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Naoji Yamamoto Last modified date:2017.05.06

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

Graduate School
Undergraduate School

Academic Degree
Doctor of engineering
Field of Specialization
Outline Activities
I have been studying advanced space propulsions, especially, electric propulsion, for using as a deep space probe.
I have been investigating the mechanism of plasma production and loss in order to improve the thrust performance of these propulsion.
Research Interests
  • Improvement of an ion engine performance
    keyword : Electric propulsion, plasma, measurement
    2005.04Hall thrusters are a class of electric propulsion device in which a propellant gas is ionized and accelerated to produce thrust. They offer an attractive combination of high thrust efficiency (exceeding 50%) and specific impulse (~1,000-3,000 s). In comparison to chemical rockets, the high specific impulse is attractive for large delta V missions such as satellite positioning and station-keeping, and space exploration. Hall thrusters also have a higher thrust density than ion thrusters due to the existence of electrons in the ion acceleration zone. In addition, the lack of grids is attractive owing to the potential for reduced failures. Since the 1970s over 200 Hall thrusters have been operated in space. A key requirement for the practical use of Hall thrusters is the ability to operate for long durations, for example a Hall thruster used for north-south station keeping (NSSK) of a commercial spacecraft will have to operate for over 5,000 hours over the course of its mission. The primary life-limiter for Hall thrusters is acceleration channel wall erosion. A thruster is generally considered to have reached end of life when the channel is fully eroded and the underlying magnetic yoke becomes exposed. The physical mechanism causing the erosion is sputtering of the channel material due to bombardment by energetic particles, primarily propellant ions having undergone radial acceleration. In addition to causing channel erosion and associated lifetime concerns, sputtered particles can redeposit on spacecraft components such as solar-arrays, thereby degrading their performance and potentially compromising spacecraft operation. Ideally, the problems of lifetime and redeposition would be addressed with both numerical modeling and experimental measurement. Research in the former area is underway but the fidelity of current models tends to be limited by the accuracy in modeling the fluxes of ions to the channel walls (angular and energy distributions) and lack of knowledge of the sputter yields of the wall channel materials (especially at the needed low ion energies). Experimental lifetime measurements are also very challenging. With proposed thrust durations now as long as 5-10+ years, ground-based life tests over the full thruster duration are becoming increasingly expensive and limiting in terms of technology insertion schedules. And, even when such tests are performed, it is hard to infer the effect of varying thruster operating parameters such as voltage and mass flow rate. What is needed, therefore, is a method of quantitatively measuring thruster erosion rates non-intrusively in real- or near real-time, for example by in situ measurement of the eroded wall material (as we demonstrate here). Such measurements would be dramatically faster (and cheaper) than full life testing, and would readily allow the study of the effects of operating conditions and thruster design changes on erosion. .
  • Physics inside Hall thruster
    keyword : Hall thruster
    2004.04The discharge current oscillation at a frequency range of 10–100 kHz in Hall thrusters was investigated with the objective of extending their stable operational range. The amplitude of oscillation was measured using two types of Hall thrusters—the anode layer type and the magnetic layer type. The oscillation amplitude was found to be sensitive to the applied magnetic flux density, and this result indicated that the oscillation was affected by electron mobility. An oscillation model was proposed based on the experimental results, and the predicted frequency and stable operational range were found to agree qualitatively agreed with the experimental results. This model shows that the momentum transfer corresponding to plasma fluctuation, that is, the viscosity effect, is crucial to achieving stability. Thus, the oscillation amplitude for various acceleration channel configurations—divergent, parallel, and convergent—was measured because the momentum transfer could be affected by the channel configuration. The stable operational range was successfully extended by the adoption of the convergent configuration in each type of Hall thruster as shown by this model. .
  • Development of a miniature microwave discharge ion thruster
    keyword : Space propulsion, electric propulsion, Ion beam source, ion thruster
    2004.04A study of micro wave dischage ion thruster.
Academic Activities
1. 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, 83, 7, 2012.07.
2. 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.
3. 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, 19, 4, 045009, 2010.06.
4. 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, 26, 1, pp.142-148, Vol. 22, pp.925-928,, 2010.01.
5. 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, 17, 19, pp.16933-16940, 2009.12, [URL].
6. 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., 102, 123304, 2007.12.
7. 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,, Vol. 22, pp.925-928,, 2006.07.
8. Naoji Yamamoto, Kimiya Komurasaki and Yoshihiro Arakawa, Discharge Current Oscillation in Hall Thrusters, JOURNAL OF PROPULSION AND POWER, 21, 5, Vol.21, No.5, september-October, 2005, pp.870-876, 2005.09.
9. Operating Characteristics of an Anode Layer Type Hall Thruster.
Membership in Academic Society
  • THe Japan Society of Applied Physics
  • The demand for mN class miniature propulsion systems for small satellites is expected to grow in the future, due to their relatively low cost and short development time, among other reasons . Until recently, size restrictions have limited the capacity of the available propulsion systems, and this has restricted the capability of small satellites. One of the candidates for mN class miniature propulsion systems is a miniature ion thruster, since an ion thruster produces high thrust efficiency (over 50%) with a specific impulse of 3,000-8,000 sec .
    He developed a miniature microwave discharge ion thruster. This performance is competitive with that of the thruster developed by Wirz et al., which has hither to shown the best performance in this class of miniature thruster.
    This will contribute to expand the range and capabilities of small satellites; missions such as Mars exploration would become possible, as would satellite self-disposal. Miniature ion thrusters can also be used for precise high-stability attitude and position control in large spacecraft, as well as for primary propulsion of microsatellites.
  • Dependence of Thruster Configuration on Thrust Performance in Miniature Ion Thruster
  • Laser-Based Sensor for Real Time Sputter Monitoring and End Point Detection in Ion Beam Etch Systems