On the origin of high-energy particles in the cusp diamagnetic cavity
Publication date: 06 June 2012
Authors: Nykyri, K., et al.
Journal: Journal of Atmospheric and Solar-Terrestrial Physics
Issue: Special Issue on 'Physical Process in the Cusp: Plasma Transport and Energization'
Published online on 1 October 2011. To appear in a Special Issue of the journal, in press. We have analyzed Cluster magnetic field and plasma data during a high-altitude cusp crossing in 2003. The Cluster separation was ~5000 km and provided unique measurements of high energy particle properties both inside the DiaMagnetic Cavity (DMC) and surrounding magnetosheath. Most of the high energy electrons and protons had pitch angles of ~90 degrees in the cavity and the high energy particle intensities dropped as a function of distance from the cavity boundary. By assuming conservation of the first adiabatic invariant for the electrons our analysis indicates that most of the high-energy electrons in the diamagnetic cavity cannot directly originate from the magnetosheath or from the magnetosphere. Our test particle simulations in a local 3-D high-resolution MHD cusp model show that particles can gain up to 40 keV and their pitch angles become nearly 90 degrees in the local cusp geometry due to gradients in reconnection 'quasi-potential' agreeing with the Cluster RAPID observations. These results strongly support a local acceleration of particles in the cusp diamagnetic cavities.Link to publication