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 ion gyroradius is studied using nonlinear gyrokinetic particle simulations. In the sheared slab geometry it is demonstrated that in the absence of plasma 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-size drift-magnetic islands also form. When shorter wavelength electron-temperature-gradient-driven modes are included in the simulation nonlinear coupling to the drift-magnetic island is observed, which has a significant impact on its temporal evolution.