Ion Beams and Electromagnetic Instabilities

Abstract

Energetic electrons and electron beams have so far received primary attention, since their high emissivity — usually favored by the charge to mass ratio — produces most continuum emissions observed in the high energy and radio range. However, this does not mean that ion beams should be neglected. In circumstances where both energetic electrons and ions can be observed, such as in cosmic rays and in the magnetosphere, ions are energetically more important. Energetic ions may propagate over large distances and deposit their energy far from the acceleration site. Furthermore, they can excite low-frequency waves, practically invisible to direct observations but with drastic effects. There is no doubt that a great variety of ion beam phenomena, similar to those in planetary magnetospheres, must be expected also in coronae and other tenuous plasmas.