Fully Kinetic versus Reduced-kinetic Modeling of Collisionless Plasma Turbulence
Fully Kinetic versus Reduced-kinetic Modeling of Collisionless Plasma Turbulence
复制标题
DOI：
10.3847/1538-4357/aa894d
复制
发表时间：
2017-09-20
影响因子：
4.9
通讯作者：
Jenko, Frank
中科院分区：
文献类型：
--
作者：
Groselj, Daniel;Cerri, Silvio S.;Jenko, Frank
我们报告的结果之间的直接比较不同的动力学模型的无碰撞等离子体湍流在两个空间维度。所考虑的模型包括第一原理完全动力学（FK）描述、两种广泛使用的简化模型（陀螺动力学（GK）和带有流体电子的混合动力学（HK））以及一种新型简化陀螺动力学方法（KREHM）。考虑两种不同的离子β（bi）制度：0.1和0.5。对于β i = 0.5，GK和FK模型之间的良好协议被发现在尺度范围从离子到电子gyroradius，从而提供了有力的证据动力学Alfven级联的情况。在相同的范围内，HK模型产生较浅的光谱斜率，大概是由于缺乏电子朗道阻尼。对于bi = 0.1，光谱比的详细分析揭示了GK和FK描述在动力学尺度上的轻微分歧，即使动力学阿尔芬波动可能仍然发挥着重要作用。这种差异可以追溯到离子回旋半径以上的尺度，其中FK和HK的结果似乎表明在两种等离子体β区中存在快磁声和离子伯恩斯坦模式，但在低β区情况下与GK存在更显著的偏差。确定的实际限制和强度的减少动力近似，比较这里对FK模型的情况下，在个案的基础上，可能会提供有价值的洞察力的主要动力学效应在发挥作用的湍流碰撞等离子体，如太阳风。
We report the results of a direct comparison between different kinetic models of collisionless plasma turbulence in two spatial dimensions. The models considered include a first-principles fully kinetic (FK) description, two widely used reduced models (gyrokinetic (GK) and hybrid-kinetic (HK) with fluid electrons), and a novel reduced gyrokinetic approach (KREHM). Two different ion beta (bi) regimes are considered: 0.1 and 0.5. For beta i = 0.5, good agreement between the GK and FK models is found at scales ranging from the ion to the electron gyroradius, thus providing firm evidence for a kinetic Alfven cascade scenario. In the same range, the HK model produces shallower spectral slopes, presumably due to the lack of electron Landau damping. For bi = 0.1, a detailed analysis of spectral ratios reveals a slight disagreement between the GK and FK descriptions at kinetic scales, even though kinetic Alfven fluctuations likely still play a significant role. The discrepancy can be traced back to scales above the ion gyroradius, where the FK and HK results seem to suggest the presence of fast magnetosonic and ion Bernstein modes in both plasma beta regimes, but with a more notable deviation from GK in the low-beta case. The identified practical limits and strengths of reduced-kinetic approximations, compared here against the FK model on a case-by-case basis, may provide valuable insight into the main kinetic effects at play in turbulent collisionless plasmas, such as the solar wind.