Proton and heavy ion acceleration by stochastic fluctuations in the Earth's magnetotail

Abstract

Abstract. Spacecraft observations show that energetic ions are found in the Earth's magnetotail, with energies ranging from tens of keV to a few hundreds of keV. In this paper we carry out test particle simulations in which protons and other ion species are injected in the Vlasov magnetic field configurations obtained by Catapano et al. (2015). These configurations represent solutions of a generalized Harris model, which well describes the observed profiles in the magnetotail. In addition, three-dimensional time-dependent stochastic electromagnetic perturbations are included in the simulation box, so that the ion acceleration process is studied while varying the equilibrium magnetic field profile and the ion species. We find that proton energies of the order of 100 keV are reached with simulation parameters typical of the Earth's magnetotail. By changing the ion mass and charge, we can study the acceleration of heavy ions such as He ++ and O + , and it is found that energies of the order of 100-200 keV are reached in a few seconds for He ++ , and about 100 keV for O + .

Charge Proportional and Weakly Mass‐Dependent Acceleration of Different Ion Species in the Earth's Magnetotail

“…We can see that CS is well ordered with . Clearly, this is due to the fact that is proportional to the Larmor radius (see also trajectories in Figure 15 of Kronberg et al, 2014 and in Figure 5 of Catapano et al, 2016). Therefore, ions that spend a long time in the CS interact many times with the random fluctuations and undergo a Fermi-like process, thus developing the power law tail.…”

“…• Test particle simulations of the acceleration of different ion species by stochastic fluctuations in the Earth's magnetotail are performed • For the top 10% energetic ions, the energy gain grows almost linearly with the ion charge, while the dependence on the ion mass is weaker • We propose that the possible presence of O 5+∕6+ ions may contribute to explain the strong oxygen energization observed in the magnetotail 10.1002/2017GL075092 has been pointed out by Ono et al (2009) andNosé et al (2014). Recently, Catapano et al (2016) studied the acceleration of H + , He + , and O + while varying the equilibrium magnetic field profile and the intensity of the perturbations. Also, high charge state ions are observed in the magnetosphere (Kremser et al, 1987).…”

“…This model allows to adjust the level of plasma temperature and density inhomogeneities across the CS in a wide range of configurations, with the magnetic field profile being obtained self‐consistently (see Catapano et al, , for more details). Catapano et al () studied the ion acceleration while changing the parameters of the model like the equilibrium magnetic field profile and the strength of the perturbations. However, Catapano et al () have found that the details of the magnetic field profile B x ( z ) have little influence on the energization process, so that for further investigations we will use only one solution for the magnetic field profile, in particular, the solution for which the ratio between electron and proton temperature is .…”

“…Catapano et al (2016) studied the ion acceleration while changing the parameters of the model like the equilibrium magnetic field profile and the strength of the perturbations. However, Catapano et al (2016) have found that the details of the magnetic field profile B x (z) have little influence on the energization process, so that for further investigations we will use only one solution for the magnetic field profile, in particular, the solution for which the ratio between electron and proton temperature is 1 3 . We consider a coordinate system in which the x axis is directed along the Sun-Earth direction, the z axis is oriented perpendicular to the CS, and the y axis is directed along the electric current flow.…”

Acceleration of Ions in Jovian Plasmoids: Does Turbulence Play a Role?

“…There are many acceleration mechanisms responsible for the ion energization in the magnetotail. These include adiabatic processes, such as first Fermi and betatron acceleration, as well as nonadiabatic processes, such as (1) large-scale convection electric field during "demagnetization" 10.1029/2019JA026553 near the current sheet center (e.g., Lyons & Speiser, 1982) and (2) inductive electric fields generated during transient processes such as the formation of a magnetic X-line (e.g., Luo et al, 2014;Wygant et al, 2005), dipolarization fronts (e.g., Delcourt & Sauvaud, 1994;Greco et al, 2015), plasmoids (e.g., Zong et al, 1997), and electromagnetic turbulence (e.g., Catapano et al, 2016) as shown for the terrestrial magnetosphere.…”