Observations of Electrons Accelerated Upwards to keV Energies at 1000 km Wayne Keith, David Winningham, Olle Norberg, Goran Marklund, and Tomas Karlsson Observed by the MEDUSA instrument aboard the Swedish Astrid-2 Satellite MEDUSA characteristics: 360° FOV in spin plane 22.5° azimuthal resolution 5° elevation acceptance 31 energy steps 16 electron spectra per second 8 ion spectra per second 460 meter electron resolution 920 meter ion resolution Energy range ~ 1 eV to 22 keV Very fast sweeps give sub-km resolution in low Earth orbit. Normal mode returns all sectors all the time Select mode returns only 3 sectors, which are chosen for each sweep to be those closest to the parallel, perpendicular, and antiparallel velocity vectors of the particles with respect to the magnetic field. MEDUSA modes: Normal Mode 16 azimuthal sectors Sectors co-rotate with satellite Select Mode 3 azimuthal sectors Sectors chosen to be closest to B field parallel, perpendicular, and antiparallel

Miniaturized Electrostatic Dual-top-hat Spherical Analyzer Cutaway view Electron and ion top hat analyzers top-to-top Aperture (orange area) has 360 degree view in spin plane Accumulation and data selection (in select mode) done in DPU R1 = 14.8 R2 = 16 R3 = 17.2 mm

Astrid-2 Coordinate System x z Spin direction Rotation rate about 6 seconds per revolution, or 10 RPM Sun-pointing, with MEDUSA on the anti-sunward side Aperture plane wobbles + / - 3 degrees from spin plane. This is to prevent the opposite corner of the upper platform from blocking the field of view. Electric field booms also in spin plane 3 axis magnetometer located on star-camera boom Sun is in –z direction MEDUSA is always anti-sunward Aperture plane ± 3° of spin plane E-field measured in spin plane

Possible Electric Field Configurations Candidate Electric field configurations associated with upward accelerated electrons. Further analysis is needed to determine which one applies to this event. Upper panel is parallel (downward) electrons Lower panel is anti-parallel (upward) electrons Red line plot is electric field, upper panel is E parallel to B, lower panel is E perpendicular to B. Color bar range is from 2000 counts per second to 500,000 counts per second Red intense area centered at about 5 keV, duration is about ½ second. Entire event is about 1 second, or about 7 km along the orbit. Red 1/2 second area covers about 3.7 km along the orbit, or 12.7 arc minutes as seen from the ground.

Plot of energy of the peak intensity for each sweep. Throughout the event it shows no clear V shaped pattern. Plot is for entire event. Red bar indicates high intensity (red) region Peak Energy fluxes are about 50-60 ergs/cm2/s

Conclusions Upward electron acceleration as seen by Freja at about 1750 km are observed by MEUDSA to occur below 1000 km with keV intensities. This raises the intensity of the electric field required for such accelerations and lowers the altitude at which acceleration occurs. Work is ongoing to fine-tune the measurements, model the physical processes involved, and locate similar events in this and other data sets.