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Effects of sub-Alfvénic shear flows on the complicated properties of three types of unstable eigenmodes, namely, coupled triple tearing mode (M1), coupled double tearing mode (M2), and three single tearing modes (M3), in a triple current sheet configuration are studied by means of an eigenvalue analysis. It is identified that the difference of velocity among three resonant surfaces rather than the local flow shear rate plays the more important role in the three types of eigenmodes. Thus, it is found that for the symmetric shear flow (SSF), the growth rate of the M1/M3 mode decreases/increases with the increasing strength of the shear flow, while the growth rate of the M2 mode is almost uninfluenced by SSF. For the antisymmetric shear flow (ASF), it is interestingly observed that in the small wavenumber regime, the M1 and M2 modes degenerate into similar eigenmode states with the same growth rate and opposite traveling frequencies. In the large wavenumber regime, the M2 and M3 modes degenerate into similar eigenmode states. Moreover, for both SSF and ASF, the growth rates of the three types of modes are almost the same in the small and large wavenumber limits. [ABSTRACT FROM AUTHOR]

The linear behavior of plasmoid instability in double current sheet configurations, namely, double plasmoid mode (DPM), is analytically and numerically investigated within the framework of a reduced magnetohydrodynamic model. Analytical analysis shows that if the separation of double current sheets is sufficiently small [ κxs«κ2/9S1/3L], the growth rate of DPMs scales as κ2/3S0L in the non-constant-ψregime, where κ=kLCS/2 is the wave vector measured by the half length of the system LCS/2, 2s is the separation between two resonant surfaces, and SL=LCSVA/2κ is Lundquist number with VA and η being Alfven velocity and resistivity, respectively. If the separation is very large [κxs»κ2/9S1/3L], the growth rate scales as κ-2/5S2/5L in the constant-ψ regime. Furthermore, it is also analytically found that the maximum wave number scales as xs-9/7sS3/7L at the transition position between these two regimes, and the corresponding maximum growth rate scales as xs-6/7SL-2/7there. The analytically predicted scalings are verified in some limits through direct numerical calculations. [ABSTRACT FROM AUTHOR]