Mitsuo Maeda

Laser-aided diagnostics of plasmas and gases

PART I: FUNDAMENTALS Laser-aided diagnostics of gases and plasmas Basic principles of different laser-aided measurement techniques Hardware for laser measurements PART II: APPLICATIONS AND MEASUREMENTS Plasma measurements Combustion measurements Measurements in gas flow systems Laser processing measurements Analytical chemistry Remote sensing

Application of two‐photon‐excited laser‐induced fluorescence to atomic hydrogen measurements in the edge region of high‐temperature plasmas

A two‐photon‐excited laser‐induced fluorescence (LIF) was applied to measurement of atomic hydrogen densities in the edge region of high‐temperature plasmas of Heliotron E for the first time. In this application, fluorescence signals were observed coaxially to the laser beam. This was possible because, in two‐photon‐excitation LIF, the visible fluorescence is localized at the laser focus and stray light can be completely eliminated by optical spatial filters, allowing much easier optical access than in previous LIF experiments. The densities at the initiation of the discharge and at the quasisteady state of the discharge were determined to be 3×1016 and 1×1016 m−3, respectively within an error of a factor of 2. Optimization to maximize the signal‐to‐noise ratio of the observation and resulting detection limit were discussed and confirmed the above results.

Studies of particle behaviour in Heliotron E by means of balmer-alpha laser fluorescence spectroscopy

Measurements of atomic hydrogen density profiles in Heliotron E plasmas were performed, where attention was focussed on the anisotropy of the profiles in the poloidal cross section. Obtained penetration profiles of atomic hydrogen agreed well with the Monte Carlo code calculations of the penetration of Franck-Condon neutrals when averaged electron densities bar n e are larger than 10 19 m -3 . For bar n e <10 19 m -3 , however, experimental profiles decreased steeper than calculated ones. Degree of the anisotropy of the neutral profiles in the poloidal cross section was also found to change with the value of bar n e . Global particle confinement time τ p was evaluated from the measured atomic hydrogen profile. The results showed that τ p is arourud 20 ms for B =1 .9 T. In case of NBI plasma, τ p increases as increasing the magnetic field strength, while it decreases as increasing the absorbed power.

Studies of Hydrogen Atoms in High-Temperature Plasmas by Laser Fluorescence Spectroscopy at Balmer Series

Technique of the laser fluorescence spectroscopy at Balmer series, for studies of hydrogen behaviour in high-temperature plasmas, was critically examined in terms of atomic hydrogen sources, SN ratios for measurements by Balmer alpha and beta fluorescence, and hardwares (tunable dye lasers and detection optics). It was concluded that Balmer alpha gave better SN ratio for all conditions investigated. In addition, detection limit and the means of improving the SN ratio were shown. Based on these discussions, atomic hydrogen in RFC-XX-M mirror-cusp device was measured, firstly to verify the above argument, and then to study the origin and behaviour of hydrogen atoms in the machine.

Instantaneous velocity-distribution measurement of atoms in high-temperature plasma devices by a rapid-frequency-scan laser.

An instantaneous determination for the velocity distribution of metallic atoms sputtered by the plasma-surface interaction in high-temperature plasma devices has been studied by the use of the laser fluorescence spectroscopy. A flashlamppumped long-pulse dye laser is developed for this purpose, whose frequency is linearly scanned by a PZT-tuned etalon inside the cavity. The Doppler profiles of their resonance lines can be determined during a single laser shot. Doppler profiles of sodium atoms in a vapor cell and iron atoms sputtered by ion-beam bombardment, were successfully measured by this technique. The distortion error caused by the line saturation is analytically calculated for two and three level systems. Some problems of the measurement in large plasma devices are discussed, and a preliminary experiment on the dye laser with the high repetition rate is briefly described.