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Zusammenfassung:
Whistler-mode waves scatter ultrarelativistic electrons in the radiation belts and accelerate them through resonant interactions. In simplified models, nonlinear phase trapping by high-amplitude waves can increase electron energy by several MeV within seconds. However, the acceleration rate in realistic wave packets is slower due to small-scale wave field structures reducing trapping efficiency. While previous studies focused on short field-aligned amplitude modulations and phase jumps, we examine the effects of transverse modulations, which have been observed to reach scales comparable to ultrarelativistic electron gyroradii. Using test-particle simulations, we demonstrate that these modulations disrupt the acceleration process. Our numerical results suggest that nonlinear trapping plays a negligible role in accelerating electrons above a certain energy limit, reinforcing the diffusive nature of wave-driven electron transport at multi-MeV energies. Unlike field-aligned structures, transverse phase incoherence modifies the effective wave spectrum and allows for resonance, making amplitude modulations a necessary component for suppression of acceleration.
