Low-energy Langmuir cavitons: Asymptotic limit of weak turbulence
Low-energy Langmuir cavitons: Asymptotic limit of weak turbulence
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低能朗缪尔空穴：弱湍流的渐近极限
DOI：
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发表时间：
2011
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通讯作者：
A. Mangeney
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作者：
P. Henri;F. Califano;C. Briand;A. Mangeney
朗缪尔湍流是等离子体物理中波动湍流的一种原型。通过1D-1V Vlasov-Poisson模拟，我们发现Langmuir弱湍流的长期演化产生了称为Langmuir空腔的相干结构，从而说明了弱湍流状态的破坏。这些结构对应于压力和由高频朗缪尔振荡产生的质动势之间的平衡。Langmuir空腔是强Langmuir湍流的典型特征，预计会在高能量下产生，并在Langmuir能量与等离子体热能量级时达到饱和。尽管有这种普遍的看法，但我们在这里观察到，从弱朗缪尔湍流演化中产生的空腔，在低得多的能量下饱和。我们表明，这些朗缪尔相干结构的特征是相对于德拜长度具有更大的长度尺度。这为在太空等离子体观测中应该看到“大”和“浅”稳定的空腔提供了证据。向强湍流的过渡被证明是一个初始弱湍流逆级联的结果。最后，从动力学模型出发，对离子声振荡的有效状态方程进行了数值验证。
Langmuir turbulence is an archetype of wave turbulence in plasma physics. By means of 1D-1V Vlasov-Poisson simulations, we show that coherent structures, called Langmuir cavitons, are generated by the long-time evolution of Langmuir weak-turbulence, thus illustrating the breakdown of a weak-turbulence regime. These structures correspond to an equilibrium between the pressure forces and the ponderomotive force resulting from high-frequency Langmuir oscillations. Langmuir cavitons are typical features of strong Langmuir turbulence expected to be generated at high energy and to saturate when Langmuir energy is of the order of the plasma thermal energy. Despite this wide-spread belief, here we observe that cavitons, emerging from weak Langmuir turbulence evolution, saturate at much lower energies. We show that these Langmuir coherent structures are characterized by a much larger length scale with respect to the Debye length. This gives evidence that “large” and “shallow” stable cavitons should be seen in space plasma observations. The transition toward strong turbulence is shown to be a consequence of an initial weak turbulent inverse cascade. Finally, the effective equation of state for ion acoustic oscillations is tested numerically from the kinetic model.