Educational Activities

Graduate school: Advanced nuclear fusion science and engineering

Research Activities

Nuclear fusion will occur in plasmas (hot ionized gases) under the appropriate temperature,
density, and confinement conditions in a magnetic field. To develop smaller, more economical fusion reactors,
we are researching the confinement of a higher plasma pressure for a given magnetic field strength
(high-beta plasma confinement).


Improvement and application of field-reversed configurations (ref 1)
A field-reversed configuration (FRC) is a compact toroid confined solely by a poloidal magnetic field and has
an extremely high beta value close to unity. It has some essential advantages, such as simplicity,
axial translatability, and high-beta nature, but an FRC plasma with sufficient performance for a nuclear fusion core
has not achieved yet. The lack of efficient current drive and additional heating methods hindered the FRC research
to develop into the fusion-relevant regime. Effective current drive and heating methods are required
to improve the confinement and stability of the FRC plasma.

Ultra high-beta spherical tokamaks (ref 2)
A spherical tokamak (ST) has a much tighter ring shape than a conventional tokamak and provides both a high-beta property
and good confinement. An intermediate region, which may provide a better configuration for advanced nuclear fusion core
plasmas, has been suggested to exist between FRCs and STs. We have proposed a novel formation of an ultra-high-beta
ST by applying an external toroidal field to an FRC produced by a plasma merging method.

Neutral beam injection heating in high-beta plasmas (ref 3)
Neutral beam injection (NBI) is an important plasma heating method particularly in high-beta plasmas.
The plasma is heated through collisions with injected high-energy particles, hence an FRC plasma with large magnetic
flux is required for effective confinement of the fast ions. An oblate FRC plasma produced by the plasma merging method
has larger magnetic flux than prolate FRC plasmas produced by other conventional methods and has potential as a target plasma
for NBI heating. Numerical calculation of the particle orbits will be utilized to optimize the NBI heating in the FRC plasma.

Literature

1) Inomoto, Kitano, Okada: Field-reversed configuration maintained by rotating magnetic field with high spatial harmonics, Phys. Rev. Lett., 99, 175003 (2007).
2) Ono, Inomoto: Ultra-high-beta spherical tokamak formation by use of an oblate field-reversed configuration, Phys. Plasmas 7, pp.1863-1869, (2000).
3) Inomoto, Asai, Okada: Neutral beam injection heating on field-reversed configuration plasma decompressed through axial translation, Nucl. Fusion 48, 035013 (2008).

Other Activities

American Physical Society (APS)
The Physical Society of Japan (JPS)
The Japan Society of Plasma Science and Nuclear Fusion Research (JSPF)
Institute of Electrical Engineers of Japan (IEEJ)

Future Plan

Our final goal is to achieve high-beta plasma confinement for an economic and compact fusion reactor that may be
located between STs and FRCs. We hope to acquire a comprehensive understanding of high-beta physics through laboratory
experiments and to contribute to actualizing advanced nuclear fusion for a commercial power plant.

Messages to Students

Laboratory plasma experiments require interpretation of experimental results, hypothesis formation, and planning of
subsequent experiments to verify the hypothesis. This process, which will lead to new knowledge, is the nature of
our research and will provide a good environment for promoting science through development of the diagnostics and
operation of devices.

URL

http://www.ts.k.u-tokyo.ac.jp/inomoto/