ELECTRON HEAT CONDUCTION IN THE SOLAR WIND: TRANSITION FROM SPITZER-HARM TO THE COLLISIONLESS LIMIT
ELECTRON HEAT CONDUCTION IN THE SOLAR WIND: TRANSITION FROM SPITZER-HARM TO THE COLLISIONLESS LIMIT
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DOI：
10.1088/2041-8205/769/2/l22
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发表时间：
2013-06-01
影响因子：
7.9
通讯作者：
Quataert, E.
中科院分区：
文献类型：
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作者：
Bale, S. D.;Pulupa, M.;Quataert, E.
我们使用一组具有统计意义的测量结果表明，在温度梯度尺度大于几个平均自由程L-T大于或接近3.5 λ (fp)的情况下，1 AU处太阳风中的场向电子热流通量q（平行于）与斯皮itzer- harm碰撞热流通量q（sh）是一致的。这代表了大约65%的测量数据，主要对应于高β，弱碰撞等离子体（“慢太阳风”）。在更无碰撞的λ (fp)/L-T大于或接近0.28时，电子热流被限制在q（平行于）/q(0)近似于0.3，与平均自由程无关，其中q(0)为“自由流”值；测量的q（平行于）没有达到完整的q(0)。这种约束q（平行于）/q(0)类似于0.3，可能归因于波粒相互作用、行星际电势的影响或固有的通量限制。我们还证明了β (e)对这些结果的依赖关系与局部径向电子温度分布T-e相一致，这与热电子的函数r（- α）相似，即β α = α (β (e))，并且无碰撞调节约束的β依赖关系与哨声热流不稳定性并不明显一致。可能观测到的热通量的饱和只是碰撞输运的一个特征。我们在更广泛的天体物理学背景下讨论这些结果。
We use a statistically significant set of measurements to show that the field-aligned electron heat flux q(parallel to) in the solar wind at 1 AU is consistent with the Spitzer-Harm collisional heat flux q(sh) for temperature gradient scales larger than a few mean free paths L-T greater than or similar to 3.5 lambda(fp). This represents about 65% of the measured data and corresponds primarily to high beta, weakly collisional plasma ("slow solar wind"). In the more collisionless regime lambda(fp)/L-T greater than or similar to 0.28, the electron heat flux is limited to q(parallel to)/q(0) similar to 0.3, independent of mean free path, where q(0) is the "free-streaming" value; the measured q(parallel to) does not achieve the full q(0). This constraint q(parallel to)/q(0) similar to 0.3 might be attributed to wave-particle interactions, effects of an interplanetary electric potential, or inherent flux limitation. We also show a beta(e) dependence to these results that is consistent with a local radial electron temperature profile T-e similar to r(-alpha) that is a function of the thermal electron beta alpha = alpha(beta(e)) and that the beta dependence of the collisionless regulation constraint is not obviously consistent with a whistler heat flux instability. It may be that the observed saturation of the measured heat flux is a simply a feature of collisional transport. We discuss the results in a broader astrophysical context.