Plasma in laboratory and space

H. Alfvén

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.

Domaines: Articles anciens

H. Alfvén. Plasma in laboratory and space. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-1-C7-19. ⟨10.1051/jphyscol:19797425⟩. ⟨jpa-00219427⟩