SOLPS5 modelling of ELMing H-mode on TCV

Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 1 of 12

Centre de Recherches en Physique des Plasmas

SOLPS5 modelling of ELMing H-mode on TCV

Barbora Gulejová,

Richard Pitts, Marco Wischmeier, Roland Behn, Jan Horáček

OUTLINE

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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



Edge plasma - Edge plasma - terminologyterminology

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 closedflux surface

LFSHFS



Edge localised mode (ELM)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

LFSHFS

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

Dα

Small ELMs on TCV – same phenomena !=> Used to study SOL transport



SScrape-crape-OOff ff LLayer ayer PPlasma lasma SSimulationimulation Suite of codes to simulate transport in edge plasma of tokamaks

B2B2 - 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 5SOLPS 5 – coupled EIRENE + B2.5

Main inputs: magnetic equilibrium Psol = Pheat – Prad

core upstream separatrix density ne

Free parameters: cross-field transport coefficients (D┴, ┴, v┴)

B2 plasma background =>recycling fluxes

EIRENE

Sources and sinks due to neutrals and molecules

measured

systematicallyadjusted

Mesh

72 grid cells poloidallyalong separatrix

24 cells radially



Elming H-mode at TCVElming H-mode at TCV

[kA

]

ne

Ip

Dα

Vl

Wheat[kW

][V

][a

u][1

018

m3 ]

# 26730

Type III ELMs

# 26730ELMs - 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

tpre ~ 2 ms

telm ~ 100 μs

tpost ~ 1 ms



upstreamEdge Thomson scatteringEdge Thomson scattering

ne and Te upstream profiles

Diagnostic profiles used to constrain the codeDiagnostic 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

LangmuirLangmuir probesprobesjsat target profiles

jsat [A.m-2]

R-Rsep [m]

outer target

jsat

R-Rsep [m]

inner target

RCP – reciprocating probeRCP – reciprocating probe

ne

pedestal

Te

R-Rsep [m]

pedestal

R-Rsep [m]



Theory – steady state simulationTheory – steady state simulationCross-field transport coefficientsCross-field transport coefficients

nrDeff ).(

nvdr

dnD

))(5( nvdr

dnDT

dr

dTnq

Cross-field radial transport in the main SOL - complex phenomena

Ansatz:( D┴, ┴, v┴) - variationradially – transport barrier (TB)poloidally – no TB in div.legs

outer div.leg

┴

SOL

div.legs

sep

D┴

SOL

div.legs

sep

v┴ SOL

div.legs

sep

main SOL

diffusion (D┴) + convection (v┴)

SOL radial heat fluxheat flux:

SOL radial particle fluxparticle flux:

main SOL

Inner div.leg

x

x

Pure diffusion: v┴=0 everywhere

More appropriate: Convection

simulations with D┴= D┴class in progress



Comparison of experimental data with simulationComparison of experimental data with simulationPurely Purely diffusivediffusive approach approach

1.step: Only radial variation of D┴, ┴

upstream

targets

Excellent agreement !!!Excellent agreement !!!

Code overestimates data

=>

Poloidal variation necessary

=>

Remove transport barrier from divertor legs

=>

=>

outer

Jsat [A.m-2]

LPs

SOLPS

R-Rsep [m]

innerjsat

R-Rsep

LPs

SOLPS

D┴,Χ┴ = constant in div. legs

ne

D┴

TS

RCP

SOLPS

pedestalwall

Te

Χ┴

TSRCP

SOLPS

R-Rsep

R-Rsep



Removing transport barrier from divertor legsRemoving 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-Rsep [mm]

LP

jsat [A.m-2]

R-Rsep [mm]

jsat [A.m-2]

Transport barrier

0.5

1

2

3

56

Transport barrier

0.5

1

2

3

5

6

outer target

inner target

LP

6 m2.s-1 in div.legs1m2.s-1 in SOL ! NO DRIFTS !



Other issues to considerOther issues to consider

1.) Inner and outer divertor leg assymetry – inner is much shorter2.) Private flux region (PFR) rescaling in div.legs – different processes in PFR region and SOL region of divertor legs3.) Ballooning – (Btot/Bloc )α => poloidal variation

Inner div.leg

outer div.leg

sep

PFR

SOL

**

*Sensitivity study for the steady state Sensitivity study for the steady state simulationssimulations

=>

Very small effect

LP

α =0.5

α =1

outer target

R-Rsep [mm]

No ballooning

LP

Inner target

R-Rsep

α =0.5

α =1

inner target

No ballooning



Next step : Next step : ELMELM

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…



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First attempt to simulate Scrape-Off layer in H-mode on TCVwith 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)

ConclusionsConclusions

SOLPS5 modelling of ELMing H-mode on TCV

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