FullFull-tungsten plasma edge simulations with SOLPS * Xavier Bonnin a, David Coster a LIMHP, b Max-Planck-Institut

b

Université Paris XIII, CNRS, Institut Galilée, F-93430 Villetaneuse, France für Plasmaphysik, EURATOM Association, D-85748 Garching-bei-München, Germany

* Work supported in part by contract ANR-09-BLAN-0070-01 and performed under FR-FCM and EU PWI TF action WP09-PWI-04-02

Motivation and Summary • Modern tokamaks have been increasing the use of tungsten as a • The various strategies currently pursued with the SOLPS suite of plasma edge simulation codes to include tungsten in the calculations are: plasma-facing material: 0 +74 • A complete fluid treatment including all 75 charge states from W to W • A bundled charge state model (which leaves freedom to the user as to how to bundle together the ions, thus reducing significantly the number of species considered) • A coupled fluid plasma – kinetic tungsten treatment (SOLPS-IMPGYRO coupling, see M. Toma et al., this conference, poster P2-29)
Only this last solution can include prompt redeposition of W+ during its first Larmor gyration and other FLR effects across the H-mode pedestal, for example
But breaks implicit quasi-neutrality and introduces instead electron particle sources

• ASDEX-Upgrade, JET ITER-like wall project, ITER itself, DEMO • Need a good way to introduce tungsten in plasma edge models • Mixed materials issues must also be considered • Co-deposition and formation of mixed layers, alloying, change of surface properties following layer composition, etc…

Which tungsten bundles ?

Bundling ‘xb_03’ tries to join together ionization stages with similar behavior  Bundle ‘All’ corresponds to the full fluid treatment  Initial set of bundles was built with JET core transport applications in mind  Need not be the same as best representation of W ions relevant to the edge  Bundle ‘xb’ is a truncated full treatment up to W+20 (i.e. we include separately all ions with significant edge plasma densities as deduced from the ‘All’ runs, the rest are all bundled together)  Bundle ‘xb_03’ is a “bundle of bundles”: we make a ‘natural’ bundling of the low-lying ionization stages, starting from the truncated ‘xb’ bundle, being as aggressive as possible

Comparison of various W bundles : particle and energy balance, erosion/deposition erosion/deposition Wall erosion/deposition rates

AUG comparison B2.5 run parameters and wall model #16151, L-mode, PSOL = 1.6 MW, ncoreD+ = 2.0 × 1019 m-3, with 1% He, trace Be and 1.5% C content, and self-consistent production of W from sputtering • • • •

Best match: ‘jett’

Wall is located directly at edge of mesh Each boundary cell is a separate wall element Each boundary is a separate wall segment Each wall element can have its own: • Material properties (Cp, k, e, Z, …) • Thickness (L) • Coolant temperature or inertial vessel temperature (TL) • Coating with separate properties • A surface layer containing mixed materials inventory

• In general, the different bundlings agree relatively well with each other (within 5 to 20%).

AUG computational grid and wall geometry

Walls are assumed to be: • inertially cooled CFC bulk (starting temperature 300K) • 3 µm thick W coating on main chamber walls and inner divertor • 200 µm thick W coating on outer divertor Best match: ‘s’

• We notice that runs with very aggressive bundling of W ions tend to showcase plasma oscillations (currently still unexplained). In the case of the ‘edg’ bundling, these oscillations yield much lower erosion/deposition rates. But the difference between ‘edg’ and ‘jett’ lies in the W+10 to W+20 range, which points to the importance of this intermediate range of ion charges.

Conclusions

Energy balance Radiative

losses are underestimated by the bundles Power flux to the inner divertor can vary up to 50%, and to the outer divertor by a factor 2 Power flux to the walls almost identical across bundling schemes Private flux region walls (PFW) Main chamber wall (MCW) Outer divertor (OD) Inner divertor (ID)

LIMHP-CNRS-UPR 1311 Institut Galilée Université Paris 13, 99 avenue J. B.Clément – F-93430 Villetaneuse, France Fax : +33-(0)1.49.40.34.14


Several different bundling schemes (tungsten superstages) have been tested for an L-mode AUG benchmark case
From full fluid treatment including all species to very aggressive bundling with only a few low-lying ionization stages
Some macroscopic quantities such as wall erosion/deposition rates remain well described in most cases
But details of power balance can show wide variations
Not all bundling schemes show stable plasma behavior
Some W features due to FLR effects (esp. prompt redeposition) can only be included with a kinetic ion treatment (see paper P2-29) Corresponding author :

Xavier BONNIN – [email protected] +33-(0)1.49.40.34.24 http://www.limhp.fr

19th International Conference on Plasma Surface Interactions, San Diego, California – May 24-28, 2010 – Poster P3-5