INTERACTION OF BOOTSTRAP-CURRENT-DRIVEN MAGNETIC ISLANDS

The formation and interaction of fluctuating neoclassical pressure-gradient-driven magnetic islands is examined. The interaction of magnetic islands produces a stochastic region around the separatrices of the islands. This interaction causes the island pressure profile to be broadened, reducing the island bootstrap current and drive for the magnetic island. A model is presented that describes the magnetic topology as a bath of interacting magnetic islands with low to medium poloidal mode number (m congruent-to 3-30). The islands grow by the bootstrap current effect and damp due to the interaction of the magnetic islands. The effect of this sporadic growth and decay of the islands ("magnetic bubbling") is not normally addressed in theories of plasma transport due to magnetic fluctuations. The nature of the transport differs from statistical approaches to magnetic turbulence since the transfer of particles and heat occur as discrete, abrupt events, not as a random walk process. This model suggests that tokamak experiments have relatively short-lived, coherent, long-wavelength magnetic oscillations present in the steep pressure-gradient regions of the plasma.