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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]

Error-field penetration in reversed magnetic shear (RMS) configurations is numerically investigated by using a two-dimensional resistive magnetohydrodynamic model in slab geometry. To explore different dynamic processes in locked modes, three equilibrium states are adopted. Stable, marginal, and unstable current profiles for double tearing modes are designed by varying the current intensity between two resonant surfaces separated by a certain distance. Further, the dynamic characteristics of locked modes in the three RMS states are identified, and the relevant physics mechanisms are elucidated. The scaling behavior of critical perturbation value with initial plasma velocity is numerically obtained, which obeys previously established relevant analytical theory in the viscoresistive regime. [ABSTRACT FROM AUTHOR]

Effects of poloidal rotation profile on tearing and Kelvin-Helmholtz (KH) instabilities in a cylindrical plasma are investigated by using a reduced magnetohydrodynamic model. Since the poloidal rotation has different effects on the tearing and KH modes in different rotation regimes, four unstable domains are numerically identified, i.e., the destabilized tearing mode domain, stabilized tearing mode domain, stable-window domain, and unstable KH mode domain. It is also found that when the rotation layer is in the outer region of the rational surface, the stabilizing role of the rotation can be enhanced so significantly that the stable window domain is enlarged. Moreover, Alfven resonances can be induced by the tearing and KH modes in such rotating plasmas. Radially wide profiles of current and vorticity perturbations can be formed when multiple current sheets on different resonance positions are coupled together. [ABSTRACT FROM AUTHOR]