Fast Ions and the Integrity of the ITER First Wall

Doc. Taina Kurki-Suonio

Aalto University

taina.kurki-suonio-miumau-hut.fi

The overall goal of the project is to ensure that the final design of the ITER first wall will be free of any known weaknesses as far as energetic particles and hydrocarbons containing tritium are concerned. This can be accomplished by providing the international fusion community with true-to-life quantitative predictions of fast ion power loads to the wall and by resolving the unknown mechanisms related to impurity migration at the tokamak edge. Realistic fast ion power loads can only by obtained by true 3D simulations that also include transport due to microturbulence and MHD activity. The subtleties of carbon transport will be addressed with new simulation tools that avoid the shortcomings of the fluid approach usually applied to this problem.

The primary research tool is ASCOT, a locally developed Monte Carlo guiding center orbit-following code that operates in five dimensions (2 velocity and 3 spatial coordinates) with experimental magnetic and plasma backgrounds. Today, ASCOT is the most complete code of its kind in Europe. It accurately accounts for all neoclassical physics and can now be operated with 3D wall structures and magnetic fields with practically any kind of aberrations. It has been used to predict ITER wall loads with realistic, non-periodic magnetic field and is currently used to simulate DIII-D experiments, carried out in November 2009, where local field perturbations were produced by external coils. Full orbit following can be adopted in situations where Larmor effects are suspected to play a significant role. ASCOT also has numerical models for various fast ion diagnostics, providing a straightforward way of validating simulations against experiments.

The detailed goals of the ASCOT Upgrade research programme are:

-  developing numerical models to account for fast ion transport due to turbulence and various MHD phenomena

-  predictive simulations of fusion alpha and NBI ion wall power loads for different ITER scenarios

-  international networking and researcher training: experiments at JET and AUG tokamaks, researchers partly trained at these laboratories, weekly video participation, modeling linked to ITM, ITPA and various EFDA activities, EFDA GOTiT programme for inter-European researcher training

-  raising the public awareness on energy issues and on fusion in particular

The code development efforts are expected to make the ASCOT Upgrade code the world’s most complete fast ion simulation tool that can also be used for evaluating 3D effects of impurity migration. The simulations can yield critical data in a timely manner so that clear weaknesses could still be remedied in the ITER wall design.