QUASI-PERIODIC OSCILLATIONS IN A RAREFIED HIGH-TEMPERATURE PLASMA CAUSED BY THE DISPERSION OF ACOUSTIC WAVES

Based on the effects of thermal conductivity and heating/radiation losses, the dispersion of acoustic waves in a rarefied high-temperature plasma is studied using the example of the plasma of the solar corona. For the radiation loss function, an analytical approximation is used, based on the values found using the CHIANTI code. It is shown that the appearance of quasi-periodic oscillations can be explained by the specific properties of dispersion associated with the presence of a minimum group velocity in the space of wave numbers. The wavelet spectrum of acoustic vibrations in this case has a structure called “a boomerang”. A procedure for calculating periods using the constructed boomerang curve is proposed. It is assumed that the initial plasma disturbance has the form of a localized pulse having high dispersion qualities due to its wide spectrum. This approach has grounds, it is known, for example, that various kinds of non-stationary processes in the solar corona are generated under the action of short-term pulses from convective cells. The spectrum of the time signal considered at some point of observation is continuous, and the periods are determined based on the local maxima available in the spectrum. In this sense, the concept of quasi-periodic oscillations differs from the traditional one, which refers to the presence of a finite or countable number of periods between which there is a certain relationship. Calculations are carried out on the example of high-temperature plasma of the solar corona, where quasi-periodic oscillations are observed everywhere and can serve as a tool for studying the physical properties of coronal plasma.

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