TY - JOUR

T1 - Collisionality dependence and ion species effects on heat transport in He and H plasma, and the role of ion scale turbulence in LHD

AU - Tanaka, K.

AU - Nagaoka, K.

AU - Murakami, S.

AU - Takahashi, H.

AU - Osakabe, M.

AU - Yokoyama, M.

AU - Seki, R.

AU - Michael, C. A.

AU - Yamaguchi, H.

AU - Suzuki, C.

AU - Shimizu, A.

AU - Tokuzawa, T.

AU - Yoshinuma, M.

AU - Akiyama, T.

AU - Ida, K.

AU - Yamada, I.

AU - Yasuhara, R.

AU - Funaba, H.

AU - Kobayashi, T.

AU - Yamada, H.

AU - Du, X. D.

AU - Vyacheslavov, L. N.

AU - Mikkelsen, D. R.

AU - Yun, G. S.

N1 - Publisher Copyright: © 2017 IAEA, Vienna.

PY - 2017/8/1

Y1 - 2017/8/1

N2 - 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 (χ i) is lower than electron heat conductivity (χ e) in the core region at ρ < 0.7. On the other hand, in high collisionality, with high density and low heating power, χ i is higher than χ e across the entire range of plasma. These different confinement regimes are associated with different fluctuation characteristics. In ion ITB, fluctuation has a peak at ρ = 0.7, and in normal confinement, fluctuation has a peak at ρ = 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 χ i only in the edge region (ρ ∼ 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.

AB - 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 (χ i) is lower than electron heat conductivity (χ e) in the core region at ρ < 0.7. On the other hand, in high collisionality, with high density and low heating power, χ i is higher than χ e across the entire range of plasma. These different confinement regimes are associated with different fluctuation characteristics. In ion ITB, fluctuation has a peak at ρ = 0.7, and in normal confinement, fluctuation has a peak at ρ = 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 χ i only in the edge region (ρ ∼ 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.

KW - heat transport

KW - helical

KW - ion species

KW - isotope effect

KW - ITB

KW - stellarator

KW - turbulence

KW - ENERGY CONFINEMENT

KW - DENSITY-FLUCTUATIONS

KW - MODE POWER THRESHOLD

UR - http://www.scopus.com/inward/record.url?scp=85028451549&partnerID=8YFLogxK

U2 - 10.1088/1741-4326/aa79c6

DO - 10.1088/1741-4326/aa79c6

M3 - Article

AN - SCOPUS:85028451549

VL - 57

JO - Nuclear Fusion

JF - Nuclear Fusion

SN - 0029-5515

IS - 11

M1 - 116005

ER -