Collaborative Research: GEM--The Excitation and Propagation of Fast Magnetosonic Waves and Their Effect on Radiation Belt Electrons

本项目将研究磁层内部区域磁声波的产生、传播和耗散，以及辐射带电子与磁层相互作用的过程。在地球附近的太空环境中，等离子体非常稀薄，等离子体粒子（离子和电子）很少碰撞。 然而，尽管如此，磁层中的电子的一部分达到危险的高能量超过一百万电子伏特。这种能量高到足以对磁层内部区域内的卫星构成威胁，而磁层内部区域是通信、导航、搜索和救援、天气预报和国家安全卫星的首选位置。 等离子体波主要负责加速辐射带电子到这些高能量，但它们也有助于辐射带粒子散射到地球大气层中。 许多类型的等离子体波是在磁场存在的情况下在无碰撞等离子体中产生的，并且每一种都具有与等离子体中的带电粒子的一组相互作用。 这些波在内磁层和辐射带的动力学中起着重要的作用。 磁声波，拟议的调查的重点，被发现在磁赤道面附近的一个广泛的区域附近的磁层的昼侧部分。 波电场的分量沿着磁场线排列，可以连续地加速以接近波浪速度行进的电子，就像冲浪者被海浪向前推一样。 这被称为朗道阻尼。磁声波被认为是由环电流质子产生的，并在加速辐射带电子中消散，实际上充当不同粒子群之间能量无碰撞传输的媒介。 作为一个更广泛的影响，这个项目是由一个早期的职业科学家领导，从而有助于下一代科学家的培训。本研究的主要目标是使用线性理论和动力学粒子在细胞（PIC）模拟，探索激发和传播的快磁声波驱动的观察类型的环状质子速度分布，并使用收集的见解来解释观察到的波测量，这两个数据集从双货车艾伦探针。此外，辐射带电子的散射将使用测试粒子计算进行量化，提供了明确的标准，是否以及在什么条件下可以应用传统的准线性方法。两个基本的科学问题将得到解决：（1）如何激发和传播的快磁声波产生的复杂模式的观察波频谱？和（2）与通常假设的准线性理论中使用的冷等离子体色散相比，波的复杂动力学色散特性对辐射带电子散射的评估有多重要？全动力学PIC代码的推广，以考虑在一个不均匀的介质中的偶极磁场将是一个额外的有价值的资源，辐射带社区，使整个频谱的新的研究以前不可能。

This project will investigate the generation, propagation and dissipation of magnetosonic waves in the inner region of the magnetosphere as well as the energization of radiation belt electrons interacting with them. In the space environment near Earth, the plasma is so tenuous that plasma particles (ions and electrons) rarely collide. However despite this, some portion of the electrons in the magnetosphere reach dangerously high energies exceeding a million electron volts. This energy is high enough to pose a risk to satellites orbiting within the inner regions of the magnetosphere, a preferred location for communications, navigation, search-and-rescue, weather prediction and national security satellites. Plasma waves are mainly responsible for the acceleration of radiation belt electrons to these high energies but they can also contribute to the scattering of radiation belt particles into the Earth's atmosphere. Many types of plasma waves are generated in a collisionless plasma in the presence of a magnetic field and each has its own set of interactions with the charged particles in the plasma. These waves play a significant role in the dynamics of the inner magnetosphere and radiation belts. Magnetosonic waves, the focus of the proposed investigation, are found in the vicinity of the magnetic equatorial plane in a wide region near the dayside portion of the magnetosphere. The component of the wave electric field, which is aligned along a magnetic field line, can continuously accelerate electrons traveling near the speed of the wave in much the same way that a surfer is pushed forward by an ocean wave. This is termed Landau damping. Magnetosonic waves are thought to be generated by ring current protons, and dissipated in accelerating radiation belt electrons, in effect acting as intermediaries in the collisionless transport of energy between different particle populations. As a broader impact, this project is led by an early-career scientist thus contributing to the training of the next generation of scientists. The primary goal of this research is to use linear theory and kinetic particle-in-cell (PIC) simulations to explore the excitation and propagation of fast magnetosonic waves driven by observed types of ring-like proton velocity distributions and to use insights gathered to interpret the observed wave measurements, both datasets from the twin Van Allen Probes. Furthermore, scattering of radiation belt electrons will be quantified using test-particle computations, providing clear criteria as to whether and under what conditions the conventional quasi-linear approach can be applied. Two fundamental science questions will be addressed: (1) how does the excitation and propagation of fast magnetosonic waves produce the complex pattern of the observed wave frequency spectra? and (2) how important to the evaluation of radiation belt electron scattering are the complex kinetic dispersion properties of the waves compared to the commonly assumed cold plasma dispersion used in quasi-linear theory? The generalization of the full kinetic PIC code to account for the dipole magnetic field in an inhomogeneous medium will be an additional valuable resource for the radiation belt community enabling a whole spectrum of new studies not previously possible.