Longitudinal variation of the pickup-proton-injection efficiency and rate at the heliospheric termination shock
Longitudinal variation of the pickup-proton-injection efficiency and rate at the heliospheric termination shock
复制标题
日光层终止激波处拾取质子注入效率和速率的纵向变化
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
S. Ferreira
中科院分区：
文献类型：
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作者：
H. Fahr;K. Scherer;M. Potgieter;S. Ferreira
上下文拾取离子被认为是异常宇宙线的种子粒子。拾取离子在太阳风终止激波处的加速取决于它们被注入第一反射模式的效率，从那里开始加速成高能异常宇宙射线。在这封信中，我们研究了这种效率的纵向变化。目标。我们考虑了终端激波纵向位置处的特定MHD条件，该条件对磁场与激波法线之间的局部倾角高度敏感。我们确定的概率拾取离子成为反射，这取决于如何随经度的倾斜角变化。这是将拾取离子加速为异常宇宙射线的第一个相关步骤。方法.当两个连续的不同极性的太阳风扇区结构经过激波时，磁倾角的最大变化发生在电流片上。我们认为这种影响，通过模拟纵向变化的注射效率。从计算的拾取离子的反射概率作为一个函数的磁倾斜角相对于正常的，我们找到一个解析表达式的注入效率：要做到这一点，我们需要的磁倾斜角作为经度的函数，我们获得的终止冲击波形状的解析表示。这使我们能够确定喷射效率的纵向依赖性。结果我们发现，当从逆风部分到终止激波的侧翼时，喷射效率发生了3倍的显著变化。将其与拾取离子密度的纵向依赖性进行折叠，给出了注入率的解析表达式，该注入率在向上和黄道侧风方向之间变化为2倍，在横向和顺风方向之间变化为5倍。结论.我们的模型表明，异常宇宙线加速的注入主要发生在黄道侧风方向，例如终止冲击的侧翼。
Context. Pickup ions are considered to be the seed population of the anomalous cosmic rays. The acceleration of the pickup ions at the solar wind termination shock depends on the efficiency with which they are injected into the first reflection mode, from where acceleration into high energy anomalous cosmic rays begins. In this letter, we study the longitudinal variation of this efficiency. Aims. We consider the specific MHD conditions at the longitudinal position of the termination shock, which are highly sensitive to the local inclination angle between the magnetic field and the shock normal. We determine the probability for pickup-ions to become reflected which depends on how the inclination angle varies with longitude. This is the first and relevant step in the acceleration of pickup ions to anomalous cosmic rays. Methods. The most dramatic change in the magnetic tilt angle occurs in the current sheet between two consecutive solar wind sector structures of different polarity, when they pass over the shock. We consider this effect by modeling the longitudinal variation in the injection efficiency. Starting from calculations of the pickup-ion reflectance probability as a function of the magnetic tilt angle with respect to the normal, we find an analytic expression for the injection efficiency: to do this we need the magnetic tilt angle as a function of longitude, which we obtain from an analytic representation of the termination shock shape. This enables us to determine the longitudinal dependence of the injection efficiency. Results. We find that a substantial variation in the injection efficiency of a factor of 3 occurs when passing from the upwind part to the flanks of the termination shock. Folding this with the longitudinal dependence of the pickup ion density gives an analytic expression the injection rate which varieis by a factor of 2 between up- and ecliptical crosswind direction and a factor of 5 between cross- and downwind direction. Conclusions. Our model indicates that injection into the anomalous cosmic ray acceleration predominantly occurs in the ecliptical crosswind direction e.g. in the flanks of the termination shock.