Lifetime of ring current particles due to coulomb collisions in the plasmasphere
Lifetime of ring current particles due to coulomb collisions in the plasmasphere
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DOI：
10.1029/90ja02620
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发表时间：
1991-05
影响因子：
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通讯作者：
M. Fok;J. Kozyra;A. Nagy;T. Cravens
中科院分区：
文献类型：
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作者：
M. Fok;J. Kozyra;A. Nagy;T. Cravens
俘获带中的环电流离子和电子被散射并减慢到与等离子体层中的热等离子体的库仑相互作用，最终从俘获轨道上移走。利用Wentworth等人发展的方法，导出了反弹平均库仑寿命的表达式。(1959)，但考虑了热等离子体分布的更真实的表示，作为麦克斯韦函数而不是增量函数，并考虑了环电流和热等离子体中的重离子。给出了主要环流离子的反弹平均库仑寿命，并与文献中的库仑寿命进行了比较。能量小于约10keV的环流离子的库仑寿命比用以前推导的公式预测的库仑寿命长；但在这些能量下，库仑寿命与电荷交换寿命相当或更短。对于外层等离子体层的真实热等离子体密度，环电流重离子的库仑寿命可以与环电流微分数密度峰值附近的电荷交换寿命相当。这些结果表明，库仑衰变是数十keV离子的一个重要的环电流损失过程，并可能解释Kistler等人(1989)注意到的环电流分布与AMPTE/CCE在磁活动条件下测量的环电流通量之间的差异。
Ring current ions and electrons in the trapped belt are scattered and slowed down to Coulomb interactions with the thermal plasma in the plasmasphere and are eventually removed from trapped orbits. An expression for bounce-averged Coulomb lifetimes is derived using methods developed by Wentworth et al. (1959) but with the improvements of considering a more realistic representation of the thermal plasma distribution, as a Maxwellian rather than a delta function, and considering heavy ions in the ring current and thermal plasmas. Bounce-average Coulomb lifetimes for the major ring current ions are presented and are compared to Coulomb lifetimes in the literature. Coulomb lifetimes for ring current ions with energies less than {approximately} 10 keV are longer than those predicted using previously derived expressions; however, they are comparable to, or shorter than, charge exchange lifetimes at these energies. For realistic thermal plasma densities in the outer plasmasphere, Coulomb lifetimes for ring current heavy ions can be comparable to charge exchange lifetimes at energies near the peak of the ring current differential number density. These results suggest that Coulomb decay is an important ring current loss process for tens of keV ions and might explain the discrepancy noted by Kistler et al.more » (1989) between model ring current distributions and the ring current fluxes measured by AMPTE/CCE during magnetically active conditions.« less