Acceleration of solar wind ions to 1 MeV by electromagnetic structures upstream of the Earth's bow shock

Abstract

PACS 95.30.Qd -Magnetohydrodynamics and plasmas PACS 47.35.Fg -Solitary waves PACS 52.50.Lp -Plasma production and heating by shock waves and compression Abstract -We present measurements from the ESA/NASA Cluster mission that show in situ acceleration of ions to energies of 1 MeV outside the bow shock. The observed heating can be associated with the presence of electromagnetic structures with strong spatial gradients of the electric field that lead to ion gyro-phase breaking and to the onset of chaos in ion trajectories. It results in rapid, stochastic acceleration of ions in the direction perpendicular to the ambient magnetic field. The electric potential of the structures can be compared to a field of moguls on a ski slope, capable of accelerating and ejecting the fast running skiers out of piste. This mechanism may represent the universal mechanism for perpendicular acceleration and heating of ions in the magnetosphere, the solar corona and in astrophysical plasmas. This is also a basic mechanism that can limit steepening of nonlinear electromagnetic structures at shocks and foreshocks in collisionless plasmas.Introduction. -It is generally believed that the acceleration of particles to super thermal energies in the inner heliosphere is done mainly by shock waves [1,2]. These may be driven by solar flares and coronal mass ejections, and are also formed at planetary bow shocks, and at boundaries between streams of fast and slow solar wind plasma in co-rotating interaction regions [3,4]. The origin of the energetic ions observed upstream of the Earth's bow shock [5] is generally attributed to shock drift acceleration [6] of solar ions or to leakage from the magnetosphere [7]. In this letter, we present measurements that show in situ acceleration of ions to energies of 1 MeV outside the bow shock, incompatible with both the concepts of leakage and shock drift acceleration. The observed heating can be associated with the presence of electromagnetic structures with gradients of the electric field that lead to ion gyro-phase breaking and to rapid, stochastic acceleration of ions in the direction perpendicular to the ambient magnetic field. This heating mechanism prefers heavy ions, which is supported by the measurements reported in this paper. Our results may be directly

Extreme ionospheric ion energization and electron heating in Alfvén waves in the storm time inner magnetosphere

“…This process is schematically represented in Figure b. For a single Alfvén wave, the upper energy limit attainable via this process can be much larger than the wave potential [ McChesney et al ., ] and in multiple waves or nonplanar field variations, which seem appropriate for our case, the stochastic threshold can be considerably lower than given by equation and the energy gain commensurately larger [ Stasiewicz et al ., ]. Simulations of this process based on observations from the FAST satellite of large‐amplitude dispersive Alfvén waves [ Chaston et al ., ] have demonstrated rapid gains in perpendicular ion energy as a consequence of trapping and multiple transitions through the wave potential to energies in excess of 10 keV over timescales of the order of a minute—much of this energy appears in the parallel direction due to the action of the mirror force.…”

Identification of the dominant ULF wave mode and generation mechanism for obliquely propagating waves in the Earth's foreshock

“…The electromagnetic activity is commonly associated with increased fluxes of energetic particles [ Ipavich et al , ; Burgess et al , , ]. It is believed that interactions of charged particles with the shock and the foreshock wave structures lead to particle acceleration and heating of the plasma, but these processes are not fully understood in detail [ Lee , ; Gordon et al , ; Stasiewicz et al , ]. For this reason studies of the foreshock's waves and related wave‐particle interactions are important for better understanding of similar processes in astrophysics, in particular the generation of cosmic rays.…”

Extreme ultra-violet burst, particle heating, and whistler wave emission in fast magnetic reconnection induced by kink-driven Rayleigh-Taylor instability

“…The electron-ion energy transfer rate (5 Â 10 5 < Eei < 1:2 Â 10 6 s À1 for T e ¼ 10 eV) could marginally explain T i reaching 10 eV if n e is at its maximum but could not explain the observed T i exceeding T e . Stochastic ion heating [42][43][44][45] is a likely candidate to explain such a strong ion heating. This heating mechanism occurs when a radially dependent electrostatic potential fluctuation satisfies the stochasticity threshold condition…”