Nicolaou Georgios, Livadiotis George, Wicks Robert T
Department of Space and Climate Physics, Mullard Space Science Laboratory, University College London, Dorking, Surrey RH5 6NT, UK.
Southwest Research Institute, San Antonio, TX 78238, USA.
Entropy (Basel). 2020 Feb 13;22(2):212. doi: 10.3390/e22020212.
The velocities of space plasma particles, often follow kappa distribution functions. The kappa index, which labels and governs these distributions, is an important parameter in understanding the plasma dynamics. Space science missions often carry plasma instruments on board which observe the plasma particles and construct their velocity distribution functions. A proper analysis of the velocity distribution functions derives the plasma bulk parameters, such as the plasma density, speed, temperature, and kappa index. Commonly, the plasma bulk density, velocity, and temperature are determined from the velocity moments of the observed distribution function. Interestingly, recent studies demonstrated the calculation of the kappa index from the speed (kinetic energy) moments of the distribution function. Such a novel calculation could be very useful in future analyses and applications. This study examines the accuracy of the specific method using synthetic plasma proton observations by a typical electrostatic analyzer. We analyze the modeled observations in order to derive the plasma bulk parameters, which we compare with the parameters we used to model the observations in the first place. Through this comparison, we quantify the systematic and statistical errors in the derived moments, and we discuss their possible sources.
空间等离子体粒子的速度通常遵循κ分布函数。标记和控制这些分布的κ指数是理解等离子体动力学的一个重要参数。空间科学任务通常会搭载等离子体仪器，这些仪器观测等离子体粒子并构建它们的速度分布函数。对速度分布函数进行适当分析可得出等离子体的整体参数，如等离子体密度、速度、温度和κ指数。通常，等离子体的整体密度、速度和温度是根据观测到的分布函数的速度矩来确定的。有趣的是，最近的研究表明可以从分布函数的速度（动能）矩计算κ指数。这种新颖的计算方法在未来的分析和应用中可能非常有用。本研究通过典型的静电分析仪使用合成等离子体质子观测数据来检验该特定方法的准确性。我们分析模拟观测数据以得出等离子体的整体参数，并将其与最初用于模拟观测数据的参数进行比较。通过这种比较，我们量化了导出矩中的系统误差和统计误差，并讨论了它们可能的来源。
