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Particle sources and radiation distributions in the TCV tokamak edge

Particle sources and radiation distributions in the TCV tokamak edge. Thesis committee. Candidate : Barbora Gulejov á Supervisor of thesis : Dr. Richard Pitts Acknowledgements : Xavier Bonnin, Marco Wischmeier, David Coster, Roland Behn , Jan Hor áč ek, Janos Marki. OUTLINE.

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Particle sources and radiation distributions in the TCV tokamak edge

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  1. Particle sources and radiation distributions in the TCV tokamak edge Thesis committee Candidate: Barbora Gulejová Supervisor of thesis: Dr. Richard Pitts Acknowledgements: Xavier Bonnin, Marco Wischmeier, David Coster, Roland Behn,Jan Horáček, Janos Marki

  2. OUTLINE Research plan – change of direction … SOLPS 5 code package (B2 - EIRENE) Theoretical model of simulation Comparison of experimental data with simulation Simulation of ELM itself Drifts implementation Future plans * * * * * * *

  3. RESEARCH PLAN Considering title change to SOLPS5 modelling of ELMing H-mode AIM:contribute to understanding transport in the SOL * using new unique experimental data from TCV (AXUV, IR) * interpretative modelling employing the SOLPS5 fluid/Monte Carlo code *transient events => ELMs * rigorous benchmarking = seeking the possible agreement between the experiment and simulation Twin camera system • Bolometry - total radiated power  • Lyman alpha – edge radiation  => investigation during summer shutdown => * scratches = source of light seen * low peak transmission of the L absorption filters (10%) * strong angular dependence of the emission (only 1% at incident angle 60) * strong ageing effect due to exposure to boronisation, He glow discharge and plasma operation observed on the unfiltered bolometric diodes NEXT STEP: D alpha - higher transmission

  4. Ageing effect with filter removed “New LYMAN” without filter “old AXUV” G.Veres Huge increase in signal when filters removed – layer deposition + ageing

  5. 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

  6. Type III 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

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

  8. 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 diffusion (D┴) + convection (v┴) SOL * Pure diffusion: v┴=0 everywhere sep outer div.leg v┴ 2 approaches SOL More appropriate: Convection simulations with D┴= D┴class * div.legs sep

  9. Comparison of experimental data with simulation1. Purely “diffusive” approach separatrix upstream neSOLPS TS RCP D┴doesn’t require too much variation through confined region In the main SOL- increase : D┴= 1 m2.s-1 Χ┴ = 6 m2.s-1 in order to flatten Te profile pedestal core wall TeSOLPS TS RCP D┴ Χ┴ 6 1 Good agreement !!! R-Rsep Accepted to JNM 2007

  10. Comparison of experimental data with simulation1. Purely “diffusive” approach targets With only radial variation of D┴, ┴ code overestimates data Poloidal variation necessary Remove transport barrier from divertor legs Description of cross-field transport in divertor as radially constant is more appropriate inner outer Jsat [A.m-2] LP, average SOLPS D┴= 3 m2.s-1 in div.legs 1m2.s-1 in SOL Χ┴= 5 m2.s-1 in div.legs 6 m2.s-1 in SOL NO DRIFTS yet! => D┴,Χ┴= constant in div. legs Te [eV] Perp.heat flux[MW.m-2] LP, average SOLPS inner ne [m-3] outer IR Accepted to JNM 2007

  11. Comparison of experimental data with simulation2.“Convective” approach upstream targets outer inner separatrix Density ne in SOL is too high ! Reason: Competition between radial & parallel fluxes v┴ acts towards radial direction Parallel flux is smaller than in “conductive approach” combination of all 3 parameters D┴, ┴, v┴ ??? Jsat [A.m-2] LP SOLPS neSOLPS TS RCP pedestal Te [eV] wall TeSOLPS TS RCP ne [m-3] => D┴ Χ┴ 6 Perp.heat flux[MW.m-2] LP SOLPS inner => 0.1 30 v┴ outer IR 2 Reasonable agreement R-Rsep

  12. Type III ELM simulation 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 TCV Type III ELM Dα HFS Simulation of ELM * Instantaneous increase of the cross-field transport parameters D┴, ┴, v┴! LFS W~200J 1.) for ELM time – from experiment coh.averaged ELM = tELM = 10-4s 2.) at poloidal location -> expelled from area AELM at LFS From the cross-field radial transport can be estimated the combination of trasnport parameters corresponding to the given expelled energy WELM, tELM and AELM Time AELM= 6m2 W = 400 J D┴ Many different appraches possible => changes in D┴,  ┴only or in v┴too … ┴

  13. Tools to simulate ELM in SOLPS Several options in SOLPS transport inputfiles : *Multiplying of the transport coefficients in the specified poloidal region * In 3 different radial regions (core, pedestal, SOL) by different multipliers Added new options: *Poloidal variation of the multiplicator * Step function * Gaussian function * Choosing completely different shape of radial profile for chosen poloidal region main SOL ELM Inner div.leg main SOL No TB ELM x M preelm outer div.leg core pedestal wall

  14. ELM simulations (example) upstream Increase of D┴, ┴5 times in poloidal region of the whole LFS! Time evolution of D┴ and ne D┴ ne time time R-Rsep R-Rsep tELM=100 µs TS measurements (R.Behn) => *Drop in pedestal width and height appears only for ne SOLPS*bigger pedestal collaps * higher ne and Te in SOL But the right tendency – pedestal collapse Problem:Time-dependent pre-ELM solutionnecessary !!! as a starting state for time-dependent ELM simulation (X.Bonnin+D.Coster) Time steps of B2 and Eirene parts of the code must be the same = 10-6 s (not the case for steady state: eir_step=10-1s) => must be done in the steps by decreasing the time steps gruadually and seeking for convergence => difficult and time-consuming process – in progress R-Rsep

  15. ErxB, pxB EqxB Ballooning Pfirsch-Schlüter Bj Divertor sink BxB REV Bj SOLPS5 simulations with DRIFTS SOL flows DRIFTS – contribute to in/out assymetries TCV : unconventional equilibrium with an extremely short X point to inner strike points position -> might dominate over drifts and divertor physics effects R. Pitts • Poloidal SOLPS:X.Bonnin • implememtation of drift terms * Anomalous contribution (ExB) * Diamagnetic contribution (pxB) * Viscous contribution • Parallel Switching on drifts it’s likely • to decrease the predicted Te at outer target • may have only small effect at the inner target

  16. First attempt of SOLPS simulation with DRIFTS targets upstream inner outer separatrix Jsat [A.m-2] LP SOLPS neSOLPS TS RCP Not yet completely converged solution… Te [eV] pedestal wall TeSOLPS TS RCP ne [m-3] R-Rsep Perp.heat flux[MW.m-2] LP SOLPS inner D┴ Χ┴ 6 outer 1 IR R-Rsep R-Rsep R-Rsep

  17. First attempt of SOLPS simulation with DRIFTS NO DRIFTS DRIFTS inner outer inner outer NO DRIFTS: Overestimation of outer target Te DRIFTS: Decrease of outer target Te as expected Same effect on jsat and heat flux! Inner target : not significant effect as expected Jsat [A.m-2] LP SOLPS Jsat [A.m-2] LP SOLPS Te [eV] Te [eV] ne [m-3] ne [m-3] R-Rsep Perp.heat flux[MW.m-2] LP SOLPS R-Rsep inner Perp.heat flux[MW.m-2] LP SOLPS inner outer outer IR IR Good early promise !!! R-Rsep R-Rsep

  18. After obtaining the trully time-dependent pre-ELM solution! continue in the attepmts to simulate the small TCV ELM properly -use several different approaches Planed visit to JET in february –march 2007 : simulate the big JET ELM Continue in the simulation with DRIFTs included in SOLPS Future plans * * *

  19. Thank you for attention !

  20. 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) * * * * *

  21. 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

  22. Comparison of neoclassical values with SOLPS D┴, ┴

  23. ELM simulations (example) Time evolution at targets targets inner outer inner outer Perp.heat flux[MW.m-2] Jsat [A.m-2] Jsat [A.m-2] inner ne [m-3] => Te [eV] outer Te [eV] ne [m-3] Ti [eV] PSOL~ 100 J Time of arrival of particles to targets much shorter than expected … Jsat at inner target ~ 20 <-> Exp. ~ 40 outer target ~ 10 <-> Exp. ~ 35 SOLPS lower than experiment not enough energy expelled (~200 J from exp.)! Problem: Time-dependent pre-ELM solution to start the ELM necessary!! Difficult process : Time steps of B2 and Eirene parts of the code must be the same = 10-6 s - must be done in the steps by decreasing the time steps gruadually and seeking for convergence => difficult and time-consuming process – in progress

  24. Parallel Mach Flows

  25. preELM time-dependent solution necessary !!!

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