Electron driven instabilities around dipolarizing flux bundles in Earth’s magnetotail

Dipolarization fronts (DFs) are transient phenomena in the magnetotail with various types of waves observed in their vicinity. The potential effect of these fluctuations on particle distributions and energy conversion near DFs is poorly understood. In this study, we aim to determine the relations between waves and dipolarization fronts. Using observational data from Time History of Events and Macroscale Interactions during Substorms (THEMIS), we established whistler wave event database and electron cyclotron harmonic (ECH) wave event database near dipolarization fronts from year 2007-2017. We find that electron temperature anisotropies are well-constrained by the marginal stability thresholds of whistler instability and electron firehose instability. During earthward transport of electrons, a significant portion of the suprathermal electron energy flux is evacuated in the form of whistler wave Poynting flux. Later we investigate the generation mechanism of ECH waves near dipolarization fronts. We find that moderately oblique (with wave normal angle at around 70⁰) ECH waves are frequently observed behind DFs and they are driven unstable by low energy electron beams. By performing a parametric survey of beam-driven ECH waves, we demonstrate that these waves are unstable under a wide range of plasma conditions. This work emphasizes the importance of wave-particle interaction in the magnetotail