Keiji Matsuo

Laser diagnostics of edge plasmas and laser diagnostics of plasmas for industrial applications (invited)

In plasma physics, laser diagnostics were first developed to probe the core region of magnetically confined high‐temperature plasmas, but the advent of various new lasers has turned out to be useful for edge plasma studies. The recent developments of various arc and glow discharges for industrial plasma applications have required measurement of the same quantities as in the edge plasma studies and expertise in the latter has been fully exploited for the former. The experience thus gained has then been used for the advantage in the studies of edge plasma behavior in high‐temperature plasmas. The interplay of these two fields of plasma studies, where laser diagnostics of plasmas (which we call ‘‘laser‐aided plasma diagnostics’’) is extensively used, is discussed.

Development of Laser Imaging Method for Measurements of Electron Density Fluctuations in Plasmas

A generalized analysis of the laser imaging method is presented for measurements of long-wavelength electron density fluctuations in plasmas, so as to enable its application to practical situations, such as oblique incidence of laser light and identification of the position of the fluctuations. Experimental verification of the more salient features of the theory is also described.

Characteristics of Electron Density Fluctuations in Heliotron E Measured Using a Wide Beam Laser Phase Contrast Method

Electron density fluctuations in Heliotron E were measured using a wide beam laser phase contrast method in a frequency range of 2.5≤ f ≤500 kHz and a wavenumber range of 0.1 ≤ k ≤1.3 rad/mm. Two branches of S ( k , f ) spectra were detected, which we have called a high speed branch and a low speed branch because of a difference in their measured phase velocities. Their characteristics were studied from spatial distributions, correlation with magnetic fluctuations, phase velocities, fluctuation levels and theoretical considerations. The high speed branch is consistent with a Magneto Hydro Dynamic (MHD) mode driven by a resistive interchange instability and mainly existed inside the limiter, and the low speed branch is explained as a microturbulence driven by a drift instability and mainly existed outside the limiter. The implications of these findings for studies of plasma confinement in Heliotron E are discussed.

Applicability of laser phase contrast method for the measurements of electron density fluctuations in high-temperature plasmas

We have demonstrated the potential of the laser phase contrast (LPC) method for measurements of electron density fluctuations in high-temperature plasmas, by measuring the direction of propagation and intensity of fluctuations in Heliotron E.

Identification and Role of Low-Frequency Microinstability in RFC-XX-M Studied by the Fraunhofer-Diffraction Method

The low-frequency electron-density fluctuations in the mirror-cusp device RFC-XX-M were measured using the Fraunhofer-diffraction method. The density fluctuations by the microinstability were identified to be of the drift-wave mode, by the discussions of the dispersion relation, range of the wave-numbers ( k ⊥ ρ i ≃1, where k ⊥ is the wave-number in the plane perpendicular to a magnetic field and ρ i is the ion Larmor radius), the localization at the density gradient, and the growth rate. Further, effects of the fluctuations on mirror confinement were discussed and the particle confinement time was deduced from the measured fluctuation intensity.

Applicability of Laser Imaging System Using a Near Infrared Laser to Measure Density Fluctuations in High-Temperature Plasmas

A new type of laser imaging method using a near infrared laser rather than a CO2 one (10.6 µm) is developed and its applicability to the density fluctuation measurement in high-temperature plasmas is evaluated. A near-infrared yttrium aluminum garnet (YAG) laser system is installed on the Compact Helical System (CHS) at the National Institute for Fusion Science (NIFS). The applicability of this laser imaging method to a middle sized toroidal device is tested. The minimum detectable signal level of 6.9×1011 cm-2 for the density fluctuation has been obtained, which is required for practical use.

Atomic hydrogen behaviour in Heliotron E

Abstract In order to understand atomic hydrogen behaviour and particle confinement properties in Heliotron E plasmas, techniques of laser induced fluorescence (LIF) have been extensively used, combined with measurements of absolute Balmer alpha emissions and density fluctuations. The results revealed that for an average electron density n ¯ e > 1.5 × 10 19 m −3 , Hα fluorescence allowed the measurements of atomic hydrogen densities and yielded the recycled Franck-Condon neutrals (~ 3 eV) to penetrate into core plasmas, whereas for n ¯ e 19 m −3 , such measurements were perturbed by dissociative-excitation of H 2 molecules into the n = 2 state. Also, the global confinement times showed a clear correlation with electron density fluctuations.

Application of Fraunhofer-Diffraction Method for Measurements of Electron Density Fluctuations in Heliotron E

Electron density fluctuations in Heliotron E were measured using the Fraunhofer diffraction method of a CO 2 laser radiation. The deduced dispersion relation was found to be consistent with the drift wave, Doppler-shifted by a poloidal rotation resulting from a radial electric field. The measured intensities of the fluctuations were used to estimate the diffusion coefficient and particle confinement time, the latter (10 ms) being the same order of magnitude as that obtained independently from laser fluorescence and plasma emission, both at the Balmer alpha line.

Cooperative function of Fmp30, Mdm31, and Mdm32 in Ups1-independent cardiolipin accumulation in the yeast Saccharomyces cerevisiae

Cardiolipin (CL) is synthesized from phosphatidic acid (PA) through a series of enzymatic reactions occurring at the mitochondrial inner membrane (MIM). Ups1-Mdm35 mediates PA transfer from the mitochondrial outer membrane (MOM) to the MIM in the yeast Saccharomyces cerevisiae. Deletion of UPS1 leads to a ~80% decrease in the cellular CL level. However, the CL accumulation in ups1∆ cells is enhanced by the depletion of Ups2, which forms a protein complex with Mdm35 and mediates phosphatidylserine (PS) transfer from the MOM to the MIM for phosphatidylethanolamine (PE) synthesis by a PS decarboxylase, Psd1. In this study, we found that the accumulation of CL in ups1∆ cells was enhanced by deletion of not only UPS2, but also PSD1 and CHO1 encoding a PS synthase, suggesting that low PE levels in mitochondria were relevant to the enhancement of CL accumulation in ups1∆ cells. Furthermore, the Ups1-independent and low-level PE-enhanced CL accumulation was shown to depend on the functions of FMP30, MDM31, and MDM32. In addition, the physical interactions of Fmp30 with Mdm31 and Mdm32 were revealed. Thus, when the mitochondrial PE level is reduced, Fmp30, Mdm31, and Mdm32 seem to function cooperatively for the accumulation of CL in a UPS1-independent manner.

Neutral-particle behaviour and particle confinement studies in Heliotron E

Abstract Measurements of neutral-hydrogen density by laser fluorescence spectroscopy on Heliotron E revealed the anisotropy of its distribution in the poloidal cross section and the dependence of the anisotropy on the average electron density for the first time. This indicates the relative importance of the recycling of charged particles localized at divertor traces and that of charge-exchanged neutrals distributed over a surface. These results are used to calculate the global particle confinement time, which is to be correlated with the measurements of H α emission intensity and the electron density fluctuations, the initial results of which are also shown.