrode immersed in NaCl solution, magnetic NPs were synthesized without using FeCl2 solutions. When plasma-assisted electrolysis was operated, the iron electrode eluted Fe cations, resulting in the formation of magnetic NPs at the plasma-liquid interface. Magnetic NP synthesis depended on the concentration of NaCl solution and discharge current. The magnetic NPs were identified to be magnetite. By using this method, more magnetite NPs were synthesized than in the case of plasma-assisted electrolysis with FeCl2 aqueous solutions. The pH of the liquid used in plasma-assisted electrolysis was important for the synthesis of magnetite NPs. (C) 2017 The Japan Society of Applied Physics
  • Fumiyoshi Tochikubo, Takuya Aoki, Naoki Shirai, Satoshi Uchida
    Japanese Journal of Applied Physics 56 4 46201 - 046201 2017年 [査読有り][通常論文]
     
    © 2017 The Japan Society of Applied Physics. In this work, we investigated the characteristics of liquid flow induced by atmospheric-pressure dc glow discharge in contact with a liquid. The spatiotemporal development of liquid flow was visualized by the schlieren method, and the temperature distribution was measured using microencapsulated thermotropic liquid crystal particles dispersed in a liquid. We confirmed the appearance of specific downward liquid flow immediately below the dc glow discharge. The characteristics of downward liquid flow were reproduced by fluid simulation considering a downward driving force at the plasma-liquid interface. Our results suggest that the probable driving force for the downward liquid flow was the momentum transfer of charged species at the liquid surface.
  • Keiichiro Urabe, Naoki Shirai, Kentaro Tomita, Tsuyoshi Akiyama, Tomoyuki Murakami
    PLASMA SOURCES SCIENCE & TECHNOLOGY 25 4 045004 - 045004 2016年08月 [査読有り][通常論文]
     
    The density and temperature of electrons and key heavy particles were measured in an atmospheric-pressure pulsed-dc helium discharge plasma with a nitrogen molecular impurity generated using system with a liquid or metal anode and a metal cathode. To obtain these parameters, we conducted experiments using several laser-aided methods: Thomson scattering spectroscopy to obtain the spatial profiles of electron density and temperature, Raman scattering spectroscopy to obtain the neutral molecular nitrogen rotational temperature, phase-modulated dispersion interferometry to determine the temporal variation of the electron density, and time-resolved laser absorption spectroscopy to analyze the temporal variation of the helium metastable atom density. The electron density and temperature measured by Thomson scattering varied from 2.4 x 10(14) cm(-3) and 1.8 eV at the center of the discharge to 0.8 x 10(14) cm(-3) and 1.5 eV near the outer edge of the plasma in the case of the metal anode, respectively. The electron density obtained with the liquid anode was approximately 20% smaller than that obtained with the metal anode, while the electron temperature was not significantly affected by the anode material. The molecular nitrogen rotational temperatures were 1200 K with the metal anode and 1650 K with the liquid anode at the outer edge of the plasma column. The density of helium metastable atoms decreased by a factor of two when using the liquid anode.
  • Kentaro Tomita, Keiichiro Urabe, Naoki Shirai, Yuta Sato, Safwat Hassaballa, Nima Bolouki, Munehiro Yoneda, Takahiro Shimizu, Kiichiro Uchino
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 6 066101 - 066101 2016年06月 [査読有り][通常論文]
     
    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 N-2 or synthesized air (N-2 : O-2 = 4 : 1) 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 x 10(21)m(-3) for plasma generated with N-2/O-2 shielding gas, 50% higher than that generated with N-2 shielding. (C) 2016 The Japan Society of Applied Physics
  • Naoki Shirai, Ryuto Sekine, Satoshi Uchida, Fumiyoshi Tochikubo
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 1 2016年01月 [査読有り][通常論文]
  • 石田 高広, 白井 直機, 内田 諭, 杤久保 文嘉
    電気学会論文誌E 136 12 505 - 510 2016年 [査読有り][通常論文]
     
    © 2016 The Institute of Electrical Engineers of Japan. Constant monitoring and detailed examination of microbial metabolism have been required for advanced qualit control in bioindustry. Although microbial evaluation using dielectrophoresis (DEP) should be an attractiv scheme, the relationship with metabolism has not been understood well. In this paper, the membrane states an metabolic change of injured Saccharomyces cerevisiae (S. cerevisiae) with heat treatment were investigated usin DEP velocimetry in a micro cell. As a result, the treatment time at low temperature and afterheat stress sensitivel influenced DEP velocity of S. cerevisiae. The fluorescent observation of stained S. cerevisiae indicated DEP velocit has a correlation with the transmembrane state and growth activity. These results suggest that DEP velocimetr would be available for rapid and simple metabolic evaluation.
  • T. Akiyama, R. Yasuhara, K. Kawahata, K. Nakayama, S. Okajima, K. Urabe, K. Terashima, N. Shirai
    JOURNAL OF INSTRUMENTATION 10 09 P09022  2015年09月 [査読有り][通常論文]
     
    A CO2 laser dispersion interferometer (DI) has been developed for both magnetically fusion plasmas and high pressure industrial plasmas. The DI measures the phase shift caused by dispersion in a medium. Therefore, it is insensitive to the mechanical vibrations and changes in the neutral gas density, which degrade the resolution of the electron density measurement. We installed the DI on the Large Helical Device (LHD) and demonstrated a high density resolution of 2 x 10(17) m(-3) without any vibration-free bench. The measured electron density with the DI shows good agreement with results of the existing far infrared laser (a wavelength of 119 mu m) interferometer. The DI system is also applied to the electron density measurement of high-pressure small-scale plasmas. The significant suppression of the phase shift caused by the neutral gas is proven. The achieved density resolution was 1.5 x 10(19) m(-3) with a response time of 100 mu s.
  • Fumiyoshi Tochikubo, Yudai Shimokawa, Naoki Shirai, Satoshi Uchida
    JAPANESE JOURNAL OF APPLIED PHYSICS 53 12 126201 - 126201 2014年12月 [査読有り][通常論文]
     
    We experimentally investigated some of the initial reactions in a liquid induced by electron or positive-ion irradiation from an atmospheric-pressure dc glow discharge in contact with the liquid. Aqueous solutions of NaCl, AgNO3, and HAuCl4 are used as the electrolyte. We measured the pH and conductivity in the liquid at approximately 1 cm below the solution surfaces. OH radical generation in the liquid was observed by a chemical probe method. Experimental results showed that electron irradiation of the liquid surface generates OH- in water and that positive-ion irradiation of the liquid surface generates H+ in water even without the dissolution of gas-phase nitrogen oxide. A possible reaction process is qualitatively discussed. In particular, the contribution of charge transfer collision between impinging low-energy positive ions and water molecules to the ionic species in the liquid is used to explain the overall tendency of the experimental results. (C) 2014 The Japan Society of Applied Physics
  • Naoki Shirai, Satoshi Uchida, Fumiyoshi Tochikubo
    PLASMA SOURCES SCIENCE & TECHNOLOGY 23 5 054010 - 054010 2014年10月 [査読有り][通常論文]
     
    Self-organized luminous pattern formation is observed in the liquid surface of an atmospheric dc glow discharge using a liquid electrode with a miniature helium flow. The factors affecting pattern formation are the gap length, discharge current, helium mass flow rate and polarity. The pattern shape depends on the conductivity and temperature of the liquid electrode. A variety of patterns were observed by changing the conductivity and temperature of the liquid. We clarified that the self-organized pattern formation depends on the amount of electronegative gas, such as oxygen, in the gas in the electrode gap. When an oxygen gas flow was fed to the liquid surface from the outside in an obliquely downward direction, namely, the amount of oxygen gas on the liquid surface was increased locally, self-organized pattern formation was observed in the region with the increased amount of oxygen gas. When the amount of oxygen in the gas in the gap was changed by using a sheath flow system, the appearance of the pattern changed. The presence of oxygen gas strongly affected the self-organized pattern formation of the atmospheric dc discharge using a liquid anode.
  • Naoki Shirai, Satoshi Uchida, Fumiyoshi Tochikubo
    JAPANESE JOURNAL OF APPLIED PHYSICS 53 4 046202 - 046202 2014年04月 [査読有り][通常論文]
     
    For the synthesis of metal nanoparticles in aqueous solution, we propose dual plasma electrolysis, which consists of a Hoffman electrolysis apparatus with two atmospheric glow discharge plasmas as electrodes instead of conventional metal electrodes immersed in a liquid. The plasma anode irradiates positive ions to the solution surface while the plasma cathode irradiates electrons to the solution surface. The dual plasma electrolysis system enables us to simultaneously investigate the influence of electron and positive ion irradiation to a solution surface on metal nanoparticle generation at the same current. In this work, we used aqueous solutions of AgNO3, HAuCl4, and their mixture. In dual plasma electrolysis with AgNO3, Ag nanoparticles were only synthesized on the plasma cathode side. This means that Ag nanoparticles are generated via the reduction of Ag+ by electrons. With HAuCl4 solution, Au nanoparticles were synthesized on both the plasma anode and plasma cathode sides. Ion irradiation with the plasma anode is more effective than electron irradiation for Au nanoparticle synthesis. This finding suggests that positive ions from the plasma trigger the dissociative reaction of AuCl4- at the plasma-liquid interface. When a AgNO3-HAuCl4 mixture was used, the synthesized nanoparticles have a structure consisting of a Au core covered with a Ag shell. (C) 2014 The Japan Society of Applied Physics
  • Naoki Shirai, Ryuto Sekine, Satoshi Uchida, Fumiyoshi Tochikubo
    JAPANESE JOURNAL OF APPLIED PHYSICS 53 2 026001 - 026001 2014年02月 [査読有り][通常論文]
     
    We examined the characteristics of atmospheric negative corona discharge using a liquid needle cathode. As a liquid needle cathode, a Taylor cone with conical shape was adopted. A micronozzle was filled with liquid, and a plate electrode was placed above the nozzle. By applying a de voltage between electrodes, a Taylor cone is formed. To change the liquid property, we added sodium dodecyl sulfate to reduce the surface tension, sodium sulfate to increase the conductivity, and polyvinyl alcohol to increase the viscosity, in distilled water. Liquids with a high surface tension such as pure water could not form a Taylor cone. When we reduced the surface tension, a Taylor cone was formed and a stable corona discharge was observed at the tip of the cone. When we increased viscosity, a liquid filament protruding from the solution surface was formed and corona discharge was observed along the filament at a position 0.7-1.0 mm above the tip of the cone. Increasing the conductivity resulted in the higher light intensity of the corona and the lower corona onset voltage. Using a Taylor cone, different types of corona discharge were observed by changing the property of the liquid. (C) 2014 The Japan Society of Applied Physics
  • Yudai Minagawa, Naoki Shirai, Satoshi Uchida, Fumiyoshi Tochikubo
    JAPANESE JOURNAL OF APPLIED PHYSICS 53 1 010210 - 010210 2014年01月 [査読有り][通常論文]
     
    We analyzed the physical behavior of water molecules to assess the effect of ion bombardment from atmospheric-pressure plasma to a liquid surface by classical molecular dynamics simulation. As the incident ions, O+ was considered. The number of sputtered water molecules, liquid temperature, and ion penetration depth in liquid were investigated after O+ ions with kinetic energies of 10 and 100 eV impinged on the liquid surface. The average numbers of sputtered water molecules by ion impact were 0.5 at 10 eV and 7.0 at 100 eV. The sputtering of water molecules depended on the ion penetration depth and near-surface liquid temperature. The sputtering dynamics was discussed in detail. In addition, we presented the effect of an impinging ion on a liquid surface under an external electric field. The result shows that the number of sputtered water molecules increases with increasing electric field strength, which affects the water molecule orientation. (C) 2014 The Japan Society of Applied Physics
  • Fumiyoshi Tochikubo, Naoki Shirai, Satoshi Uchida
    27TH SUMMER SCHOOL AND INTERNATIONAL SYMPOSIUM ON THE PHYSICS OF IONIZED GASES (SPIG 2014) 565 012010  2014年 [査読有り][通常論文]
     
    We experimentally investigated some of the initial reactions in a liquid induced by electron or positive-ion irradiation from an atmospheric-pressure dc glow discharge in contact with the liquid. We used an H-shaped glass reactor to observe the effects of electron irradiation and positive-ion irradiation on the liquid-phase reaction separately and simultaneously. Aqueous solutions of NaCl, AgNO3, HAuCl4, and FeCl2 are used as the electrolyte. Solutions of AgNO3 and HAuCl4 are used for the generation of Ag and Au nanoparticles, respectively. Solution of FeCl2 is used for the generation of ferromagnetic particles. Experimental results showed that electron irradiation of the liquid surface generates OH-in water and that positive-ion irradiation of the liquid surface generates H+ in water even without the dissolution of gas-phase nitrogen oxide. A possible reaction process is qualitatively discussed. We also showed that the control of reductive and oxidative environment in the liquid is possible not only by the gas composition for the plasma generation but also by the liquid composition.
  • 青木 玲仁, ,白井直機, ,内田諭, ,杤久保文嘉
    電気学会論文誌E 134 7 235 - 240 2014年 [査読有り][通常論文]
     
    For strict application of food hygiene regulation such as hazard analysis - critical control point system, the development of rapid and simple measurement scheme for biological particles is essential. Recently, a hybrid method using dielectrophoretic manipulation and micro fluidic operation has attracted attention for the bioparticle detection. However, the influence of electrode structure on the dielctrophoretic force has not been fully understood. For effective design of dielectrophoretic devices, it is important to investigate quantitatively the capture characteristics. In the present work, we numerically simulated the particle dynamics in the capture region of a dielectrophoretic micro device with interdigitated electrodes. The dependence of dielctrophoretic force on the electrode width and gap length showed that there was the maximum of capture height of particles for adequate electrode structure. Furthermore, the number of captured particles was accurately evaluated in consideration of the effective region ratio. Under typical condition, the number of captured particles almost agreed with the experimental result. © 2014 The Institute of Electrical Engineers of Japan.
  • 高澤晋, 白井直機, 高澤晋, 内田諭, 杤久保文嘉
    静電気学会誌 37 263 - 268 2013年 [査読有り][通常論文]
  • Naoki Shirai, Masato Nakazawa, Shinji Ibuka, Shozo Ishii
    ELECTRICAL ENGINEERING IN JAPAN 178 4 8 - 15 2012年03月 [査読有り][通常論文]
     
    Stable electrolyte cathode atmospheric DC glow microdischarges were generated by using a miniature helium gas flow from a nozzle electrode in air. We developed two schemes to control the temporal evolution of the discharge and the interaction between the discharge column and the ambient air. The vaporization of electrolyte solutions takes place and affects the discharge characteristics. This takes time from the start of the discharge. Therefore, the discharge was controlled by applying pulse-modulated DC voltages. If the voltage was dropped down to zero before the vaporization, the gas discharge developed without the ionization of the solution components. A helium gas discharge without air developed when the nozzle electrode was placed in a glass capillary. This was confirmed by examining the change in pH of the solution, which usually decreased owing to the generation of nitrogen oxides in the discharge in air. (C) 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(4): 815, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21222
  • Naoki Shirai, Koki Matsui, Shinji Ibuka, Shozo Ishii
    IEEE TRANSACTIONS ON PLASMA SCIENCE 39 11 2210 - 2211 2011年11月 [査読有り][通常論文]
     
    We propose a new scheme for generating atmospheric dc corona discharges using a Taylor cone. When a negative high voltage was applied to an ethanol solution containing sodium sulfate, a Taylor cone was generated, and negative corona discharges were observed at the tip of the cone. When a polyvinyl alcohol solution with higher viscosity was used, corona discharges appeared along the liquid filament at positions 0.7-1.0 mm higher from the tip of the cone. Various modes of corona discharge were observed by varying the viscosity, electrical conductivity, and applied voltage.
  • Naoki Shirai, Satoshi Uchida, Fumiyoshi Tochikubo, Shozo Ishii
    IEEE TRANSACTIONS ON PLASMA SCIENCE 39 11 2652 - 2653 2011年11月 [査読有り][通常論文]
     
    Self-organized anode patterns were observed on the surface of a liquid or metal anode when an atmospheric dc glow discharge with helium flow was generated. The pattern formation depends on current, gap length, and helium flow rate. With increasing discharge current or gap length, an anode luminous spot changed to self-organized patterns. In the case of using a liquid anode, anode pattern formation depends on liquid conductivity.
  • Naoki Shirai, Kosuke Ichinose, Satoshi Uchida, Fumiyoshi Tochikubo
    PLASMA SOURCES SCIENCE & TECHNOLOGY 20 3 034013-1 - 034013-9 2011年06月 [査読有り][通常論文]
     
    An atmospheric dc glow discharge using a liquid cathode and an axial miniature helium flow was generated stably between a nozzle anode and an electrolyte cathode (NaCl solution) in ambient air. Under low-current operation, the typical structure of dc glow discharges, i.e. a negative glow, a Faraday dark space and positive column, was observed. With increasing discharge current, the visible negative glow became weak and was replaced by an intense yellow-light emission, which was considered to originate from sodium atoms vaporized from the electrolyte surface by local heating due to ion bombardment from the glow discharge. To examine the effect of the liquid electrode temperature on the discharge characteristics, we controlled the electrolyte cathode temperature using an injection-type cooler or heater. The intensity of the sodium emission decreased when the electrolyte cathode was cooled, while it increased when the electrolyte cathode was heated. When a pulse-modulated dc voltage was applied, the sodium emission appeared with a delay relative to the inception of discharge, while nitrogen molecular lines appeared in the emission spectra and reached their peak intensities immediately. The temperature of the liquid cathode is an important factor in controlling the plasma-liquid interaction from the discharge and in resolving the detailed mechanism of the electrolyte cathode discharge.
  • Fumiyoshi Tochikubo, Naoki Shirai, Satoshi Uchida
    APPLIED PHYSICS EXPRESS 4 5 56001 - 1 2011年05月 [査読有り][通常論文]
     
    In this work, we carried out two-dimensional numerical simulation of atmospheric pressure dc glow discharge with miniature helium flow in nitrogen. The glow discharge is generated along the helium flow, which is injected from the nozzle anode into the discharge region filled with nitrogen. The purpose of this study is to clarify the relationship between the glow discharge structure and the helium flow. We found that the glow discharge generation is limited in the region with a very high helium mole fraction. Therefore, the helium mole fraction is an important parameter to determine the discharge structure along the helium flow. (C) 2011 The Japan Society of Applied Physics
  • 石井 彰三, 白井 直機, 井深 真治, 金丸 誠, 菊地 淳
    電気学会論文誌. A, 基礎・材料・共通部門誌 = The transactions of the Institute of Electrical Engineers of Japan. A, A publication of Fundamentals and Materials Society 130 10 899 - 906 社団法人 電気学会 2010年 [査読有り][通常論文]
     
    We developed noble schemes to generate atmospheric-pressure microplasmas, in which the mass of initial materials such as gases or liquids is limited to a small amount. A miniature gas flow through a nozzle electrode was used to generate direct current glow or corona microdischarges with a metal or an electrolyte cathode. High-power microplasmas were operated by fast pulsed voltages. Pulsed microplasmas were created using a droplet or a filament of aqueous solution of ethanol.
  • Naoki Shirai, Hiroaki Shito, Shinji Ibuka, Shozo Ishii
    Applied Physics Express 2 7 76001 - 076001-3 2009年07月 [査読有り][通常論文]
     
    We discussed the corona-to-glow transition of DC discharges using intersecting axial miniature gas flows under atmospheric pressure. The stable dc discharges generated along the intersecting two axial miniature helium flows were operated from low current of 0.1 mA to high current of 20 mA. With increasing the discharge current, the discharges appeared as corona-mode and then developed to glow-mode. The gas temperature characterized by rotational temperature of nitrogen molecules changed from 400 to 1500K. © 2009 The Japan Society of Applied Physics.
  • Naoki Shirai, Masato Nakazawa, Shinji Ibuka, Shozo Ishii
    Japanese Journal of Applied Physics 48 3 036002 - 036002 2009年03月 [査読有り][通常論文]
     
    We developed a new scheme to generate atmospheric dc glow discharges with a combination of an electrolyte cathode and a miniature gas flow. Stable glow discharges were obtained for a gap separation of 100-700mm with a cathode of a sodium sulfate solution. The gap voltage increased with increasing a current up to 15 mA, above which the voltage became constant as the low-pressure glow discharges. Local boiling by the discharge at the surface of the sodium sulfate solution began at 15mA. At the same time, the emission of an intense sodium atomic line appeared in the negative glow region. The pH of the solution decreased when the discharge was generated in ambient air. The reduction of pH was attributed to the existence of nitrogen oxide, which dissolved in the solution. © 2009 The Japan Society of Applied Physics.
  • Naoki Shirai, Shinji Ibuka, Shozo Ishii
    Applied Physics Express 2 3 36001 - 036001-3 2009年03月 [査読有り][通常論文]
     
    An atmospheric glow microdischarge is generated with an electrolyte anode and axial miniature helium flow. A stable operation under atmospheric pressure can be achieved using an axial miniature helium flow. When the electrode separation is 10 mm and the discharge current is greater than 30 mA, self-organization patterns, which depend on the electrolyte anode concentration, are observed at the electrolyte anode surface, indicating that the anion and cation in electrolyte solution are important for electrolyte anode discharges. © 2009 The Japan Society of Applied Physics.
  • 白井 直機, 中澤 将人, 井深 真治, 石井 彰三
    電気学会論文誌. A, 基礎・材料・共通部門誌 = The transactions of the Institute of Electrical Engineers of Japan. A, A publication of Fundamentals and Materials Society 129 4 16 - 274 社団法人 電気学会 2009年 [査読有り][通常論文]
     
    Stable electrolyte cathode atmospheric dc glow microdischarges were generated by using a miniature helium gas flow from a nozzle electrode in air. We developed two schemes to control the temporal evolution of the discharge and the interaction between the discharge column and the ambient air. The vaporization of electrolyte solutions takes place and affects the discharge characteristics. It takes time from the start of the discharge. Therefore the discharge was controlled by applying pulse modulated dc voltages. If the voltage was dropped down to zero before the vaporization, the gas dischar...
  • Naoki Shirai, Masato Nakazawa, Shinji Ibuka, Shozo Ishii
    IEEE TRANSACTIONS ON PLASMA SCIENCE 36 4 1160 - 1161 2008年08月 [査読有り][通常論文]
     
    Stable dc electrolyte-cathode atmospheric glow discharges with a wide-gap separation were obtained using a miniature helium gas flow. A thin discharge column formed because of the gas flow exhibited intense sodium atom line emission from the cathode region for high-current operation.
  • Naoki Shirai, Shinji Ibuka, Shozo Ishii
    IEEE Transactions on Plasma Science 36 4,Pt.1 960 - 961 2008年08月 [査読有り][通常論文]
  • Shirai Naoki, Onaka Yu, Ibuka Shinji, Ishii Shozo
    Jpn J Appl Phys 47 4 2244 - 2249 Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physics 2008年04月 [査読有り][通常論文]
     
    One of the advantages of microplasmas is that it can be generated using any phase of materials, namely, gases, liquids, and solids. We developed methods to generate microplasmas by pulsed discharge utilizing ethanol filaments grown from the tip of a Taylor cone, which were created by the electrostatic force between electrodes in air. The structures of the filament and Taylor cone were affected by electrode separation, applied voltage, electrode shape, and the mass of liquid. Vaporization and dissociation of ethanol were confirmed in the pulsed discharge of the liquid filament, because the a...
  • Naoki Shirai, Yu Onaka, Shinji Ibuka, Koichi Yasuoka, Shozo Ishii
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 1 370 - 374 2007年01月 [査読有り][通常論文]
     
    An ethanol droplet of 300 mu m in diameter is used to create a dense microplasma by pulsed discharge. The pulsed discharge took place when the droplet came into the space between miniature electrodes across which a dc high voltage was applied. The vaporization and dissociation of the ethanol droplet were confirmed in the discharge because the atomic line of hydrogen was observed by optical emission spectroscopy. Molecular hydrogen was detected as a product after the discharge of the ethanol droplet. The discharge of a droplet in air and that of a micro bubble in liquid are in opposite configurations, which is a duality in nature. A single microbubble discharge in pure water was conducted. The gas breakdown of air took place in the bubble and bright emission was observed locally at the interface between the bubble and the electrode.

その他活動・業績

受賞

  • 2018年03月 Outstanding Reviewers of 2017 (Plasma Sources Science and Technology )
  • 2017年11月 プラズマ核融合学会第1回フォトコンテスト最優秀賞
  • 2017年03月 Outstanding Reviewers of 2016 Journal of Physics D: Applied Physics.
     
    受賞者: 白井直機
  • 2015年09月 応用物理学会学術講演会 ポスターアワード
     
    受賞者: 白井直機
  • 2014年02月 ICRP-8/SPP-31 Young Scientist Awards: Gold Medal
     
    受賞者: 白井直機
  • 2013年03月 SPM1 (International Wokshop on Solution Plasma and Molecular Technology) The Best Poster Presentation Award
     
    受賞者: 白井直機
  • 2012年01月 電気学会 電気学会優秀論文発表賞 基礎・材料・共通部門表彰
     
    受賞者: 白井直機
  • 2011年11月 応用物理学会 第31回(2011年秋季)応用物理学会講演奨励賞
     
    受賞者: 白井直機
  • 2010年03月 IWPL2010 (International Workshop pn Plasma with Liquids) Outstanding Poster Paper Award
     
    受賞者: 白井直機
  • 2009年12月 日本MRS 第19回日本MRS学術シンポジウム奨励賞
     
    受賞者: 白井直機
  • 2007年08月 ISPC-18 (18th International Symposium on Plasma Chemistry ) Best Paper Awards for Young Researchers
     
    受賞者: 白井直機
  • 2006年03月 電気学会 電気学会全国大会「優秀論文発表賞」(平成18年)
     
    受賞者: 白井直機

共同研究・競争的資金等の研究課題

  • プラズマと相互作用する液相界面現象の学理構築
    日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 佐々木 浩一, 白井 直機
  • 文部科学省:科学研究費補助金(基盤研究(C))
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 白井直機
  • 文部科学省:科学研究費補助金(基盤研究(A))
    研究期間 : 2016年04月 -2020年03月 
    代表者 : 佐々木浩一
  • 文部科学省:挑戦的萌芽研究
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 杤久保文嘉
  • 文部科学省:科学研究費補助金(若手研究(B))
    研究期間 : 2011年 -2011年 
    代表者 : 白井直機
  • 文部科学省:科学研究費補助金(新学術領域研究(研究領域提案型))
    研究期間 : 2009年 -2011年 
    代表者 : 杤久保文嘉, 内田諭, 白井直機
     
    低気圧環境という制約のない非熱平衡大気圧プラズマでは、液体、生体などの多様な媒質にプラズマ照射が可能である。本研究は、非熱平衡プラズマが液相と接する場であるプラズマ気液界面に生じる諸現象を、数値シミュレーション、及び、実験によって解明することを目的としている。安定したプラズマ気液界面の形成、界面への荷電粒子照射の制御性より、大気中での微細希ガス流による直流グロー放電を対象とした。平成21年度は研究計画に則り、以下の成果を得た。1. 実験微細希ガス流を用い、ノズル-液体電極間に直流グロー放電を生成し、電圧電流特性、CCDカメラと高速ビデオカメラによる放電形態の動的観測、発光分光分析により放電特性の詳細を調査した.液体電極としてはNaCl溶液を用い、放電に伴うNaの発光特性を液体電極の温度をパラメータとして調べた。Na発光の出現は、液体表面の状態や液体温度と強い相関があり、放電によって液体が局所的に過熱されることで気相へ放出されたNaがプラズマ中で励起されて発光するものと推測される。2. 数値シミュレーションプラズマ気液界面での現象の解明を最終的な目的として、微細希ガス流と液体電極を用いた大気圧直流グロー放電のモデリングを開始した。モデルは、気相中の直流グロー放電、液中での電解反応、気液界面現象の各シミュレーションから構成される。直流グロー放電のモデルは、二成分圧縮性流体計算と流...
  • 文部科学省:科学研究費補助金(若手研究(スタートアップ), 研究活動スタート支援)
    研究期間 : 2009年 -2010年 
    代表者 : 白井直機
     
    電解質溶液を電極とした放電の電極間に微細なヘリウムガス流を導入して、大気圧空気中で安定な直流駆動のグロー放電を生成した。気流界面では、溶液の気化、イオン衝突、電子放出、ラジカルの発生、窒素酸化物の溶解、電気分解等、様々な反応が発生していると考えられ、その複雑さ故に、明確な放電維持機構については十分な理解がなされていない。本研究では、特に液体プラズマ間の熱の輸送に着目して、液体を陰極とした放電の特性を実験的に調べ検討した。最初に直流駆動の放電についてNaCL溶液電極の温度を外部から加熱または冷却して、特性の変化を調べた。電流を増加させていくと、水面付近より橙色のNaの発光が観測された。この発光は、放電部の熱に依存するものと考え、液体電極冷却した際にはNaの発光は弱くなり、加熱した際には発光は強くなった。このことから、液体を電極とした放電は、熱の影響が大きいことが明らかとなった。次に、電源を直流からパルス駆動に変えることで、放電部から液体電極への熱輸送を制御した。パルス駆動の方法は2種類検討し、直流電圧を半導体スイッチによってパルス変調した放電、パルス幅1μs程度のコンデンサ放電について実験を行った。パルス変調駆動時にはパルス幅を減少させていくとNaの発光強度が減少した。発光の時間変化を計測するとNaの発光は電圧・電流に比べて遅れて発生しており、その遅延時間のためにパルス幅を減少...

教育活動情報

主要な担当授業

  • プラズマ生成工学特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : プラズマ,パルスパワー,静電気,プラズマ応用
  • 量子理工学特別講義
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : 高電圧、パルスパワー、放電、プラズマ
  • プラズマ生成工学特論
    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : プラズマ,パルスパワー,静電気,プラズマ応用
  • 応用数学Ⅰ
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 常微分方程式,ベクトル解析
  • 一般教育演習(フレッシュマンセミナー)
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 量子ビーム、プラズマ、触媒、ナノ材料

大学運営

委員歴

  • 2016年04月 - 2021年03月   応用物理学会講演会 プログラム編集員(2016年4月-)
  • 2018年03月 - 2019年07月   XXXIV ICPIG & ICRP-10 現地実行委員
  • 2017年04月 - 2019年03月   応用物理学会 プラズマエレクトロニクス会 幹事
  • 2018年03月 - 2019年01月   第36回プラズマプロセッシング研究会 第31回プラズマ材料科学シンポジウム 現地実行委員
  • 2016年04月 - 2017年01月   第34回プラズマプロセッシング研究会 第29回プラズマ材料科学シンポジウム 現地実行委員
  • 2015年05月 - 2015年12月   国際学会 9th APSPT 28th SPP WEB担当
  • 2012年04月 - 2014年08月   電気学会A部門委員
  • 2012年04月 - 2014年03月   電気学会 プラズマ技術委員会   幹事補


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