Keiichiro Yamagiwa

On the leak width of line- and point-cusp magnetic fields

Abstract Plasma leak widths of the line- and point-cusp magnetic fields formed by arrays of permanent magnets were investigated. The leak width was defined by the half width of the electron density distribution measured by a Langmuir probe. Argon and helium plasmas were used. It is found that the leak width of the point-cusp field is qualitatively different from and is very large compared with that of the line-cusp field which is nearly equal to the hybrid gyrodiameter 2 ϱ h =2(m e ×m i T e T i ) 1 4 eB .

OBSERVATION OF LOWER HYBRID WAVE PACKETS WITH VERY LARGE AMPLITUDE IN A HIGH-VOLTAGE LINEAR PLASMA DISCHARGE

Abstract We have observed repetitive, large-amplitude (> 80 kV/cm) parallel electric-field wave packets with electron density modulation in the current limiting phase of a high-voltage linear plasma discharge. The power spectral density of the whole span of the wave packets shows the peak frequency, 65 MHz, in the vicinity of the lower hybrid frequency.

Experimental Srudy of an Ion-Acoustic Soliton with Dissipation

The propagation of an ion-acoustic soliton in an Ar (or Ar–He) plasma is investigated experimentally in a double plasma device. The various patterns of signals propagating from the separation grid into the target region are classified into three types, Besides the normal soliton pattern, there appear signals with either a shallow dip or a deep valley. The K–dV equation with a term expressing the effect of ion Landau damping is solved numerically with parameters corresponding to the experimental conditions. One of the types observed in the experiment (with a shallow dip) is fully reproduced theoretically with the corresponding plasma parameters. Effects of the initial height of the perturbation on the evolution of the signal are investigated experimentally and theoretically. The minority He ion which causes an increase of the ion Landau damping rate had the same effect as the decrease of the initial height of the signal.

Ion heating by lower hybrid waves

Abstract An ion heating by excited lower hybrid waves has been observed in a coaxial type double plasma device. The lower hybrid resonance heating is examined on the two components of the kinetic energy perpendicular and parallel to the magnetic field.

NONLINEAR EFFECTS ON A PARAMETRIC EXCITATION OF ION PLASMA WAVES.

Abstract Asymmetrical and hysteresis behavior on a parametric excitation of ion plasma waves was observed in a mercury discharge plasma with no magnetic field.

Ion mass separation by use of spatial cyclotron resonance

Abstract Spatial cyclotron resonance of an ion beam in a wavy magnetic field is investigated to realize the separation of stable isotopes. To perform the experiment, a surface-ionizing lithium ion beam source, which is collisionless and charge-neutralized, has been developed. A wavy magnetic field is produced by setting two magnet-arrays face to face. At the resonance condition, clear scattering of the lithium ion beam is observed and the concentration of 6 Li is obtained on a target.

Discovery of two categories of electron energization associated with a strong Buneman double layer

Abstract Two categories of electron energization associated with a strong Buneman double layer are discovered by the simultaneous observation of both the directivity of hard X-ray (bremsstrahlung) fluxes and the plasma diamagnetism. One is characterized by production of nonthermal electrons with a highly anisotropic velocity distribution, and the other by production of a hot electron plasma, almost thermal in the bulky sense.

Ion energy and plasma density increase in mirror magnetic field by lower hybrid wave excitation

Abstract Using a coaxial double plasma device we excited the lower hybrid wave in an argon plasma in mirror magnetic fields. When the lower hybrid wave was excited the perpendicular ion energy E⊥ and the plasma density n were increased. A relation between the relative changes of the average energy ΔE ⊥/ E ⊥ and the density Δn n agrees very well with a relation expected from loss-cone considerations.

Nonlinear Evolution of Unstable Waves in an Electron‐Beam Plasma:Relation to Beam Energy Distribution

Experimental studies were performed to investigate one‐dimensional evolution and formation of nonlinear structure of linearly unstable waves in an electron‐beam plasma. The beam energy distribution function was also measured in connection with the formation of the nonlinear structure.

Plasma instabilities excited around a line cusp magnetic field

Abstract Plasma density distribution and low frequency noise spectrum have been measured in detail around a line cusp field generated by permanent magnet arrays in Ar, Ne and He plasmas. Low frequency broad noise spectrum with a fairly sharp peak or peaks, respectively, 10, 15 and 30 kHz were observed in those plasmas. The frequencies of these peaks are consistent with an interpretation in terms of a low frequency drift wave instability of the universal type, with k ·B = kB . Another possible explanation in terms of an ion-cyclotron wave is discussed.