Nonlinear dynamics of small-scale magnetic islands in high temperature plasmas

The growth and nonlinear evolution of small-scale magnetic islands having a characteristic width of the order of the skin depth and smaller than an io n gyroradius is studied using nonlinear gyrokinetic particle simulations. I n the sheared slab geometry it is demonstrated that in the absence of plasm a pressure gradients, in a collisionless plasma, skin-size magnetic islands are spontaneously generated and form a nonlinear Bernstein-Greene-Kruskal- type asymptotic state. In the presence of electron thermal gradients skin-s ize drift-magnetic islands also form. When shorter wavelength electron-temp erature-gradient-driven modes are included in the simulation nonlinear coup ling to the drift-magnetic island is observed, which has a significant impa ct on its temporal evolution. (C) 2001 American Institute of Physics.