Mean-field and turbulent transport in divertor geometry Davide Galassi In collaboration with: Ph. Ghendrih, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, C. Colin and E. Serre
Our goal: quantify turbulence in divertor performance Cross-field transport 2D transport codes experiments Turbulent transport impacts: Diffusive Ballistic, filaments Poloidal asymmetries Heat deposition on divertor targets Confinement properties Turbulence in the divertor: still little explored domain TOKAM3X in divertor configuration 2
Different geometries in TOKAM3X PhD C. Colin LIMITER JET - like 3 COMPASS - like
Similar turbulence properties far from the X-point Ballooning at the LFS midplane Strong fluctuations in PFR (P.Tamain CPP 2014) PDF at LFS midplane LIMITER geometry JET-like geometry 4
Mean-field and turbulent transport In our simulations, mean-field and turbulent fluxes have comparable order Mean-field flux, already introduced in 2D transport codes[1,2] of magnitude Turbulent flux Beyond linear analysis where Mean fields = const. Xp HFS Top HFS midplane [1] T.D. Rognlien, G.D. Porter, D.D. Ryutov, J. Nucl. Mater. 266 269 (1999) 654 [2] A.V. Chankin, D.P. Coster, J. Nucl. Mater. 438 (2013) S463 5 LFS midplane Xp LFS
Gradients around X-point drive complex patterns of fluxes Divertor acts as a big plasma sink Xp HFS Xp LFS Big density gradients in the poloidal direction Top HFS midplane LFS midplane Complex ExB flux pattern around X-point EDGE SOL SOL PFR 6
The global effect of cross-field transport TOKAM3X results Xp HFS HFS midplane Top LFS midplane (N. Asakura JNM 2007) 7 HFS midplane Top LFS midplane COMPASS-like Xp LFS Xp HFS JET-like Xp LFS
Different instabilities can rise in Private Flux Region The Sheath Negative Resistance[4] instability has higher growth rate than the interchange TOKAM2D nonlinear simulations (C. Baudoin PET 2015) Interchange SNR also for negative curvature Kelvin-Helmoltz Objective: include these instabilities in a 2D transport code [3] C. Baudoin, P. Tamain, G. Ciraolo et al., Proceedings of the 15th International Workshop on Plasma Edge Theory in Fusion Devices. [4] H. Berk, D. Ryutov, and Y. A. Tsidulko, Physics of Fluids B: Plasma Physics (1989-1993) 3(6), 1346 1354 (1991). 8
An alternative way to describe turbulence in plasma edge (more details in the talk of G. Ciraolo, tomorrow) Courtesy SimScale Interchange produces turbulence Description still based on empirical coefficients [5] H. Bufferand, G. Ciraolo, Ph. Ghendrih et al., Proceedings of the 15th International Workshop on Plasma Edge Theory in Fusion Devices. [6] B. Launder, D. Spalding, Computer Methods in Applied Mechanics and Engineering, Vol 3, 1974 9
A physical guideline for 2D codes TOKAM2D Detailed description of instabilities: interchange, SNR, Kelvin-Helmoltz Interchange and drift waves TOKAM3X Mean field flows together with turbulent transport Effects related to the 3D geometry TOKAM3X turbulence 1st principle Courtesy H. Bufferand 10
CONCLUSIONS Ø First TOKAM3X simulations in divertor configuration show that: there is an analogy with limiter cases in turbulence properties mean-field and turbulent fluxes coexist with similar order of magnitude. Complex drift flux patterns are found around the X-point in different geometries, flows in parallel direction are in qualitative agreement with experiments. Ø Anisothermal, 2-D models give an insight on a wider range of physical phenomena: they show the importance of turbulence in the whole divertor volume. Ø The 2D and 3D turbulent codes can give important physical guidelines to 2D transport codes about different instability mechanisms, with the objective of getting a predictive modelling. 11
TOKAM3X model: multi-fluid with drifts Now in isothermal version 12
TOKAM3X geometry with X-point Flux surface aligned mesh JET-like geometry Realistic geometry, with coordinates aligned to flux surfaces EDGE + SOL Now in isothermal version
Simulation parameters Physics Geometry
Mean fields in a JET-like geometry 15
Flux expansion plays a major role JET like geometry COMPASS like geometry Poloidal asimmetries in density decay length Same pattern is found on poloidal distribution of density decay length 16
Work in progress: comparison with Eich s expression 17
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