SOLPS5 modelling of ELMing H-mode on TCV

1. 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 * * * * *

2. Edge plasma - terminology Poloidal cross-section • Scrape-off layer (SOL) • Cool plasma on open field lines • SOL width ~1 cm ( B) • Length usually 10’s m (|| B) LFS HFS Core plasma • Divertor • Plasma guided along field lines to targets remote from core plasma: low T and high n Last closed flux surface Separatrix Private flux region Inner Outer • ITER will be a divertor tokamak Divertor targets

3. 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  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 => LFS HFS Dα W~200J Small ELMs on TCV – same phenomena ! => Used to study SOL transport

4. Scrape-Off Layer Plasma Simulation Suite of codes to simulate transport in edge plasma of tokamaks B2 - solves 2D multi-species fluid equations on a grid given from magnetic equilibrium EIRENE - kinetic transport code for neutrals based on Monte - Carlo algorithm SOLPS 5 – coupled EIRENE + B2.5 Mesh plasma background => recycling fluxes 72 grid cells poloidally along separatrix 24 cells radially B2 EIRENE Sources and sinks due to neutrals and molecules measured Main inputs: magnetic equilibrium Psol = Pheat – Pradcore upstream separatrix density ne Free parameters: cross-field transport coefficients (D┴, ┴, v┴) systematically adjusted

5. 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 # 26730 telm ~ 100 μs tpost ~ 1 ms tpre ~ 2 ms Pre-ELM phase = steady state ELM = particles and heat are thrown into SOL ( elevated cross-field transport coefficients) Post-ELM phase

6. Diagnostic profiles used to constrain the code upstream Edge Thomson scattering neand Te upstream profiles downstream Langmuirprobes jsattarget profiles laser beam RCP – reciprocating probe jsat [A.m-2] outer target pedestal ne R-Rsep [m] jsat R-Rsep [m] Strategy: Match these experimental profiles with data from SOLPS simulation runs by changing cross-field transport parameters D┴,Χ┴, v┴ inner target pedestal Te R-Rsep [m] R-Rsep [m]

7. Theory – steady state simulationCross-field transport coefficients Cross-field radial transportin the main SOL - complex phenomena main SOL SOL radial heat flux: SOL radial particle flux: x x div.legs D┴ Ansatz:( D┴, ┴, v┴) - variation SOL sep radially – transport barrier (TB) poloidally – no TB in div.legs Inner div.leg div.legs ┴ main SOL SOL diffusion (D┴) + convection (v┴) sep outer div.leg Pure diffusion: v┴=0 everywhere More appropriate: Convection simulations with D┴= D┴class in progress v┴ SOL div.legs sep

8. Comparison of experimental data with simulationPurely diffusive approach upstream SOLPS TS targets ne RCP Code overestimates data 1.step: Only radial variation of D┴, ┴ pedestal wall outer => Jsat [A.m-2] SOLPS D┴ Poloidal variation necessary => R-Rsep LPs Remove transport barrier from divertor legs SOLPS TS R-Rsep [m] RCP Te jsat inner SOLPS => Χ┴ D┴,Χ┴= constant in div. legs R-Rsep LPs Excellent agreement !!! => R-Rsep

9. Removing transport barrier from divertor legs D =  = const. - same value in both divertor legs ! Transport barrier 0.5 1 2 3 5 6 Transport barrier 0.5 1 2 3 5 6 Inner target inner target jsat [A.m-2] outer target jsat [A.m-2] LP LP LP R-Rsep [mm] R-Rsep [mm] Outer target – better agreement obtained! It appears that a description of cross-field transport in divertor as radially constant is more appropriate 6 m2.s-1 in div.legs 1m2.s-1 in SOL ! NO DRIFTS !

10. 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 – (Btot/Bloc)α => poloidal variation * * Inner div.leg SOL => Sensitivity study for the steady state simulations sep PFR outer div.leg Very small effect No ballooning No ballooning α =0.5 α =0.5 Inner target α =1 α =1 inner target outer target LP LP R-Rsep [mm] R-Rsep

11. 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…

12. Conclusions 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) * * * * *