Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 3D MHD simulation of linearly polarised Alfven wave dynamics in
  Arnold-Beltrami-Childress magnetic field   Previous studies [Malara et al ApJ, 533, 523 (2000)] considered
small-amplitude Alfven wave (AW) packets in Arnold-Beltrami-Childress (ABC)
magnetic field using WKB approximation. In this work linearly polarised Alfven
wave dynamics in ABC magnetic field via direct 3D MHD numerical simulation is
studied for the first time. Gaussian AW pulse with length-scale much shorter
than ABC domain length and harmonic AW with wavelength equal to ABC domain
length are studied for four different resistivities. While it is found that AWs
dissipate quickly in the ABC field, surprisingly, AW perturbation energy
increases in time. In the case of the harmonic AW perturbation energy growth is
transient in time, attaining peaks in both velocity and magnetic perturbation
energies within timescales much smaller than resistive time. In the case of the
Gaussian AW pulse velocity perturbation energy growth is still transient in
time, attaining a peak within few resistive times, while magnetic perturbation
energy continues to grow. It is also shown that the total magnetic energy
decreases in time and this is governed by the resistive evolution of the
background ABC magnetic field rather than AW damping. On contrary, when
background magnetic field is uniform, the total magnetic energy decrease is
prescribed by AW damping, because there is no resistive evolution of the
background. By considering runs with different amplitudes and by analysing
perturbation spectra, possible dynamo action by AW perturbation-induced
peristaltic flow and inverse cascade of magnetic energy have been excluded.
Therefore, the perturbation energy growth is attributed to a new instability.
The growth rate appears to be dependent on the value of the resistivity and
spatial scale of the AW disturbance. Thus, when going beyond WKB approximation,
AW damping, described by full MHD equations, does not guarantee decrease of
perturbation energy.

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The categories of this paper are: hep-th
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The categories of this paper are: q-alg
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The categories of this paper are: chao-dyn
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The categories of this paper are: cs
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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The categories of this paper are: adap-org
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-bio
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-ex
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The categories of this paper are: plasm-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: math
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The categories of this paper are: gr-qc