Simulation of Effective data and Diagnostic Signals at the Boundary of Tokamak Plasmas – SEDIBA

The main aim of the project is to provide synthetic diagnostic modules for probes, fast cameras and Doppler back-scattering and reflectometry, and to implement them in the TOKAM3X turbulence code developed in the frame of the ESPOIR project. Once the quantities measured are clearly identified, they will be crosschecked and compared to the predictions of the TOKAM3X code. In addition to this, the production of synthetic input data (.i.e. properly averaged over turbulence) for transport codes will be adressed.

Six months in the project, work on the synthetic diagnostics modules has started, and the first results concerning the interpretation of fast camera data have been presented to the Plasma Surface Interactions conference (Aachen, Germany).
A first publication (letter) dealing with synthetic data for transport codes is in press.

The partners of the projet will work to strengthen their links, in particular by investing themselves in common experiments projects on Tore Supra as well as on other machines. The synthetic diagnostics modules will first be tested on the 2D code TOKAM2D, much less demanding than TOKAM3X. The coupling between the SOLEDGE2D transport code and the EIRENE Monte Carlo solver which deals with neutral species should yield the first results in time. All these steps are necessary in order for us to address the main physics issues related to the project.

Y. Marandet, P. Tamain et al. Influence of neutral particles on scrape-off layer turbulence with application to the interpretation of fast camera data(submitted).
A. Mekkaoui, Y. Marandet et al., A coarse-grained kinetic equation for neutral particles in turbulent fusion plasmas, Phys. Plasma 2012 (to appear)

One of the major challenges of ITER tokamak, currently being built in Cadarache (France), is related to edge turbulence, which plays an important role in plasma wall interactions. The latter control both the lifetime of wall components and the fusion performance to some extent. As a result, large efforts are put worldwide in the development of numerical simulations of edge turbulence. At the plasma edge, the standard approach remains the fluid one. A new generation of full torus 3D codes is under development in the frame of the ESPOIR ANR project, which will incorporate the physics of plasma wall interactions. On the experimental side, an aggressive effort has been undertaken to develop a set of diagnostics allowing to measure edge plasma fluctuations. These diagnostics include probes, ultra-fast CCD cameras and reflectometry/scattering diagnostics. However, at the time of writing, there is still a “missing link” between simulations and diagnostics. This situation result both from the complexity of the geometry of the edge plasma, and from the principles of the measurements, which are often indirect and/or perturbative. The most direct solution to close this gap is to rely on forward modelling, i.e. on the implementation of synthetic diagnostics in the simulations. This is an essential step in the process of validating turbulence codes against experimental data. The situation is similar as far as transport codes (such as the SOLPS code suite used for the design of ITER) are concerned, in the sense that input data (sputtering yields, radiative losses) should be considered as synthetic data accounting for the effects of turbulence.
The first aim of the project is to provide synthetic diagnostic modules for probes, fast cameras and Doppler back-scattering and reflectometry, and to implement them in the SOLEDGE3D turbulence code developed in the frame of the ESPOIR project. This will allow to clarify which physical quantity each of these diagnostics really measures, and to what extent the measurements perturb the plasma. This work entails diagnostic development and testing in laboratory experiments (in particular for the fast camera).
Once the quantities measured are clearly identified, they will be crosschecked and compared to the predictions of the SOLEDGE3D code. This will provide valuable data to address open issues, for instance to determine whether filaments propagating through the outer edge of the plasma are born inside or outside the separatrix (which is the limit between the confined plasma and the region where magnetic field lines are connected to the wall, the SOL). Whether asymmetries of the flows in the SOL are correctly reproduced by the code is a stringent test, and will improve our understanding of plasma rotation and momentum transport. Finally, determining the scaling of the e-folding length of the mean plasma parameters in the SOL as a function of different dimensionless numbers is essential to guaranty the integrity of plasma facing components.
The second aim of the project, closely related to the first one, deals with the calculation of effective, i.e. properly including the effects of turbulent fluctuations, data for transport codes such as the SOLPS (B2/EIRENE) code suite (such as particle sources, radiative losses). In fact, the equations solved by such transport codes can be seen as time averages of those describing turbulence. Currently, the effect of this averaging procedure on source and sink terms are not taken into account at all. The work done in this project will consist in properly calculating these averages using the TOKAM2D and SOLEDGE3D turbulence codes. This will provide guidelines for developing stochastic models for the calculations of these quantities. These models will be tested against VUV measurements in Tore Supra, and spectroscopic measurements in the laboratory.