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.
Plasma in laboratory and space
Plasma phenomena are studied in the laboratory, in the magnetospheres, and in more distant astrophysical regions. The basic properties of plasmas are likely to be the same everywhere but the transfer of knowledge between the regions requires laws of scaling by a factor of up-to 1027 (= ratio between Hubble distance 1028 cm and laboratory dimensions, say 10 cm). Plasma phenomena are complicated and can be understood only with the help of a very sophisticated diagnostics. Up to recently, diagnostics in the laboratory was best developed and space plasma physics must be based on a flow of knowledge from the laboratory. However, in situ measurements in the magnetospheres (including the heliosphere = the solar magnetosphere) has now reached such a sophistication that in some respects magnetospheric plasma physics is ahead of laboratory plasma physics. Hence the exploration of astrophysical regions (defined as those regions not yet accessable to in situ measurements) must be based on a transfer of knowledge not only from laboratory physics but also from magnetospheric physics. Further, a transfer of knowledge from the magnetospheres to the laboratory may rejuvenate fusion research. Magnetospheric research has demonstrated that there are plasma regions of two different kinds : - passive plasma regions, which can be described by classical hydrodynamic theory. They transmit waves and high energy charged particles but if the field-aligned currents exceed a certain value they are transferred into. - active plasma regions. These carry field-aligned currents which give them a filamentary or sheet structure with thickness down to a few cyclotron radii (ionic or even electronic). They transmit energy from one region to another and produce electric double layers which accelerate particles to high energies. Active regions cannot be described by hydromagnetic theories. Boundary conditions are essential and may be introduced by circuit theory. (Erroneous treatment of boundary conditions is often fatal in magnetic merging theories.) Transfer of knowledge from the laboratory and the magnetospheres is now starting a revolution in astrophysics. For example the theory of formation of the solar system can be based on extrapolation of what is known from magnetospheric and laboratory plasma physics. However, there are two kinds of astrophysically important plasmas which cannot yet be studied in the laboratory or in the magnetospheres : dusty plasmas, of importance in interstellar clouds, and ambiplasmas (consisting of both matter and antimatter), of importance in the cosmological discussion.
Microwave source with enhanced radiation power based on orbitron MASERs
We have proposed the design of high power microwave source in a vacuum tube based on the theory of negative mass instability. The proposed source does not operate based on a slow-wave structure but instead makes use of accelerated charged particles. In our structure, an electron emitter injects the charged particles into to the cavity. Emitted particles move around the anode, which leads to electron acceleration and emission of electromagnetic waves with a specific frequency. In this paper, we have enhanced the output power and frequency of microwave source by variation of particles initial energy and the number of anodes incorporating their specific arrangement and applied voltages. Working at room temperature, compactness, wide bandwidth, and tunability of output frequency are among the advantages of the proposed source.