Thermal misbalance effect strong enough to create slow magnetoacoustic wave trains

Plasma inhomogeneities are known to lead to the formation of quasi-periodic fast magnetoacoustic wave trains, observed in solar coronal loops and plumes and other astrophysical and laboratory plasmas.

For slow magnetoacoustic waves when the fluctuations of magnetic and plasma pressures oppose one another, this waveguide dispersion effect is weak and often ignored in theoretical models.

However, Dmitrii Zavershinskii et al. show that the misbalance between heating and cooling processes — intrinsic to the continuously heated and cooled plasma of the solar corona — can lead to the new dispersion strong enough to create slow-wave trains, even in a uniform plasma.

“We examined a uniform plasma and showed that the dispersion, due to the thermal misbalance that is characterized by specific heating and cooling time scales rather than spatial scales, can develop the initial broadband splash of a slow magnetoacoustic wave into a quasi-periodic wave train,” said author Dmitrii Kolotkov.

The researchers considered linear perturbations of a dense and warm plasma, with the wavelengths long enough to make wavelength-dependent non-adiabatic effects, such as thermal conduction and viscosity, negligible. This allowed the authors to isolate and investigate the effect of the thermal misbalance in the dynamics of slow magnetoacoustic waves.

They found that, by an order of magnitude, the wave train periodicity is about the same as the typical periods of slow magnetoacoustic oscillations detected in the solar corona. Since it is possible for the new dispersion effect to occur in other astrophysical and laboratory plasmas with the processes of heating and cooling, the researchers plan to further explore this effect on fast waves in the future.

Source: “Formation of quasi-periodic slow magnetoacoustic wave trains by the heating/cooling misbalance,” by D. I. Zavershinskii, D. Y. Kolotkov, V. M. Nakariakov, N. E. Molevich, and D. S. Ryashchikov, Physics of Plasmas (2019). The article can be accessed at https://doi.org/10.1063/1.5115224 .