Radulescu, Cristian Robert; (2025) Heavy ion distribution and influence on the Saturnian magnetosphere. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The primary components of plasma throughout the solar system are protons and electrons. However, heavy ions represent important mass fractions within many magnetospheric plasmas. One of the most notable examples of a magnetospheric plasma strongly affected by the physics of heavy ions is Saturn’s magnetosphere. Here, water-group ions represent the majority species in much of the inner and middle magnetosphere and are still the majority ion species even at large radial distances. In this thesis, I explore the distribution of heavy ions in the Saturnian magnetosphere and determine some of the interactions they have with magnetospheric processes. I use data from the Cassini spacecraft’s CAPS and magnetometer instruments to extract information about the distribution of water-group pick-up ions and ion cyclotron waves in the inner and middle magnetosphere. A comparison of these distributions reveals an anti-correlation, explained by slow scattering times relative to the bounce timescales. I further explore the role of heavy ions by looking at magnetic reconnection. I use particle-in-cell simulations to simulate reconnection events with varying current sheet thickness and heavy ion abundances while keeping the total plasma density constant. Our results confirm the finding of previous literature and show that heavy ions have an important effect on the reconnection rate that goes beyond the thickening of the current sheet. Heavy ions are found to be important energy sinks, reducing the energy available for accelerating lighter species. I further explore these effects by looking at Cassini data. I find that reconnection preferentially occurs at certain radial distances and that the likelihood of reconnection is influenced by the plasma density, heavy ion abundance and current sheet thickness at Saturn. Similarly, dipolarizations created by reconnection events stop at different radial distances, with higher stopping probabilities being found closer to Saturn.

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