中文摘要：

等离子体层已有数十年研究历史，但对其核心等离子体区域却一直没有一个相对准确的界限和模型定义．基于范阿伦辐射带卫星RBSP—A在2012年9月18日至2014年10月13日约两年的观测，我们统计研究了磁宁静期间核心等离子体层电子密度随磁地方时（MLT）及磁壳指数（L—value）的分布特征．发现了核心等离子体层电子密度在不同MLT条件下随L值的变化趋势几乎一致，但与以前的等离子体层经验模式计算的电子密度存在较大的偏差．在不同L值下电子密度随MLT的变化趋势也相差不大，而且随MLT存在明显的逐日和半日变化．最后我们获得了等离子体层电子密度随L值和MLT变化的经验公式．研究结果对空间等离子体层建模及研究具有重要的意义．

英文摘要：

Although the plasmasphere has been studied for decades, an accurate boundary or model for the core plasma area of the plasmasphere has not been obtained yet. Based on the data of RBSP--A satellite from 2012 to 2014, we statistically analyze the variations of the plasmaspheric electron density with L-values and MLT during geomagnetic quiet-time, respectively. The electron density almost has the same trend with L-values in different MLT, but there is an obvious deviation between our observed electron density of the core plasmasphere and that calculated from the previous empirical plasmaspheric model. Also it has the same trend with MLT for different L- values, as well as obvious diurnal and semidiurnal variations. Finally, we obtain the empirical formula of the electron density of the core plasmaphere with L-values and MLTs. This model will be important to the research of the plasmasphere.