Hiroshi Inuzuka

Observation of a current-limited double layer in a linear turbulent-heating device

Time‐ and space‐resolved measurements of strong double layers (DLs) have been carried out for the first time on a linear turbulent‐heating device, together with those of fluctuation spectra and precise current measurements. A stable stong DL is formed even when the electric current through the DL is less than the so‐called Bohm value. Discussion of the formation and decay processes is given, indicating a transition from an ion‐acoustic DL to a monotonic DL.

Dual homodyne detection system for measuring asymmetric spectra in the far-infrared regime

A dual homodyne detection system for measuring scattered radiation from plasmas has been fabricated. The system is operative in the far‐infrared regime, and with it the power spectral distribution of the scattered radiation in the upper and lower sidebands with respect to the frequency of the incident wave can be obtained. Theory of operation and experimental results for simulated radiation fields are given.

Numerical simulations of current‐limited double layers observed in a linear mirror device

Simulations based on the Vlasov–Poisson scheme are carried out to observe the temporal and spatial development of dopuble layers (DLs) in a linear mirror field. Simulation results show that the magnetic mirrors have a substantial effect in reducing the current passing through the DL. Development of a negative potential region on the low potential side of the DL is also observed, in agreement with the experimental results. The observed strong DLs appear to be formed, triggered by the ion‐acoustic instability.

Spectroscopic Measurement of Cyclotron Radiations from Linear Device with Field-Gradient along the Axis

A spectroscopic measurement is carried out of the second harmonic electron cyclotron radiations from a linear turbulent-heating device at an angle oblique to the external magnetic field, from which a radial profile of the electron temperature Te is evaluated. An enhancement of Te is observed around the periphery of the cylindrical plasma, presumably due to the skin effect.

Direct observation of a strong electron hole in a linear turbulent heating device

Appearance of a high potential region whose potential is larger than the externally applied potential difference, has been observed for the first time in a linear turbulent heating device. The positive potential pulse is identified as a strong electron hole. After the decay phase of the hole, a strong double layer is formed. A one-dimensional numerical simulation has been also carried out, showing qualitative agreement with the experimental results.

Spontaneous collapse of double layers in a simple mirror confinement device

An empirical law τDIDL =const has been found for the lifetime τD of the double layers (DL) observed in a linear turbulent‐heating device NU‐II [Phys. Fluids 28, 703 (1985)], where IDL is the current passing through the DL.

Observations of Time-Dependent Asymmetric Spectra of Density Fluctuations in a Linear Turbulently Heated Plasma by Far-Infrared Laser Scattering

Time-dependent asymmetric spectra of the density fluctuations in a linear turbulently heated plasma are measured by far-infrared laser scattering using a newly developed dual homodyne detection system. The low frequency ( < 25 MHz) density fluctuations are found to propagate toward the axis of the cylindrical plasma initially. However, only those propagating outward are observed at a later time. The frequency spectra for various wavenumbers are also shown.

Evolution of nonlinear phenomena in a linear turbulent-heating plasma (Observation of electron hole, double layer and turbulent heating).

An overview is given on some nonlinear phenomena such as electron hole, double layer and turbulent-heating processes which have been observed in a mirror-confined, plasma. Results of computer simulations are also presented to compare with the experimental results.