Hybrid Ion-Kinetic, Fluid-Electron Modelling of Radial Plasma Flows in the Magnetospheres of the Outer Planets

Wiggs, Josh and Arridge, Chris (2024) Hybrid Ion-Kinetic, Fluid-Electron Modelling of Radial Plasma Flows in the Magnetospheres of the Outer Planets. PhD thesis, Lancaster University.

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Abstract

The magnetospheres of the gas giants, Jupiter & Saturn, are both loaded internally with plasma. The source of this material in the Jovian system is the volcanic moon of Io and the icy moon of Enceladus in the Saturnian, creating the Io plasma torus and the Enceladus neutral torus. In both systems plasma is removed from these tori mainly via ejection as energetic neutrals and by bulk transport into the outer magnetosphere. The physical mechanism responsible for the bulk transport process is the radial-interchange instability (reviewed in §3). In order to improve understanding of the bulk transport process a new hybrid kinetic ion, fluid-electron plasma model is constructed in 2.5-dimensions. The Jovian magnEtospheRIC kinetic-ion, fluid-electron Hybrid plasma mOdel, JERICHO, is detailed in §4 & 5. The technique of hybrid modelling allows for the probing of plasma motions from the scale of planetary-radii down to the ion-inertial length scale, considering constituent ion species kinetically, as charged particles, and forming the electrons into a single magnetised fluid continuum. Simulation results permit the examination of bulk transport on spatial scales not currently accessible with state-of-the-art models. To ensure JERICHO is physically accurate a series of physical benchmarks are examined in §6 and the parameter space within which it must be operated is identified. Application to Saturnian magnetospheric system is presented in §7. Plasma injections are introduced and develop radial-interchange instabilities on spatial scales of 10−1 RS. These motions create fingers of dense plasma interspersed with narrow tenuous plasma channels. A parameter survey is performed, varying the magnetic field strength & density of plasma injections. A potential link between the temporal scales of the instability and magnetic field strength is identified, however no correlation is found between either of these parameters and the spatial scales of the instabilities.