For decades, radio remote-sensing techniques have been used to probe the plasma structure of the solar corona at distances of 2 – $20~\mathrm{R}_{\odot }$ . Measurement of Faraday rotation, the change in the polarization position angle of linearly polarized radiation as it propagates through a magnetized plasma, has proven to be one of the best methods for determining the coronal magnetic-field strength and structure. Faraday-rotation observations of spatially extended radio sources provide the unique opportunity to measure differential Faraday rotation [ $\Delta $ RM] the difference in the Faraday-rotation measure between two closely spaced lines of sight (LOS) through the corona. $\Delta $ RM is proportional to the electric current within an Amperian loop formed, in part, by the two closely spaced LOS. We report the expected $\Delta $ RM for two sets of models for the corona: one set of models for the corona employs a spherically symmetric plasma density, while the other breaks this symmetry by assuming that the heliospheric current sheet (HCS) is a finite-width streamer-belt region containing a high-density plasma. For each plasma-density model, we evaluate the $\Delta \mathrm{RM}$ for three model coronal magnetic fields: a radial dipole and interplanetary magnetic field (DIMF), a dipole + current sheet (DCS), and a dipole + quadrupole + current sheet (DQCS). These models predict values of $0.01\lesssim \Delta \mathrm{RM}\lesssim 120~\mbox{rad}\,\mbox{m}^{-2}$ over the range of parameter space accessible by modern instruments such as the Karl G. Jansky Very Large Array. We conclude that the HCS contribution to $\Delta $ RM is not negligible at moderate heliocentric distances ( $<8~\mathrm{R}_{\odot }$ ) and may account for $\lesssim 20\,\%$ of previous observations of $\Delta $ RM (e.g. made by Spangler, Astrophys. J. 670, 841, 2007).

中文翻译：

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模拟日冕中的微分法拉第旋转

几十年来，无线电遥感技术一直被用于探测距离 2 – $20~\mathrm{R}_{\odot }$ 的日冕等离子体结构。法拉第旋转的测量，即线性极化辐射在磁化等离子体中传播时极化位置角的变化，已被证明是确定日冕磁场强度和结构的最佳方法之一。空间扩展射电源的法拉第旋转观测提供了独特的机会来测量差分法拉第旋转 [$\Delta $ RM] 穿过日冕的两条紧密间隔的视线 (LOS) 之间的法拉第旋转测量的差异。$\Delta $ RM 与安培环路内的电流成正比，部分由两个紧密间隔的 LOS 形成。我们报告了两组日冕模型的预期 $\Delta $ RM：一组日冕模型采用球对称等离子体密度，而另一组模型通过假设日球层电流片 (HCS) 是一个包含高密度等离子体的有限宽度流光带区域。对于每个等离子体密度模型，我们评估了三个模型日冕磁场的 $\Delta \mathrm{RM}$：径向偶极子和行星际磁场 (DIMF)、偶极子 + 电流片 (DCS) 和偶极子 +四极杆 + 电流表 (DQCS)。这些模型预测 $0.01\lesssim \Delta \mathrm{RM}\lesssim 120~\mbox{rad}\,\mbox{m}^{-2}$ 在现代仪器可访问的参数空间范围内的值，例如Karl G. Jansky 超大阵列。