Perpendicular Ion Heating by Cyclotron Resonant Dissipation of Turbulently Generated Kinetic Alfvén Waves in the Solar Wind
Perpendicular Ion Heating by Cyclotron Resonant Dissipation of Turbulently Generated Kinetic Alfvén Waves in the Solar Wind
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DOI：
10.3847/1538-4357/ab4e12
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发表时间：
2019-10
期刊：
影响因子：
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通讯作者：
P. Isenberg;B. Vasquez
中科院分区：
文献类型：
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作者：
P. Isenberg;B. Vasquez
观测到太阳风离子在垂直于大尺度磁场的方向上被加热，重离子优先被加热。在日冕中，这种加热可能是风本身产生的原因。这种加热很可能是由于等离子体湍流的耗散，但产生这些优先效应的具体动力学机制尚不清楚。质子尺度的太阳风湍流通常以高斜向动力学阿尔文波（KAWs）为特征，这种波被认为通过朗道共振消散并产生平行加热。我们表明，KAWs和太阳风离子之间的准线性共振回旋相互作用实际上可以产生垂直离子加热。我们提出了一个稳定的，临界平衡的频谱KAWs作用于均匀的离子分布与等离子体β = 0.1，代表湍流条件下的快速太阳风近20 Rs的说明性计算。KAWs在这里由双流体色散关系描述。我们发现，热质子在数千个陀螺周期的典型准线性时间内在垂直方向上被强烈加热，这相当于20 Rs时的几分钟。在同一个涨落场中的α粒子被加热到相似的垂直热速度，相当于通常观察到的大于质量比例的垂直温度。我们讨论改进这个简单的模型，可能会决定这种机制是否可以负责所观察到的日冕和太阳风离子加热。
Solar wind ions are observed to be heated in the directions perpendicular to the large-scale magnetic field, with preferential heating given to heavy ions. In the solar corona, this heating may be responsible for the generation of the wind itself. It is likely that this heating results from the dissipation of plasma turbulence, but the specific kinetic mechanism that produces these preferential effects is not known. Solar wind turbulence at proton scales is often characterized in terms of highly oblique kinetic Alfvén waves (KAWs), which have been thought to dissipate through the Landau resonance and yield parallel heating. We show that the quasilinear resonant cyclotron interaction between KAWs and solar wind ions can actually produce perpendicular ion heating. We present an illustrative calculation of a steady, critically balanced spectrum of KAWs acting on homogeneous ion distributions with a plasma β = 0.1, representative of turbulent conditions in the fast solar wind near 20 Rs. The KAWs are described here by a two-fluid dispersion relation. We find that thermal protons are strongly heated in the perpendicular direction within a typical quasilinear time of several thousand gyroperiods, which corresponds to only a few minutes at 20 Rs. Alpha particles in the same fluctuation field are heated to similar perpendicular thermal speeds, equivalent to the greater than mass proportional perpendicular temperatures that are commonly observed. We discuss improvements to this simple model that may determine whether this mechanism can be responsible for the observed coronal and solar wind ion heating.