Barbora Gulejová 1 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 SOLPS5 modelling of ELMing H-mode on TCV Barbora Gulejová, Richard Pitts, Marco Wischmeier, Roland Behn, Jan Horáček OUTLINE * * * * * * Edge plasma – SOL - terminology Why is understanding of ELM important? SOLPS 5 code package (B2 - EIRENE) Theoretical model of simulation Comparison of experimental data with simulation Strategy for next step: simulation of ELM itself

Barbora Gulejová 2 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 Edge plasma - terminology Core plasma Divertor targets Private flux region Separatrix Scrape-off layer (SOL) –Cool plasma on open field lines –SOL width ~1 cm (  B) –Length usually 10’s m (|| B) Poloidal cross-section Outer ITER will be a divertor tokamak Divertor –Plasma guided along field lines to targets remote from core plasma: low T and high n Inner Last closed flux surface LFS HFS

Barbora Gulejová 3 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 Edge localised mode (ELM) H-mode  Edge MHD instabilities  Periodic bursts of particles and energy into the SOL - leaves edge pedestal region in the form of a helical filamentary structure localised in the outboard midplane region of the poloidal cross-section LFS HFS  divertor targets and main walls erosion  first wall power deposition ELMing H-mode=baseline ITER scenario Energy stored in ELMs: TCV  200 J JET  200kJ ITER  8-14 MJ => unacceptable => W~200J DαDα Small ELMs on TCV – same phenomena ! => Used to study SOL transport

Barbora Gulejová 4 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 Scrape-Off Layer Plasma Simulation Suite of codes to simulate transport in edge plasma of tokamaks B2 B2 - solves 2D multi-species fluid equations on a grid given from magnetic equilibrium EIRENE EIRENE - kinetic transport code for neutrals based on Monte - Carlo algorithm SOLPS 5 SOLPS 5 – coupled EIRENE + B2.5 Main inputs: magnetic equilibrium P sol = P heat – P rad core upstream separatrix density n e Free parameters: cross-field transport coefficients (D ┴,  ┴, v ┴ ) B2 plasma background => recycling fluxes EIRENE Sources and sinks due to neutrals and molecules measured systematically adjusted Mesh 72 grid cells poloidally along separatrix 24 cells radially

Barbora Gulejová 5 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 Elming H-mode at TCV # ELMs - too rapid (frequency ~ 200 Hz) for comparison on an individual ELM basis => Many similar events are coherently averaged inside the interval with reasonably periodic elms Pre-ELM phase = steady state ELM = particles and heat are thrown into SOL ( elevated cross-field transport coefficients) Post-ELM phase t pre ~ 2 ms t elm ~ 100 μs t post ~ 1 ms

Barbora Gulejová 6 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 upstream Edge Thomson scattering n e and T e upstream profiles Diagnostic profiles used to constrain the code laser beam Strategy: Match these experimental profiles with data from SOLPS simulation runs by changing cross-field transport parameters D ┴,Χ ┴, v ┴ downstream Langmuir probes j sat target profiles j sat [A.m -2 ] R-R sep [m] outer target j sat R-R sep [m] inner target RCP – reciprocating probe nene pedestal TeTe R-R sep [m] pedestal R-R sep [m]

Barbora Gulejová 7 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 Theory – steady state simulation Cross-field transport coefficients Cross-field radial transport in the main SOL - complex phenomena Ansatz:( D ┴,  ┴, v ┴ ) - variation radially – transport barrier (TB) poloidally – no TB in div.legs outer div.leg  ┴ ┴ SOL div.legs sep D┴D┴ SOL div.legs sep v┴v┴ SOL div.legs sep main SOL diffusion (D ┴ ) + convection (v ┴ ) heat flux SOL radial heat flux: particle flux SOL radial particle flux: main SOL Inner div.leg x x Pure diffusion: v ┴ =0 everywhere More appropriate: Convection simulations with D ┴ = D ┴ class in progress

Barbora Gulejová 8 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 Comparison of experimental data with simulation Purely diffusive approach 1.step: Only radial variation of D ┴,  ┴ upstream targets Excellent agreement !!! Code overestimates data => Poloidal variation necessary => Remove transport barrier from divertor legs => outer J sat [A.m -2 ] LPs SOLPS R-R sep [m] inner j sat R-R sep LPs SOLPS D ┴,Χ ┴ = constant in div. legs nene D┴D┴ TS RCP SOLPS pedestal wall TeTe Χ┴Χ┴ TS RCP SOLPS R-R sep

Barbora Gulejová 9 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 Removing transport barrier from divertor legs It appears that a description of cross-field transport in divertor as radially constant is more appropriate D =  = const. - same value in both divertor legs ! Outer target – better agreement obtained! LP Inner target R-R sep [mm] LP j sat [A.m -2 ] R-R sep [mm] j sat [A.m -2 ] Transport barrier Transport barrier outer target inner target LP 6 m 2.s -1 in div.legs 1m 2.s -1 in SOL ! NO DRIFTS !

Barbora Gulejová 10 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 Other issues to consider 1.) Inner and outer divertor leg assymetry – inner is much shorter 2.) Private flux region (PFR) rescaling in div.legs – different processes in PFR region and SOL region of divertor legs 3.) Ballooning – (B tot /B loc ) α => poloidal variation Inner div.leg outer div.leg sep PFR SOL * * * Sensitivity study for the steady state simulations => Very small effect LP α =0.5 α =1 outer target R-R sep [mm] No ballooning LP Inner target R-R sep α =0.5 α =1 inner target No ballooning

Barbora Gulejová 11 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 Next step : ELM Instantaneous increase of the cross-field transport parameters! Strong poloidal variation - localized on outboard midplane of TCV Requires time-dependent iteration in code - much bigger problem ! Simulations in progress…

Barbora Gulejová 12 of 12 Centre de Recherches en Physique des Plasmas SPS Annual Meeting in Lausanne, 14/2/2006 * * * * * First attempt to simulate Scrape-Off layer in H-mode on TCV with aim to simulate Type III ELMs Simulations conducted using coupled fluid-Monte Carlo (B2-EIRENE) SOLPS5 code constrained by upstream profiles of ne and Te and at the targets profiles of jsat Using exp. data as a guide to systematic adjustments of perpendicular particle and heat transport coefficients Code experiment agreement ONLY possible if transport coefficients are varied radially AND polloidally Excellent match obtained for inter-ELM phase  good basis for simulation of ELM itself (in progress) Conclusions