Reconnection and transport in high temperature regimes

Magnetic reconnection and transport are recognized as key issues on the path to ignition in magnetically confined plasmas. The excitation of m = 1 modes involving magnetic reconnection is considered, and collisionless regimes where these modes are suppressed or prevented from having significant growth rates (of the type consistent with the observed crash phase of sawtooth oscillations) are identified. An analytical model for the early non-linear topology and evolution of modes of this kind is given. The effective diffusion coefficients are assumed to result from the combined effects of modes excited in the body of the plasma column and at the edge of it. The impurity driven mode is considered to be a candidate for excitation at the edge. The transport resulting from this mode is assessed while it is pointed out that it can account for the observation of the 'isotopic' effect on the energy confinement time. A global transport model is presented. In the injected heating regimes the enhanced diffusion process is attributed to the excitation of trapped electron ubiquitous modes in the body of the plasma. The form of the diffusion coefficient is suggested by the theory and its temperature dependence (is proportional to T) is consistent with the most recent analyses of advanced experiments on transport. The evolution toward ignition of the high density plasmas for which the Ignitor-Ult experiment is designed is investigated. The conditions under which ignition can be achieved are found to depend on the evolution of the temperature and current density profiles that can be controlled in order to avoid the onset of large scale sawtooth oscillations. The envisioned favourable characteristics of high density, high magnetic field experiments to investigate fusion burn regimes are confirmed by this analysis. 17 refs, 2 figs, 1 tab