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

Our goal: quantify turbulence in divertor performance

Turbulent transport impacts:

• Poloidal asymmetries
• Heat deposition on divertor targets
• Confinement properties

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

Cross-field transport Turbulence in the divertor: still little explored domain TOKAM3X in divertor configuration 2D transport codes experiments Ballistic, filaments Diffusive

Different geometries in TOKAM3X

COMPASS - like JET - like LIMITER

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PhD C. Colin 29th September 2015 | IAEA Headquarters 1st IAEA Technical Meeting on Divertor Concepts

Similar turbulence properties far from the X-point

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LIMITER geometry JET-like geometry

(P.Tamain CPP 2014)

PDF at LFS midplane

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

Ballooning at the LFS midplane Strong fluctuations in PFR

Mean-field and turbulent transport

Xp HFS LFS midplane HFS midplane Top Xp LFS

In our simulations, mean-field and turbulent fluxes have comparable order

• f magnitude

Mean-field flux, already introduced in 2D transport codes[1,2] Turbulent flux

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

Beyond linear analysis where Mean fields = const.

Gradients around X-point drive complex patterns of fluxes

Divertor acts as a big plasma sink Big density gradients in the poloidal direction Complex ExB flux pattern around X-point

Xp HFS LFS midplane HFS midplane Top Xp LFS

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

PFR SOL SOL EDGE

The global effect of cross-field transport

TOKAM3X results (N. Asakura JNM 2007)

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Xp HFS Xp LFS Top HFS midplane LFS midplane Xp HFS Xp LFS Top HFS midplane LFS midplane

JET-like COMPASS-like

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

Different instabilities can rise in Private Flux Region

(C. Baudoin PET 2015) TOKAM2D nonlinear simulations The Sheath Negative Resistance[4] instability has higher growth rate than the interchange

[4] H. Berk, D. Ryutov, and Y. A. Tsidulko, Physics of Fluids B: Plasma Physics (1989-1993) 3(6), 1346–1354 (1991). [3] C. Baudoin, P. Tamain, G. Ciraolo et al. , Proceedings of the 15th International Workshop on Plasma Edge Theory in Fusion Devices.

Interchange SNR Kelvin-Helmoltz

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

Objective: include these instabilities in a 2D transport code also for negative curvature

An alternative way to describe turbulence in plasma edge

Courtesy SimScale

[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

Interchange produces turbulence Description still based on empirical coefficients

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

(more details in the talk of G. Ciraolo, tomorrow)

TOKAM3X turbulence 1st principle A physical guideline for 2D codes

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Courtesy H. Bufferand

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

Detailed description of instabilities: interchange, SNR, Kelvin-Helmoltz Interchange and drift waves Mean field flows together with turbulent transport Effects related to the 3D geometry

TOKAM2D TOKAM3X

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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.

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

TOKAM3X model: multi-fluid with drifts

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Now in isothermal version

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

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

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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

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

COMPASS – like geometry JET – like geometry

Flux expansion plays a major role

Same pattern is found on poloidal distribution of density decay length Poloidal asimmetries in density decay length

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

Work in progress: comparison with Eich’s expression

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

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