26aE05P
三次元MHD平衡計算コード
平衡計算コードHINT2における境界条件の影響における境界条件の影響
三次元平衡計算コード
Influence of boundary condition in three-dimensional calculation code HINT2寺田遼平1), 鈴木康浩2) , 中村祐司1)
Ryohei Terada1), Yasuhiro Suzuki2), Yuji Nakamura1)
1) 京都大学エネルギー科学研究科 2) 核融合科学研究所
1) GSES, Kyoto University 2) NIFS

Since tokamaks are usually regarded as theaxisymmetric devices, the 2D MHD equilibrium
analyses have been carried out in tokamak plasmas
by the VMEC code. However, some external factors
such as Toroidal Field (TF) ripple and Resonant
Magnetic Perturbation (RMP) field create the
non-axisymmetric fields. For equilibrium analysisof tokamaks including such non-axisymmetric 3Deffects, we usually use the vacuum approximationthat a vacuum helical perturbed field due to RMP
coils is superimposed on a 2D MHD equilibrium.
The previous study [1] shows that the vacuum
approximation is good approximation. However, thevacuum approximation does not include the effectof the magnetic field produced by plasmas on theequilibrium. This 3D effect cannot be ignored
completely especially in high-β plasmas. Therefore,consistent 3D equilibrium calculation of
non-axisymmetric tokamaks is an important work.
The HINT2 code [2], three-dimensional MHD
equilibrium calculation code, is widely used toanalyze the equilibrium of helical plasmas. The
HINT2 can calculate equilibrium condition byiterating two relaxation steps: the pressure
relaxation step (step-A) and the field relaxation step(step-B). In contrast to the VMEC code, the HINT2code can calculate the equilibrium condition
without assumption of the existence of nested flux
surfaces. Thus, the HINT2 code can be applied tothe calculation of the equilibrium including
magnetic islands and stochastic region. However,the HINT2 code assumes fixed normal componentof the magnetic field at the computational boundary.
Few influences of that boundary condition havebeen predicted in Large Helical Device (LHD) [3].
But this boundary condition is not suitable for theequilibrium analysis in plasma with large current
such as tokamak plasmas because the magnetic
field near the boundary is changed by plasma
current.
For those reasons, we apply the Virtual Casing
Principle (VCP) for the calculation of the magnetic
field on the boundary in tokamaks. In the VCP, weassume the “virtual casing” between the plasmas
and the external conductors. Then, we can introduce
the surface currents and the magnetic surface
charges on the casing that cancel the external fieldby plasma and coil currents. By using them, we cancalculate the external field by plasma currents andthe internal field by coil currents without a detailed
calculation of the precise structure due to thosecurrents. In our study, the VCP will be used only tocompute the external field from plasma currents.
In this study, we will include the new boundary
condition obtained by the VCP into the HINT2 code.
Comparison of the equilibrium field obtained by the“new HINT2 code” which includes the boundary
condition to that by the conventional HINT2 code is
now under investigation. Furthermore, application
to the equilibrium calculation of tokamak plasmas
and comparison to other equilibrium calculation
codes such as the VMEC code are planned.

References[1] Y. Nakamura : J. Plasma Fusion Res. 88(2012)
168-172[2] Y. Suzuki et al. : Nucl. Fusion 46(2006) L19-24[3] H. Kamiuttanai et al. : “Influence of boundary
conditioninthree-dimensional
MHD
calculation code HINT2” Plasma Conference
2014 18PB-055