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複合大域シミュレーションユニットセミナー（2025年7月9日）

[日時]　2025年 7月 9日(水) 15:00〜16:00

[場所]　核融合科学研究所 シミュレーション科学研究棟1階会議室 ＋ オンライン併用

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[講師]　Sharad K Yadav (Sardar Vallabhbhai National Institute of Technology (SVNIT), India)

[講演題目]　Magnetic Prandtl number dependent fluctuation spectra and intermittency in 3D Hall- magnetohydrodynamics (HMHD) plasma turbulence

[講演概要]
Hall- magnetohydrodynamics (HMHD) is a simplified fluid description of plasma that accounts the two-fluid effects to some extent. It include Hall term via generalized Ohm’s law and reduces to magnetohydrodynamics (MHD) if di = 0 where di is the ion-inertial
length. Hall- MHD equations are employed in many space and laboratory plasma processes such as magnetic-reconnection processes, sub-Alfvenic plasma expansion and magnetic-field transport in plasma opening switches. Turbulence in the solar wind[1] is often studied using the Hall magnetohydrodynamics (HMHD) equations. In this work[2, 3], we mainly carry out extensive pseudospectral direct numerical simulations (DNSs) of decaying three-dimensional (3D) Hall magnetohydrodynamics (3D HMHD) plasma turbulence at three magnetic Prandtl numbers Prm = 0.1, 1.0 and 10.0. In our simulations, we find two different inertial regions – in the first inertial region k < ki(≡ 1/di), both the kinetic-energy and magnetic-energy spectra, Eu(k) and Eb(k), respectively, display power-law regions with an exponent that is consistent with Kolmogorov-type -5/3 scaling, at all values of Prm. In the second inertial region k > ki, the scaling of Eb(k) depends upon Prm , at Prm = 0.1, the spectral-scaling exponent is -17/3, but for Prm = 1 and 10 this exponent is -11/3. We then show theoretically that Eb(k)∼ k-2Eu(k) for Prm ≪ 1 and Eb(k)∼ k2Eu(k) for Prm ≫ 1; our DNS results are consistent with our theoretical predictions. Moreover, we also show that 3D HMHD turbulence shows signatures of intermittency that we uncover by analyzing the scale dependence of probability distribution functions of velocity- and magnetic-field increments, their structure functions, and their flatnesses as functions of di and Prm.

[1] K. H. Kiyani, S. C. Chapman, Y. V. Khotyaintsev, M. W. dunlop and F. Sahraoui, Phys. Rev. Lett., 103, 075006 (2009).
[2] S. K. Yadav, H. Miura and R. Pandit, Phys. Fluids, 34, 095135 (2022)
[3] P. Patel, S. K. Yadav, H. Miura and R. Pandit, https://arxiv.org/abs/2505.09537 (May,2025)

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