Studies of Electron Cyclotron Plasma in a Mirror Trap

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概要

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• Hot electron plasma is produced in a magnetic mirror field (TPM machine) by high power microwave discharge (5kW at 6.4GHz). The electrons are heated to a temperature over 100keV and microwave interferometer measurements give electron densities greater than 10^<12>cm^<-3>, when microwave power is applied. The hot electrons are observed to be bunched in a shell structure with a radius of 10cm in diameter. Because of the structure, the plasma exhibits paramagnetism on the axis of the machine. The life time of the plasma is measured by turning off the microwave power. For pressures greater than 10^<-4> Torr, the plasma is stable and decays with a time constant of about several tens of millisecond. During the stable decay, instabilities can be artificially triggered by irradiation of a pulsed microwave (∿100W) at the same frequency as the heating microwaves. No difference is observed between the triggered instability and spontaneous ones which occur uncontrollably for opperating pressures below 10^<-4> Torr. The instabilities are characterized by a sudden disappearance of plasmas and is accompanied with a burst of energetic electrons escaping from the trap in radial and axial directions, a fast rising x-ray signal, a sudden increase of light intensity, and an intense burst of microwave radiation. The microwave burst is composed of harmonics of the fundamental frequency, 2.1GHz. This frequency cannot be interpreted by the electron cyclotron frequencies associated with the magnetic field intensity within the plasma chamber. The microwave signal is sampled and frequency-analyzed for every successive 0.5 microsecond after the initial onset of the instability. As the time proceeds, the line spectrum at 2.1GHz becomes broader and tends to shift lower frequency side producing satellite lines. Interference detection reveals that the radiation is circularly polarized and mostly composed of transverse waves. These observations suggest that the instability is ascribed to the electron cyclotron overstability.

• 核融合科学研究所の論文

著者

• Ikezi Hiroyuki

  Research Information Center, Institute of Plasma Physics, Nagoya University

• Ikezi Hiroyuki

  Research Information Center Institute Of Plasma Physics Nagoya University

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• Studies of Electron Cyclotron Plasma in a Mirror Trap

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