Speaker
Yasuhiro Suzuki
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1049.pdf
Anisotropic heat diffusion on stochastic magnetic fields
Yasuhiro Suzuki
National Institute for Fusion Science,322-6 Oroshi-cho, Toki 509-5292, Japan
SOKENDAI, Graduate University for Advanced Studies, 322-6 Oroshi-cho, Toki 509-5292, Japan
suzuki.yasuhiro@LHD.nifs.ac.jp
The magnetic topology is a key issue in fusion plasma researches. An example is the Resonant
Magnetic Perturbation (RMP) to control the transport and MHD activities. However, the
physics how the RMP affects the transport and MHD is not clear. One reason is the change of
the magnetic topology by the plasma response. Since the vacuum approximation cannot
interpret experimental observations in many cases, the magnetic topology might be changed by
the plasma response. In addition, the change of the magnetic topology is predicted by numerical
simulations. However, the identification of the magnetic topology in the experiment is very
difficult.
Recently, ideas to identify the magnetic topology experimentally are proposed in many
experiment devices. Those are the heat pulse propagation by modulated ECH and
measurements of the radial electric field. However, those techniques give only one dimensional
profiles. In the peripheral region of the perturbed tokamak and stellarator, the magnetic field
structure is very sophisticated because island chains are overlapped by strong magnetic shear.
Thus, the heat pulse propagation and radial electric field might be distributed by two- or three-
dimensionally. That means the experimental study of the magnetic topology is still very difficult.
In this study, we study numerically the anisotropic heat diffusion on the stochastic magnetic
field. The anisotropic heat diffusion is given by a following equation,
𝜕𝑇
= ∇ ∙ (𝜅∥ ∇∥ 𝑇 + 𝜅∥ ∇⊥ 𝑇) + 𝑄.
𝜕𝑡
Numerically solving this equation, we can simulate the heat transport on the stochastic magnetic
field. A difficulty is the time scale of the parallel and perpendicular to the magnetic field. In the
realistic case, the parallel heat transport is much faster than the perpendicular transport. So, the
numerical integration of the anisotropic heat diffusion equation is very difficult, because the
time step of the numerical integration is defined by the parallel transport. If a ratio of 𝜅∥ and 𝜅⊥
is huge, the time step must be small and that is very time consuming. To resolve that problem,
we are developing an implicit scheme of the time integration in fully three-dimensional
geometry.
In this study, we discuss initial results from a new code to solve the anisotropic heat diffusion
based on the implicit scheme. We applied the new code to a perturbed tokamak and a stellarator.
The distribution of the electron temperature on the stochastic magnetic field is obtained. Hudson
et al pointed out the KAM surface is a barrier to keep the finite temperature. We simulate those
results in realistic magnetic field of the perturbed tokamak and stellarator.
