Concerning the Dynamics of Energetic Protons in Coronal Magnetic Loops: Dispersion Effects of Alfven Waves

Extract

It is shown that the existence of plasma density inhomogeneities (ducts) elongated along the magnetic field in coronal loops, and of Alfven wave dispersion, associated with the taking into account of gyrotropy U ≡ ω/ω_i ≪ 1 (Leonovich et al., 1983), leads to the possibility of a quasi-longitudinal k_⊥ < √U k_‖ propagation (wave guiding) of Alfven waves. Here ω is the frequency of Alfven waves, ω_i is the proton gyrofrequency, and k is the wave number. It is found that with the parameter ξ = ω² R/ω_i A > 1, where R is the inhomogeneity scale of a loop across the magnetic field, and A is the Alfven wave velocity, refraction of Alfven waves does not lead, as contrasted to Wentzel's inference (1976), to the waves going out of the regime of quasi-longitudinal propagation. As the result, the amplification of Alfven waves in solar coronal loops can be important. A study is made of the cyclotron instability of Alfven waves under solar coronal conditions.