Magnetic island induced bootstrap current on island dynamics in tokamaks

When a magnetic island is embedded in toroidally symmetric tokamaks, the toroidal symmetry in ∫B∫ is broken [K. C. Shaing, Phys. Rev. Lett. 87, 245003 (2001)]. Here, B is the magnetic field. This broken symmetry induces an additional bootstrap current density in the vicinity of the island. It is illustrated that this island induced bootstrap current density modifies the island evolution equation and imposes a lower limit on the absolute value of the tearing mode stability parameter ∫ Δ′ ∫ for the island to be unstable. This lower limit depends on the local poloidal plasma beta Βp, the ratio of the plasma pressure to the poloidal magnetic field pressure. If Βp is high enough, the magnetic island is stable. This mechanism provides an alternative route to stabilize the island.