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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
******
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 SPS Annual Meeting in Lausanne, 14/2/2006 2 of 12
Centre de Recherches en Physique des Plasmas
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
Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 3 of 12
Centre de Recherches en Physique des Plasmas
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
Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 4 of 12
Centre de Recherches en Physique des Plasmas
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
Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 5 of 12
Centre de Recherches en Physique des Plasmas
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
Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 6 of 12
Centre de Recherches en Physique des Plasmas
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]
Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 7 of 12
Centre de Recherches en Physique des Plasmas
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
Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 8 of 12
Centre de Recherches en Physique des Plasmas
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
Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 9 of 12
Centre de Recherches en Physique des Plasmas
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 !
Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 10 of 12
Centre de Recherches en Physique des Plasmas
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
Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 11 of 12
Centre de Recherches en Physique des Plasmas
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…
Barbora Gulejová SPS Annual Meeting in Lausanne, 14/2/2006 12 of 12
Centre de Recherches en Physique des Plasmas
*
*
*
*
*
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