Mean-field and turbulent transport in divertor geometry Davide - PowerPoint PPT Presentation

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

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts Our goal: quantify turbulence in divertor performance Cross-field transport Turbulent transport impacts: 2D transport codes Diffusive • Poloidal asymmetries • experiments Ballistic, filaments Heat deposition on divertor targets • Confinement properties Turbulence in the divertor: still little explored domain TOKAM3X in divertor configuration 2

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts Different geometries in TOKAM3X PhD C. Colin COMPASS - like JET - like LIMITER 3

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts 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

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts Mean-field and turbulent transport In our simulations, mean-field and turbulent fluxes have comparable order of magnitude Mean-field flux, Turbulent flux already introduced in 2D Beyond linear analysis where transport codes [1,2] Mean fields = const. Xp LFS Top Xp LFS midplane HFS 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

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts Gradients around X-point drive complex patterns of fluxes Divertor acts as a big plasma sink Xp Xp HFS LFS Big density gradients in the poloidal direction Top HFS LFS midplane midplane Complex ExB flux pattern around X-point EDGE SOL SOL PFR 6

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts The global effect of cross-field transport TOKAM3X results JET-like Xp LFS Xp HFS HFS LFS midplane midplane Top COMPASS-like Xp LFS Xp HFS HFS LFS midplane midplane Top (N. Asakura JNM 2007) 7

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts 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

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts 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

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts A physical guideline for 2D codes Detailed description of instabilities: TOKAM2D 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 Courtesy H. principle Bufferand 10

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts 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

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts TOKAM3X model: multi-fluid with drifts Now in isothermal version 12

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts TOKAM3X geometry with X-point Flux surface aligned mesh • Realistic geometry, with coordinates aligned to flux surfaces • EDGE + SOL • Now in isothermal version JET-like geometry 13

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts Simulation parameters Physics Geometry 14

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts Mean fields in a JET-like geometry 15

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts 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

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts Work in progress: comparison with Eich’s expression 17

29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts 18