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Extension of the operational regime of the LHD towards a deuterium experiment
Takeiri, Y.,Morisaki, T.,Osakabe, M.,Yokoyama, M.,Sakakibara, S.,Takahashi, H.,Nakamura, Y.,Oishi, T.,Motojima, G.,Murakami, S.,Ito, K.,Ejiri, A.,Imagawa, S.,Inagaki, S.,Isobe, M.,Kubo, S.,Masamune, S IOP 2017 Nuclear fusion. Fusion nucléaire. &n.Illiga Vol.57 No.10
<P>As the finalization of a hydrogen experiment towards the deuterium phase, the exploration of the best performance of hydrogen plasma was intensively performed in the large helical device. High ion and electron temperatures, <I>T</I> <SUB>i</SUB> and <I>T</I> <SUB>e</SUB>, of more than 6 keV were simultaneously achieved by superimposing high-power electron cyclotron resonance heating onneutral beam injection (NBI) heated plasma. Although flattening of the ion temperature profile in the core region was observed during the discharges, one could avoid degradation by increasing the electron density. Another key parameter to present plasma performance is an averaged beta value <img ALIGN='MIDDLE' ALT='$\left\langle \beta \right\rangle $ ' SRC='http://ej.iop.org/images/0029-5515/57/10/102023/nfaa7fc2ieqn001.gif'/>. The high <img ALIGN='MIDDLE' ALT='$\left\langle \beta \right\rangle $ ' SRC='http://ej.iop.org/images/0029-5515/57/10/102023/nfaa7fc2ieqn002.gif'/> regime around 4% was extended to an order of magnitude lower than the earlier collisional regime. Impurity behaviour in hydrogen discharges with NBI heating was also classified with a wide range of edge plasma parameters. The existence of a no impurity accumulation regime, where the high performance plasma is maintained with high power heating >10 MW, was identified. Wide parameter scan experiments suggest that the toroidal rotation and the turbulence are the candidates for expelling impurities from the core region.</P>
Characteristics of Beam Attenuation in the High Temperature Plasma with High-Z Discharge in LHD
katsunori Ikeda,K. Tsumori,K. Nagaoka,M. Osakabe,O. Kaneko,S. Morita,Y. Oka,Y. Takeiri 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
Behavior in attenuation of a high-energy neutral beam has been investigated by visible spectroscopy in the Large Helical Device (LHD). The measurement system consists of optical fibers, a spectrometer and an ICCD detector. A spectrum of beam emission is clearly observed by the Doppler effect. In order to increase the ion-heating power, we have adopted a high-Z discharge with argon gas. An ion temperature of 13.5 keV ± 2 keV is achieved by the injection of a neutral beam power of 10.5 MW. We have observed the behavior of the neutral beam emission in the high-temperature plasma. The intensity of the beam emission in the argon discharge is lower than that in the hydrogen discharge when the ion temperature increases. After the maximum ion temperature, the intensity of the beam emission increases as the electron density increases. This behavior is similar to the hydrogen discharge. It is indicated that the particle configuration of the plasma has changed. This result will contribute to the monitoring of the neutral beam absorption in fusion plasma.
Tanaka, K.,Nagaoka, K.,Murakami, S.,Takahashi, H.,Osakabe, M.,Yokoyama, M.,Seki, R.,Michael, C.A.,Yamaguchi, H.,Suzuki, C.,Shimizu, A.,Tokuzawa, T.,Yoshinuma, M.,Akiyama, T.,Ida, K.,Yamada, I.,Yasuhar IOP 2017 Nuclear fusion Vol.57 No.11
<P>Surveys of the ion and electron heat transports of neutral beam (NB) heating plasma were carried out by power balance analysis in He and H rich plasma at LHD. Collisionality was scanned by changing density and heating power. The characteristics of the transport vary depending on collisionality. In low collisionality, with low density and high heating power, an ion internal transport barrier (ITB) was formed. The ion heat conductivity (<I>χ</I> <SUB>i</SUB>) is lower than electron heat conductivity (<I>χ</I> <SUB>e</SUB>) in the core region at <I>ρ</I> < 0.7. On the other hand, in high collisionality, with high density and low heating power, <I>χ</I> <SUB>i</SUB> is higher than <I>χ</I> <SUB>e</SUB> across the entire range of plasma. These different confinement regimes are associated with different fluctuation characteristics. In ion ITB, fluctuation has a peak at <I>ρ</I> = 0.7, and in normal confinement, fluctuation has a peak at <I>ρ</I> = 1.0. The two confinement modes change gradually depending on the collisionality. Scans of concentration ratio between He and H were also performed. The ion confinement improvements were investigated using gyro-Bohm normalization, taking account of the effective mass and charge. The concentration ratio affected the normalized <I>χ</I> <SUB>i</SUB> only in the edge region (<I>ρ</I> ~ 1.0). This indicates ion species effects vary depending on collisionality. Turbulence was modulated by the fast ion loss instability. The modulation of turbulence is higher in H rich than in He rich plasma.</P>