Kouzi Matsunaga

Space-Resolved Measurement of Electron Density by Neutral Li Beam Probing in NBT

The spatial profiles of electron density in Nagoya Bumpy Torus (NBT) have been measured with a fast neutral Li beam probing, which utilizes the photon emission due to the electron impact excitation of the injected atoms. It is shown that plasmas are well contained inside the hot electron annuli. The attenuation of thermally injected Li atoms has been measured for the estimation of electron density as a cross check.

Space‐resolved measurement of internal magnetic field in a bumpy torus by Li0‐beam probe spectroscopy

A new method combining Li0‐beam probing and spectroscopic techniques has been developed to measure local magnetic fields in a bumpy torus. A collimated thermal Li0 beam is injected into the plasma. The Zeeman pattern of the lithium resonance radiation (22S–22P, 6708 A) is observed with a Fabry–Perot interferometer. The strength of the local magnetic field is determined from the splitting between two π components of the 22S1/2–22P1/2 transition with the spatial resolution of about 7 mm. The magnetic fields from 2 to 4 kG were measured with accuracy of ±2%. This method is applicable to plasmas of a line‐integrated electron density below 5×1012 cm−2.

Quasi-Steady Laser Oscillation in the Recombining Hydrogen Plasma

A quasi-steady laser oscillation at 1.88 µm has been observed in a pure hydrogen plasma. The high density plasma produced by a high power quasi-steady MPD arc-jet operating at 8.1 kA of the discharge current and 0.1 g/s of hydrogen flow is cooled by expanding itself into the vacuum chamber. Experimental results confirm that some population inversions occur as a consequence of recombination and subsequent electron thermalization.

Measurement of the Magnetic Field in a Plasma Using an Impurity Probe Spectroscopy

The magnetic field strength has been obtained from the Zeeman splitting. Thermal He atoms, as an impurity, were injected into a low density (ne~5×1010 cm-3) hydrogen plasma produced by electron cyclotron resonance. A singlet line at 6678 A from He atoms excited by the plasma electrons splits into a normal Zeeman triplet in the magnetic field. The line profile was measured with a high resolution Fabry-Perot interferometer. This diagnostic allows the determination of the Zeeman splitting at magnetic fields as low as 1.2 kG, lower than which the splitting is masked by the Doppler broadening of the injected atoms.

The Hydrogen Balmer- α Line Profile in RF-Discharge Plasmas

The spectral line profiles produced by neutral hydrogen atoms have been measured using a high resolution Fabry-Perot Interferometer. The Hα line 6563 A is found to have an asymmetric profile in non-magnetized and low density plasmas. The line profile calculated taking into account the fine structure of the Hα line shows a reasonable agreement with the experimental results. The atom temperature obtained from the Doppler broadening is about 0.1 eV.

Effects of a transverse magnetic field on HeCd+ laser output

Abstract The effect of a transverse magnetic field B ⊥ on the cataphoresis type HeCd + laser was investigated experimentally. For a 3 mm i.d. tube, the laser power was found to reach a maximum at B ⊥ = 300 Gs.

Observation of population inversions in a freely expanding pure hydrogen plasma.

The possibility of a hydrogen plasmadynamic recombination laser is experimentally investigated. A high density plasma produced by a high-power quasi-steady MPD arc-jet is cooled by expanding itself into the vacuum chamber. Experimental results confirm that large population inversions between i=4–3 and i=5–3 levels exist over 12–22 cm downstream of the anode. A comparison is made between experimental data and calculated results based on the collisional-radiative model on populations of hydrogen levels.

Observation of the current-driven high frequency drift wave

Abstract The current-driven instability in a inhomogeneous plasma is investigated experimentally. The excited wave is identified as the high frequency drift wave having ω pi > ω ⪢ Ω i and k ∥ ≈ k ⊥ ≠ 0 which propagates in the direction of the ion diamagnetic drift.