Anisotropic ExB shearing rate in a magnetic island

© 2021 Author(s).We derive the E × B shearing rate associated with vortex flow inside a macroscopic magnetic island (MI) in axisymmetric toroidal geometry. Due to the elongation of the MI and incompressibility of the E × B flow, the shearing rate near X-points is much lower than that near the mid-plane (x-axis of the local Cartesian coordinate) of the MI on the same flux surface. Furthermore, the rate formally vanishes at the X-points where the local poloidal magnetic field associated with the MI stagnates. This calculation of E × B shearing profile and, in particular, minimal E × B shear near the X-points is consistent with the recent experimental finding that turbulence tends to spread into an MI through regions around the X-points [K. Ida et al., Phys. Rev. Lett. 120, 245001 (2018)] and can contribute to more thorough quantitative interpretation of the results from experiments and simulations.N

Simulation study on internal transport barrier formation using gyrofluid model

ジャイロ流体モデルを用いてトカマクプラズマにおける内部輸送障壁形成のシミュレーション研究を行った。新古典輸送をモデルに実装し、準線形的な変化を考慮し、加熱分布を変化させ、内部輸送障壁の強度依存性を調べた。その結果、負磁気シャーを形成する部分を局所的に加熱することにより強い輸送障壁が形成されることを初めて示した。第14回核燃焼プラズマ統合コード研究

Extended bounce-kinetic model for trapped electron mode turbulence

© 2022 Author(s).The bounce-kinetic model based on the modern nonlinear bounce-kinetic theory [Fong and Hahm, Phys. Plasmas 6, 188 (1999)] has been developed and used for simulations previously. This work reports on an extension of the bounce-kinetic model including more accurate treatment of barely trapped particles and its implementation in the Gyro-Kinetic Plasma Simulation Program gyrokinetic code [Kwon et al., Comp. Phys. Commun. 215, 81 (2017)]. This leads to more accurate gyrokinetic simulations of the collisionless trapped electron mode at low magnetic shear.N

Parallelization of Spectral Landau Fluid Code Using MPI

3-field Landau fluid (LF3) model describes the ion tem-perature gradient driven drift wave (ITG) turbulence in Toka-mak plasmas[1]. It is applied to investigate the internal trans-port barrier formation which gives the improved energy con-finement time[2]. The code is developed using the spectralmethod[3] which is parallelized using Message Passing Inter-face (MPI)[4, 5]. Since the calculation cost of nonlinear modecoupling is most expensive part, so that various schemes forthe decomposition of do loop are tested to optimize it. It isfound that the best scheme gives roughly 30% faster than thestandard decomposition method

内部輸送障壁形成における新古典効果

ジャイロ流体コードGK-ITGに新古典流を実装した。新古典流に起因する分布の準線形的変化を考慮した。揺動温度の発展方程式に加熱源を導入し内部輸送障壁形成に対する加熱位置の依存性を調べた。飽和したイオン温度勾配駆動ドリフト波乱流に対し熱源を印加しその後のイオン温度分布発展を調べた。磁気軸からはずれた位置に加熱源を置いた場合、弱い内部輸送障壁が形成されることが明らかとなった。第11回 核融合エネルギー連合講演

Experimental observation of the non-diffusive avalanche-like electron heat transport events and their dynamical interaction with the shear flow structure

We present experimental observations suggesting that non-diffusive avalanche-like transport events are a prevalent and universal process in the electron heat transport of tokamak plasmas. They are observed in the low confinement mode and the weak internal transport barrier plasmas in the absence of magnetohydrodynamic instabilities. In addition, the electron temperature profile corrugation, which indicates the existence of the E x B shear flow layers, is clearly demonstrated as well as their dynamical interaction with the avalanche-like events. The measured width of the profile corrugation is around 45(rho i), implying the mesoscale nature of the structure

Tailoring tokamak error fields to control plasma instabilities and transport

Abstract A tokamak relies on the axisymmetric magnetic fields to confine fusion plasmas and aims to deliver sustainable and clean energy. However, misalignments arise inevitably in the tokamak construction, leading to small asymmetries in the magnetic field known as error fields (EFs). The EFs have been a major concern in the tokamak approaches because small EFs, even less than 0.1%, can drive a plasma disruption. Meanwhile, the EFs in the tokamak can be favorably used for controlling plasma instabilities, such as edge-localized modes (ELMs). Here we show an optimization that tailors the EFs to maintain an edge 3D response for ELM control with a minimized core 3D response to avoid plasma disruption and unnecessary confinement degradation. We design and demonstrate such an edge-localized 3D response in the KSTAR facility, benefiting from its unique flexibility to change many degrees of freedom in the 3D coil space for the various fusion plasma regimes. This favorable control of the tokamak EF represents a notable advance for designing intrinsically 3D tokamaks to optimize stability and confinement for next-step fusion reactors

Mesoscopic transport in KSTAR plasmas: avalanches and the E × B staircase

Abstract: The self-organization is one of the most interesting phenomena in the non-equilibrium complex system, generating ordered structures of different sizes and durations. In tokamak plasmas, various self-organized phenomena have been reported, and two of them, coexisting in the near-marginal (interaction dominant) regime, are avalanches and the E × B staircase. Avalanches mean the ballistic flux propagation event through successive interactions as it propagates, and the E × B staircase means a globally ordered pattern of self-organized zonal flow layers. Various models have been suggested to understand their characteristics and relation, but experimental researches have been mostly limited to the demonstration of their existence. Here we report detailed analyses of their dynamics and statistics and explain their relation. Avalanches influence the formation and the width distribution of the E × B staircase, while the E × B staircase confines avalanches within its mesoscopic width until dissipated or penetrated. Our perspective to consider them the self-organization phenomena enhances our fundamental understanding of them as well as links our findings with the self-organization of mesoscopic structures in various complex systems