Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Naoji Yamamoto Last modified date:2018.06.29

Professor / Engineering Science for Advanced energy system / Department of Advanced Energy Science and Engineering / Faculty of Engineering Sciences


Papers
1. Naoya Saito, Naoji Yamamoto, Taichi Morita, Masafumi Edamoto, Hideki Nakashima, Shinsuke Fujioka, Akifumi Yogo, Hiroaki Nishimura, Atsushi Sunahara, Yoshitaka Mori, Tomoyuki Johzaki, Experimental demonstration of ion extraction from magnetic thrust chamber for laser fusion rocket, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.7567/JJAP.57.050303, 57, 5, 2018.05, A magnetic thrust chamber is an important system of a laser fusion rocket, in which the plasma kinetic energy is converted into vehicle thrust by a magnetic field. To investigate the plasma extraction from the system, the ions in a plasma are diagnosed outside the system by charge collectors. The results clearly show that the ion extraction does not strongly depend on the magnetic field strength when the energy ratio of magnetic field to plasma is greater than 4.3, and the magnetic field pushes back the plasma to generate a thrust, as previously suggested by numerical simulation and experiments..
2. Taichi Morita, Masafumi Edamoto, Satoshi Miura, Atsushi Sunahara, Naoya Saito, Yutaro Itadani, Tomihiko Kojima, Yoshitaka Mori, Tomoyuki Johzaki, Yoshihiro Kajimura, Shinsuke Fujioka, Akifumi Yogo, Hiroaki Nishimura, Hideki Nakashima, Naoji Yamamoto, Control of unsteady laser-produced plasma-flow with a multiple-coil magnetic nozzle, Scientific Reports, 10.1038/s41598-017-09273-3, 7, 1, 2017.12, We report an experimental demonstration of controlling plasma flow direction with a magnetic nozzle consisting of multiple coils. Four coils are controlled separately to form an asymmetric magnetic field to change the direction of laser-produced plasma flow. The ablation plasma deforms the topology of the external magnetic field, forming a magnetic cavity inside and compressing the field outside. The compressed magnetic field pushes the plasma via the Lorentz force on a diamagnetic current: j × B in a certain direction, depending on the magnetic field configuration. Plasma and magnetic field structure formations depending on the initial magnetic field were simultaneously measured with a self-emission gated optical imager and B-dot probe, respectively, and the probe measurement clearly shows the difference of plasma expansion direction between symmetric and asymmetric initial magnetic fields. The combination of two-dimensional radiation hydrodynamic and three-dimensional hybrid simulations shows the control of the deflection angle with different number of coils, forming a plasma structure similar to that observed in the experiment..
3. Yushi Hamada, Junhwi Bak, Rei Kawashima, Hiroyuki Koizumi, Kimiya Komurasaki, Naoji Yamamoto, Yusuke Egawa, Ikkoh Funaki, Shigeyasu Iihara, Shinatora Cho, Kenichi Kubota, Hiroki Watanabe, Kenji Fuchigami, Yosuke Tashiro, Yuya Takahata, Tetsuo Kakuma, Yusuke Furukubo, Hirokazu Tahara, Hall thruster development for Japanese space propulsion programs, Transactions of the Japan Society for Aeronautical and Space Sciences, 10.2322/tjsass.60.320, 60, 5, 320-326, 2017.09, Three different types of high power Hall thrusters—anode layer type, magnetic layer type with high specific impulse, and magnetic layer type with dual mode operation (high thrust mode and high specific impulse mode)—have been developed, and the thrust performance of each thruster has been evaluated. The thrust of the anode layer type thruster is in the range of 19–219 mN, with power in the range of 325–4500 W. The thrust of the high specific impulse magnetic layer type thruster was 102 mN, with specific impulse of 3300 s. The thrust of the bimodal operation magnetic layer thruster was 385 mN with specific impulse of 1200 s, and 300 mN with specific impulse of 2330 s. The performance of these thrusters demonstrates that the Japanese electric propulsion community has the capability to develop a thruster for commercial use..
4. Naoji Yamamoto, Kohei Takase, Yuya Hirano, Kimiya Komurasaki, Akira Kakami, Ryudo Tsukizaki, Satoshi Hosoda, Hitoshi Kuninaka, Shigeru Yokota, Thrust Performance in a 5 kW Class Anode Layer Type Hall Thruster, Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan, http://doi.org/10.2322/tastj.14.Pb_183, 14, No. ists30 (ISTS Special Issue: Selected papers from the 30th International Symposium on Space Technology and Science), Pb_183-Pb_187, 2017.02.
5. Indranuj Dey, Naoji Yamamoto, Hideki Nakashima, Effect of orifice diameter on the performance of a miniature microwave neutralizer, Transactions of the Japan Society for Aeronautical and Space Sciences, 10.2322/tjsass.60.259, 60, 4, 259-262, 2017.01, A miniature electron cyclotron resonance (ECR) plasma source is operated as a neutralizer, and the effect of orifice diameter on the output is studied. The output is quite promising for accompanying 1-mN-class ion thrusters with an output ion-beam current of 12–15mA. The optimum orifice diameter is independent of neutral mass flow rate, implying that factors other than electron-neutral collisions are dominant. The variation in orifice diameter is expected to alter the microwave field boundary conditions inside discharge chamber (DC), and also influence the dc-electric field existing between the orifice and collector. The convolution of these two factors would be primarily responsible for the optimum orifice diameter..
6. Masataka Iwamoto, Naoji Yamamoto, Taichi Morita, Hideki Nakashima, Kentaro Tomita, Kiichiro Uchino, Rayleigh scattering measurement of neutral atom number density downstream of a hall thruster under cold flow conditions, Transactions of the Japan Society for Aeronautical and Space Sciences, 10.2322/tjsass.60.327, 60, 5, 327-330, 2017.01, The approach presented in a study uses the laser Rayleigh scattering technique. This is a non-intrusive method, and it does not disturb the plasma and neutral flow. Number densities can be measured quantitatively by calibration using 104 Pa nitrogen, so a complicated collisional-radiative model is not required. The Rayleigh scattering spectrum reflects the velocity distribution of the atoms, so propellant xenon atoms can be distinguished from the ambient xenon atoms. In addition, even when both ions and electrons are present, the neutral number density can be estimated, since the scattering spectrum is a convolution of Rayleigh and Thomson spectra..
7. Koichi Ushio, Yuji Toyoda, Naoji Yamamoto, Taichi Morita, Hideki Nakashima, Development of a Miniature Microwave Discharge Thruster, Transactions of Japan Society for Aeronautical and Space Sciences, Space Technology Japan,, http://doi.org/10.2322/tastj.14.Pb_141, 14, pb_141-pb_147, 2016.12.
8. Naoji Yamamoto, Takumi Ito, Haruki Takegahara, Hiroki Watanabe, Taichiro Tamida, Hiroyuki Osuga, Thrust Performance in Hall Thruster with Pulsating Operation, Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan, http://doi.org/10.2322/tastj.14.Pb_173, 14, No. ists30 (ISTS Special Issue: Selected papers from the 30th International Symposium on Space Technology and Science), Pb_173-Pb_176, 2016.12.
9. Naoji Yamamoto, Atsushi Yamaguchi, Atsushi Kibe, Taichi Morita, Hideki Nakashima, Measurement of Aluminum Erosion Rate by Cavity Ring-Down Spectroscopy, Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan, http://doi.org/10.2322/tastj.14.Pb_111, 14, No. ists30 (ISTS Special Issue: Selected papers from the 30th International Symposium on Space Technology and Science), Pb_111-Pb_116 , 2016.11.
10. Taichi Morita, Naoji Yamamoto, R. Kawashima, N. Saito, M. Edamoto, S. Fujioka, Y. Itadani, T. Johzaki, S. Miura, Y. Mori, H. Nishimura, A. Sunahara, A. Yogo, H. Nakashima, Plasma structure and energy dependence in a magnetic thrust chamber system, Journal of Physics: Conference Series, 10.1088/1742-6596/717/1/012071, 717, 1, 2016.05, We demonstrate a magnetic thrust chamber system, in which an expanding plasma is controlled by an external magnetic field to produce a thrust. The plasma structure and energy dependences are discussed in terms of the drive laser energy and magnetic field strength. The density distribution from two different experiments show identical structure despite the laser energy is different by two order of magnitude when the ratio of magnetic field to plasma energy is more or less same. The experimental results indicate that this ratio is one of the essential factors to extrapolate the plasma dynamics for much larger energy such as inertial confinement fusion plasmas..
11. A. Yamaguchi, A. Kibe, Naoji Yamamoto, Taichi Morita, Hiroshi Nakashima, M. Nakano, Erosion rate measurement in ion thrusters using Cavity Ring-Down Spectroscopy technique, Journal of Instrumentation, 10.1088/1748-0221/11/01/C01079, 11, 1, 2016.01, We have built a sputter erosion sensor using Cavity Ring-Down Spectroscopy (CRDS) for validating the numerical analysis tool called ''JIEDI tool''. In this paper, we measured the velocity distribution function of the aluminum atoms sputtered from an aluminum acceleration grid of the ion thruster. The experimentally obtained aluminum velocity distribution have been found to be compatible with those calculated by the numerical analysis method..
12. Naoji Yamamoto, Yushi Maeda, Hideki Nakashima, Hiroki Watanabe, Ikkoh Funaki, Investigation of erosion and deposition in a microwave discharge neutralizer, Transactions of the Japan Society for Aeronautical and Space Sciences, 10.2322/tjsass.59.100, 59, 2, 100-103, 2016.01, A one hundred hour test of a 100mA class microwave discharge neutralizer was performed to investigate the erosion rate and deposition in the neutralizer. The mass loss of each component (antenna, discharge chamber wall, front yoke, back yoke, insulator and orifice) was measured in diode mode (contact voltage of 50 V) at a constant incident microwave power of 8W and xenon mass flow rate of 49 μg/s. The measured erosion rates of the discharge chamber and the antenna were 180 μg/hr and 10 μg/hr, respectively. The element concentration of the deposited material on the back yoke and insulator were measured; the contamination on the insulator was found to contain 34% copper from the wall and 6% molybdenum from the antenna..
13. Ryosuke Kawashima, Taichi Morita, Naoji Yamamoto, Naoya Saito, Shinsuke Fujioka, Hiroaki Nishimura, Hiraku Matsukuma, Atsushi Sunahara, Yoshitaka Mori, Tomoyuki Johzaki, Hideki Nakashima, The measurement of plasma structure in a magnetic thrust chamber, Plasma and Fusion Research, 10.1585/pfr.11.3406012, 11, 2, 2016.01, Magnetic thrust chamber is a propulsion system controlling plasma by a magnetic field and is expected as a propulsion system of laser fusion rocket. This rocket obtains thrust due to the interaction between plasma and magnetic field in the system. We examine the plasma structure in a magnetic thrust chamber by observing the light emission from the plasma with several magnetic field strength. The experiments imply that anisotropic plasma expansion is induced by the applied magnetic field and the velocity is decreased at the magnetic field above 0.67 T..
14. Indranuj Dey, Yuji Toyoda, Naoji Yamamoto, Hideki Nakashima, Development of a miniature microwave electron cyclotron resonance plasma ion thruster for exospheric micro-propulsion, Review of Scientific Instruments, 10.1063/1.4937353, 86, 12, 2015.12, A miniature microwave electron cyclotron resonance plasma source [(discharge diameter)/(microwave cutoff diameter) < 0.3] has been developed at Kyushu University to be used as an ion thruster in micro-propulsion applications in the exosphere. The discharge source uses both radial and axial magnetostatic field confinement to facilitate electron cyclotron resonance and increase the electron dwell time in the volume, thereby enhancing plasma production efficiency. Performance of the ion thruster is studied at 3 microwave frequencies (1.2 GHz, 1.6 GHz, and 2.45 GHz), for low input powers (<15 W) and small xenon mass flow rates (<40 μg/s), by experimentally measuring the extracted ion beam current through a potential difference of ≅1200 V. The discharge geometry is found to operate most efficiently at an input microwave frequency of 1.6 GHz. At this frequency, for an input power of 8 W, and propellant (xenon) mass flow rate of 21 μg/s, 13.7 mA of ion beam current is obtained, equivalent to an calculated thrust of 0.74 mN..
15. Naoya Saito, Hiroshi Tominaga, Ryosuke Kawashima, Taichi Morita, Naoji Yamamoto, Hideki Nakashima, Shinsuke FUJIOKA,, Atsushi SUNAHARA, Yoshitaka MORI,, Tomoyuki JOHZAKI, Acceleration of Miniature Targets by Kilo-Tesla Magnetic Field, TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 13, 17-21, 2015.06.
16. Naoji Yamamoto, Haruki Takegahara, Junichiro Aoyagi, Kyoichi Kuriki, Taichiro Tamida, Hiroyuki Osuga, Development of a novel power processing unit for hall thrusters, IEEE Transactions on Plasma Science, 10.1109/TPS.2014.2370066, 43, 1, 158-164, 2015.01, A newly developed power processing unit (PPU) offers the advantages of smaller size and lighter weight than conventional PPUs. The thrust performance of a magnetic layer type Hall thruster developed at Kyushu University with this new PPU was investigated; it showed a good performance as compared with conventional power supplies. The thrust to power ratio was improved to 58 mN/kW at discharge voltage of 150 V and anode xenon mass flow rate of 1.0 mg/s..
17. Taichiro Tamida, Hiroyuki Osuga, Naoji Yamamoto, Haruki Takegahara, Junichiro Aoyagi, Kyoichi Kuriki, Performance improvement of Hall thrusters using a pulse-synchronous driver system, Journal of Propulsion and Power, 10.2514/1.B35273, 31, 3, 956-961, 2015.01, A new pulse-synchronous driver system is proposed for Hall thrusters.By applyingapulsating drive voltage with a frequency close to that of the discharge oscillation, the stable and synchronized operation of a Hall thruster can be realized. A pulsating boost chopper circuit is also proposed that is suitable for use as a pulse-synchronous drive and has many attractive features as the driver circuit for Hall thrusters. Moreover, it is demonstrated that the thrust performance is improved approximately 30% at 200 W input power by using the driver circuit. Pulse-synchronous driving isa new driving method optimized for thruster operation, and it is expected to become anessential technology for high-power Hall thrusters..
18. Keisuke TANAKA, Ryosuke KAWASHIMA, Naoji Yamamoto, Taichi Morita, Hideki Nakashima , Diagnostics of Fireball by Discharge on the Surface of an Electrolyte Floating Particulates , Frontier of Applied Plasma Technology , 2015.01.
19. Indranuj Dey, Yuji Toyoda, Naoji Yamamoto, Hideki Nakashima, Experimental investigation of microwave interaction with magnetoplasma in miniature multipolar configuration using impedance measurements, Physics of Plasmas, 10.1063/1.4894476, 21, 9, 2014.09, A miniature microwave plasma source employing both radial and axial magnetic fields for plasma confinement has been developed for micro-propulsion applications. Plasma is initiated by launching microwaves via a short monopole antenna to circumvent geometrical cutoff limitations. The amplitude and phase of the forward and reflected microwave power is measured to obtain the complex reflection coefficient from which the equivalent impedance of the plasma source is determined. Effect of critical plasma density condition is reflected in the measurements and provides insight into the working of the miniature plasma source. A basic impedance calculation model is developed to help in understanding the experimental observations. From experiment and theory, it is seen that the equivalent impedance magnitude is controlled by the coaxial discharge boundary conditions, and the phase is influenced primarily by the plasma immersed antenna impedance..
20. I. Dey, Y. Toyoda, K. Hirano, N. Yamamoto, and H. Nakashima, Development of a Low Power Multipole Confined Microwave Plasma Ion Thruster, Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan,, http://dx.doi.org/10.2322/tastj.12.Pb_7, 12, No. ists29, Pb_7-Pb_12, 2014.03.
21. B. C. Lee, W. Huang, L. Tao, Naoji Yamamoto, A. D. Gallimore, A. P. Yalin, A cavity ring-down spectroscopy sensor for real-time Hall thruster erosion measurements, Review of Scientific Instruments, 10.1063/1.4879135, 85, 5, 2014.01, A continuous-wave cavity ring-down spectroscopy sensor for real-time measurements of sputtered boron from Hall thrusters has been developed. The sensor uses a continuous-wave frequency-quadrupled diode laser at 250 nm to probe ground state atomic boron sputtered from the boron nitride insulating channel. Validation results from a controlled setup using an ion beam and target showed good agreement with a simple finite-element model. Application of the sensor for measurements of two Hall thrusters, the H6 and SPT-70, is described. The H6 was tested at power levels ranging from 1.5 to 10 kW. Peak boron densities of 10 ± 2 × 1014 m-3 were measured in the thruster plume, and the estimated eroded channel volume agreed within a factor of 2 of profilometry. The SPT-70 was tested at 600 and 660 W, yielding peak boron densities of 7.2 ± 1.1 × 1014 m-3, and the estimated erosion rate agreed within ∼20% of profilometry. Technical challenges associated with operating a high-finesse cavity in the presence of energetic plasma are also discussed..
22. Akihiro Maeno, Tomoyuki Hinaga, Naoji Yamamoto, Atsushi Sunahara, Shinsuke Fujioka, Hideki Nakasima, Effect of magnetic field strength on a magnetic thrust chamber system, Journal of Propulsion and Power, 10.2514/1.B34911, 30, 1, 54-61, 2014.01, To confirm the validity of the modified numerical simulation performing a series of numerical simulations for highenergy laser injection onto a spherical target and the ablation plasma behavior in a magnetic field, the modified numerical simulation is compared with experiments and original numerical simulation. The modified numerical simulation consists of a one-dimensional Lagrangian radiation hydrodynamic code to calculate the creation process of laser-produced plasma and a three-dimensional hybrid particle-in-cell code. The original numerical simulation does not consider the creation process. The measured impulse bit due to the interaction between the diamagnetic current in a laser-produced plasma and the magnetic field generated by neodymium permanent magnets is 2.42 ± 0.23 μN · s. The calculated impulse bit in the modified and original numerical simulations is 10.3 and 72.7 μN · s, respectively. These results reveal that the modified numerical simulation models closer to the experiment than the original numerical simulation. In addition, to investigate the effect of the magnetic field strength on the plasma behavior in a magnetic thrust chamber system for a laser fusion rocket, the modified numerical simulation is performed. As a result, it is revealed that there is an approximation region of the magnetic field strength for high thrust performance..
23. Kentaro Hirata, Kenichiro Furumoto, Naoji Yamamoto, Tetsuo Tanabe, Application of pulsed laser irradiation for removal of hydrogen retained in tungsten, Journal of Nuclear Materials, 10.1016/j.jnucmat.2013.07.047, 443, 1-3, 298-301, 2013.08, For the purpose of removal of tritium retained in tungsten (W), pulsed laser irradiation has been applied. The laser light used here was the fourth harmonic of Nd: YAG laser (wavelength; 266 nm, pulse width; 20 ps, pulse frequency; 10 Hz, laser energy up to 3 mJ/pulse). Samples were pure W plates and those saturated with D by D2+ ion implantation at room temperature with using a 2.5 keV ion gun. Released ions and molecules by the laser irradiation were measured by a time-of-flight mass spectrometer (TOFMS) and a quadrupole mass spectrometer (Q-mass), respectively. Ablation of W was observed by the laser irradiation with a deposited power density above 1.5 × 1011 W/cm2 (3 J/cm2/pulse) (an ablation threshold) and D removals below and above the ablation threshold were quite different. The most effective removal of tritium retained in W could be realized by the pulsed laser irradiation with the power density of just below the ablation threshold..
24. Akihiro Maeno, Naoji Yamamoto, Shinsuke Fujioka, Yoshitaka Mori, Atsushi Sunahara, Tomoyuki Johzaki, Hideki Nakashima, Analysis of laser wavelength and energy dependences of the impulse in a magnetic thrust chamber system for a laser fusion rocket, Transactions of the Japan Society for Aeronautical and Space Sciences, 10.2322/tjsass.56.170, 56, 3, 170-172, 2013.05, Experiments using a pendulum thrust stand are performed to determine the dependences of the impulse on the laser wavelength and energy in a magnetic thrust chamber system for a laser fusion rocket. The impulse is generated by the interaction between a diamagnetic current in a laser-produced plasma and a magnetic field. The plasma is produced by irradiating a spherical polyacetal target with a single-beam glass laser (laser pulse duration: 1.3 ns; laser wavelengths: 1,053, 527 and 351 nm; laser energy: 30-900 J). The magnetic field is generated by a cylindrical neodymium permanent magnet (50mm diameter and 40mm long) placed in a position 33mm from the target. Impulses in the range 0.02- 10 mNs are measured using a pendulum thrust stand. The experiments reveal that the impulse for 2ω is similar to that for 3ω, and is larger than that for ω..
25. Masato Yasunaga, Akihiro Maeno, Naoji Yamamoto, Hideki Nakashima, Demonstration Experiment of Magnetic Thrust Chamber for a Laser Fusion Rocket, Transactions of Japan Society for Aeronautical and Space Sciences, Space Technology Japan,, http://dx.doi.org/10.2322/tastj.10.Pb_109, 2013.02.
26. Shinsuke Fujioka, Zhe Zhang, Kazuhiro Ishihara, Keisuke Shigemori, Youichiro Hironaka, Tomoyuki Johzaki, Atsushi Sunahara, Naoji Yamamoto, Hideki Nakashima, Tsuguhiro Watanabe, Hiroyuki Shiraga, Hiroaki Nishimura, Hiroshi Azechi, Kilotesla magnetic field due to a capacitor-coil target driven by high power laser, Scientific Reports, 10.1038/srep01170, 3, 2013.02, Laboratory generation of strong magnetic fields opens new frontiers in plasma and beam physics, astro-and solar-physics, materials science, and atomic and molecular physics. Although kilotesla magnetic fields have already been produced by magnetic flux compression using an imploding metal tube or plasma shell, accessibility at multiple points and better controlled shapes of the field are desirable. Here we have generated kilotesla magnetic fields using a capacitor-coil target, in which two nickel disks are connected by a U-turn coil. A magnetic flux density of 1.5 kT was measured using the Faraday effect 650 μm away from the coil, when the capacitor was driven by two beams from the GEKKO-XII laser (at 1 kJ (total), 1.3 ns, 0.53 or 1 μm, and 5 × 10 16 W/cm2)..
27. Kenichiro Furumoto, Tetsuo Tanabe, Naoji Yamamoto, Takeshi Daio, Syo Matsumura, Kazuhiro Yasuda, Development of novel optical fiber system for cathodoluminescence detection in high voltage transmission electron microscope, Materials Transactions, 10.2320/matertrans.M2013025, 54, 5, 854-856, 2013, We have installed a new system to observe cathodoluminescence (CL) in a high voltage transmission electron microscope (HVTEM). The system is constructed of a ball lens for collection of CL, an optical fiber and a multi-channel optical detector. The system can be operated without any disturbance of TEM observation. The system was proved to be very useful to observe CL in HVTEM and will be a powerful tool to investigate production mechanisms of luminescence centers by observing CL changes with incident electron energy and flux (displacement damage effect), and temperature, together with simultaneous TEM observations of microstructure changes..
28. Akihiro MAENO, Yoshihiro KAJIMURA, Atsushi SUNAHAR, Naoji Yamamoto, Masato YASUNAG, omoyuki HINAGA, Tomonari HANAYA, Shinsuke FUJIOKA, Tomoyuki JOHZAKI, Yoshitaka MORI, Hideki Nakashima, Numerical Analysis of Magnetic Thrust Chamber System for Laser Fusion Rocket Considering the Creation Process of Laser-Produced Plasma, TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, http://dx.doi.org/10.2322/tastj.10.Pb_71, 2012.08.
29. Naoji Yamamoto, Yoshiaki Hiraoka, Kensaku Sugita, Tomoaki Kurita, Kentaro Tomita, Kiichiro Uchino, Hideki Nakashima, Thomson Scattering Diagnostics in the Plasma of an Ion Thruster, TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, SPACE TECHNOLOGY JAPAN, 10.2322/tastj.10.Pb_79, 10, 28, Pb_79-Pb_83, 2012.08, In order to validate the grid erosion evaluation code for the lifetime validation of ion thrusters, the electron number density/temperature in the vicinity of a screen gird in a 30 W class microwave discharge ion thruster were measured by means of laser Thomson scattering (LTS) technique. A photon counting method and a triple grating spectrometer were used against a small Thomson scattering signal and a strong stray laser light. Observed Thomson scattering spectrum tells that the electron energy distribution function was Maxwellian. From this spectrum and the Rayleigh scattering calibration using nitrogen gas, electron number density and electron temperature were calculated to be (3.8±0.2)×1017m-3 and 6.2±0.1 eV, respectively at incident microwave power of 8 W and krypton mass flow rate of 6.2 μg/s. The ion saturation currents estimated from the LTS measurement are in good agreement with ion beam currents through the screen grid for several conditions. These results show that LTS technique is a useful non-intrusive tool for measuring plasma property in the vicinity of the screen grid..
30. Naoji Yamamoto, KENTARO TOMITA, Kensaku Sugita, Tomoaki Kurita, Hideki Nakashima, Kiichiro Uchino, Measurement of xenon plasma properties in an ion thruster using laser Thomson scattering technique, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.4737144, 83, 7, 2012.07.
31. Naoji YAMAMOTO , Toru EZAKI and Hideki NAKASHIMA, Thrust performance of a low power Hall thruster, Transactions of Japan Society for Aeronautical and Space Sciences, Space Technology Japan,, 9, ists28, 2012.05.
32. Hiroyuki Osuga, Fujio Kurokawa, Taichiro Tamida, Naoji Yamamoto, High efficiency control method for the hall thruster system through constant flow rate control by power supply control, IEICE Transactions on Communications, 10.1587/transcom.E95.B.133, E-95-B, 1, 133-142, 2012.01, We present a new power supply control method, which achieves constant flow Rate control for the thrust of a 20 mN-class Hall thruster. First, we present observations of a 20mN-class Hall thruster with oscillation-mode-map. We make a theoretical study of the thrust and experiments on electrical characteristics of the Hall thruster, and conclude that thrust, thrust efficiency and low frequency oscillation are clearly determined by the external control parameters, anode voltage, gas flow rate, and magnetic flux density. Second, we discuss how to control the power supplies to suppress the power consumption, especially when the operation or thruster conditions change temporarily during use. The new method will be a very important guideline for Hall thruster system design and operation, in particular making it easy to manage the power consumption in a satellite by controlling the thrust resources. As a result of performance experiments for a 20mN-class Hall thruster, over 36% thrust efficiency of the Hall thruster was found to be sensitive to the anode voltage and applied magnetic flux density. The new power control method achieves constant flow rate control method of the thrust. The benefits are light weight and low cost..
33. Akihiro Maeno, Naoji Yamamoto, Hideki Nakashima, Shinsuke Fujioka, Tomoyuki Johzaki, Yoshitaka Mori, Atsushi Sunahara, Direct measurement of the impulse in a magnetic thrust chamber system for laser fusion rocket, Applied Physics Letters, 10.1063/1.3626600, 99, 7, 2011.08, An experiment is conducted to measure an impulse for demonstrating a magnetic thrust chamber system for laser fusion rocket. The impulse is produced by the interaction between plasma and magnetic field. In the experiment, the system consists of plasma and neodymium permanent magnets. The plasma is created by a single-beam laser aiming at a polystyrene spherical target. The impulse is 1.5 to 2.2 μNs by means of a pendulum thrust stand, when the laser energy is 0.7 J. Without magnetic field, the measured impulse is found to be zero. These results indicate that the system for generating impulse is working..
34. N. Yamamoto, L. Tao, A. P. Yalin, Development of Real-time Erosion Monitoring System for Hall Thrusters by Cavity Ring-Down Spectroscopy, Transactions of Japan Society for Aeronautical and Space Sciences, Space Technology Japan,, 8, ists27, pp.Pb_39-Pb_44., 2011.03.
35. T. Ezaki, N. Yamamoto, T. Tsuru, Y. Kotani, H. Nakashima, N. Yamasaki, K. Tomita, and K. Uchino, Plasma Properties in a Miniature Microwave Discharge Ion Thruster, Transactions of Japan Society for Aeronautical and Space Sciences, Space Technology Japan,, 8, ists27, pp.Pb_39-Pb_44., 2011.03.
36. N. Yamamoto, J Shimokawatoko, M. Oya and H. Nakashima, Temperature Measurement in a Radio Frequency Electro-thermal Thruster by Integrated Cavity Output Spectroscopy, Frontier of Applied Plasma Technology, 4, 1, pp.12-15, 2011.01.
37. N Yamamoto, K Tomita, N Yamasaki, T Tsuru, T Ezaki, Y Kotani, K Uchino and H Nakashima, Measurements of electron density and temperature in a miniature microwave discharge ion thruster using laser Thomson scattering technique,and Technology, Plasma Sources Science and Technology, 10.1088/0963-0252/19/4/045009, 19, 4, 045009, 2010.06.
38. Kentaro Tomita, Naoji Yamamoto, Yamasaki Naoto, Tsuru Teppei, Kiichiro Uchino, Nakashima Hideki, Thomson-scattering diagnostics of plasmas produced in a miniature microwave discharge ion engine, Journal of Propulsion and Power, 10.2514/1.39145, 26, 2, 381-383, 2010.03, A study was conducted to measure plasma properties by laser Thomson scattering (LTS) to understand the physics inside this engine. The photon-counting method with a double monochromator was used to overcome the difficulties of applying the method to the plasma produced in the miniature microwave ion engine. Microwave power at 2.45 GHz was fed through a coaxial line and into an antenna in the engine. The screen grid and the ion source body were biased at +1500 V relative to ground and the acceleration grid was biased at -300 V. The primary electrons were confined in the mirrorlike magnetic field formed between the central and front yokes, gaining energy from microwave emission by electron cyclotron resonance heating. Two small holes to inject the laser and another hole collect scattering light were made to measure the plasma inside the discharge chamber..
39. N. Yamamoto, L. Tao,B. Rubin, J.D. Williams and A.P. Yalin, Sputter Erosion Sensor for Anode Layer-Type Hall Thrusters Using Cavity Ring-Down Spectroscopy, Journal of Propulsion and Power, 10.2514/1.44784, 26, 1, pp.142-148, Vol. 22, pp.925-928,, 2010.01.
40. N. Yamamoto, L. Tao, and A.P. Yalin, Single-mode delivery of 250 nm light using a large mode area photonic crystal fiber, Optics Express, 10.1364/OE.17.016933, 17, 19, pp.16933-16940, 2009.12, [URL].
41. Naoji YAMAMOTO, Makoto MIYOSHI, Yoshiyuki TAKAO and Hideki NAKASHIMA, Development of a Microwave Discharge Ion Thruster Using Argon, TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES,SPACE TECHNOLOGY JAPAN, 10.2322/tstj.7.Pb_119, 7, ists26, pp.Pb_119-Pb_124, 2009.05.
42. Yoshiyuki TAKAO, Akihiro KUGIMIYA, Shinobu NAGAI, Naoji YAMAMOTO, Yoshihiro KAJIMURA and Hideki NAKASHIMA, Study of 2.5-10cm Size Microwave Discharge Ion Thruster, TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, SPACE TECHNOLOGY JAPAN, 10.2322/tstj.7.Pb_155, 7, ists26, pp.Pb_155-Pb_158, 2009.05.
43. Naoji YAMAMOTO, Azer P.YALIN, Lei TAO, Timothy B. SMITH, Alec D. GALLIMORE and Yoshihiro ARAKAWA, Development of Real-time Boron Nitride Erosion Monitoring System for Hall Thrusters by Cavity Ring-Down Spectroscopy, TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES,SPACE TECHNOLOGY JAPAN, 10.2322/tstj.7.Pb_1, 7, ists26, pp. pb_1-pb_6, 2009.04.
44. Yamamoto, N., Yalin, A. P., Tao, L., Smith, T. B., Gallimore, A. D. and Arakawa, Y.,, Development of Real-time Boron Nitride Erosion Monitoring System for Hall Thrusters by Cavity Ring-Down Spectroscopy, Transactions of Japan Society for Aeronautical and Space Sciences, Space Technology Japan,, 10.2322/tstj.7.Pb_1, 7, ists26, pp. pb_1-pb_6, 2009.04.
45. Y. Kajimura, T. Kanagawa, N. Yamamoto, H. Nakashima,, Numerical Analysis of the Plasma Behavior in a Miniature Microwave Discharge Ion Thruster, AIP(American Institute of Physics) Conference Proceedings, 2009.01.
46. L. Tao, N. Yamamoto, A.P. Yalin, Cavity Ring-Down Spectroscopy Sensor for Ion Beam Etch Monitoring and End-Point Detection of Multilayer Structures, Review of Scientific Instruments, 10.1063/1.2995765, Volume 79, 115107, 2008.12.
47. Dependence of Thruster Configuration on Thrust Performance in Miniature Ion Thruster.
48. A. P. Yalin, L. Tao, Naoji Yamamoto, Sputtering measurements by cavity ring-down spectroscopy and application to electric propulsion and plasma engineering, Quaternary International, 2008, We describe the use of cavity ring-down spectroscopy for measurement of number densities of sputtered particles. Applications for thruster characterization in electric propulsion and process monitoring in plasma engineering are discussed..
49. Naoji Yamamoto, Shinya Kondo, Takayuki Chikaoka, Hirokazu Masui and Hideki Nakashima, Effects of Magnetic Field Configuration on Thrust Performance in A Miniature Microwave Discharge Ion Thruster, JOURNAL OF APPLIED PHYSICS., 10.1063/1.2822456, 102, 123304, 2007.12.
50. T.Kanagawa, H.Masui, N.Yamamoto, H.Nakashima, Numerical Analysis for Effect of Magnetic Field Configuration on the Trust Performance in a Miniature Ion Engine, Proc. of the 6th International Symposium on Applied Plasma Science,, Vol. 6, pp.89-92., 2007.09.
51. Masashi Oya, Naoji Yamamoto, Shinji Ogawa, Yoshihiro Kajimura, and Hideki Nakashima, Energy Balance in a Radio Frequency Electrothermal Thruster with Water Propellant, Proc. of the 6th International Symposium on Applied Plasma Science,, Vol. 6, pp.101-105, 2007.09.
52. N. Yamamoto, S. Kondo, T. Kanagawa, T. Chikaoka, K. Yoshihiro, H. Nakashima, Development of Miniature Microwave Discharge Ion Thruster, Proceedings of the VI-th International Workshop on Microwave Discharges: Fundamentals and Applications,, pp.211-215, pp.211-216, 2006.12.
53. Takayuki Chikaoka, Shinya Kondo, Naoji Yamamoto, Hideki Nakashima, Yoshiyuki Takao,, Magnetic Field Configuration Effects on Thrust Performance of Miniature Microwave Discharge Ion Engine, Proc. of the 25th Int. Symposium on Space Technology and Science, pp. 254-258, pp. 254-259, 2006.12.
54. Yoshiyuki Takao, Hiroshi Kataharada, Takashi Miyamoto, Hirokazu Masui, Naoji Yamamoto and Hideki Nakashima,, Performance Test of Micro Ion Thruster using Microwave Discharge,, Vacuum, 80, 11月12日, pp. 1239-1243, Volume 80, Issues 11-12, Pages 1239-1243,, 2006.09.
55. H. Masui, Y. Tashiro, N. Yamamoto, H. Nakashima, I. Funaki, Analysis of Electron and Microwave Behaviors in Microwave Discharge Neutralizer,, Trans. Jpn. Society for Aeronautical and Space Sciences,, Vol.49, No.164, pp.87-93,, 2006.08.
56. N. Yamamoto, H. Masui, H. Kataharada, H. Nakashima, Y. Takao,, Antenna Configuration Effects on Thrust Performance of Miniature Microwave Discharge Ion Engine, J. Propulsion and Power,, 10.2514/1.18833, Vol. 22, pp.925-928,, 2006.07.
57. H. Kataharada, Y. Takao, N. Yamamoto, H. Ijiri, H. Nakashima, Development of Small Microwave Discharge Ion Thruster, Thin Solid Films, Vol.506-507, pp.605-608,, 2006.03.
58. Naoji YAMAMOTO, Shigeru YOKOTA, Keiko WATANABE, Akihiro SASOH, Kimiya KOMURASAKI, Yoshihiro ARAKAWA, Suppression of Discharge Current Oscillations in a Hall Thruster, Transactions of The Japan Society for Aeronautical and Space Sciences, 10.2322/tjsass.48.169, 48, 161, 169-174, Vol.48 No.161,, 2005.11.
59. Naoji Yamamoto, Kimiya Komurasaki and Yoshihiro Arakawa, Discharge Current Oscillation in Hall Thrusters, JOURNAL OF PROPULSION AND POWER, 10.2514/1.12759, 21, 5, 870-876, Vol.21, No.5, september-October, 2005, pp.870-876, 2005.09.
60. Naoji Yamamoto, Shigeru Yokota, Makoto Matsui and Kimiya Komurasaki,Yoshihiro Arakawa, MEASUREMENT OF EROSION RATE BY ABSORPTION SPECTROSCOPY IN A HALL THRUSTER, Review of Scientific Instruments, 10.1063/1.2001630, 76, 8, Volume 76, Issue 8, 083111, 2005.08.
61. Y. Takao, T. Miyamoto, H. Kataharada, H. Nakashima, H. Masui, T. Kai, H. Ijiri, Y. Mori, N. Yamamoto,, Development of Small-Scale Ion Thruster Utilizing Microwave Discharge Plasma, Proc. of the 24th Int. Symposium on Space Technology and Science,, pp.161-165, pp.161-166, 2004.12.
62. T. Miyamoto, N. Yamamoto, H. Ijiri, Y. Takao, H. Nakashima, Development of a Microwave Discharge Ion Engine by Using Monopole Antennas,, Proc. of the 24th Int. Symposium on Space Technology and Science, pp.137-141, pp.137-142, 2004.12.
63. N. Yamamoto, K. Watanabe, A. Sasoh, K. Komurasaki, Y. Arakawa, Control of Discharge Current Oscillations in Hall Thrusters, Proc. of the 24th Int. Symposium on Space Technology and Science,, pp. 191 -195, pp. 191 -196, 2004.12.
64. Number Density Measurement of Oxygen Atoms in a Hall-Type Ion Source
Plume

Naoji YAMAMOTO, Takafumi NAKAGAWA, Makoto MATSUI, Kimiya KOMURASAKI
and Yoshihiro ARAKAWA.
65. Experimental Investigation of a Hall Thruster using Oxygen as the propellant

Takafumi NAKAGAWA, Naoji YAMAMOTO, Makoto MATSUI, Kimiya KOMURASAKI
and Yoshihiro ARAKAWA.
66. Operating Characteristics of an Anode Layer Type Hall Thruster.
67. Ion Beam Characteristics in Hall Accelerators Using Oxygen Gas

Naoji YAMAMOTO, Takafumi NAKAGAWA, Kimiya KOMURASAKI and Yoshihiro ARAKAWA.
68. Yamamoto N., Nakagawa T., Komurasaki K. and Arakawa Y.,, Effect of Discharge Oscillations on Hall Thruster Performance, Proceedings of the 23rd International Symposium on Space Technology and Science,, pp.319-324, 2002.10.
69. Naoji Yamamoto, Takafumi Nakagawa, Kimiya Komurasaki, Yoshihiro Arakawa, Discharge plasma fluctuations in hall thrusters, Vacuum, 10.1016/S0042-207X(01)00445-6, 65, 3-4, 375-381, 2002.05, Characteristics of plasma fluctuations at the frequencies 10-100 kHz in Hall thrusters were investigated since the fluctuations might affect not only its performance but also its lifetime. Measured fluctuation characteristics varied with magnetic flux density of the applied field and they were categorized into the four regimes. Since the electron mobility strongly depends on applied field strength, it was thought that electrons would play an important role on this oscillation. Therefore, the oscillation model derived from ionization instability considering electron mobility was proposed. The predicted stable/unstable operating condition map agreed well with the measured one..
70. Relation between Discharge Oscillations and Performance in Hall Accelerators

Naoji YAMAMOTO, Takafumi NAKAGAWA, Kimiya KOMURASAKI, and Yoshihiro ARAKAWA.
71. Yamamoto N., Momo, S, Komurasaki K. and Arakawa Y.,, Discharge-current Oscillations in Hall Thrusters, Proceedings of the 22nd International Symposium on Space Technology and Science, pp.349-353, pp.349-354, 2000.10.
72. Discharge Oscillations in Hall Thrusters

Naoji Yamamoto, Kimiya Komurasaki, and Yoshihiro Arakawa.
73. Yamamoto N., Nakagawa T., Komurasaki K. and Arakawa Y.,, Observation of Plasma Fluctuations in Hall Accelerators, Proceedings of the 3rd International Symposium on Applied Plasma Science, Advances in Applied Plasma Science, Vol. 3, (2001), pp.95-100, 2001.07.