K. Tsuchida

Plasma diagnostics by neutral beam probing

A new method using both techniques of a neutral beam and spectroscopy has been developed to measure the spatial electron density profile of a plasma. This neutral beam probing technique utilizes the photons emitted by impact excitation of the probing lithium beam with plasma electrons. The spatial electron density distribution of the plasma of Te approximately 10 eV, ne approximately 1011 cm-3 has been determined from the measurements of the local photon flux and beam intensity by using the excitation rate coefficient calculated from the available cross-section data. The comparison of these results with those of conventional methods proves this new method is of practical use in the space-resolved measurements of plasma parameters, especially when a Langmuir probe is no longer usable. The cross sections for excitation of the Li beam in collisions with He, Ar and H2 have been also measured and used to estimate the neutral lithium beam intensity.

High-power argon excimer laser at 126 nm pumped by an electron beam

A high-power argon excimer laser has been developed with an output power exceeding 2 MW in the VUV region at 126 nm. As an alternative to a conventional Al/MgF(2)-coated mirror, which was susceptible to damage, an uncoated quartz plate was successfully used as a reflector for reproducible high-power operation of the argon excimer laser without any mirror damage. Observation of the temporal behavior of the laser pulse in relation to that of the gain coefficient is discussed.

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.

Plasma electron density measurements by the laser- and collision-induced fluorescence method

A new method based on the laser-induced fluorescence method has been developed to measure the spatial electron density distribution in plasmas. The local electron density can be determined by observing the intensity ratio of the laser- to the collision-induced fluorescence. A spatial electron density distribution of a helium plasma (Te approximately 6 eV, ne:1011-12 cm-3) has been determined by observing the He(31P to 21S) laser-induced fluorescence and the He(31D to 21P) collision-induced fluorescence resulting from the He(31P to 31D) process due to collisions with electrons. The comparison of the result with that of a conventional method proves this new method is of practical use in the space-resolved measurements of plasma electron density.

Tunable oscillation of a high-power argon excimer laser in the vacuum-ultraviolet spectral region

Successful oscillation of a tunable, high-power argon excimer laser is reported. The wavelength was tuned from 124.5 to 127.5 nm with a spectral width of 0.3 nm. The output power of 2.2 MW, obtained at the line center, is 3 orders of magnitude larger than the value reported previously by Wrobel et al. [Appl. Phys. Lett. 36, 113 (1980)]. The possibility of frequency conversion of the argon excimer laser radiation to other wavelengths by a stimulated Raman scattering process is discussed.

Density Measurement of Helium Metastable Atoms in a Plasma by the Laser-Induced Fluorescence Method

Density profiles of helium metastable atoms in 23S and 21S levels have been measured in a plasma (ne~1012 cm-3, Te~7 eV, radius of the plasma column ~1 cm) by the Laser-Induced Fluorescence Method (LIFM), where both quenching effects of fluorescence by plasma and characteristics of laser radiation are taken into account. The He(23S) metastable atoms are distributed in inverse proportion to the radius in the periphery of the plasma column (r>1 cm), while the profile of He(21S) metastable atoms has a gentle slope compared with that of He(23S) atoms. The difference in the density distributions is thought to be caused by the production of He(21S) atoms in the plasma periphery through the n1P (n2) levels due to optical excitation processes of He(11S) by resonance lines emitted from the plasma column.

Measurement of atomic carbon densities by the laster-induced fluorescence method with an Ar2∗ laser

A high power argon excimer laser (Ar2∗ laser; 5 MW/cm2 nm at λ = 126 nm, Δλ ~ 1.7 nm) has been developed to measure the density and transport of carbon atoms in edge plasmas by the laser-induced fluorescence method (LIFM). The first measurement of carbon atoms has been performed by the observations of 1.16 μm fluorescence light due to the 3d 3Po → 3p 3S transition during the laser pumping through the 2p 3P → 3d 3Po transition. The density of carbon atoms released from a thin carbon film (90 nm) with the laser blow-off technique was determined to be 6 × 109 cm−3 at a distance of 30 mm from the target, indicating that almost all carbon atoms are in states other than the ground state (~ 10−4). The thermal velocity was measured, by the time-of-flight technique, to be 8 × 105 cm/s which was almost the same as the average velocity of sputtered carbon atoms.