Parametric excitation of magnetic oscillations and waves

2020 ◽  
pp. 245-281
Author(s):  
A.G. Gurevich ◽  
G.A. Melkov
1971 ◽  
Vol 43 ◽  
pp. 480-486
Author(s):  
E. I. Mogilevsky

A possible statistical model of the solar magnetoplasma in solar active regions consisting of a totality of small-scale current vortex plasma elements (‘subgranules’) is discussed. Some results are given which naturally follow from such a model: the small value of effective conductivity in the macro-structures of the plasma (hence, the possibility of a greater mobility and changeability of field and plasma for a short time), the formation of filamentary-structural elements, the oscillating regime of the magnetoplasma in an active region. A principal scheme is given of the experiment on a solar magnetograph with very high resolution, which is able to reveal discrete fields of the subgranules. The dispersion equation is derived for macro-magnetic oscillations of the statistical ensemble of magnetized subgranules. The possibility is noted to reveal macro-magnetic oscillations and waves during observations of low-frequency modulation in the solar radio-emission. It is shown that at solar radioburst propagation in the corona, (according to the model under consideration, some regularly located plasma inhomogeneities should be present in the active region) Bragg's diffraction takes place. Typical properties of complex radiobursts may be received (extreme narrowness of the band, short lifetime, directivity).


1961 ◽  
Vol 28 (3) ◽  
pp. 330-334 ◽  
Author(s):  
Eugene Sevin

The free motion of an undamped pendulum-type vibration absorber is studied on the basis of approximate nonlinear equations of motion. It is shown that this type of mechanical system exhibits the phenomenon of auto parametric excitation; a type of “instability” which cannot be accounted for on the basis of the linearized system. Complete energy transfer between modes is shown to occur when the beam frequency is twice the simple pendulum frequency. On the basis of a numerical solution, approximately 150 cycles of the beam oscillation take place during a single cycle of energy interchange.


1977 ◽  
Vol 17 (1) ◽  
pp. 93-103 ◽  
Author(s):  
N. F. Cramer

The parametric excitation of slow, intermediate (Alfvén) and fast magneto-acoustic waves by a modulated spatially non-uniform magnetic field in a plasma with a finite ratio of gas pressure to magnetic pressure is considered. The waves are excited in pairs, either pairs of the same mode, or a pair of different modes. The growth rates of the instabilities are calculated and compared with the known result for the Alfvén wave in a zero gas pressure plasma. The only waves that are found not to be excited are the slow plus fast wave pair, and the intermediate plus slow or fast wave pair (unless the waves have a component of propagation direction perpendicular to both the background magnetic field and the direction of non-uniformity of the field).


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