Electrostatic Plasma Oscillations

In the absence of a magnetic field, in addition to the usual acoustic oscillations there is only one other oscillation which is characteristic of plasmas. This oscillation is a result of charge separation. When we spoke of quasi neutrality above we noted that any displacement of charges of one sign in a plasma leads to oscillations, As noted previously, these oscillations are called electrostatic, or Langmuir, or simply plasma oscillations since they are a very general type of oscillation; indeed, the capacity for this kind of oscillation can be taken as part of the definition of a plasma. In a magnetic field, this kind of oscillation can be observed in pure form if the direction of the electric field and the motion of the particles are parallel to the magnetic field. In this case the magnetic field does not affect the motion of the particles.