Excitation of negative energy surface magnetohydrodynamic waves in an incompressible cylindrical plasma

Abstract

Negative energy wave phenomena may appear in shear flows in the presence of a wave decay mechanism and external energy supply. We study the appearance of negative energy surface waves in a plasma cylinder in the incompressible limit. The cylinder is surrounded by an axial magnetic field and by a plasma of different density. Considering flow inside and viscosity outside the flux tube, we derive dispersion relations, and obtain analytical solutions for the phase speed and growth rate (increment) of the waves. It is found that the critical speed shear for the occurrence of the dissipative instability associated with negative energy waves (NEWs) and the threshold of Kelvin--Helmholtz instability (KHI) depend on the axial wavelength. The critical shear for the appearance of sausage NEW is lowest for the longest axial wavelengths, while for kink waves the minimum value of the critical shear is reached for the axial wavelength comparable to the diameter of the cylinder. The range between the critical speed of the dissipative instability and the KHI threshold is shown to depend on the difference of the Alfvén speeds inside and outside of the cylinder. For all axial wavenumbers, NEW appears for the shear flow speeds lower than the KHI threshold. It is easier to excite NEW in an underdense cylinder than in an overdense one. The negative energy surface waves can be effectively generated for azimuthal number $m=0$ with a large axial wave number and for higher modes ($m>0$) with a small axial wave number.

arXiv comment11 pages, 8 figures, accepted in ApJ

References in corpus (9)

• MHD Waves and Coronal Seismology: an overview of recent results
• Solar Coronal Jets: Observations, Theory, and Modeling
• Stability of rotating magnetized jets in the solar atmosphere. I. Kelvin-Helmholtz instability
• MHD wave modes resolved in fine-scale chromospheric magnetic structures
• Numerical simulation of dark lanes in post-flare supra-arcade
• Dissipative instability in partially ionised prominence plasmas
• Energy of eigen-modes in magnetohydrodynamic flows of ideal fluids
• Ultra-high-resolution Observations of MHD Waves in Photospheric Magnetic Structures
• Nature and dynamics of overreflection of Alfven waves in MHD shear flows

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