Speaker
Motoki Nakata
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.105.pdf
Isotope effects on turbulent transport and confinement in helical and
tokamak plasmas: theory and experiment
M. Nakata1,2, M. Nunami1,2, H. Sugama1,2, T. –H. Watanabe3, S. Satake1,2, M. Yokoyama1,2,
K. Tanaka1, H. Takahashi1,2, and K. Nagaoka1,3
1
National Institutes of Natural Sciences / National Institute for Fusion Science, Toki, Japan
2
The Graduate University for Advanced Studies, Toki, Japan
3
Department of Physics, Nagoya University, Nagoya, Japan
Impacts of the hydrogen isotope ion mass on the energy confinement, which are observed
in earlier tokamak and helical plasma experiments, have been a long-standing issue in plasma
and fusion research, despite its broad interests and importance. One of the scientific goals in
new deuterium plasma experiments in Large Helical Device (LHD) is to explore such
“isotope effects” on transport and confinement.
In this talk, we present a recent progress in gyrokinetic turbulence simulation studies and
the related experiments in LHD. Gyrokinetic Vlasov simulations of trapped-electron-mode
(TEM) and ion-temperature-gradient (ITG) driven turbulence in LHD plasmas with hydrogen
isotope ions and real-mass kinetic electrons are carried out. It has been clarified that
combined effects of the collisional TEM stabilization by the isotope ions and the associated
increase of the steady zonal flows at the near-marginal linear stability lead to the transport
reduction [1, 2], which is distinct from the ion mass dependence in the conventional gyro-
Bohm scaling. On the other hand, the gyro-Bohm like dependence is found for the ITG case
without the effect of poloidal rotations by equilibrium radial electric fields. The universal
nature of the isotope effects on the TEM-driven turbulence and zonal flows is theoretically
verified also for tokamak plasmas. In addition, by using PCI and HIBP/CXS measurements
in LHD, TEM-like fluctuations propagating to the electron diamagnetic direction have been
identified in high-Te/Ti deuterium and hydrogen experiments with ECRH. A moderate
isotope mass dependence in the global energy confinement is also found.
[1] M. Nakata, M. Nunami et al., Physical Review Letters 118, 165002 (2017)
[2] M. Nakata, M. Nunami et al., Plasma Physics and Controlled Fusion 58, 074008 (2016)
