Advanced Modelling of Island Control for ITER – AMICI

The XTOR-2F code evolves MHD equations in toroidal geometry with drift and neoclassical physics. The XTOR-K version couples these equations with 6D kinetic module, so as to describe the dynamics of fast particles (in particular alpha particles produced by fusion reactions).

• Stabilization efficiency : validation of the implementation in a global MHD [Février16]
• Response of a magnetic island to a localized RF source: flip instability and island drive [Février16]
• Extended MHD model for the simulation of neoclassical tearing modes : validation of neoclassical equilibrium and nonlinear dynamics [Maget16]

Prospects for 2016:
- comparison of different control stratégies (continuous fixed source, modulation, sweeping)
- validation hybrid version of the code (XTOR-K)

Publications :
1. O Février, et al, « First principles fluid modelling of magnetic island stabilization by electron cyclotron current drive (ECCD) », Plasma Physics and Controlled Fusion 58(4), 045015 (2016), hal.archives-ouvertes.fr/hal-01286131
2. P Maget, O Février, H Lütjens, J F Luciani, and Xavier Garbet. « Bifurcation of magnetic island saturation controlled by plasma viscosity ». Plasma Physics and Controlled Fusion 58(5), 055003 (2016)https://hal.archives-ouvertes.fr/hal-01292516

Conférences:
1. O. Février, P. Maget, H. Lütjens, J.F. Luciani, J. Decker, G. Giruzzi, P. Beyer, M. Reich, and Asdex-Upgrade Team. Modeling of magnetic island modications by ECCD using XTOR-2F. volume 38, 2014. 41th EPS Conf. on Plasma Physics, Berlin (Germany), (P1.087
2. O. Février, P. Maget, H. Lütjens, J.F. Luciani, J. Decker, G. Giruzzi, M. Reich, P. Beyer, E. Lazzaro, S. Nowak, and Asdex-Upgrade Team. Modeling of magnetic island modications by ECCD using XTOR-2F. Frascatti (Italy), 2015. 7th IAEA Technical Meeting, Theory of Plasma Instabilities.
3. O. Février, P. Maget, H. Lütjens, J.F. Luciani, J. Decker, G. Giruzzi, M. Reich, P. Beyer, E. Lazzaro, S. Nowak, and Asdex-Upgrade Team. First principle Fluid modeling of magnetic island stabilization by ECCD. ITER, Vinon sur Verdon (France), 2015. 25th Meeting of the ITPA MHD TG.
4. O. Février, P. Maget, H. Lütjens, J.F. Luciani, J. Decker, G. Giruzzi, M. Reich, P. Beyer, E. Lazzaro, S. Nowak, and Asdex-Upgrade Team. Modeling of the impact of ECCD sweeping on NTM stability in ASDEX-Upgrade. volume 39, 2015. 42th EPS Conf. on Plasma Physics, Lisbon (Portugal), (P1.104)
5. P. Maget, O. Février, H. Lütjens, J.-F. Luciani, and Xavier Garbet. « Viscosity effect on tearing modes in toroidal geometry ». 16th European Fusion Theory Conference, Lisbon (Portugal), 2015.
6. H. Lütjens, J.-F. Luciani, « Effect of kinetic ions on internal kink modes with XTOR-K » 16th European Fusion Theory Conference, Lisbon (Portugal), 2015.

Magnetic islands degrade the confinement of fusion plasmas obtained in tokamaks, and could decrease the energy production of a future fusion reactor. This occurs in present day machines, and several means for avoiding or mitigating the growth of such islands have been successfully tested. The use of a localized current source has proved to be the most efficient tool for this purpose, and such a system is planned in the ITER project design. But the extrapolation of these control tools to future devices remains uncertain, because the fundamental understanding of the physics processes at play is not supported by an integrated first principle modelling of all the strongly interdependent mechanisms. The AMICI project is aimed at addressing this modelling issue, by integrating the control process from the sensors to the actuators, including the control of the primary modes that trigger the magnetic islands. The developments associated to this project will be implemented in XTOR, a non-linear code solving the two-fluid Magneto-Hydro-Dynamic (MHD) equations in the tokamak toroidal geometry that has been recently upgraded to include the important collisional (neoclassical) physics that drive the islands, and a Particle In Cell (PIC) module aiming at addressing the interaction of MHD with fast particles. These new ingredients are an essential starting point for the AMICI project because magnetic islands in ITER will be driven by neoclassical forces, and because the source of excitation for these neoclassical islands will be sensitive to the 3.5 MeV fusion born alpha-particle population.
The developments foreseen in the project include a realistic localized current source, a comprehensive neoclassical module, a source term for the regeneration of fast particles, and a controller acting on the current source. The Radio Frequency (RF) source will be adapted from the 1D results of a Fokker-Planck code to a 3D formulation that accounts from the fact that the current driven inside the 3D structure of an island remains confined in it. The heating and current drive sources depend on the RF power, the antenna localization and mirror orientation, in addition to the plasma profiles. The neoclassical module, consistent with the bi-fluid formulation of the XTOR code, will received an improved numerical implementation that will allow a better covering of non-circular plasma cross-sections, and will be completed with the parallel heat flow contribution. The PIC module will be completed with a source term that will rebuild the fast particle population after their redistribution by MHD activity, thus allowing the simulation of the periodic relaxation events that usually trigger neoclassical islands. Finally, a controller using synthetic magnetic and temperature fluctuations as sensors, and acting on the characteristics of the RF source, will be implemented in the MHD code. A comparison of the code simulations with experimental results, as well as predictions for future devices (mostly ITER, but also WEST at CEA Cadarache), will be realized. These developments will be performed by a team having a recognised expertise in MHD, RF and control issues.