Spatial Ion-Wave Echoes

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概要

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• Theory and experiments of spatial ion-wave echoes are reported. Emphasis is placed on the investigation of the line-shape of the echo and on the collisional effects. In the collisionless approximation, the calculated line-shape of the second-order echo is found to be a universal function of Δχ/δ, the distance from the expected position of the echo divided by the Landau damping length of the ion-wave constituting the echo. This feature is demonstrated experimentally for the case of a small separation ℓ between the two exciters. Higher-order echoes predicted by Gould are observed up to the fourth order with respect to the external fields at the predicted positions with the predicted dependence of their amplitude on the amplitude of the primary waves. In addition to these, new types of higher-order echoes (the secondary echoes) which result from the electric fields of other echoes are predicted and observed (on the third and fourth-orders). Measurements of the peak amplitude of the second-order echo as a function of ℓ indicates that the memory of the past excitation retained in the distribution function damps exponentially with the attenuation length proportional to the wavelength of the excited wave. This attenuation length is, however, too much short compared with that estimated from the ion-ion and ion-neutral collisions and has only a slight dependence on the plasma density. For a separation length ℓ exceeding the attenuation distance of the echo, the echo line-shape deviates considerably from that predicted by the collisionless theory. The effect of ion-neutral collisions on the peak amplitude is studied and explained fairly well by a simple relaxation time model, but the predicted effect of ion-ion collisions based on a Fokker-Planck type equation is not observed within the separation length ℓ of 20cm and the plasma density of 10^<10>/cc.

• 核融合科学研究所の論文

著者

• Ikezi H.

  Research Information Center Institute Of Plasma Physics Nagoya University

• Nishikawa K.

  Research Information Center Institute Of Plasma Physics Nagoya University:faculty Of Science Hiroshi

• TAKAHASHI N.

  Research Information Center, Institute of Plasma Physics, Nagoya University

• Ikezi H.

  Research Information Center Institute Of Plasma Physics Nagoya University:(present Address)departmen

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• Experiments on Ion-Acoustic Solitary Waves

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