Kunio Yuasa

Decay of Metastable Argon Atoms in the Afterglow Plasma

Time-dependent studies of the particle density in 1s5 state of Ar plasma are performed using single-frequency laser absorption probing. The applied voltage on the 400 Pa striated plasma (current: 0.01–20 mA DC) is cut off, and from the decay curve studies of the density, the following rates are obtained: the rate of collision between 1s5–1s5 metastable atoms α (cm3 s-1)=(2.0±0.5)×10-8, the rate of collision between 1s5 metastable atoms and electrons Fe (cm3 s-1)=3.8×10-7 and the electron loss rate in the afterglow γe (s-1)=250+1.0×10-7×ne, where ne (cm-3) is the electron density. We also present the time-dependent ne behavior in one striation peak using values obtained here.

Ar lowest excited state densities in Ar and Ar-Hg hot cathode discharge

The densities of the Ar lowest excited levels in Ar and Ar–Hg gas-filled discharge lamps were measured using the absorption and laser-induced fluorescence methods from the positive column to the vicinity of the cathode. The lamp current was between 20 to 200 mA. A contour of the density distributions was obtained. Near the cathode, the exponential decay of these densities was observed within a distance of 20 mm from the cathode. This spatial decay characteristic can be explained by the result that the main deexcitation of the lowest excited atoms is caused by three-body and electron collision depopulation processes. In the Ar discharge, time-dependent density oscillations were observed in the positive column. High as well as very low (close to zero) densities were observed alternately. No density oscillations existed in the vicinity of the cathode. The behavior of the densities in such oscillations is also reported.

High-speed imaging system of luminous intensity distribution of plasma using light emission CT

The authors developed a light emission computed tomography (LECT) system for plasma diagnosis supporting the high speed data collection function. In this paper, we describe the principles of the system and experiments in reconstructing the luminous intensity distribution of plasma in a discharge tube with the system.