Exploration of Propagation Window for Ion Acoustic Waves in Multi-cusp Plasma Device

The Multi-pole line cusp Plasma Device (MPD) has adopted cusp magnetic field geometry produced using six electromagnets for plasma confinement. The variation in cusp magnetic field strength gives us the opportunity to explore the propagating and non-propagating regimes for the ion-acoustic (IA) wave.

An experimental study is performed to explore the window for ion-acoustic wave propagation by changing the various parameters, like plasma density, electron temperature, neutral density, and cusp magnetic field strength. While varying these parameters the propagation of IA wave ceases to exist or gets damp in a certain regime. In a quest for that, the possible causes to make the IA wave damp in plasma and limitations to IA wave propagation are investigated. After an elaborate experimental investigation, it is observed that the IA wave can propagate below the plasma density. When the plasma density reaches this critical value it falls into the non-propagating regime. This suggests that MPD plasma behaves as a low pass filter for IA wave propagation.