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| 2. |
- Alfvén, Hannes
(författare)
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Paradigm transition in cosmic plasma physics
- 1982
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Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847. ; T2, s. 10-19
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Tidskriftsartikel (refereegranskat)abstract
- In situ measurements in the magnetospheres together with general advancement in plasma physics are now necessitating introduction of a number of effects that have been recently discovered or earlier neglected. Examples are:Electric double layers (like in the lower magnetosphere);Thin current layer (like in the magnetopause) giving space a cellular structure;Current produced filaments (e.g., in prominences, solar corona and interstellar clouds).Further it is important to use the electric current (particle) description and to study the whole circuit in which the current flows.The pinch effect cannot be neglected as is now usually done.The critical velocity phenomenon is essential, for example for the band structure of solar system.Theory of dusty plasmas is important. The result is a change in so many theories in cosmic plasma physics that it is appropriate to speak of an introduction of a new paradigm. This should be based on empirical knowledge from magnetospheric and laboratory investigations. Its application to astrophysics in general, including cosmology, will necessarily lead to a revision of, e.g., the present theories of the formation of stars, planets and satellites. It is doubtful whether the big bang cosmology will survive.
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| 3. |
- Alfvén, Hannes
(författare)
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Plasma universe
- 1987
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Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847. ; T18, s. 20-28
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Tidskriftsartikel (refereegranskat)abstract
- Traditionally the views on our cosmic environment have been based on observations in the visual octave of the electromagnetic spectrum, during the last half-century supplemented by infrared and radio observations.Space research has opened the full spectrum. Of special importance are the x-ray-γ-ray regions, in which a number of unexpected phenomena have been discovered. Radiations in these regions are likely to originate mainly from magnetised cosmic plasmas. Such a medium may also emit synchrotron radiation which is observable in the radio region.If we try to base a model of the universe on the plasma phenomena mentioned we find that the plasma universe is drastically different from the traditional visual universe.Information about the plasma universe can also be obtained by extrapolation of laboratory experiments and magnetospheric in situ measurements of plasmas. This approach is possible because it is likely that the basic properties of plasmas are the same everywhere.In order to test the usefulness of the plasma universe model we apply it to cosmogony. Such an approach seems to be rather successful. For example, the complicated structure of the Saturnian C ring can be accounted for. It is possible to reconstruct certain phenomena 4-5 billions years ago with an accuracy of better than 1%.
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| 4. |
- Anderson, D, et al.
(författare)
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Analysis of profile effects on high Q subignited Tokamak fusion plasmas
- 1998
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Ingår i: PHYSICA SCRIPTA. - : ROYAL SWEDISH ACAD SCIENCES. - 0281-1847. ; 58:3, s. 256-261
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- An analysis is made of the maximum power multiplication factor Q, achievble in subignited Tokamak fusion plasmas where the burn is sustained by feedback controlled auxiliary heating. Using a 1-D model equation for the plasma temperature, simple analytical
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| 5. |
- Anderson, D., et al.
(författare)
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Exact Schrödinger Solitons in Optical Fibers in the Presence of Space Dependent Damping or Amplification
- 1999
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Ingår i: Physica scripta. T. - 0281-1847. ; 82, s. 42-43
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that the nonlinear Schrödinger equation describing pulse propagation in optical fibers in the presence of a properly space-tailored damping or amplification is exactly integrable. A simple transformation of variables is given which transforms the inhomogeneous nonlinear Schrödinger equation into the standard form with constant coefficients, thus generating new explicit bright and dark soliton solutions in the cases of anomalous and normal dispersion, respectively.
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| 6. |
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| 7. |
- Asp, Elina, et al.
(författare)
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Localising Effects of a Peaked Diamagnetic Frequency on Drift Modes in Rotating Tokamak Plasmas
- 2002
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Ingår i: Physica scripta. T. - 0281-1847. ; T98:-, s. 151-154
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we investigate the effects of a diamagnetic frequency peaking and velocity shear on a two-dimensional drift mode structure. Previous study made by Horton et al. showed that a strong diamagnetic frequency peaking can trap the wave energy both radially and along the magnetic field lines. We show that the localising effect of the diamagnetic frequency peaking can be suppressed by a strong velocity shear in the edge plasma. The same phenomenon is present in the bulk plasma, but due to the velocity shear not being as pronounced there, the effect is nominal.
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| 8. |
- Asp, Elina, et al.
(författare)
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Ship-Wave Eigenmodes of Drift Type in Rotating Tokamak Plasmas
- 2000
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Ingår i: Physica scripta. T. - 0281-1847. ; 62:2-3, s. 169-176
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Tidskriftsartikel (refereegranskat)abstract
- Ship waves of drift type in rotating plasma of axisymmetric, large aspect-ratio tokamaks with concentric, circular magnetic surfaces are investigated. Plasma rotation is driven by an electrostatic radial electric field and the waves under consideration may be excited by plasma flow past some static obstacle. The analysis performed is based on rigorously derived eigenmode equations coupled in poloidal mode numbers through toroidal effects. The existence of two qualitatively different types of ship wave eigenmodes is demonstrated. Namely (i) global modes that have a structure of quasimodes localised in both radial and poloidal directions and correspond to the bounded states in a potential well which are marginally stable and (ii) propagating modes that experience shear convective damping. The dispersion relations for both types of eigenmodes are obtained both in the weak and the strong coupling approximation.We find the analytical solutions of the dispersion relations and the regions of their existence which are defined, mainly, by the value and direction of the poloidal rotation velocity. An accumulation point for global ship eigenmodes is determined. For propagating ship waves the real and the imaginary parts of the poloidal wavenumber are found. It is shown that the imaginary part always corresponds to convective damping of these waves
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| 9. |
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| 10. |
- Beckman, O., et al.
(författare)
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Susceptibility Measurements and Magnetic Ordering of Hexagonal FeGe
- 1972
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Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 6:2-3, s. 151-157
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Tidskriftsartikel (refereegranskat)abstract
- The spin structure of the metallic hexagonal B 35 phase of FeGe has been studied by means of susceptibility and magnetization measurements. Below the Neel temperature TN = 411 K hexagonal FeGe is a uniaxial antiferromagnet with the spins parallel to the c-axis. In each c-plane all spins are ferromagnetically coupled with an exchange constant J0 ≈ 22 meV. The antiferromagnetic exchange constant between nearest neighbour and next nearest neighbour c-planes are J1 = -3.5 meV and J2 = -0.9 meV resp. in the molecular field model. Susceptibility and spin flop experiments indicate that the spins tilt away from the c-axis below 30 K. We suggest that the spins then form a double cone structure with a cone halfangle of 20° at 4.2 K. In the double cone the c-plane components have a turn angle in the vicinity of 180° between nearest neighbour planes, which implies absence of long range order. The result is in good agreement with Fermi surface calculations by Sundström (Physica Scripta, following paper), which show the existence of several spin density wave vectors between Q = 0.89 π/c and Q = 1.3 π/c calipering different parts of the Fermi surface in a direction parallel to the c-axis.
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