Nobunao Takeuchi

Observations of earthquake waves by the vertical earth potential difference method

Abstract It is still not clear what relationship exists between earthquake phenomena and electromagnetic ones. The earth self-potential difference has been observed with high time resolution for continuously monitoring earthquakes at Sendai, where artificial leakage current sources always exist. A simple method to reduce the unnecessary signals induced by artificial and natural earth current sources is proposed. With this method the potentil difference is measured through two electrodes buried at different vertical positions under the ground. For all earthquakes with seismic intensities of more than 1 at Sendai we have observed clear variations in the potential difference signal. The observed electric P and S wave arrival times agree exactly with seismic data obtained by the Japan Meteorological Agency (JMA).

Frequency Spectrum of Fluctuations Near a Rational Surface in a Toroidal Heliac

Density and space potential fluctuations have been studied in electron cyclotron resonance heating (ECRH) plasma of a helical axis stellarator TU Heliac using Langmuir probe techniques. These fluctuations are coherent and global, which can be explained by a drift instability model in cylindrical geometry. A particular fluctuation mode vanishes inside a rational surface. The ratio of this mode, n/m, corresponds to the rotational transform ι/ of this rational surface, (m, n: poloidal, toroidal fluctuation modes, respectively). This phenomenon near the rational surface can also be explained by a drift instability theory.

A New Capacitive / Resistive Probe Method for Studying Magnetic Surfaces

A new capacitive/resistive probe method for mapping the magnetic surfaces from resistance or capacitance between a magnetic surface and a vacuum vessel was developed and tested. Those resistances and capacitances can be regarded as components of a simple electrical bridge circuit. This method exploits electrical transient response of the bridge circuit for a square pulse. From equiresistance or equicapacitance points, the magnetic surface structure can be deduced. Measurements on the Tohoku University Heliac, which is a small-size standard heliac, show good agreement with numerical calculations. This method is particularly useful for pulse-operated machines.

Characteristics of earth potential difference generated by seismic waves

To clarify the relationship between earthquakes and electrical phenomena, the earth potential difference has been observed continuously at Aobayama in Sendai and at Tsukidate, 60 km north of Senday.

Measurement of small variations of atmospheric electrical field signals in fair weather

The variations in atmospheric electrical field signals in fair weather were observed both at Aobayama in Sendai and at Tsukidate in the Miyagi Prefecture. The measurements were made using a slow antenna type electrical field meter composed of a metal plate electrode and a CR integrator. They were recorded using a portable pen-recorder. A field meter of this type is suitable for measuring relatively rapid variations. The observations were made in a period of a few minutes in fair breezy weather. The data collected using a bare metal electrode were compared with those using an insulated electrode in order to detect an air-earth current. Examination of the dependence of the amplitude of the variation to the electrode size and height showed that the atmospheric electrical field is affected by these parameters. Observation of signals at two different positions gave the time delay between positions. This indicated that the electrical field perturbation was about several hundred meters. The well known atmospheric circulation with a period of a few minutes suggests that the observed variations in the electrical field signals were caused by electrical charges moving together with the atmospheric circulation.

Forecast of Winter Thundercloud by Frequency Analysis of Athmospheric Pressure

The electric power facilities such as large nuclear power plants and ultra high voltage principal transmission lines have recently increased so much along the coast of the Japan Sea. Particularly in winter seasons, these facilities have been frequently suffering from serious lightning troubles. Brook et al.1 have pointed out that winter lightning in this district has different characteristic features compared with summer ones. The exact forecast of thunderstorms and the detailed knowledge of weather circumstances that cause thunderstorms are urgently needed to protect these facilities and execute effective system control of power facilities against winter thunderstorms.