Yasushi Ono / Professor / Graduate School of Frontier Sciences
Department of Advanced Energy / /

Career Summary
1983: Graduated, Faculty of Engineering, The University of Tokyo
1986-88: Visiting Scholar, Plasma Physics Laboratory, Princeton University
1988: Doctor of Engineering from The University of Tokyo
1988: Research Associate, The University of Tokyo
1989: Lecturer, The University of Tokyo
1993: Associate Professor, The University of Tokyo
2004: Professor, The University of Tokyo
Educational Activities
Graduate School: Plasma Physics and Engineering, Plasma Diagnostics, Energy Transformation Technology
Research Activities
The main research fields of Ono laboratory are PLASMA PHYSICS and ENGINEERING, especially development of new efficient plasma confinement for economical nuclear fusion reactor, alternative energy sources, space / solar plasmas and plasma applications.

Our main motivation is the energy and environmental crisis that we will encounter around 2050. They are caused by (1) environmental devastation by CO2, NOX and SOX from fossil fuels, (2) depletion of energy sources:, especially oil and gasses, (3) expanding energy consumption. We have to replace the present fossil fuels - causes for CO2, NOX, SOX by nuclear fusion reactors which provide us exhaustless energy without any global warming gas. The present fusion research already realized fusion power output larger than the input power. The remaining issue is to realize economic and compact fusion reactor suitable for commercial power system as early as possible. Its key question is whether we can develop ultra-high-beta and compact confinement whose efficiency overcomes the present mainstream: called conventional tokamak. The beta value: P/(B2/2?0) is defined as the plasma thermal pressure P confined by the unit magnetic field pressure B2/2?0.
We have been developing a number of new ideas related with spherical torus confinements: Spherical Tokamak (ST) and Field-Reversed Configuration (FRC) using the TS-3 and TS-4 devices. Recent fusion research put more emphasis on economical efficiency and simplicity of confinements, leading us to the construction of world largest merging spherical torus device UTST.

 TS-3 Spherical Torus Device
TS-3 Spherical Torus Device

 TS-4 Merging Device
TS-4 Merging Device

 UTST Spherical Tokamak Device
UTST Spherical Tokamak Device

1) Ultra-High Beta ST Experiment
Recently, the spherical tokamak (ST) has received increased attention as a promising candidate for economical and highly-efficient fusion reactor. The STs have a unique "apple"-like shape with a sphere boundary as shown in the figure above. Its aspect ratio is decreased down to 1-2 from 3-4 of the conventional tokamaks for increasing the plasma beta. An important question is how high is the upper limit of the ST plasma beta. In 2000, we produced the ultra-high beta (>50%) ST in TS-3 using our new idea: high-power heating of magnetic reconnection. Its highest beta was as large as 60%, the world-record vale. Its high thermal pressure was maintained efficiently by small magnetic field, because its equilibrium was located for the first time in the second-stable state against ballooning instability which is the most dangerous mode for high-beta plasmas. Based on this successful results, new upgraded project: TS-4 spherical torus merging experiment started operation in 2000 and recently, a new spherical tokamak experiment UTS was accepted by Japanese government at 2006 and will start full operation soon.

 Spherical Tokamak Discharge  (START)
Spherical Tokamak Discharge (START)

2) Key Experiments for Solving Magnetic Confinement Problems
We have developed new experiments to solve keys for the magnetic confinement. Questions are for example why the instability and reconnection of magnetic field lines takes place for those magnetic configurations. We developed a new laboratory experiment for magnetic reconnection using torus plasma merging. Its magnetic Reynolds number, temperature and density are much higher than the conventional method. Using this merging scheme, the number of reconnection experiments is increasing: MRX (Princeton U.), VTF(MIT), Swift-FRC(NASA), SSX(Swarthmore C.) and Colorado FRC (Colorado Univ.) etc. We are now promoting international collaboration of magnetic reconnection and merging, based on the international symposium on magnetic reconnection (MR2000-MR2008) and international exchange programs for researchers and students.

Recent World Merging/ Reconnection Experiments
Recent World Merging/ Reconnection Experiments

1) Y. Ono, M. Inomoto, T. Okazaki and Y. Ueda: "Experimental Investigation of Three-Component Magnetic Reconnection by Use of Merging Spheromaks and Tokamaks", Physics of Plasmas, Vol. 4, No. 5, Pt. 2, (1997), 1953.
2) Y. Ono and M. Inomoto: "Ultra-High Beta Spherical Tokamak Formation by Use of Oblate Field-Reversed Configuration", Physics of Plasmas, Vol. 7, No. 5, (2000), 1863.
3) Y. Ono, T. Kimura, E. Kawamori, Y. Murata, S. Miyazaki, Y. Ueda, M. Inomoto, A. L. Balandin and M. Katsurai "First and Second-Stable Spherical Tokamaks in Reconnection Heating Experiments", Nuclear Fusion, Vol. 43, No. 8, (2003), 789.
4) E. Kawamori and Y. Ono, ""Effect of Ion Skin Depth on Relaxation of Merging Spheromaks to a Field-Reversed Configuration "", Physical Review Letters, Vol. 95, No. 18, 085003, (2005).
Other Activities
American Physical Society (APS)
The Physical Society of Japan (JPS)
Institute of Electrical Engineers of Japan (IEEJ)
The Japan Society of Plasma Science and Nuclear Fusion Research (JSPF)
Institute of Electrical and Electronics Engineers (IEEE)
2001-2003 Chairman of JSPF Spherical Torus Research Committee
2002-2003 Chief Editor, IEEJ Transactions on Fundamentals and Materials
2006-2007 Chairman of JPS Plasma Physics Division,
Future Plan
Optimization of Spherical Torus Plasmas
Our goal is to optimize the small/ compact fusion confinement using promising ideas of STs and FRCs. The FRC has the simplest magnetic field structure solely composed of the poloidal magnetic field, while the ST has both poloidal and toroidal magnetic fields. The FRCs are already equipped with a promising beta~100% due to its simplest field structure but are needed to improve its poor confinement time and inefficient formation method. We developed a new economical formation method of FRCs using axial merging of two spheromaks. Its energy efficiency is a few times higher than the conventional theta-pinch formation, realizing the new-stage experiment of FRC formation and sustainment. The mixture of STs and FRCs can be a key to optimize the spherical torus confinement with high-beta and long confinement.

Magnetic Field Lines of  ST and FRC
Magnetic Field Lines of ST and FRC

Messages to Students
I hope my students to be internationally competitive researchers who can think and learn on their owns. Our laboratory will provide them the international research environment, such as their presentations and international collaboration in US and Europe.