The Alfven+ mission to explore Magnetosphere-Ionosphere coupling

Abstract:

We present the Alfvén+ mission concept proposed to the ESA M4 competition. The primary objective of the Alfvén+ mission is to understand the physical processes that enable electromagnetic energy to be converted to charged particle kinetic energy in a low beta plasma, using Earth’s natural laboratory provided by the Auroral Acceleration Region (AAR). These poorly understood fundamental plasma physical processes play a central role in the physics of magnetosphere-ionosphere coupling. Energy conversion must happen where magnetic field aligned currents are accompanied by magnetic field aligned electric fields. Previous missions have discovered large scale quasi-static parallel electric fields in the AAR, but it is currently unknown how they are created and maintained. Similarly, earlier missions suggest that Alfvén waves must transmit their energy to auroral electrons, but it is unknown where, when, and how this conversion mechanism operates.

To answer these fundamental, long-standing questions in a system-science approach, simultaneous coordinated measurements of electromagnetic fields and waves and particle energy flux from two spacecraft in the AAR region are required, along with high-resolution auroral imaging. Alfvén+ will provide the required coordinated two-spacecraft observations within the AAR several times per day. Using variable separations along and across the magnetic field lines, from a 3,000x9,000 km altitude, 90° inclination orbit and with a comprehensive suite of inter-calibrated particles and fields instruments Alfvén+ will measure the particle flux and wave energy required to answer the open questions on energy conversion. Alfvén+ will enable a new generation of global geosphere models by providing the data needed to derive the key transport laws that describe Magnetosphere-Ionosphere coupling.