Plasma Maser Effect and Adiabatic Invariants in Non-linear Interactions
It is well known that wave amplification can be the result not only of a linear maser effect, but also of a non-linear maser effect. In the latter case themaser effect may be produced by the inverse population of particles which are participating in the non-linear interactions or by the inverse population of waves. We have discussed earlier that a plasma is a strongly non-linear state of matter, and that it may contain a large number of waves which can be described, like the particles, by a distribution function. Moreover, nonlinear processes make it possible that waves are emitted by the particles and this kind of stimulated processes may be responsible for the non-linear amplification of waves. In some sense these are trivial non-linear amplification processes. The name plasma maser effect is given to a different, non-trivial wave amplification mechanism which is based upon the fact that a plasma is often in a turbulent state which results in the formation of small-scale inhomogeneities in the fields and in the particle distributions. These inhomogeneities are characteristic features of the plasma state of matter since a plasma is often turbulent.
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