Papers - SAKAI Osamu

Mode conversion of fast magnetosonic waves and minority ion heating in a longitudinally inhomogeneous magnetic field

O. Sakai, Y. Yasaka

Physics of Plasmas   1 ( 12 )   3896 - 3904   1994

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Publishing type：Research paper (scientific journal)  

Mode conversion process in ICRF (Ion Cyclotron Range of Frequencies) in a longitudinally inhomogeneous two-ion-species plasma is clarified in the HIEI tandem mirror experiments. Measurements of wave number parallel to the magnetic field reveal that the fast magnetosonic wave of low-field-side incidence converts into the slow ion-cyclotron wave near the ion-ion hybrid resonance. The propagation of the slow wave is detected between the ion-ion hybrid resonance and minority ion cyclotron resonance layers, which shows good agreement with the calculated dispersion relation based on one- and two-dimensional plasma models. Simultaneous minority ion heating is observed, and it is due to the presence of the slow wave that resonates with minority ions at the minority ion cyclotron resonance. © 1994 American Institute of Physics.

DOI： 10.1063/1.870861

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Selective ion and electron heating and potential formation using mode conversions of ICRF waves in HIEI

Y. Yasaka, O. Sakai, H. Takeno, H. Hojo

Nuclear Fusion   34 ( 9 )   1263 - 1269   1994

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Publishing type：Research paper (scientific journal)  

Plasma heating and potential formation by ion cyclotron range of frequencies (ICRF) waves are investigated in the HIEI tandem mirror. It is demonstrated that ions and electrons are selectively heated by the appropriate waves that have been mode converted from the fast magnetosonic wave in a two-ion-species plasma. In the central cell, the minority ions can be heated up to 0.3 keV with the presence of the mode-converted slow ion cyclotron wave. Plug cell electrons are heated by the mode-converted electrostatic slow wave resulting in the formation of an ion confining potential. The dependence of the ion confining potential on the plug electron temperature is in qualitative agreement with values predicted by the improved modified Boltzmann relation which includes velocity space diffusion of electrons due to the ICRF wave. The axial confinement of the core plasma is improved by the ICRF produced potential.

DOI： 10.1088/0029-5515/34/9/I07

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High radial confinement mode induced by dc limiter biasing in the HIEI tandem mirror

O. Sakai, Y. Yasaka, R. Itatani

Physical Review Letters   70 ( 26 )   4071 - 4074   1993

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Publishing type：Research paper (scientific journal)  

A transition from low to high radial confinement mode is triggered by biasing a limiter in the HIEI tandem mirror. Positive dc biasing gives rise to reduction of fluctuation level in density and potential in the periphery, drop of neutral line emission, and bifurcation in limiter current. After the transition, the plasma exhibits density rise in the bulk and steepening of the density gradient. Significant radial rotational shear is observed when the edge turbulence is suppressed by the biasing. The total feature shows similar characteristics of L- to H-mode transition observed in tokamak devices. © 1993 The American Physical Society.

DOI： 10.1103/PhysRevLett.70.4071

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Nonlinear ion Bernstein wave heating experiment in the WT-3 tokamak

Y. Yasaka, H. Takeno, M. Sakka, O. Sakai, R. Itatani, T. Fujimoto, H. Suemitsu, K. Takahata, M. Fukao, S. Tanaka, Y. Terumichi

Plasma Physics and Controlled Fusion   35 ( 3 )   379 - 389   1993

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Publishing type：Research paper (scientific journal)  

Ion Bernstein wave (IBW) heating at ion cyclotron half-harmonic frequencies was performed in hydrogen (H) discharges in the WT-3 tokamak. The bulk ion temperature increase was measured by a charge exchange analyser and a spatially scanning polychrometer. The latter diagnostics can provide radial ion-temperature profiles. The incremental ion temperature has shown a peak at the exact location where the IBW frequency omega equals 3/2 of the ion cyclotron frequency, indicating the nonlinear direct acceleration of H ions. The wave electric field was measured by a Langmuir probe in the scrape-off layer. The electric field at the second harmonic of the excited IBW frequency was observed to vary depending on the power level and the toroidal magnetic field. These experimental results are compared with the theoretical prediction of nonlinear IBW damping. The measured dependences of the ion heating and the wave amplitude at 2 omega on the toroidal magnetic field are in reasonable agreement with the prediction.

DOI： 10.1088/0741-3335/35/3/007

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