Plasma convection in force-free magnetic fields as a mechanism for chemical separation in cosmical plasmas
DURING the past two decades, progress in space research has forced us to abandon the earlier idea of a cosmical plasma as being a homogeneous medium. Filament formation and chemical separation are two important phenomena that are often observed in cosmical plasmas and illustrate the importance of inhomogeneity. An average composition from the Sun's atmosphere used to be taken as a standard when expressing cosmic abundancies in general. Numerous observations, however, of the chemical composition in the solar wind from in situ measurements and from lunar soil and meteorite samples, indicate a great variability in these ratios1. The proton to α-particle flux ratio for solar flare energetic particle events varies widely between and within events2. Recent observations show that this variability is connected with the flare process itself and the earlier history of the flare, rather than propagation effects between the flare site and the observer. Some local chemical differentiation mechanism in the preflare history of the specific active region is probably responsible for the composition of the emitted, energetic particles. The phenomena of filamentation and chemical separation may be coupled, as in the presence of a temperature gradient, the plasma convection associated with filamentary structures provides an effective means of selective transport. The general principles of this mechanism are described here. These principles may be important not only in solar flares but in many other cosmical plasmas where force-free fields and thermal gradients occur.
Composition of the solar wind: Present and past
Studies of the elemental, isotopic, and ionic composition of the solar wind are vital to an understanding of the interactions of plasma species both in the solar wind and at its source, the solar corona. Such studies are also of importance to more general problems of solar physics and the history of the solar system. Although the heavier component of the solar wind is much more difficult to observe than the proton component, data have been collected from plasma probes, from lunar foil experiments, and from lunar samples, and the analysis of these data has been undertaken in many studies with unexpected results. Less effort has been devoted to the theoretical understanding of the observations, although it has been well established for many years that the observations cannot be explained by the theoretical models.
Drifts and Purification of a Fast Plasma Injected into a Double Bend Magnetic Field
Drifts of plasma moving in a curved magnetic field are studied experimentally. Depolarization currents of the plasma are measured directly and compared with the values deduced from the distribution of the ion density at a given time. The curvature drift is used to remove fast heavy impurities. The electric drift is used to separate the fast component from the slow component of the plasma puff.