[en] Magnetic resonance imaging continues to elicit new application software through the recent technological advances of MR equipment. This paper describes several applications of our newly developed clinical software. The fast SE sequence (RISE) has proved to reduce routine examination time and to improve image quality, and ultra-fast FE sequence (SMASH) was found to extend the diagnostic capabilities in the field of cardiac study. Diffusion/perfusion imaging achieved in our MR system showed significant promise for providing novel information regarding tissue characterization. Furthermore, Image quality and practicalities of MR angiography have been improved by advanced imaging sequences and sophisticated post-processing software. (author)

[en] An edge transport barrier (ETB) formation and an improved L-mode (IL mode) have been simultaneously realized in high density region (n-bar_e - 1.2x10²⁰m^-3) on Compact Helical System (CHS). When the ETB is formed during the IL mode, the density reduction in the edge region is suppressed by the barrier formation. As a result of the continuous increasing of the temperature by the IL mode, the stored energy during the combined mode increased up to the maximum stored energy (W_p - 9.4 kJ) recorded in CHS experiments. The plasma pressure in the peripheral region increases up to three times larger than that of the L-mode, and the large edge plasma pressure gradient is formed accompanying the pedestal structure. That is caused by the anomalous transport reduction that is confirmed from the sharp drop of the density fluctuation in the edge region. The neutral particle reduction in the peripheral region and the metallic impurity accumulation in the core plasma are simultaneously observed during the high density ETB formation. (author)

[en] Magnetic configurations of LHD experiment are analyzed based on the Fourier modes of the plasma boundary shapes. It was found that a small number of Fourier modes is sufficient to determine the confinement characteristics of different configurations with the magnetic axis shift of LHD. A new configuration is proposed with a different combination of Fourier modes, which has good particle orbits and a favorable property of high beta equilibrium. This solution has a smaller Shafranov shift than the inward-shifted configuration of LHD. (author)

No abstract available

[en] In the vacuum magnetic field configuration of CHS, the MHD stability depends on the position of magnetic axis (R_ax). When R_ax> 95 cm, the magnetic well in the central region and the strong magnetic shear in the boundary region give the MHD stability for the ideal interchange. For the inward shifted configuration, the Mercier unstable region comes out. The volume-averaged equilibrium beta 2.1 % was obtained in 1993 with R_ax = 92 cm configuration. The self-stabilization effect of high-beta plasma gave Mercier stable equilibrium while the R_ax = 92 cm configuration has the Mercier unstable region for low-beta plasmas. The measurements of magnetic fluctuations and the soft X-ray signals did not show strong instabilities in these discharges. In order to evaluate the stability boundary for ideal interchange instabilities, the efforts of producing high-beta plasmas have been made for more inward shifted magnetic axis configurations (89 cm< R_ax < 92 cm). The strong MHD activities were observed for those discharges. 2 refs., 7 figs

No abstract available

[en] The physical confinement properties of stellarators are analyzed for the neo-classical transport and the magnetic well. Three typical concepts of stellarators (LHD, Wendelstein 7-X and TJ-II) are compared in terms of the helical movement of cross sections of the last closed magnetic surface. It is shown that this geometric element strongly determines the confinement properties of both non-planar axis and planar axis stellarators. (author)

[en] The temporal behavior of electron density profiles of edge plasmas in the Compact Helical System (CHS) during high beta discharges was measured with a thermal neutral lithium beam probe. A large outward shift of the plasma edge boundary was observed with an increase in the beta value. The position of the plasma edge boundary measured experimentally was compared with that of the last closed flux surface (LCFS) calculated by the VMEC code, and qualitative agreement was found between experimental and theoretical results. The experiment on the dynamic poloidal field control during the discharge was also performed successfully to fix the position of the edge plasma boundary when the plasma beta was raised. 10 refs., 6 figs

[en] In order to understand the confinement characteristics of different types of stellarators from the common point of view, characteristics of the geometric shape of the last closed magnetic surfaces are analyzed in terms of the Fourier modes. Magnetic configurations of LHD and CHS are compared for their different operational modes with shifted magnetic axis positions. Total number of Fourier modes is reduced for their outward shifted configurations to find out the essential modes for creating magnetic well. It is shown that the helical axis structure is important for the control of magnetic field configuration even for the planar-axis stellarators (heliotrons) of LHD and CHS. (author)

[en] A new compact helical system CHS-qa has been designed based on the advanced stellarator concept of the quasi-axisymmetry in the magnetic field configuration. This new concept of quasi-axisymmetry makes it possible to realize the two-dimensional vacuum magnetic field structure (a tokamak-like configuration) without using plasma current. In this system, the neoclassical transport is greatly reduced compared with conventional helical systems because the helical ripples are very small. Good MHD stability for the interchange and ballooning modes are obtained. The possibility of finding the confinement improvement is also discussed from the viewpoint of plasma rotation and maximum-J criterion. (author)