Modeling hydrocarbon generation / transportIn fusion experiments

John HoganFusion Energy Division

Oak Ridge National Laboratory

First Meeting Co-ordinated Research Program

” Atomic and Molecular Data for Plasma Modelling ”IAEA

Vienna International CentreSeptember 26-28, 2005

ITER tritium retention issues G. Federici, ITER GWS PSIF Workshop*

(to be published, Physica Scripta)

ITER predictions still uncertain due to – chemical erosion yields at high temperature and fluxes – effects of type I ELMs (ablation)– effects of gaps– effects of mixed materials– lack of code validation in detached plasma.

• T issues will be heavily scrutinised by licensing authorities.

• Scale-up of removal rate required is 104.• Potential options for T removal techniques for ITER.

1) Remove whole co-deposit by:

• oxidation (maybe aided by RF)• ablation with pulsed energy (laser or flashlamp).

2) Release T by breaking C:T chemical bond:• Isotope exchange • Heating to high temperatures e.g. by laser, or ...

* “New directions for computer simulations and experiments in plasma–surface interactions for fusion”: Report on the Workshop (Oak Ridge National Laboratory, 21–23 March 2005) J.T. Hogan, P.S. Krstic and F.W. Meyer Nucl Fus 49 (2005) 1202

Fusion applications of hydrocarbon rate data

Erosion / re-deposition / tritium retention

(DIII-D, Tore Supra, JET examples)

- long discharges -> hydrocarbon films

- chemical erosion and T inventory

Use of presently available data

PISCES linear reflex arc (Erhardt-Langer)

throat of Tore Supra neutralizer

(compare E-L and Janev - Reiter)

DIII-D gaps

ELMs

a. 2/3D Kinetic codes

Code WBC ERO BBQ DIVIMP DORIS MCI EDDY

Geometry 3D 2/3D 3D 2D 3D 2D 3D

Model TR TR TR TR TR TR TR

Dynamics GO GO GC GO GC GO GC

b. 2D fluid codes

Code SOLPS EDGE2D UEDGE

Geometry 2D 2D 2D

Model SC SC SC

Dynamics FL FL FL

Codes in use for erosion/deposition/retention (D Coster, J Hogan PSIF Workshop Summary Nucl Fus 2005)

TR - trace impurity in fixed backgroundSC - self-consistent background and impurity solution

GO - gyro orbit following (classical diffusion)GC - guiding center fluid (anomalous transport)FL - fluid + kinetic corrections

CD / CH Molecular Band is analyzed todetermine the H/D concentration in the divertor(G. Duxbury - Univ Strathclyde)

0

0.1

0.2

0.3

0.4

0.5

0.6

50 52 54 56 58 60

Divertor Spectroscopy Sub-Divertor - PenningCH-CD Spectroscopy

Hydr

ogen

Con

cent

ratio

n

Time (s)

48280

H wall loading first 5 shotsOf D-->H changeover

H concentration as deduced from the CH-CD Molecular Band

Relation between chemical erosion processes and H/D/T retentionJET deuterium - hydrogen change-over experiment

D Hillis, J Hogan et al J Nucl Mater 2001

Interior view of Tore Supra

Tore Supra

Full toroidal limiter CIEL

Θ poloidal direction

ϕ

θ

φ toroidal direction

machine axis

Coupled core/ SOL/PFC code system

CASTEM-TOKAFLU-IMPFLU BBQ

ITC-SANCO-MIST

Self- sputtering iteration

Deuterium sputtering stage

BBQ

MIST/ITC

ne(ρ)Te(ρ)

λΤe

ΓD+

Superstructureleading edgeneutralizer

physicalchemicalRES

ΓCin(Zi)

=> ΓCout(Zi) Core C efflux: D+ - sputtered

BBQ

MIST/ITC => ΓCout(Zi) Core C efflux: self - sputtered C

=> Core C influx Sum over processes and geometries

0.9 0.95 1.0 1.03 1.06 radius (ρ/a)

LCFS

0

1.2

0.6

V VIVII

IVIII

Mid SOL heating< NC >

10 18 m-3

< NC >BBQ carbon densityaveraged over θ, φ

8.8

0

4.4

0 0.5 1.0 ρ ( r/a)

2.3

0

1.15

0

1.5

0.75

1 9 iteration

< NC > (1016 m-3)NC (1016 m-3)

1.05

0

0.525

0 0.5 1.0 ρ ( r/a)

.

NC (1018 m-3)

System evolution forlocalized heating ininner, mid- and far-SOL

for:

- TRIM self-sputter (TOP)

- enhanced self-sputter (BOTTOM)

Tore Supra heat, particle flux deposition is stronglyinfluenced by magnetic field ripple (~7%)

R Mitteau et al J Nucl Mater 2001.

34909 34930Modelled C emission(TOKAFLU / BBQ)

Physical sputtering source

Te,b=35 eV, ne,b=0.67 1019 m-3Pinj-Prad=0.7 MW

Measured CII radiation(E Dufour, C Lowry et al, EPS 2005)

Model validation requires attention to impurity generationfrom non-ideal features, e.g., intra-tile gaps

Tore Supra example

φ(°)0 20

Toroidal angle

R(m)

2.25

2.5

Majorradius

φ(°)0 20

Toroidal angle

Sources of BBQ CD4 Rate Data [W. Langer, A. Erhardt, PPPL Technical Report]

# Reaction Product Comment1 e- + CD4 CD4

+ + 2 e- M2 CD3

+ + D + 2 e- M3 CD3 + D + e- M4 e- + CD4

+ CD3 + D+ + e- NM: = 1/4 R15 CD3

+ + D + e- NM: = 3/4 R16 CD3 + D Tot. R6+R7

M for E < 1 eV,Ex (E > 1 eV) = 1/4 Rexp

7 CD2 + 2 D As for R6,R7 = 3/4 Rexp

8 e- + CD3 CD3+ + 2 e- CD3 M

Ex (E<15 eV)

9 CD2+ + D + 2 e- From CD3 (M)

10 CD2 + D + e- NM, = 3/4 R3

11 e- + CD3+ CD2 + D+ + e- NM, = 1/3 R10

M = Measured, NM = Not Measured, Ex = Extrapolated, A = Assumed

Sources of the BBQ CD4 Rate Data [W. Langer, A. Erhardt]

12 CD2+ + D + e- NM, = 2/3 R10

13 CD2 + D Total M for E < 1 eV, Ex (E>1 eV)neglect other channels

14 e- + CD2 CD2+ + 2 e- From CD2 M(E<200eV)

and CD4 for E> 200eV)15 CD+ + D + 2 e- M (CD2)16 CD + D + e- NM, = 1/2 R317 e- + CD2

+ CD + D+ + e NM, = 1/2 R1618 CD+ + D + e- NM = 1/2 R1619 CD + D Total M (E < 1 eV)

Ex (E>1eV) neglect other channels20 e- + CD CD+ + 2 e- NM, adopted CD4 data21 C+ + D + 2 e- NM total R21+R22

A=1/2 R9; R21=1/2 total22 C + D+ + 2 e- NM, total R21+R22

A= 1/2 R9; R22=1/2 total23 C + D + e- NM = 1/4 R324 e- + CD+ C + D+ + e- NM = 1/2 R2325 C+ + D + e- NM = 1/2 R23M = Measured, NM = Not Measured, Ex = Extrapolated, A = Assumed

PISCES - A (UCLA) experiments: A. Pospieszczyk, FZ-Juelich

Reflex arc linear mirror plasma

Spectroscopic arrangementOptical multi channel analyzer

Code - experiment comparisonBBQ - Monte Carlo multi-species simulation ( Erhardt-Langer database)OMA ( A. Pospieszczyk, FZ-Juelich)

Nozzlelocation

Downstream distance(cm)

0 2 4 6

Rel. density

1.0

0.5

0

PISCES-A 13417

BBQ

CH2 axial density CH axial density

Rel. density

1.0

0.5

0

Nozzlelocation

Downstream distance(cm)

0 2 4 6

PISCES-A 13417

BBQ

Optical Multi-channel Analyzer(A. Pospieszczyk FZ-Juelich)

Schematic diagram of experiment onTore Supra Midplane Limiter (Phase II)

E Gauthier, A Cambe J Hogan et alJ Nucl Mater 2003

Model comparison using partial pressure- sensitivity to sputtering model

CD emission

CD4 partial pressure

510 670 830 Tsurf(K)

LHCD: High Tsurf

PCD4∝ PD20.70

(N. Hosogane)

PCD4∝ϕD0.73

JT-60U

Increased productionof CD4 with flux

Deuteron impact charge exchange data [Alman, Ruzic]D+ + CnDm --> D + CnD4+

Reaction Product Rate Known (10-9 cm3/s) (total)

CD4D+ + CD4 D + CD4

+ 1.880 4.150D2 + CD3

+ 1.880D+ + CD3 D + CD3

+ 1.800D2 + CD2

+ 1.800D+ + CD2 D + CD2

+ 1.700D2 + CD+ 1.700

D+ + CD D + CD+ 3.236C2D2D+ + C2D2 D + C2D2

+ 2.250 6.300 D2 + C2D+ 2.250

D+ + C2D D + C2D+ 4.358

C2D2 C2D2+ C2D+ C2+

Heavy hydrocarbon production: dominant species frombreak-up of C2D2.BBQ calculation using Alman-Ruzic database

Janev-Reiter database rates have been implemented in BBQ. A comparison, with the same background plasma conditions, for the Tore Supra pump limiter case, shows significant differences in comparison with the Erhardt-Langer rates

CH+ CH+ CH+

CH4 CH4 CH4

ne,LP= 2 1018 m-3

Te,LP= 20 eV Te,LP= 10 eV Te,LP= 5 eV

Janev-Reiter profiles

TeLP = 20 eV

ne,LP = 2 1018 m-3

E - L

J - R

CH+ density

Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24

TeLP = 10 eV

TeLP = 5 eV

CH+ density

Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24

E - L

J - R

Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24

CH+ density

E - L

J - R

CH+ CH+ CH+

CH4 CH4 CH4

ne,LP= 6 1018 m-3

Te,LP= 20 eV Te,LP= 10 eV Te,LP= 5 eV

Janev-Reiter profiles

TeLP = 20 eV

ne,LP = 6 1018 m-3

E - L

J - R

CH+ density

Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24

TeLP = 10 eV

TeLP = 5 eV

CH+ density

Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24

E - L

J - R

Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24

CH+ density

E - L

J - R

Given D+ flux (or Cn+for self-sputter) to surface and surfacetemperature, calculate impuritytype, rate and velocitydistribution .

Mechanisms: - physical sputtering, - chemical sputtering (thermal, athermal) - RES

Impurity generationmodels

0.09

0.045

0.0250 875 1500 Tsurf (K)

Te (eV)103050

70 90

9070

50

30Te (eV)

Chemical

RES

Yield[C / ion ]

Surface-temperature dependence of chemical and RES yields forTe=10 -> 90 eV.

- 3-D, time-dependent finite-elements thermal analysis code

- developed by CEA-DEMT

Modifications (CSPUTTER) include:

- self-consistent heat flux (includes SEE, thermionic emission)

- local impurity redeposition generation due to Tsurf-dependent mechanisms as well as physical sputtering

- ablation cooling (Vieder model)

RDP-2000RDP-1999

0.4 0.6 0.8 1.0 1.2 1.4 Time (s)

3

8

0

0

Carbon concentration (%)Edge

Core

Filterscope(schematic)

0001

0203

0411

13

12

DIII-D intrinsicimpuritiesbefore/after new tileinstallation

Some evidence ofT-dependentprocesses

0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5 Time (s)

NBI

Maximum Tsurfon heated surface

T sur

f(K)

2.5 mm

1 m

m

Ychem @ t ~ 4swhen Tmax = 1010K

Ychemmin = 1. 10-2

Ychemmax = 0.14

C flu

x(1

018

parts

/cm

2 /s)

0 1 2 3 4 5 Time (s)

0.4

0.8

1.2

1.6

0 NBI

C flu

x(1

018

parts

/cm

2 /s)

0.6

1.0

1.6

2.0

00 1 2 3 4 5 Time (s)

NBI

RES

Chemical

NBI

CASTEM-2000 simulation of time-dependent carbon generationfrom simulated DIII-D localized source

edge / pedestal only,low-field side only

Semi-empirical model for ELM transport enhancement

Green: ELM-affected region in the model

Red: C neutrals and ionsYellow: D neutrals ion ions

1

2

34

ELM event

time

radius

1

2

3

separatrix

Transport time dependence(schematic)1. Pre-ELM (barrier)2. Strong enhancement (100 µsec) ELM3. Loss of barrier, 2 x pre-ELM value4. reducing to pre-ELM value as barrier is re-established

Intra-ELM transport radial dependence(schematic)1. barrier2. enhancement toward SOL3. SOL radial transport

C6+(ρ) vs time, solpsoutboard mid-plane

Separatrix

Normalized Radius = 0.81 0.90 0.94 0.96 0.99 Shot = 119434

~ separatrix

�0.01 �0.005 0 0.005 0.01Time Relative to ELM (s)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Impurity DensityC6

+ de

nsity

C6+ density CER

C6+ density solps

HFS separatrix

core

LFS separatrix

C6+

dens

ity

�0.005 0 0.005Time Relative to ELM (s)

CIII 4650.1 evolutionsolps 'standard' model

Roth et al 'annealing' model

Inner leg pre-ELM detached during attached re-detaching after recovery of detachment

DIII-D experimental:fast (CID) camera

CIII evolution:M Groth et al,J Nucl Mater 2003

Modeling

solps 5.0 / Eirene99

IPP-Garching/Greifswald, FZ-Juelich

Solps simulation of

CIII emission

seen by 240par

(lower divertor)camera

W Meyer,

M Fenstermacher,

M Groth

LLNL

ELM heat flux mitigation byInjection of extrinsic impurities

10 100 1000

0.1

1

10

chem

ical

spu

tterin

g yi

eld

(per

ion)

energy (eV)

N+2

Ar+

Ne+

He+

H+2 = 2 H+

Flux ratio H/ion = 400

Chemical sputtering of carbon materials due to combined bombardment by ions and atomic hydrogen W Jacob, C. Hopf, M. Schlüter, T. Schwarz-SelingerMax-Planck-Institut für Plasmaphysik Garching

CONCLUSIONS

Intrinsic (carbon) impurity sources play a key role in ITER, both as regards erosion and fortritium retention

The ITER problem (addressed also by JET) requires a decision about the first wallmaterial - carbon or an alternative

Development of validated models for C generation, deposition and retention requiresexperimental comparison: this typically introduces multiple uncertainties; e.g., sputteringyield models vs hydrocarbon break-up rates

ITER relevant experimental scenarios involve fast timescale ELM events, for whichspectroscopy is an key tool

The importance of hydrocarbon generation processes has been seen in manyexperiments, and thus a quantitative, evaluated, integrated model for break-up processesin the plasma is needed.