Izumi Hayashi

Simultaneous measurement of two orthogonal components of electric field using a Pockels device

A new optical method using a Pockels device is developed to simultaneously measure two directional components of an electric field. In this method, an output light beam from a Pockels device is split into two beams and then each of the beams is transmitted through a polarizing plate whose polarization direction is different, depending on the measured field component. The relation between two measured field components and the required polarization direction of the polarizing plate is theoretically derived for representative materials of the Pockels device and is also examined experimentally. A field sensor is made on the basis of this new idea and is used to investigate a nonuniform electric field. An electric field changing spatially by 20% per centimeter can be measured with an accuracy of 5% using the Pockels sensor. The sensor is successfully applied to measure an impulse electric field between a sphere‐to‐sphere gap.

Optically-Coupled Floating Double Probe for Local Electric Field Measurements in Pinch Discharge Plasmas

Local electric field signals from a floating double probe immersed in a pinch discharge plasma are transmitted via a pair of fiber optic cables in order to achieve electrical insulation between the probe circuit and an oscilloscope. This optical coupling scheme has a higher electrical insulation voltage and a wider frequency response than the commonly-used isolation transformer methods and commercially-available photocoupler devices. The measuring system consists of a transmitter with light-emitting diodes and a receiver with PIN diodes and responds in the frequency range up to 3 MHz. Transient noise, which disturbs the probe measurements in the implosion phases of pinch discharges, has been eliminated.

Plasma behavior in reversed-field pinch configuration

Helical deformations of a plasma column in a reversed field pinch experiment have been investigated using stereoscopic framing and/or streak photographs together with magnetic search-coils. A toroidal-mode number of 6 was found to be dominant in this experiment. This number agrees with the mode number predicted by a growth-rate calculation based on an ideal magnetohydrodynamic equation. It was observed that the plasma center moved around in a circular arc in the poloidal direction with a frequency of 100 kHz. Moreover, it could be seen that the displacement of the plasma center in the major radial direction traveled in a toroidal direction with a velocity of 0.9×104 m/s.

DYNAMIC STABILIZATION OF THE M = 1 MODE ON A Z-DISCHARGE

Dynamic stabilization of the m = 1 mode on a Z-discharge was studied experimentally. The HF current was generated by a newly designed and developed RF generator. Although the quasi-stationary axial current considerably exceeded the Kruskal-Shafranov limit, the growth rate of the m = 1 mode was considerably reduced during the existence of the HF axial plasma current.

Bidirectional pulser for linear induction accelerators made from line cavities with external pulse injection.

Detailed analysis of high-efficiency, bidirectional pulsers for linear induction accelerators made from line cavities with external pulse injection is given. One of the highly efficient bidirectional pulsers has been simulated using coaxial cables as pulse forming lines. Close agreement between the observed output waveform and the theoretically predicted one has been obtained.

Effects of Error Field on a Reversed Field Pinch Plasma

The effects of error fields at a shell gap are measured both optically and magnetically in a Reversed Field Pinch experiment. The measurements show that the increase of poloidal flux consumption is caused by the error fields in the start up phase of discharge. The vertical components of error fields drive the plasma column to the tube wall. In large error fields, the plasma column touches the wall and the plasma current decays quickly.

Relationship between Toroidal Flux Enhancement and Instabilities in a Reversed Field Pinch

The enhancement of the toroidal magnetic flux in a reversed field pinch is studied experimentally in a toroidal plasma device. The perforated shell-type coil used in this experiment enables us to observe the full toroidal plasma by an image-converter camera. It is found that a helical luminous filament appears around the main plasma column only when the toroidal field at the wall of the discharge tube begins to reverse and when the toroidal flux in the tube is enhanced.

150 MVA RF Generator

小形マルクスゼネレータ, 真空ギャップ, 大容量シリコンダイオードなどを利用した新方式の発振器を動作させ, 1MHz, 150MVAの強力な高周波発振に成功した。さらに, 本発振器をトロイダルプラズマ実験に応用した。この高周波発振器は, 高ベータプラズマの動的制御の研究に極めて有用である。