title: Novel turbulence trigger for neoclassical tearings mode in tokamaks.
abstract: A stochastic trigger by microturbulence for a neoclassical tearing mode (NTM) is studied. The NTM induces a topological change of magnetic structure and has a subcritical nature. The transition rate of the probability density function for and statistically averaged amplitude of the NTM are obtained. The boundary in the phase diagram is determined as the statistical long time average of the transition conditions. The NTM can be excited by crossing this boundary even in the absence of other global instabilities.
authors.affiliation: Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan.
authors.forename: Sanae-I
authors.initials: SI
authors.lastname: Itoh
authors.forename: Kimitaka
authors.initials: K
authors.lastname: Itoh
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Yagi