Kakuyūgō kenkyū

In the present experiment, measurement of forward scattering (θ=10°) from TP-D plasma by C0₂ laser radiation has been carried out.
It was found that refraction effect of laser beam by plasma becomes important at small angle forward scattering. Electron densities, measured by interferometry, scattering and refraction as a function of discharge current shows fairly good agreement.

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The hot plasma of 50-80 Kev average energy is produced by the slow theta pinch helium discharge and confined in the magnetic mirror field (mirror ratio 1 : 1.48). The density of the confined plasma (_??_10¹³/cm³) is higher than that of the plasmas produced by other methods of the hot electron plasma production. The confinement time is about 200 μsec; this value can be explained by the multiple scatterings of the hot electrons with neutral atoms. The plasma column is a little deformed, but the deformation does not grow during 200 μsec.
During the low density phase in the discharge of initial gas pressure below the critical value, of 13 mTorr, a burst of hot electrons is observed across the magnetic lines of force. The radial burst occurs at the midplane of the mirror field, and is not observed at the mirror plane. The time of the occurence of the burst depends sensitively on the initial gas pressure or cold electron density. It is considered from these facts that the radial burst arises from the flute type instability which is conditioned by the cold to hot density ratio.
The axial loss of hot electrons along the magnetic lines of force is also observed indepenendently of the radial burst and independently of the initial gas pressure. The axial burst is composed of hot electrons with energies below 90 Kev. The energy distribution of escaping hot electron flux shows a non-Maxwellian distribution, which is not significantly change before and after the burst. The burst is observed in the plasma condition ω_pe/ω_ce_??_1.The buildup time of the burst is a few micro-seconds, much greater than that of the radial burst. The mechanisms of axial burst are discussed.

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