The TRACERS Analyzer for Cusp Electrons

Abstract

The Analyzer for Cusp Electrons (ACE) instruments on the Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission provide measurements of electron velocity distribution functions from two closely spaced spacecraft in a low Earth orbit that passes through the magnetospheric cusp. The precipitating and upward-going electrons provide a sensitive probe of the magnetic field line topology and electrostatic potential structure, as well as revealing dynamic processes. ACE measurements contribute to the top-level TRACERS goals of characterizing the spatial and temporal variation of magnetic reconnection at the terrestrial magnetopause and its relationship to dynamic structures in the cusp. ACE utilizes a classic hemispheric electrostatic analyzer on a spinning platform to provide full angular coverage with 10 degree by 7 degree resolution. ACE can measure electrons over an energy range of 20-13,500 electron volts, with fractional energy resolution of 19%. ACE provides 50 ms cadence measurements of the electron velocity distribution, enabling sub-kilometer spatial resolution of cusp boundaries and other structures.

Keywords: Electrons; Electrostatic analyzer; Magnetosphere; TRACERS mission.

Fig. 1

ACE block diagram, showing basic electrical functions and interfaces

Fig. 2

Electrostatic optics simulation for ACE, showing a projection of representative simulated 3-d electron trajectories through a cylindrically symmetric potential grid

Fig. 3

Simulated relative sensitivity for ACE, showing integrated relative sensitivity vs energy, instrument elevation angle, and instrument azimuthal angle in the top row, and corresponding 2-d response functions in the bottom row

Fig. 4

Exploded view of ACE mechanical design, showing (from left to right) back panel, electronics assembly (with anode interface assembly on top), enclosure and dog house, hemisphere assembly, and light trap assembly

Fig. 5

Mechanical elements of ACE, including light trap assembly (A), hemisphere assembly top (B) and bottom (C), anode interface assembly with MCPs installed on top of the electronics stack (D), electronics assembly side view with optics and red tag cover installed (E), back panel with purge connected (F), assembled instrument from above (G), assembled instrument from side with dog house removed (H), and assembled instrument with thermal treatments (I)

Fig. 6

Electrical elements of ACE, including anode board (A), anode interface assembly (B), charge-amp board top (C) and bottom (D), stepper board (E), stack board (F), digital board top (G) and bottom (H), and low voltage power supply board (I)

Fig. 7

ACE testing activities, including pre-calibration (A), vibration (B), thermal vacuum (C and D), pre-thermal vacuum bakeout (E), and EMI/EMC (F)

Fig. 8

Data from ACE FM1 thermal vacuum testing, showing angular and energy response to counts from Ni-63 radioactive source, and digital board temperature monitor readback

Fig. 9

Data from ACE FM1 and FM2 final calibrations, showing integrated relative sensitivity vs energy, FWHM 2-d response vs energy and elevation angle, and comparison of FWHM 2-d response to simulation results (purple shading and orange contour), for 11 different azimuthal angles

Fig. 10

Data from ACE FM1 final calibration, showing the azimuthal angle response to a mono-energetic electron beam with a fixed energy and elevation angle

Fig. 11

Data from ACE FM2 final calibration, showing the azimuthal angle response to a mono-energetic electron beam with a fixed energy and two different elevation angles

Fig. 12

Energy spectra from ACE FM1 final calibration, showing the response to a mono-energetic electron beam with energies of 20–9500 eV at a fixed azimuthal and elevation angle (inset shows expanded view of low-energy portion of sweep)