Barbora Gulejová 1 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 Particle sources and radiation distributions in the TCV tokamak edge Candidate: Barbora Gulejová Supervisor of thesis: Dr. Richard Pitts Acknowledgements: Xavier Bonnin, Marco Wischmeier, David Coster, Roland Behn, Jan Horáček, Janos Marki Thesis committee

Barbora Gulejová 2 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 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 * * * * * * *

Barbora Gulejová 3 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 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

Barbora Gulejová 4 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 Ageing effect with filter removed “New LYMAN” without filter “old AXUV” Huge increase in signal when filters removed – layer deposition + ageing G.Veres

Barbora Gulejová 5 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 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 6 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 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 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 7 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 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] I R outer target Heat flux [MW.m -2 ] IR cameras Perpendicular heat flux R-R sep [m] R.Behn J.Marki J.Horacek

Barbora Gulejová 8 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 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 2 approaches

Barbora Gulejová 9 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 Comparison of experimental data with simulation 1. Purely “diffusive” approach upstream n e SOLPS TS RCP pedestal wall 1 6 R-R sep separatrix T e SOLPS TS RCP Good agreement !!! core D┴Χ┴D┴Χ┴ D ┴ doesn’t require too much variation through confined region In the main SOL- increase : D ┴ = 1 m 2.s -1 Χ ┴ = 6 m 2.s -1 in order to flatten T e profile Accepted to JNM 2007

Barbora Gulejová 10 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 targets J sat [A.m -2 ] LP, average SOLPS outerinner T e [eV] n e [m -3 ] Perp.heat flux [MW.m -2 ] LP, average SOLPS outer inner IR Comparison of experimental data with simulation 1. Purely “diffusive” approach With only radial variation of D ┴,  ┴ code overestimates data Poloidal variation necessary Remove transport barrier from divertor legs D ┴,Χ ┴ = constant in div. legs Description of cross-field transport in divertor as radially constant is more appropriate D ┴ = 3 m 2.s -1 in div.legs 1m 2.s -1 in SOL Χ ┴ = 5 m 2.s -1 in div.legs 6 m 2.s -1 in SOL NO DRIFTS yet! => Accepted to JNM 2007

Barbora Gulejová 11 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 Comparison of experimental data with simulation 2. “Convective” approach upstream targets outer inner D┴Χ┴D┴Χ┴ n e SOLPS TS RCP pedestal wall R-R sep separatrix T e SOLPS TS RCP 30 2 v┴v┴ J sat [A.m -2 ] LP SOLPS T e [eV] n e [m -3 ] Perp.heat flux [MW.m -2 ] LP SOLPS outer inner IR Density n e 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 ┴ ??? Reasonable agreement =>

Barbora Gulejová 12 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 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 LFS HFS W~200J DαDα Simulation of ELM * Instantaneous increase of the cross-field transport parameters D ┴,  ┴, v ┴ ! TCV Type III ELM Time 1.) for ELM time – from experiment coh.averaged ELM = t ELM = s 2.) at poloidal location -> expelled from area A ELM at LFS From the cross-field radial transport can be estimated the combination of trasnport parameters corresponding to the given expelled energy W ELM, t ELM and A ELM A ELM = 6m 2 W = 400 J D┴D┴  ┴ ┴ Many different appraches possible => changes in D ┴,  ┴ only or in v ┴ too …

Barbora Gulejová 13 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 Tools to simulate ELM in SOLPS outer div.leg main SOL Inner div.leg 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 pedestalwallcore No TB preelm ELMELM x M ELM

Barbora Gulejová 14 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 ELM simulations (example) upstream Increase of D ┴,  ┴ 5 times in poloidal region of the whole LFS! TS measurements (R.Behn) => * Drop in pedestal width and height appears only for n e SOLPS * bigger pedestal collaps * higher n e and T e in SOL But the right tendency – pedestal collapse D┴D┴ nene Problem: Time-dependent pre-ELM solution necessary !!! 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 = s (not the case for steady state: eir_step=10 -1 s) => must be done in the steps by decreasing the time steps gruadually and seeking for convergence => difficult and time-consuming process – in progress R-R sep time Time evolution of D ┴ and n e t ELM =100 µs

Barbora Gulejová 15 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 SOLPS5 simulations with DRIFTS E r xB,  pxB Ballooning Pfirsch- Schlüter Divertor sink ExBExB Poloidal Parallel BB Bx  B REV B  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 Switching on drifts it’s likely to decrease the predicted T e at outer target may have only small effect at the inner target SOLPS: X.Bonnin -implememtation of drift terms * Anomalous contribution (ExB) * Diamagnetic contribution (  pxB) * Viscous contribution R. Pitts

Barbora Gulejová 16 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 First attempt of SOLPS simulation with DRIFTS upstream R-R sep D┴Χ┴D┴Χ┴ n e SOLPS TS RCP pedestal wall 1 R-R sep separatrix T e SOLPS TS RCP 6 targets outer inner J sat [A.m -2 ] LP SOLPS T e [eV] n e [m -3 ] Perp.heat flux [MW.m -2 ] LP SOLPS outer inner IR R-R sep Not yet completely converged solution…

Barbora Gulejová 17 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 First attempt of SOLPS simulation with DRIFTS outer inner J sat [A.m -2 ] LP SOLPS T e [eV] n e [m -3 ] Perp.heat flux [MW.m -2 ] LP SOLPS outer inner IR R-R sep outer inner J sat [A.m -2 ] LP SOLPS T e [eV] n e [m -3 ] Perp.heat flux [MW.m -2 ] LP SOLPS outer inner IR R-R sep NO DRIFTS DRIFTS NO DRIFTS: Overestimation of outer target T e DRIFTS: Decrease of outer target T e as expected Same effect on j sat and heat flux! Inner target : not significant effect as expected Good early promise !!!

Barbora Gulejová 18 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 Future plans 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 * * *

Barbora Gulejová 19 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 Thank you for attention !

Barbora Gulejová 20 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 * * * * * 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

Barbora Gulejová 21 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 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 22 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 Comparison of neoclassical values with SOLPS D ┴,  ┴

Barbora Gulejová 23 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 ELM simulations (example) P SOL ~ 100 J Time evolution at targets targets outerinner J sat [A.m -2 ] T e [eV] n e [m -3 ] Perp.heat flux [MW.m -2 ] outer inner J sat [A.m -2 ] T e [eV] n e [m -3 ] T i [eV] inner outer J sat at inner target ~ 20 Exp. ~ 40 outer target ~ 10 Exp. ~ 35 SOLPS lower than experiment not enough energy expelled (~200 J from exp.)! => Time of arrival of particles to targets much shorter than expected … 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 = s - must be done in the steps by decreasing the time steps gruadually and seeking for convergence => difficult and time-consuming process – in progress

Barbora Gulejová 24 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 Parallel Mach Flows

Barbora Gulejová 25 of 18 Centre de Recherches en Physique des Plasmas First Thesis Committee 30/1/2007 preELM time-dependent solution necessary !!!