Electrostatic wave generation and transverse ion acceleration by Alfvénic wave components of broadband extremely low frequency turbulence

Abstract

We present results here from 2.5‐dimensional particle‐in‐cell simulations showing that the electrostatic (ES) components of broadband extremely low frequency (BBELF) waves could possibly be generated by cross‐field plasma instabilities driven by the relative drifts between the heavy and light ion species in the electromagnetic (EM) Alfvénic component of the BBELF waves in a multi‐ion plasma. The ES components consist of ion cyclotron as well as lower hybrid modes. We also demonstrate that the ES wave generation is directly involved in the transverse acceleration of ions as commonly measured with the BBELF wave events. The heating is affected by ion cyclotron resonance in the cyclotron modes and Landau resonance in the lower hybrid waves. In the simulation, we drive the plasma by the transverse electric field, Ey, of the EM waves; the frequency of Ey, ωd, is varied from a frequency below the heavy ion cyclotron frequency, Ωh, to below the light ion cyclotron frequency, Ωi. We have also performed simulations for Ey having a continuous spectrum given by a power law, namely, ∣Ey∣ ∼ ωd−α, where the exponent α = , 1, and 2 in three different simulations. The driving electric field generates polarization and E × B drifts of the ions and electrons. When the interspecies relative drifts are sufficiently large, they drive electrostatic waves, which cause perpendicular heating of both light and heavy ions. The transverse ion heating found here is discussed in relation to observations from Cluster, Fast Auroral Snapshot, and Freja.