  Streaming instability driven by ion flow inside a finite-length collisionless
inhomogeneous system is studied with numerical Particle-In-Cell simulations
alongside kinetic equations. The inhomogeneous plasma is produced by
introducing a cold beam of ions and thermal electrons in the system. In such
systems, we observe that the ion sound waves get modified in a stable ion flow
due to acoustic wave reflections from the boundary and that it triggers
instability. Such phenomena are known to be a hydrodynamic effect. However,
there are also signatures of the two-stream type ion sound instability where
kinetic resonances are essential. The study is aimed to quantify the effects of
the finite-length system on beam--plasma instability and identify wave modes
supported by such systems. The outcome of this study is believed to improve the
design aspect of ion beam sources and provide more control over experimental
devices.

Plasma Physics