The CASSIOPE/e-POP Suprathermal Electron Imager (SEI)

Abstract

The Suprathermal Electron Imager (SEI) on the Enhanced Polar Outflow Probe (e-POP) experiment uses a microchannel-plate-intensified charge-coupled device (CCD) detector to record two-dimensional, energy-angle images of electron distributions for energies up to 350 eV. Alternatively, the SEI can be biased to measure positive ions at energies that include the ambient ionospheric population (< 1 eV) and extending to 350 eV. At the highest measurement resolution, distribution images are 64 pixels in diameter and are read out at a rate of 100 images per second. The SEI's field of view is 360• × ±4• , and includes viewing of the nadir and ram directions, nominally. At high latitude the nominal orientation allows coverage of most pitch angles. The SEI is included on e-POP to address the mission's principal scientific objectives, the first being to characterize polar ion outflow and its drivers including ambipolar electric fields generated by suprathermal electron populations, and direct energization of ions by plasma waves or through frictional heating. In addition, the SEI's focus on low energies and high time resolution allows a unique view of suprathermal particle populations and their role in wave-particle interactions, in support of e-POP's second scientific objective: to study plasma waves and wave propagation in the high-latitude ionosphere. Observations taken within geophysically quiet regions indicate that the instrument can track bulk ion flow velocity with a resolution of order 25 m/s or better.

Thermal ion imagers and Langmuir probes in the Swarm electric field instruments

“…The Swarm TII sensors operate at a fixed image rate of 16 s −1 . Much higher frame rates have been used on suborbital flights of the TII and on the CASSIOPE/ePOP satellite [ Knudsen et al , ]; however, these rates could not be supported on the Swarm mission, on which the EFI instruments have a telemetry allocation of 6 kbit/s on average. Each Swarm TII image consists of a rectangular region measuring 66 × 40 pixels (after 4 × 4 binning within the CCD itself and cropping in software), resulting in 2640 pixels sampled with 12 bits, for a total of 31,680 bits per image.…”

Low‐Altitude Ion Heating, Downflowing Ions, and BBELF Waves in the Return Current Region

“…e‐POP carries in total eight scientific instruments, five of which are used in this study: the suprathermal electron imager (SEI) (Knudsen et al, ), the rapid‐scanning ion mass spectrometer (IRM) (Yau et al, ), the magnetic field instrument (MGF) (Wallis et al, ), the radio receiver instrument (RRI) (James et al, ), and the fast auroral imager (FAI) (Cogger et al, ). Figure depicts the placement and orientation of different sensors on the spacecraft.…”

Alfvénic Dynamics and Fine Structuring of Discrete Auroral Arcs: Swarm and e‐POP Observations

“…Swarm A also captured 16 sps data from the electric field instrument (EFI) (Knudsen et al, ). No electric field data were available from Swarm C or e‐POP because the respective EFI, suprathermal electron imager (Knudsen et al, ), and imaging and rapid‐scanning ion mass spectrometer (Yau et al, ) instruments were not operating at the time.…”