Ion Cyclotron Period Research Articles

Plasma ion heating by adiabatic diamagnetization

Attention is drawn to the fact that if a collisionless plasma in a static magnetic field is subjected to the sudden switch-on of an electric field perpendicular to the magnetic field, with a rise-time short compared with the ion cyclotron period, or alternatively, if the process of ionization occurs in crossed static E and B fields, then the internal energy of the ion component will comprise not only the kinetic energy of drift but also an equal kinetic energy of gyrational motion in the drifting frame of reference. For near-collisionless ions this process will give rise to ion heating. For deuterium ions nuclear fusion collisions may be expected for sufficiently high E/B values.

Ion Cyclotron Electrostatic Instabilities

An investigation of the instabilities of longitudinal electrostatic oscillations in an infinite magnetized plasma at or near the ion cyclotron frequency has been made. This work extends that initiated by Harris. An approximate mechanical analysis of the coupling of the motion to the electrostatic field oscillations has been developed, which provides some degree of physical intuition and guides the more abstract dispersion-equation approach used in the suceeding analysis. The possible instabilities arising from the ion motion have been classified into two types. Type-A instabilities are characterized by (1) the circumstance that the electrostatic field propagates nearly transversely to the magnetic field, and (2) as the analysis shows, by the requirement that the transverse energy distribution must be peaked at other than zero energy. A monotonically decreasing transverse energy distribution is necessarily stable in this instance. Type-B instabilities arise when the oscillating electric field has a significant component along the magnetic field. Because of the effect of ion motion along the magnetic field, it is now possible for instabilities to arise when the transverse energy distribution decreases monotonically, unlike Type A. Both types of instabilities have been examined as to their dependence on the type of coupling to the plasma electrons, and the various instability criteria are stated. In these electron-ion instabilities a central feature is the coupling of the transverse ion motion to the motion of the electrons along field lines. The most rapidly growing modes are those in which electrons move one axial wavelength in one ion cyclotron period. For actual experimental plasmas, this axial wavelength may be too long to be supported in the experimental device. This can put severe restrictions on the occurrence of these particular instabilities. Another class of instabilities is of those which arise from a coupling of the ion distribution with itself, the electrons playing a passive role only. Of the several kinds of instabilities of this class discussed, the most important are those which arise from a double distribution of ions; e.g., a cold plasma in the presence of a hot ion plasma. The important feature of these instabilities is that they can occur for very low densities. The relevance of this analysis to several current experimental programs is discussed.