Particle sources and radiation distributions in the TCV tokamak edge

Barbora Gulejová First Thesis Committee 30/1/2007 1 of 18

Centre de Recherches en Physique des Plasmas

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



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

**

***

**



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 diodesNEXT STEP: D alpha - higher transmission



Ageing effect

with filter removed“New LYMAN”

without filter“old AXUV”

Huge increase in signal when filters removed – layer deposition + ageing

G.Veres



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



Type III Elming H-mode at TCVType III Elming H-mode at TCV# 26730

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

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┴

downstreamLangmuirLangmuir 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]

I R

outer target

Heat flux [MW.m-2]

IR camerasIR camerasPerpendicular heat flux

R-Rsep [m]

R.Behn

J.Marki

J.Horacek



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

2 approaches



Comparison of experimental data with simulationComparison of experimental data with simulation1.1. Purely Purely “diffusive”“diffusive” approach approach

upstream ne SOLPSTSRCP

pedestal

wall

1

6

R-Rsep

separatrix

Te SOLPSTSRCP

Good agreement !!!Good agreement !!!

core

D┴

Χ┴

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

Accepted to JNM 2007



targets

Jsat [A.m-2]LP, averageSOLPS

outerinner

Te [eV]

ne [m-3]

Perp.heat flux [MW.m-2]LP, averageSOLPS

outer

inner

IR

Comparison of experimental data with simulationComparison of experimental data with simulation1.1. Purely Purely “diffusive”“diffusive” approach 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 m2.s-1 in div.legs1m2.s-1 in SOLΧ┴= 5 m2.s-1 in div.legs6 m2.s-1 in SOL

NO DRIFTS yet! =

>

Accepted to JNM 2007



Comparison of experimental data with simulationComparison of experimental data with simulation2.2. “Convective”“Convective” approach approachupstream targets

outerinner

D┴

Χ┴

ne SOLPSTSRCP

pedestal

wall

0.1

6

R-Rsep

separatrix

Te SOLPSTSRCP

30

2

v┴

Jsat [A.m-2]LPSOLPS

Te [eV]

ne [m-3]

Perp.heat flux [MW.m-2]LPSOLPS

outer

inner

IR

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┴

???

Reasonable agreement

=>

=>



Type III ELM simulationType 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

LFSHFS

W~200J

Dα

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 = tELM = 10-4s2.) at poloidal location -> expelled from area AELM at LFSFrom the cross-field radial transport can be estimated the combination of trasnport parameters corresponding to the given expelled energy WELM, tELM and AELM

AELM= 6m2

W = 400 JD┴

┴

Many different appraches possible =>changes in D┴, ┴ only or in v┴ too …



Tools to simulate ELM in SOLPS

outer div.leg

main SOL

main SOLInner 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

pedestal wallcore

No TB

preelm

ELM

x M

ELM



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 ne

SOLPS * bigger pedestal collaps * higher ne and Te in SOL

But the right tendency – pedestal collapse

D┴ ne

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 = 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

R-RsepR-Rsep

timetime

Time evolution of D┴ and ne

tELM=100 µs



SOLPS5 simulations with DRIFTS

ErxB, pxB

Ballooning

Pfirsch-SchlüterDivertor sink

ExB

• Poloidal

• Parallel

B

BxBREV B

SOL flows DRIFTS – contribute to in/out assymetriesTCV : 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 Te 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



First attempt of SOLPS simulation with First attempt of SOLPS simulation with DRIFTS DRIFTS upstream

R-Rsep

D┴

Χ┴

ne SOLPSTSRCP

pedestal

wall

1

R-Rsep

separatrix

Te SOLPSTSRCP

6

targets outerinner

Jsat [A.m-2]LPSOLPS

Te [eV]

ne [m-3]


outer

inner

IR

R-Rsep

R-Rsep

Not yet completely converged solution…



First attempt of SOLPS simulation with First attempt of SOLPS simulation with DRIFTS DRIFTS outerinner

Jsat [A.m-2]LPSOLPS

Te [eV]

ne [m-3]


outer

inner

IR

R-Rsep

R-Rsep

outerinner

Jsat [A.m-2]LPSOLPS

Te [eV]

ne [m-3]


outer

inner

IR

R-Rsep

R-Rsep

NO DRIFTS DRIFTS

NO DRIFTS:

Overestimation of outer target Te

DRIFTS:

Decrease of outer target Te

as expected

Same effect onjsat and heat flux!

Inner target :not significant

effect as expected

Good early

promise !!!



Future plansAfter 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

*

*

*



Thank you for attention !



*

*

*

*

*

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



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



Comparison of neoclassical values with SOLPS D┴, ┴



ELM simulations (example)

PSOL~ 100 J

Time evolution at targets targets outerinner

Jsat [A.m-2]

Te [eV]

ne [m-3]

Perp.heat flux [MW.m-2]outerinner

Jsat [A.m-2]

Te [eV]

ne [m-3]

Ti [eV]

inner

outer

Jsat at inner target ~ 20 <-> Exp. ~ 40 outer target ~ 10 <-> Exp. ~ 35SOLPS 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 = 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



Parallel Mach Flows



preELM time-dependent solution necessary !!!

Documents

Particle sources and radiation distributions in the TCV tokamak edge