Acceleration mechanism of radiation belt electrons through interaction with multi-subpacket chorus waves

Abstract

We conduct test particle simulations to examine the acceleration mechanism of relativistic electrons through interaction with multi-subpacket chorus waves. As the analysis of recent observations reveals, amplitude of a rising tone element of chorus wave consists of many short wave packets. We call this single rising tone chorus element with the collective structure of multiple short wave packets as a multi-subpacket chorus wave. In this simulation, we develop the wave model with rapidly fluctuating amplitude and phase discontinuities across each subpacket, in order to examine how these features of multi-subpacket chorus wave influence the nonlinear trapping processes in efficient acceleration of relativistic electrons such as relativistic turning acceleration (RTA) and ultra-relativistic acceleration (URA). To conduct comprehensive examinations, we test more than nine million particles with various initial conditions covering the energy range from 100 to 6 MeV, and the equatorial pitch angles from 10° to 89°. The test particles interact with a single rising tone element of multi-subpacket chorus wave set up with the maximum amplitude of about 2 nT and the frequency rise from about 1.3 kHz to 3.8 kHz over 0.25 s. Relativistic electrons are accelerated by about 160 keV under preferable conditions. The energy increase verifies the high efficiency of acceleration by the wave–particle interactions, based on the fact that it is achieved by a short time interaction less than 1 s with a single element of chorus wave. By analyzing the detailed behavior of the accelerated electrons, we find successive trapping of the resonant electrons resulting in the efficient accelerations from the consecutive multiple subpackets of a chorus wave element.

Theoretical model of the nonlinear resonant interaction of whistler-mode waves and field-aligned electrons

“…30-32. The nonlinear scattering (phase bunching) results in decrease of electron energy and pitch-angle 33,34 . Although effects of realistic wave frequency drift [35][36][37][38][39] and wave amplitude modulation [40][41][42][43] alter the electron nonlinear resonant interaction, the basic concept remains the same: trapping results in electron transport away from the loss-cone and nonlinear scattering results in electron transport toward the loss-cone. A competition of these two nonlinear processes determines electron acceleration and losses.…”

Data‐Driven Simulation of Rapid Flux Enhancement of Energetic Electrons With an Upper‐Band Whistler Burst

“…(2007). Recently, the important role of the phase trapping process in an amplitude‐modulated whistler chorus wave has also been studied numerically by Hiraga and Omura (2020) and Gan, Li, Ma, Albert, et al. (2020).…”

Long-term dynamics driven by resonant wave–particle interactions: from Hamiltonian resonance theory to phase space mapping

“…The main advantage of this approach is the inclusion of an almost arbitrary (as realistic as needed) wave spectrum and characteristics (e.g. wave modulation and frequency drifts, see Kubota & Omura (2018), Artemyev, Vasiliev & Neishtadt (2019 b ) and Hiraga & Omura (2020)). The main disadvantages are an accumulation of numerical errors with running time, and the almost intractable fine details of the energy/pitch-angle space binning needed to simultaneously resolve large jumps due to trapping and small changes due to drift/diffusion.…”