Cross-section through a single SWA-EAS sensor head. Key subsystems are: (1) the VGF system “top-cap” anode; (2) (a) the entrance aperture shielding grid and (b,c) upper and lower plates of the deflection system; (3) (a,b) the upper and lower hemispheres of the electrostatic analyser; (4) the detector subsystem comprising a grid, the annular MCP, and the anode board, together with embedded HV coupling capacitors; (5) the application-specific integrated circuit (ASIC) 32 charge amplifiers. A representative electron trajectory through the sensor electron optics is shown by the blue dashed trace, for the case where the upper aperture deflection plate is charged positively.