**6.1 Streaming instability**

This type of instability occurs, when either a current or a beam of energetic particles is driven through plasma so that the different species of particles have drifts relative to one another. This drift energy attempt to excite waves and oscillation. This energy is acquired at the loss of the drift energy, which is in the unperturbed state.

### **6.2 Rayleigh–Taylor instabilities**

In this kind of instability, the plasma has a sharp boundary or a density gradient, so that it does not remain uniform. In addition to this, an external, nonelectromagnetic force is applied into the plasma. This force is responsible for driving the instability in plasma. This analogy can be realized in an inverted glass of water. Though the plane interface between the air and the water is in the state of equilibrium, where the air pressure support the weight of the water. Any ripple arising in the surface of water tend to grow at the loss of potential energy in the influence of gravitational field. Whenever a light fluid supports a heavy fluid this things happen, which is quite known in the field of hydrodynamics [1].

## **6.3 Universal instabilities**

A plasma is hardly present in perfect thermodynamic equilibrium, when it is confined by gravitational field or an electric field (driving forces). The plasma is expanded by plasma pressure and an instability is driven by the expansion energy. Any finite plasma always contains this type of free energy and the waves, which comes out as a result are called universal instabilities.
