title: Structure-driven nonlinear instability of double tearing modes and the abrupt growth after long-time-scale evolution.
abstract: The new nonlinear destabilization process is found in the nonlinear phase of the double tearing mode (DTM). This process causes the abrupt growth of DTM and subsequent collapse after long-time-scale evolution in the Rutherford-type regime. The nonlinear growth of the DTM is triggered when the triangular deformation of magnetic islands with sharp current point at the X point exceeds a certain value. Hence, the mode can be called the structure-driven one. Decreasing the resistivity increases the sharpness of the triangularity and the spontaneous growth rate in the abrupt-growth phase is almost independent of the resistivity.
authors.affiliation: Naka Fusion Research Establishment, JAERI, Naka-machi, Naka-gun, Ibaraki-ken 311-0102, Japan.
authors.forename: Yasutomo
authors.initials: Y
authors.lastname: Ishii
authors.forename: Masafumi
authors.initials: M
authors.lastname: Azumi
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Kishimoto