Modelling of impurity transport and plasma wall interaction at linear ...

Member of the Helmholtz Association 

Modelling of impurity transport and plasma 

wall interaction at linear devices using the 

ERO code 

D.Borodin 1 , A.Kirschner 1 , D.Matveev 1 , A.Kreter 1 , A.Galonska 1 , V.Philipps 1 , 

D.Nishijima 2 , R.Doerner 2 , J.Westerhout 3 , G.J. van Rooij 3 , G. van Swaaij 3 , 

R. Wieggers 3 , J.Rapp 3 

1 

Institut für Energieforschung - Plasmaphysik, Forschungszentrum Jülich, 

Association EURATOM-FZJ, Trilateral Euregio Cluster, Germany 

2 

University of California, San Diego, La Jolla, CA 92093, USA 

- 3 FOM Institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM, 

Trilateral Euregio Cluster, Nieuwegein, The Netherlands 

D.Borodin | Institute of Energy Research – Plasma Physics | Association EURATOM – FZJ

Outline 

Introduction to ERO code 

Specifics of ERO version for linear devices 

Examples of simulations 

Be injection at PISCES-B 

Chemical erosion mitigation at PISCES-B 

Methane injection at Pilot-PSI 

Summary 

02/09/2010 D.Borodin | Oak Ridge WS | Forschungszentrum Jülich 

No 2

3D MC impurity transport code ERO 

Background Plasma 

C x+ ,Be x+ ,… 

CD z 

0,+ 

re-eroded/ 

reflected particles 

Input: 

n e , T e,i , 

geometry 

C, Be, … 

CD 4 

PFC (substrate Be, C, W, Mo, …) 

Local transport: 

ionisation, dissociation 

friction (Fokker-Planck), thermal force 

Lorenz force (including ExB component) 

cross-field diffusion 

Plasma-surface interaction: 

physical sputtering/reflection 

chemical erosion (CD 4 ) 

(re-)erosion and (re-)deposition 

HMM and TRYDYN surface models 


No 3

ERO modelling strategy 

Code development: 

- PSI & transport 

- material mixing 

- castellated surfaces 

- atomic data, ADAS 

Estimations for ITER: 

- tritium retention 

- target & limiter lifetime 

- impurities into plasma 

Benchmarking: 

- PISCES-B (with beryllium) 

- Pilot-PSI 

- TEXTOR 

- JET, 

- AUG, 

- … 

Coupling with other 

codes: 

- plasma parameters from: 

e.g. B2-Eirene, Edge-2D 

- surface mixing: TriDyn, MolDyn 


No 4

ERO version for 

linear devices 


No 5

Linear device – general geometry 

PSI-2 facility. Moved from 

Berlin to FZ Juelich in 

2009. 

Modelling is always 

simplification . . . 


No 6

Particularities for linear devices 

Elastic collisions with residual gas (D 2 ) 

- example 1 

Different impact energies for molecular ions (D + , D 2+ , D 3+ ) 

Be carbide formation (suppressing chemical erosion of C) 

Tracking of metastable state (MS) in Be 

- example 2 

Bohm diffusion 

Physical effects implemented for linear devices 

can be relevant for tokamaks as well! 

Technical issues: 

o Geometry, target, Be oven, … 

o Plasma parameters (3D) - fitting formulas for radial and axial profiles 

o Electric field (3D) 

o Target biasing 

o . . . 


No 7

Linear device – radial electric field 

Radial electric field is connected with 

plasma potential 

Axial electric field is determined by 

sheath, pre-sheath and biasing 


No 8

Benchmark of elastic collisions model 

Be injection w/o plasma . . . 

A weight gain of 

1.5*10 -4 g was 

registered in 

experiment 

Be oven 

Estimated 

injection rate 

4.03*10 18 Be/s 

Target 

2g of Be is spent in 10 hours of oven operation. 

This gives a rate of about - 3.7*10 18 Be/s. 

W/o elastic collision with neutrals there would be no Be at target! 


No 9

Be metastable state (MS) tracking in ERO 

The system of 2 balance equations 

can be solved analytically . . . 

ADAS, T e =1eV, n e =2*10 12 cm -3 

Effective rates: 

1,2) transitions between "GS" and "MS" 

3,4) ionization from "GS" and "MS" 

5,6) line intensity (PEC – photon emission 

coefficient), contributions from "GS" and "MS" 

MS resolved approach allows to treat in ERO 

effectively the slow relaxation between triplet 

and singlet levels – important if MS 

population affected by extra processes and 

at high plasma parameter gradients 


No 10

Be Injection at 

PISCES-B 


No 11

Plasma parameters at PISCES-B 

• Plasma column 

width is about 5cm 

Be injection 

B 

Target 

Be injection 

B 

Target 

• Vessel radius is 

about 20cm filled 

with neutral gas 

• Be comes into the 

volume from 

injection or (and) as a 

result of Be target 

erosion 


No 12

Be spectroscopy at PISCES 

by 2D camera 

"Low density 

case" (1.2*10 12 cm -3 , 

T e =10.5eV) 

BeI, BeII emission is registered: 

by spectrometer with a spatial resolution 

(the radial profile position and direction 

can be varied) 

Experiment 

ERO modelling 

Be injection 

Target 

Be 

injection 

Target 

Axial 

profile 

Radial 

profiles 


No 13

Neutral Be emission 457nm (injection) 

The ERO modelling is in a good agreement with experiment (PSI-2008) 


No 14

Radial profiles at oven (z=150mm): Be 

Deviations of modelling from experiment: 

1) BeI max. shifted to seeding location 

2) BeII profile too narrow 

3) Absolute values of BeI intensity and ratio 

of BeII/BeI deviate by factors, which are 

different for various plasma conditions . . . 

Possible explanations: 

1) Uncertainties in plasma parameters 

(input) – e.g. plasma column width too 

large?.. 

2) Atomic data, Be-D molecules, 

metastables, . . . 


No 15

Import of plasma parameters to ERO from B2.5 

B2.5 [1] modeling results of Pilot-PSI plasma will be used 

2D multifluid code describing the quasineutral plasma beam. 

Neutral particles are treated as fluid species. 

V target =-5V 

V target =-22V 

B2.5 output for two different target potentials, showing Ohmic heating and 

detachment, particularly in the -5V case 

Presentation by PSI-2010 by R.Wieggers (FOM) 

[1] R. Schneider et al., Contrib. Plasma Phys. 46, (2006) 3 


No 16

Be/C mixing at 

PISCES-B: 

mitigation of 

chemical erosion 


No 17

PISCES-B linear divertor simulator 

z 

Neutral Be Be + 

Plasma 

source 

Plasma 

column 

Be oven 

E ax 

E rad 

B 

Simulation 

volume 

Be oven 

z=150mm 

Target 

Target 

Target 

y 

x 


No 18

Radial profiles at oven (z=150mm): Be 

M.Baldwin et. al. 

(Nucl. Fusion 46(2006) 444–450): 

I CD = exp(-t/τ(f Be )) 

1/τ ~ f Be 

2 

D.Nishijima et. al. (PSI-2006): 

1/τ ~f Be2 ⋅exp(-const/T s ) 

CD Band strength [a.u.] 

0.1 1 

Mitigation speed depends 

on Be concentration 

0.41 % Be 

1.10 % Be 

0.03 % Be 

0.13 % Be 

0.18 % Be 

0 500 1000 1500 2000 

Time (s) 

Influence of Be 2 C formation (which is observed by XPD)? 

TRIDYN surface model is necessary? 


No 19

Surface models and carbide formation 

Seeding rate 6*10 18 Be/s 

Seeding rate 3*10 19 Be/s 

Saturation 

Complete 

mitigation 

Saturation 

Carbide formation leads to stronger mitigation 

The effect is similar for both HMM and SDTrimSP surface models 

In ERO-SDTrimSP time scale is absolute, in HMM it is a subject 

of Interaction Layer (IL) depth choice 


No 20

Instantenious carbide formation – surface models 

ERO-HMM 

ERO-SDTrimSP 

Unrealistic time scale: in experiment it takes 100-1000 s! 

Current model: instantaneous carbide formation. 

Surface morphology, flux/temperature distribution, carbidisation dynamics?.. 


No 21

Carbide formation – characteristic time 

Carbide formation: t c =10s 

Fixed seeding rate 3e19Be/s 

τ char – characteristic time of carbide 

formation 

N Pot. – potential amount of carbide Be 2 C. 

τ char allows to vary the mitigation time scale . . . 


No 22

Effective mitigation time – effect of τ char 

The chemical erosion 

from beginning to 

saturation can be fitted 

as 

τ mit - effective 

mitigation time 

In a certain range τ mit is linear dependent on τ char . . . 

Any assumption for τ char e.g. dependence on T surf will 

be reproduced by τ mit . 


No 23

Effective mitigation time – effect of τ char 

Effect of Be-D molecules 

formation? 

Effect of surface 

morphology evolution? 

Surface roughness? 

In experiment 

τ mit ~(f Be ) -(1.9±0.1) 

Other effects? 

Surface changes observed at PISCES 

Simulations lead to a linear 

dependence of τ mit on the Be 

concentration in plasma. 


No 24

Pilot-PSI 

(effective D/XB for CH) 


No 25

Pilot-PSI: CD light from CD4 injection (side view) 

Experiment 

ERO 

• Narrow: 2.2mm 

• Total: 3.2mm 

E-folding lengths of axial profiles: 

total 

narrow 

• Narrow: 1.7mm 

• Total: 3.0mm 


No 26

C-H database in ERO code 

Reaction chains of hydrocarbon molecules (Janev / Reiter) 

C 2 H 6 C 2 H 5 C 2 H 4 C 2 H 3 C 2 H 2 C 2 H C 2 

C 2 H 

+ 

6 C 2 H 

+ 

5 C 2 H 

+ 

4 C 2 H 

+ 

3 C 2 H 

+ 

2 C 2 H + C 

+ 

2 

CH 4 CH 3 CH 2 CH C 

314 reactions! 

CH 4 

+ 

CH 3 

+ 

CH 2 

+ 

CH + C + C 2+ 

Emission data 

CII, CIII 

CH A-X, C 2 d-a 

ADAS 

U. Fantz et al. 2005 

Probably this is not enough . . . 


No 27

Dependence of D/XB on sticking and Te 

Width of plasma column 

is an important 

parameter: 

main sink for the CD is 

not dissociation, but 

escape. 

Deviations at low 

temperatures are 

probably due to 

additional CD excitation 

reactions (dissociateve 

excitation?) . . . 


No 28

Summary & Outlook 

The simulation of experiments of linear devices is important for 

implementation and testing of various new models, assumptions 

and underlying data in ERO. 

Several effects e.g. elastic collisions, carbide formation and 

metastable tracking were already implemented and tested. 

This effects lead to improvement of for modelling of ITER – life time 

of PFC and tritium retention (divertor, “BM-tiles”). 

It is necessary to continue the implementation of further physical 

effects e.g. Be-D molecules formation or dynamics of surface 

carbidisation. 

The modelling of plasma and residual gas of linear devices by 

B2-EIRENE (or similar) codes can provide an important input for 

ERO, which is based on test-particle approximation. 


No 29

End 


No 30

Modelling of impurity transport and plasma wall interaction at linear ...

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