The influence of a spectrum of drift wave fluctuations on the trapped ion mode is investigated and shown to inhibit the onset of these modes. The stochastic damping of the trapped ion mode becomes comparable to the linear growth rate when the drift wave spectrum is described by previous theoretical models.
A radially peaked diamagnetic frequency profile typical of some tokamak discharges is shown to lead to radial localization of the drift wave fields. A critical condition for the onset of shear stabilization is derived which balances the effects of toroidal mode coupling, the degree of peaking in ω*e(r), and the strength of the magnetic shear.
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AbstractThe dynamical model for the L-H confinement mode transitions consisting of three ordinary differential equations (3-ODE model) for the essential state variables is proposed.The model is derived from the energy balance equations for the resistive pressure-gradient-driven turbulence and describes temporal evolutions of three characteristic variables (u. k. f) the potential energy contained in the pressure gradient, the turbulent kinetic energy and the shear flow energy. The energy input to the peripheral plasma region is included as an external control parameter in the model. The model equations have stationary solutions corresponding to the L and H modes. We obtain the L to H and H to L transition with the energy input parameter cha_ed. The type of the L.H transition, whether a first-order or second-order transition, is shown to be determined by the shear flow damping coefficient. We also find the pstameter region in which the H merle stationary, solution becomes unstable and bifurcates to the iim,t cycle which shows p,_riodic oscillations characteristic of the ELM confinement state I_STRIBUTION OF THIS DOCUMENT 18 UNLIM|TF...J_
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