Collective motions in non-uniformly magnetized plasmas

While the reduced particle and fluid descriptions of magnetized plasma dynamics are based on the same set of approximations they apparently give differing results for the collective motions in non-uniform magnetic fields. Here it is shown that these two pictures give identical results when the diamagnetic effects due to charged particle gyration are taken into account. The subtle kinematical effects of the latter are revealed through many illustrations. Finally, this insight is used to explain the physical mechanism behind the ideal interchange instability. All these topics are intimately connected and have so far not been given an adequate presentation in introductory textbooks.