Acceleration of ions by electric field pulses in the inner magnetosphere
Thursday, 17 December 2015
Poster Hall (Moscone South)
Using THEMIS observations and test particle modeling, we investigate particle acceleration around L-shell ~7-9 in the nightside magnetosphere and demonstrate that intense (~5-15 mV/m), short-lived (<1 min) electric field pulses can effectively accelerate ions with tens of keV initial energy to hundreds of keV. This acceleration occurs because the ion gyroradius is comparable to the spatial scale of the localized electric field pulse at the leading edge of the earthward-propagating, dipolarizing flux bundles before it stops. The proposed acceleration mechanism can reproduce observed spectra of high-energy ions. We conclude that the electric field associated with dipolarizing flux bundles prior to their stoppage in the inner magnetosphere provides a natural site for intense local ion acceleration.