Rocket to the Aurora: Rockets (Electrostatic Analyzers)

The Electrostatic Analyzer, or ESA instrument, consists of two closely spaced hemispheres. When a voltage is applied between the hemispheres, incoming charged particles are deflected by an amount proportional to the applied voltage. Only charged particles within a specific range of velocities will be admitted to the detector and measured by the micro-channel plates near the bottom. Micro-channel plates are special glass plates that amplify a single particle impact into a large number of electrons which form a charge pulse which is easily measured by electronic counters.

Particle A: This particle is moving too slow. As it enters the detector, it will be deflected into the inner hemisphere wall and be lost.

Particle B: This particle is moving at the exact right speed. It will be deflected down the curved path between the hemispheres and impact the micro-channel plates.

Particle C: This particle is moving too fast. The deflection due to the voltage between the hemispheres doesn't occur in time to prevent this particle from impacting the outer hemisphere wall.

As the voltage between the hemispheres is varied with time, particles of different velocities are admitted to the micro-channel plates, and particles of different energies are measured. This is called a particle spectrogram.

TOP VIEW

Looking from the top of the detector, particles can arrive into the hemisphere mechanism from a variety of angles. Metal anode pads below the micro-channel plates ("MCPs") record the position of the incoming particles. Thus these detectors are able to measure both the speed and direction of auroral electrons and ions.