Intermittency of Ultrarelativistic Charged-particle Trajectories in Jupiter’s Radiation Belts

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Abstract
In our solar system, Jupiter possesses the strongest magnetosphere, with radiation belts filled with ultrarelativistic charged particles. These particles are trapped along Jupiter’s closed magnetic field lines, where they undergo gyration, bounce, and drift motions. Traditionally, the quasiperiodic behavior associated with each of these motions has been explained using gyrocenter approximation–based theoretical or simulation models. However, ultrarelativistic charged particles (with energies in the MeV–GeV range) have large gyroradii, which can give rise to nonadiabatic behavior. In such cases, while the particles remain confined within Jupiter’s magnetic field, their motion may no longer remain periodic. As a result, conventional theoretical models fail to describe their trajectories accurately. We investigate the intermittent behavior that emerges in this ultrarelativistic system of charged particles by analyzing the velocity structure function of energetic charged particles in a manner that is akin to the study of the intermittency of Lagrangian-particle trajectories in fluid turbulence. For this purpose, we have performed three-dimensional relativistic test-particle simulations, introducing protons with energies ranging from 1 to 500 GeV into Jupiter’s inner radiation belt. We have examined both the adiabatic case (1 GeV) and the nonadiabatic cases (100 and 500 GeV) in detail. Our results show that, in the nonadiabatic regime, ultrarelativistic charged-particle trajectories exhibit intermittency on timescales of 10–272 ms, which are significantly shorter than the expected gyroperiods in this region. These findings provide conclusive evidence for the multiscale nature of ultrarelativistic particle dynamics in Jupiter’s radiation belts.

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