Shoichi Ohi

Conceptual design of the D-3He reactor artemis

AbstractA comprehensive design study of the D-3He-fueled field-reversed configuration (FRC) reactor Artemis is carried out for the purpose of proving its attractive characteristics and clarifying the critical issues for a commercial fusion reactor. The FRC burning plasma is stabilized and sustained in a steady equilibrium by means of preferential trapping of D-3He fusion-produced energetic protons. A novel direct energy converter for 15-MeV protons is also presented. On the bases of consistent fusion plasma production and simple engineering, a compact and simple reactor concept is presented. The D-3He FRC power plant offers a most attractive prospect for energy development. It is environmentally acceptable in terms of radioactivity and fuel resources, and the estimated cost of electricity is low compared with a light water reactor. Critical physics and engineering issues in the development of the D-3He FRC reactor are clarified.

Experiments on additional heating of FRC plasmas

Experiments on additional heating by neutral beam injection and application of a low frequency wave to a plasma with an extremely high averaged beta value of about 90% - a field reversed configuration (FRC) plasma - are carried out using the FRC Injection Experiment (FIX) apparatus. These experiments are made possible by translating the FRC plasma produced in a formation region of a theta pinch to a confinement region in order to secure better accessibility to heating facilities and to control plasma density. By determining the appropriate injection geometry and the mirror ratio of the confinement region, it became possible to inject a neutral beam with an energy of 14 keV and a current of 23 A into the FRC in a solenoidal confining field of only 0.04-0.05 T. Plasma confinement is improved in this experiment. Ion heating is observed to result from the application of a low frequency (80 kHz, about 1/4 of the ion gyrofrequency) compressional wave. A shear wave, probably mode converted from the compressional wave, is observed to propagate axially.

Ion rotational velocity of a field‐reversed configuration plasma measured by neutral beam probe spectroscopy

The ion rotational angular velocity Ω and the ion temperature Ti of a translated field‐reversed configuration (FRC) plasma are measured using neutral beam probe spectroscopy. The value of Ω is ∼(1.0∼1.2)×Ω* at the onset time of the n=2 rotational instability, where Ω* is the ion diamagnetic frequency for a rigid‐rotor equilibrium. The ion rotational direction is the same as the ion diamagnetic direction. The value of Ω is smaller than the angular frequency ωre of the n=2 instability, which can yield experimental evidence of the ion kinetic effects on the n=2 instability in the FRC plasma. When the octupole field is applied to the plasma in order to suppress the n=2 deformation, Ω is slightly reduced. The ion temperature Ti is ∼70 eV at the onset time of the n=2 instability.

Excitation and propagation of low frequency wave in a FRC plasma

Low frequency f = ⅕ − ⅓fci, (fci: ion gyro frequency in the external field Bw) waves are excited with an antenna which is compatible with a reactor in a plasma with field reversed configuration (FRC). Near and outside the separatrix rs of the FRC plasma, though the applied wave is mainly in compressional mode, azimuthal and radial components are observed in the magnetic field disturbance of the excited wave, which propagate with the dispersion relation consistent with the shear Alfven wave. These disturbances penetrate deep into the FRC plasma across the surface where the wave frequency exceeds local ion gyro frequency and propagate along magnetic lines of force with sound velocity, which behaviour is consistent with the shear Alfven wave with finite temperature correction. Axial magnetic disturbance propagates axially and radially from the antenna across the plasma column.

Axial compression of a field reversed configuration plasma

A new concept for plasma heating using axial magnetic compression of a field reversed configuration (FRC) plasma is proposed. In this concept, the FRC plasma is compressed only axially, keeping the magnetic flux between the separatrix and the confining chamber (flux conserver) wall unchanged, while allowing the plasma to expand radially. A simple model based on an empirical scaling law of FRC confinement and on the assumption that the compression is done adiabatically predicts that, in addition to heating the plasma, improved confinement will also be accomplished with this concept. This compression is done by energizing segmented mirror coils successively in such a way as to decrease the length of the confinement region between the coils. The apparatus for this axial compression was developed and an experiment was carried out. In this experiment the plasma was compressed by about 30% and the plasma lifetime of about 500 μs was increased by about 50 μs.