Stability of relativistic surfatron acceleration

Abstract

In this paper we consider the surfatron acceleration of relativistic charged particles by a strong electrostatic wave propagating in a transverse direction relative to the background magnetic field. We investigate how high-frequency fluctuations of the background magnetic field affect the process of the resonant acceleration. We show that the presence of fluctuations leads to particle escape from the surfatron resonance and illustrate that fluctuations of different components of the magnetic field have quite a distinct effect on the energy gained by particles. In the case of the same power density, the strongest effect corresponds to fluctuations of the component directed along the background magnetic field, while the effect of the component along the wave front is substantially weaker. This is more important for particles with a large velocity component along the background magnetic field. We demonstrate that the dynamics of particles can statistically be described in terms of the adiabatic invariant diffusion. We derive the corresponding diffusion equation and compare solutions of that equation with results obtained by the explicit particle tracing.

Characteristics of Energetic Electrons Near Active Magnetotail Reconnection Sites: Tracers of a Complex Magnetic Topology and Evidence of Localized Acceleration

“…Delcourt et al (1997) presented simulation results of energetic oxygen ion motion in dipolarizing magnetotail fields, and they found distinct gyrophase bunching of oxygen ions undergoing nonadiabatic motion in the dipolarizing fields. Such a "surfatron" acceleration process, resonance for which is inherently dependent on a particle's gyrophase, was described in detail by A. V. Artemyev et al (2012Artemyev et al ( , 2014. Only those particles that experienced drift resonance with the dynamic dipolarizing fields (enhancements in Vx, Bz, and Ey), nonadiabatic motion (from the curvature of the field being comparable to the particles' gyro-radii), and acceleration became bunched in gyrophase, while those that experienced adiabatic motion maintained isotropic GPDs and were stochastically scattered by the dipolarization of the B-field.…”

“…An important topic of active study concerns the acceleration of relativistic electrons (i.e., energy ≥ 10 s of keV; note a 50 keV electron has velocity ∼ 0.4c and relativistic factor, γ = 1.1) by active reconnection. Despite much evidence of electron acceleration related to magnetic reconnection, such as solar X‐ray flares (van Driel‐Gesztely, 2008) and bursts of energetic electrons in Earth's magnetotail (Gabrielse et al., 2014; Øieroset et al., 2002; Richardson et al., 1993), the exact mechanisms responsible for the acceleration remain a topic of debate (A. Artemyev et al., 2014; Birn et al., 2013; Dahlin et al., 2014; Drake et al., 2006; Egedal et al., 2012; Jaynes et al., 2016). In the study described in this letter, we used MMS data to examine the behavior of >50 keV electrons in the immediate vicinity (i.e., within ∼2,000 km, on the order of the >50 keV electron gyroradii) of active reconnection sites.…”

Trapping (capture) into resonance and scattering on resonance: Summary of results for space plasma systems

“…6.2: a background magnetic field B 0 and a random magnetic field B Γ (t) are directed along the z-axis, a plane electromagnetic wave (with a frequency ω and wave vector k) propagates along the x-axis, particles move in the (x, y) plane. Equations of motion of a non-relativistic particle (a relativistic analog was considered in [163]) arė…”

Stability of relativistic electron trapping by strong whistler or electromagnetic ion cyclotron waves

“…To investigate the possible destruction of the trapped motion, we should consider particle dynamics in the ð/; PÞ plane. 10,11 For monochromatic waves, this dynamics is described by the following Hamiltonian equations: 5,7,59 _…”