Speaker: Dr. Jeronimo Garcia
Abstract:
Integrated simulations with the CRONOS suite of codes, developed at CEA-Cadarache, are used to study the physics involved in the Internal Transport Barrier (ITB) sustainment and to identify the main obstacles for the establishment of a steady-state scenario in ITER. It is shown that any current drive inside the ITB leads to a progressive shrinking and disappearence of the barrier (known as the current misalignment effect) which means that Neutral Beam Current Drive, which is naturally localized in the central part of the plasma, proves to be of little use in these scenarios. In contrast, a pure Radio Frequency scenario is proposed showing that it provides a solution of principle to the current alignment problem. The main feature of this scenario is that there is a strong minimum negative magnetic shear to steadily sustain the ITB for 3000s, below which low performance inductive scenarios are recovered. The actual design of the ECRH/ECCD system in ITER can provide such a negative magnetic shear, leading to a clear dependence of the temperature gradient (with a well defined threshold) on the Pech/ parameter. The threshold obtained can be characterized as a second order phase transition as it has been done previously for the ITB formation of other completely different fusion devices as, e.g. the Large Helical Device (LHD) The extension of these scenarios to the future fusion demonstration commercial reactor (usually called DEMO) will be considered.