Kyushu University Academic Staff Educational and Research Activities Database
List of Presentations
KENTARO TOMITA Last modified date:2018.06.18

Assistant Professor / Electric process engineering / Department of Advanced Energy Science and Engineering / Faculty of Engineering Sciences


Presentations
1. Yasunori Tanaka, Tomoyuki Nakano, Sun Hao, Kentaro Tomita, Yuki Inada, Akiko Kumada, Kunihiko Hidaka, Takayasu Fujino, Katsumi Suzuki, Takeshi Shinkai, Fundamental studies on switching arcs -Experimental and numerical approaches, 4th International Conference on Electric Power Equipment- Switching Technology, ICEPE-ST 2017, 2017.12, Both experimental and numerical approaches have been done on switching arc plasmas for fundamental studies. In the experimental approaches, power-semiconductor switching has been used to control intentional current injections and voltage applications to switching arcs with a high accuracy in time. The systematic experiments provided the interruption probability property for different gas kinds and gas flow rates, as well as the dielectric recovery properties between the electrodes. Time evolutions in electron density were derived by Laser Thomson Scattering (LTS) and Shack-Hartmann (SH) method for different gases. On the other hand, for this nozzle space, numerical models were developed to simulate arc dynamic behaviors with and without local thermodynamic equilibrium (LTE) assumptions for different gases. It was found that the time evolution in electron density derived by the chemically non-equilibrium model is in good agreement with the experimental results by LTS..
2. Tomoyuki Nakano, Yu Tabata, Yasunori Tanaka, Yoshihiko Uesugi, Tatsuo Ishijima, Kentaro Tomita, Yuki Inada, Katsumi Suzuki, Takeshi Shinkai, Fundamental study on re-ignition process for CO2-blast arcs in a model circuit breaker using synthetic tests highly controlled by power semiconductors, 4th International Conference on Electric Power Equipment- Switching Technology, ICEPE-ST 2017, 2017.12, This paper reports fundamental measurement results on re-ignition process in synthetic tests for CO2 arcs in a gas blast nozzle. The synthetic test system used comprises a DC current source for an arc ignition, a half cycle AC current source, a DC current source for artificial current zero point and an impulse-like voltage source for application of quasi-transient recovery voltage (quasi-TRV). The electric current and voltage were switched by power-semiconductor-switches to guarantee high time-accuracy of the arc current injection and voltage application. After current zero point, quasi-TRV with a peak of 7.5 kV was applied between the electrodes with a precise specified delay time td to judge arc re-ignition. The results indicated that td = 25 μs involves 60% probability of arc re-ignition. The re-ignition was inferred to originate in thermal mode from joule heating by a small current injection to the residual arc during the quasi-TRV application..
3. Studied of Collisionless Shocks using Collective Thomson Scattering.
4. Taichi Morita, Y. Sakawa, Y. Kuramitsu, T. Ide, K. Nishio, M. Kuwada, H. Ide, K. Tsubouchi, H. Yoneda, A. Nishida, T. Namiki, T. Norimatsu, Kentaro Tomita, K. Nakayama, K. Inoue, Kiichiro Uchino, M. Nakatsutsumi, A. Pelka, M. Koenig, Q. Dong, D. Yuan, G. Gregori, H. Takabe, High Mach-number collisionless shock driven by a laser with an external magnetic field, 7th International Conference on Inertial Fusion Sciences and Applications, IFSA 2011, 2013.12, Collisionless shocks are produced in counter-streaming plasmas with an external magnetic field. The shocks are generated due to an electrostatic field generated in counter-streaming laser-irradiated plasmas, as reported previously in a series of experiments without an external magnetic field [T. Morita et al., Phys. Plasmas, 17, 122702 (2010), Kuramitsu et al., Phys. Rev. Lett., 106, 175002 (2011)] via laser-irradiation of a double-CH-foil target. A magnetic field is applied to the region between two foils by putting an electro-magnet (∼10 T) perpendicular to the direction of plasma expansion. The generated shocks show different characteristics later in time (t > 20ns)..
5. Kiichiro Uchino, Yasushi Sonoda, Kentaro Tomita, Thomson scattering diagnostics of micro-plasmas for plasma display panel, 10th International Meeting on Information Display and International Display Manufacturing Conference and Asia Display 2010, IMID/IDMC/ASIA Display 2010, 2010, Laser Thomson scattering (LTS) has been applied to diagnostics of PDP micro-plasmas and revealed electron density ne to be of the order of 1019-1020 m-3 and electron temperature T e to be around 1-2 eV. Furthermore, ne and Te spatial profiles and their temporal changes have been successfully measured and their features have been discussed in connection with the striation phenomenon. In order to assist the development of PDP with high efficiency, LTS is tried to apply to study the structure of PDP discharges with narrow electrodes. Also, the streamer discharges which might give ultimate high efficiency are being examined..
6. Naoji Yamamoto, Shmya Kondo, Teppei Tsuru, Hideki Nakashima, Amane Majima, Naoto Yamasaki, Kentaro Tomita, Kiichiro Uchino, Plasma property measurement in a miniature microwave discharge ion thruster by laser Thomson scattering, 44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 2008.12, For understanding the mechanism of plasma production and loss in a miniature microwave discharge ion thruster, plasma parameters, electron number density and electron energy distribution function, in a miniature microwave discharge ion thruster were successfully measured by means of laser Thomson scattering. A photon counting method and a double monochromator were used against small Thomson scattering signal and strong stray laser light. The result shows an electron energy distribution function is Maxwellian, since the scattered spectrum can be fitted by Gaussian at the temperature of 1.5 eV. An electron number density is 2.3 × 1018 m-3 The measured electron number density and electron temperature values were found to be reasonable compared with estimation deduced form extracted ion beam current..
7. Collective Thomson Scattering Diagnostics of Laser Produced Plasmas for EUV Light Sources.
8. Diagnostics of PDP Micro-Discharge Plasmas Using Infrared Laser Thomson Scattering System.
9. Diagnostics Of PDP Micro-Discharge Plasmas Using Laser Thomson Scattering.
10. Measurements of Plasmas Produced in a Miniature Microwave Ion Engine by Using Laser Thomson Scattering.
11. Collective Thomson Scattering Diagnostics of Plasmas for EUV Light Sources.
12. S. Katsuki, H. Imamura, S. Akiyoshi, T. Namihira, T. Sakugawa, H. Akiyama, Kentaro Tomita, Kiichiro Uchino, Characterization of Z-pinch plasmas for EUV light sources, 2005 IEEE Pulsed Power Conference, PPC, 2007, This paper describes the characterization of Z-pinch xenon plasmas for EUV sources. The plasmas were driven by a 15 J pulsed power generator, which delivers pulsed currents (35 kA, 120 ns) to the short circuit load. We have developed a time-resolved interferogram and a Thomson scattering system to characterize the Z-pinch plasmas. The interferogram using a pulsed Nd:YAG laser (532 nm, 7 ns) shows the temporal development of the radial profile of electron density. The electron density in the core plasma during pinch phase was 1.2 × 1019 cm-3. Preliminary result of the Thomson scattering measurement shows the electron temperature and density at the decay phase of the pinch process were 5.5 eV and 3 × 1017 cm -3, respectively..
13. Y. Sonoda, A. Akune, Kentaro Tomita, S. Hassaballa, Kiichiro Uchino, K. Ishii, Y. Hirano, Y. Murakami, Diagnostics of PDP micro-discharge plasmas using infrared laser thomson scattering system, 14th International Display Workshops, IDW '07, 2007, In order to avoid laser perturbations for Xe containing discharges, the laser Thomson scattering (LTS) system having an infrared laser at a wavelength of 1064 nm as a light source has been developed. The basic behavior of electrons in the Ne/Xe discharges was investigated by using the infrared LTS system. Furthermore, it was demonstrated that the measurement of the electron energy distribution function was possible up to the electron energy corresponding to the excitation energy of the Xe atom..