What is the name of the instrument on Voyager that measures plasma waves?

The Plasma Wave Subsystem is the Voyager instrument that measures plasma waves. Often abbreviated PWS, it detects electric-field fluctuations in plasma, helping scientists study the space environment around planets and beyond the heliosphere.

The instrument uses two long antennae arranged in a V shape. Its receivers cover very low radio frequencies, allowing it to investigate waves produced by interactions between charged particles and magnetic fields. Plasma is electrically charged gas, and its waves can reveal information about electron density and the behavior of particles that cannot be seen directly.

Voyager’s Plasma Wave Subsystem gathered observations during the spacecrafts’ encounters with Jupiter, Saturn, Uranus, and Neptune. After Voyager 1 entered interstellar space, PWS measurements also helped researchers estimate the density of the thin plasma surrounding the probe. It is distinct from the Magnetometer, which measures magnetic fields, and the Cosmic Ray Subsystem, which studies energetic particles.