Kyushu University Academic Staff Educational and Research Activities Database
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KENTARO TOMITA Last modified date:2019.06.27

Graduate School

Academic Degree
Doctor of Engineering
Field of Specialization
Diagnostics of industrial plasmas
Research Interests
  • Development of a sheath electric field measurement method using an optically trapped fine particle in plasmas
    keyword : laser trapping, fine particle, electric field, sheath, plasma
  • Collective Thomson Scattering diagnostics for collisionless shocks produced with high-power laser
    keyword : Collisionless shocks, Thomson scattering
  • Diagnostics of electron properties at plasma-nano interaction
    keyword : electron density, electron temperature
  • Laser Aided Diagnostics of Discharge plasmas for producing solar cells
    keyword : solar cells, negative ions, electron density, electron temperature
  • Studies of Arc discharges for Gas Circuit Breakers
    keyword : Gas Circuit Breakers , electron density, electron temperature, laser Thomson scattering
  • Development of an electron density and electron velocity distribution function measurement system for non-equilibrium discharge plasmas produced in atmospheric pressure
    keyword : electron density, electron temperature, laser Thomson scattering
  • Develpment of Laser Thomson Scattering system for Plasmas produced for Extreme Ultra Violet Lithography
    keyword : collective Thomson scattering, Extreme Ultra Violet Lithography, electron density, electron temperature, ionic charge
Current and Past Project
  • This project tries to develop an excellent diagnostics tool of extreme ultra violet (EUV) light source plasmas, which is used as the light source of next generation lithography system. The main method of diagnostics is collective Thomson scattering. We try to measure fundamental parameters such as electron density and electron temperature of EUV light source plasmas with sufficient temporal and spatial resolutions.
Academic Activities
1. Y. Kuramitsu, T. Moritaka, Y. Sakawa, T. Morita, T. Sano, M. Koenig, C. D. Gregory, N. Woolsey, Kentaro Tomita, H. Takabe, Y. L. Liu, S. H. Chen, Shuichi Matsukiyo, M. Hoshino, Magnetic reconnection driven by electron dynamics, Nature communications, 10.1038/s41467-018-07415-3, 9, 1, 2018.12, Magnetic reconnections play essential roles in space, astrophysical, and laboratory plasmas, where the anti-parallel magnetic field components re-connect and the magnetic energy is converted to the plasma energy as Alfvénic out flows. Although the electron dynamics is considered to be essential, it is highly challenging to observe electron scale reconnections. Here we show the experimental results on an electron scale reconnection driven by the electron dynamics in laser-produced plasmas. We apply a weak-external magnetic field in the direction perpendicular to the plasma propagation, where the magnetic field is directly coupled with only the electrons but not for the ions. Since the kinetic pressure of plasma is much larger than the magnetic pressure, the magnetic field is distorted and locally anti-parallel. We observe plasma collimations, cusp and plasmoid like features with optical diagnostics. The plasmoid propagates at the electron Alfvén velocity, indicating a reconnection driven by the electron dynamics..
2. K. Tomita, Y. Sato, S. Tsukiyama, R. Fukada, K. Uchino, T. Yanagida, H. Tomuro, K. Kouge, Y. Wada, M. Kunishima, T. Kodama, H. Mizoguchi, Two-dimensional electron density and temperature profiles of EUV light sources with 4.0% CE, Proc. International workshop on EUV and Soft X-ray sources (2017 source workshop), /2017/S42.pdf, 2017.11.
3. K. Tomita, Y. Sato, S. Tsukiyama, T. Eguchi, K. Uchino, K. Kouge, H. Tomuro, T. Yanagida, Y. Wada, M. Kunishima, G. Soumagne, T. Kodama, H. Mizoguchi, A. Sunahara, K. Nishihara, Time-resolved two-dimensional profiles of electron density and temperature of laser-produced tin plasmas for extreme-ultraviolet lithography light sources, Scientific Reports 7 12328(7pages) (2017), 2017.10, Time-resolved two-dimensional (2D) profiles of electron density (ne) and electron temperature (Te) of
extreme ultraviolet (EUV) lithography light source plasmas were obtained from the ion components
of collective Thomson scattering (CTS) spectra. The highest EUV conversion efficiency (CE) of 4% from
double pulse lasers irradiating a Sn droplet was obtained by changing their delay time. The 2D-CTS
results clarified that for the highest CE condition, a hollow-like density profile was formed, i.e., the high
density region existed not on the central axis but in a part with a certain radius. The 2D profile of the inband
EUV emissivity (ηEUV) was theoretically calculated using the CTS results and atomic model (Hullac
code), which reproduced a directly measured EUV image reasonably well. The CTS results strongly
indicated the necessity of optimizing 2D plasma profiles to improve the CE in the future..
4. Kentaro Tomita, Daisuke Gojima, Takahiro Shimizu, Kiichiro Uchino, Tomoyuki Nakano, Yasunori Tanaka, Katsumi Suzuki, Takanori Iijima, Toshiyuki Uchii, and Takeshi Shinkai, Thomson scattering diagnostics of SF6 gas-blasted arcs confined by a nozzle under free-recovery conditions, J. Phys. D: Appl. Phys.,, 48 (2015) 265201 (14pp), 2015.05.
5. K. Tomita, K. Nagai, T. Shimizu, N. Bolouki, Y. Yamagata, K. Uchino, T. Kaneko, Thomson scattering diagnostics of atmospheric plasmas in contact with ionic liquids, Appl. Phys. Express, Vol. 7, 066101 (4 pages), 2014.05.
6. T. Morita, Y. Sakawa, K. Tomita, T. Ide, Y. Kuramitsu, K. Nishio, K. Nakayama, K. Inoue, T. Moritaka, H. Ide, M. Kuwada, K. Tsubouchi, K. Uchino, H. Takabe, Thomson scattering measurements of a shock in laser-produced counter-streaming plasmas, Phys. Plasmas, Vol. 20, 092115 (6 pages) (2013), 2013.09.
7. K. Tomita, D. Gojima, K. Nagai, K. Uchino, R. Kamimae, Y Tanaka, K. Suzuki, T. Iijima, T. Uchii, T. Shinkai, Thomson scattering diagnostics of decay processes of Ar/SF6 gas-blast arcs confined by a nozzle, J. Phys. D: Appl. Phys. (Fast Track Communications), Vol. 46, 382001 (5 pages) (2013), 2013.09, Spatiotemporal evolutions of electron density (ne) were successfully measured in decaying SF6 gas-blast arc discharges formed with a long gap (50 mm) in a confined nozzle using laser Thomson scattering. Precise electron density measurement was so far difficult for a long-gap decaying arc discharge in a circuit breaker because of its instability, although it is well known as essential parameter for determination of success or failure of the current interruption in a circuit breaker. Pure Ar gas and 80%Ar/20%SF6 mixture gas were used as arc quenching media at atmospheric pressure. After current zero, measured ne and the arc radius in the Ar/SF6 gas arc clearly decayed more rapidly than in the pure Ar gas arc..
8. K. Tomita, K. Nakayama, K. Inoue, A. Sunahara, K. Uchino, A collective laser Thomson scattering system for diagnostics of laser-produced plasmas for extreme ultraviolet light sources, Appl. Phys. Express, Vol. 6, 076101 (4 pages) (2013), 2013.06.
9. Kentaro Tomita, Nima Bolouki, Hiroki Shirozono, Yukihiko Yamagata, Kiichiro Uchinoa, Koichi Takaki, Two-dimensional Thomson scattering diagnostics of pulsed discharges produced at atmospheric pressure, Journal of Instrumentation, Vol. 7, C02057, 2012.02.
10. K. Tomita, N. Yamamoto, N Yamasaki, T. Tsuru, K. Uchino, H. Nakashima, Thomson Scattering Diagnostics of Plasmas Produced in a Miniature Microwave Discharge Ion Engine, Journal of Propulsion and Power, 26, 2, 381-384, 2010.03.
11. Kentaro Tomita, Taisuke Kagawa, Kiichiro Uchino,Sunao KATSUKI, Hidenori AKIYAMA, Collective Thomson Scattering Diagnostics of EUV Plasmas, Journal of Plasma and Fusion Research SERIES, 8, 1, 488-491, 2009.09.
12. Safwat Hassaballa, Masaaki Yakushiji, Young-Kee Kim, Kentaro Tomita, Kiichiro Uchino, Katsunori Muraoka, Two-Dimensional Structure of PDP Micro-Discharge Plasmas Obtained Using Laser Thomson Scattering, IEEE Trans. Plasma Sci., 10.1109/TPS.2004.823980, 32, 1, 127-134, Vol. 32, pp.127-134, 2004.02.
13. Soushi Narishige, Shuichi Kitamura, Shuji Sakemi, Kentaro Tomita, Kiichiro Uchino, Katsunori Muraoka, Tadanori Sakoda, Thomson Scattering Diagnostics of Glow Discharge Plasmas Produced in Raman Active Gases, Jpn. J. Appl. Phys., 10.1143/JJAP.41.L1259, 41, 11A, L1259-L1262, Vol. 41, pp. L1259-L1262, 2002.11.
1. Collective Thomson Scattering Diagnostics of Plasmas for EUV Light Sources.
Membership in Academic Society
  • The institute of electrical engineers in japan
  • The Japan Society of Applied Physics
  • The Japan Society of Plasma Science and Nuclear Fusion Research
Other Educational Activities
  • 2018.11, Lecture experience in overseas, title: optical diagnostics of nano-second pulsed discharges produced in atmosphere, Lecture at the Department of Materials Science and Engineering, Feng Chia University, Taichung, Taiwan, Nov. 17th, 2018.
  • 2018.10, Lecture experience in overseas. title: Introduction to plasma diagnostics, Ming Chi University of Technology, New Taipei City, Taiwan, 29th Oct. 2018..