Saturation level of Alfven waves driven by Kelvin–Helmholtz Instability

2014-10-10

The Alfven wave (AW) mode is one of the three well known ideal magnetohydrodynamic (MHD) wave modes. The intrinsic AWs exist pervasively in astrophysical and solar-terrestrial environment. Our previous work showed that the saturation level of preexisting AWs is significant, which influence the basic physics of wave–particle interaction. However, the realistic value of the saturation level is still an open problem.

In this paper, taking account of the ion-neutral collision damping in partially ionized plasmas, we investigated the saturation level of AWs driven by the Kelvin–Helmholtz instability. We obtained an equation determining the saturation level of the AWs. The results show that, for a fixed-frequency wave, the saturation level of the AWs considerably increases as the ionization degree increases as well as the sheared-flow velocity (See Figure for more detail). These results have potential importance for us to estimate the saturation level of AWs in space and astrophysical plasmas.

This work has been published on ‘Chin. Sci. Bull. , 59(28):3536–3542,2014’ and can be downloaded here: http://link.springer.com/article/10.1007/s11434-014-0421-4

By with for CHEN Lin

Fig.The normalized growth/damping rate \(\gamma /k_{\parallel }v_{\mathrm{A}}\) vs the normalized perturbed magnetic filed \(\delta B/B_0\) for (a) \(f\) = 0.1 Hz, (b) 1 Hz, and (c) 10 Hz, where the solid lines correspond to growth rate \({\gamma }_{\mathrm{I}}/k_{\parallel }v_{\mathrm{A}}\) driven by K–H instability and \(V/v_{\mathrm{A}}-(V_{\mathrm{c}}/v_{\mathrm{A}})_{\mathrm{K-H}}\approx 0.1\) has been assumed. The dashed lines correspond to damping rate \({\gamma }_{\mathrm{D}}/k_{\parallel }v_{\mathrm{A}}\) due to ion-neutral collision. The ionized degree \({\chi }_{\mathrm{i}}=0.01\) has been used

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Saturation level of Alfven waves driven by Kelvin–Helmholtz Instability