1. Max-Planck-Institut für Plasmaphysik
Report from IPP Garching on work related to the EU PWI Task Force: Oct Oct 2006 *
With contributions from
W. Bohmeyer, A. Chankin, D. Coster, R. Dux, T. Eich, A. Herrmann, C. Hopf, W. Jacob,
A. Kallenbach, C. Linsmeier, M. Mayer, H.-W. Müller, R. Neu, R. Pugno,V. Rohde, J. Roth,
K.Schmid,T. Schwarz-Selinger
Compiled by Arne Kallenbach
* + Berlin +JET+ PISCES-B

2. Topics investigated in IPP from Nov 2005 – Oct 2006
Chemical erosion (see also talk S. Brezinsek)
Tungsten tokamak (see also talk R. Neu)
Decay and migration of carbon in ASDEX Upgrade
ELM power deposition characteristics in outer midplane
ELM in-out divertor asymmetry
He retention in W-coated surfaces
Chemical erosion by N ions and simultaneous neutral impact (non-scavenging)
Be-W alloying
PISCES-B measurements on D retention and pulsed power with Be seeding
Edge modelling with B2.5 (AUG) and DIVIMP (ITER)
SOL transport and parallel flow

3. Tungsten erosion at LFS limiters on ASDEX Upgrade
R. Dux
ICRH: strongest W erosion by sheath acceleration
NBI: Loss of ripple trapped fast ions identified as
dominant W sputtering mechanism by
Monte Carlo simulations of pitch angle dependence
for both ICRH and NI, W limiter source dominated by ELMs
about 70 % of time-averaged sputtered W during ELMs

4. Tungsten erosion at LFS limiters on ASDEX Upgrade:
ICRH sheath potential from measured W yield

5. Tungsten erosion at LFS limiters on ASDEX Upgrade:
pitch angle dependence form ripple loss of fast NBI ions

6. x 40 x 5 x 9 x 4 Tungsten erosion at LFS limiters on ASDEX Upgrade
Effect of type-I ELMs
x 40
x 5
x 9
x 4

7. Structure and radial decay of ELM filaments in the omp
A. Herrmann, A. Schmid
dedicated diagnostic setup
energy carried predominantly by ions

8. experiment migration modelling
Decay of carbon concentration with increasing W PFC coating
Fraction in ASDEX Upgrade A. Kallenbach
experiment
migration modelling
scatter due to boronisations,
Exp.imerfections, calibrations,…
slow decay of the carbon concentration with increasing W surface fraction
net divertor source becomes important with diminishing C PFC area

9. Divertor becomes important net carbon source with W PFCs
recovery of C after boronisation allows to estimate net source
net outer divertor
C source:
1.5e19 ions/s
C part of divertor
not coated by boron
LFS limiter fluxes and C concentration closely coupled
heat shield lags behind (1 ML C on heat shield  30 plasma C content)

10. Erosion measurements with markers and long term samples
Matej Mayer
Erosion of tungsten in the outer divertor of JET
Tungsten erosion was determined with a marker stripe from
Large erosion at outer strike point, outer baffle and apron
Erosion at strike point >> 2.4 µm
Inhomogeneous erosion due to surface roughness
Erosion of Be, C, Ni and W at the inner vessel wall of JET
Erosion was determined with long term samples from
Whole inner vessel wall is erosion dominated,
erosion of C is about 10 times larger than erosion of Be
Erosion of carbon and tungsten in the outer divertor of ASDEX Upgrade
Carbon and tungsten erosion were determined with marker stripes from
Largest erosion at strike points, both for carbon and tungsten
Erosion of carbon times larger than erosion of tungsten
2.8 g C eroded during the campaign
factor 3 larger than migration model
uncertainties, direct losses to inner div

11. Deposition in inner divertor
Matej Mayer
2002 – 2003
4800 s
2004 – 2005
3050 s
2005 – 2006
2900 s 6A 6B 5 4 9C
Decrease of C-deposition on divertor tiles by factor 7 from 2004/2005 to 2005/2006
Decrease of C-deposition below roof baffle by factor from 2004/2005 to 2005/2006
 Outboard limiters are main carbon source

12. SOL plasma flow in upper-SN H-mode at outer midplane
Hans-Werner Müller

13. Statements on plasma flow
H.-W.Müller

14. Shot resolved gas balance in ASDEX Upgrade
Volker Rohde

15. Implications of Tungsten on Helium Gas Recycling
Klaus Schmid
High He plasma concentrations encountered in AUG since the transition from a C to a W first wall
He plasma concentration linked to He glow duration and number of discharges since last boronization
Retained He in different C and W materials (NRA)
Dedicated laboratory experiments show:
W retains ~10 times more He compared to C or boronization layers
He release due to plasma load similar for W and C
Thermal release starts at 400K for both C and W
High He plasma concentrations in AUG are due to higher retention of He in W compared to C – effect expected to vanish at higher wall temp.

16. NITROGEN PUFFING into the DIVERTOR: RESULTS from LABORATORY EXPERIMENTS with remote ECR in H2, CH4, N2 mixtures
T. Schwarz-Selinger, W. Jacob
increase of erosion rate with bias for H2/N2
and
changeover from deposition to erosion for CH4/N2 plasmas at higher ion energies can only be explained by surface effects
evidence for chemical sputtering
Because of the increased erosion due to chemical sputtering the present data base does not allow to recommend N2 admixture to divertor plasmas with carbon PFC’s.
But, the high chemical sputtering yield of carbon films in N2/H2 mixtures make them interesting for removal of redeposited layers.
Work performed under the EFDA Task
TW3-TPP-SCAVOP
Final Report available upon request
Planned work: investigation of possible scavenging action of N in laboratory plasmas using cavity probes
© Thomas Schwarz-Selinger, October 2006

17. Mixed materials formation: Be-W alloying
Ch. Linsmeier, A. Wiltner, F. Kost
W on Be
stable Be12W above 1000 K
 Tm < 2000 K
 no W in surface zone
Be on W (ITER divertor!)
< 800 K
Be metal layer deposition
 Tm ~1560 K
> 1000 K
Be2W surface alloy only (~nm)
no bulk diffusion, sublimation faster
 Tm ~2500 K
depth profile
Future work
Reactivity of Be/W alloys with carbon
Formation of ternary surface layers
Reactivity of different surface layers with atomic oxygen

18. Power pulsing experiments in PISCES-B
R. Pugno, PISCES-B team under EFDA contract TW5-TPP-CARWBER
A transitory positive voltage biasing system has been installed on PISCES-B to simulate the heat pulses associated with ELMs.
A new infra-red diagnostic system has been installed to measure the target surface temperature during the heat pulses.
From visible spectroscopy and mass loss measurements, the formation time of the Be2C protective coating on graphite samples exposed to beryllium-seeded deuterium plasmas, is reduced in presence of power transients.
The deuterium retention is increased in presence of power transients for both pure deuterium (+30%) and Be-seeded plasmas (+60%).
The infra-red measurements evidence a change in emitting area due to a surface morphology modification during plasma exposure (both for pure carbon and Be2C surfaces) in agreement with previous observations by SEM electron micrographs.

19. Work done at PISCES-B in the frame of the EFDA contract TW5-TPP-CARWBER
R. Pugno, PISCES-B team
Saturation of the surface is observed in CFC target for fluences higher than 1e26 ion/m2 and target temperature of 1100 K.
No change in deuterium retention in CFC is observed between pure deuterium plasmas and Be seeded plasmas in that conditions.
Earlier onset of thermal desorption is observed for mixed material surface i.e. after exposure to Be seeded plasmas as already observed in PISCES-B
The scaling law for the suppression time of chemical erosion in Be seeded plasmas obtained with FGG target seems to be valid also for CFC target.

20. SOLPS work, development and benchmarking D. Coster, A. Chankin, C
SOLPS work, development and benchmarking D. Coster, A.Chankin, C. Konz, M. Wischmeier
In addition to other activities, the members of the edge group took part in the Edge Modelling Campaign at JET
Coster
Edge transport Code-Code Verification/Validation/Benchmarking
Chankin
EDGE2D runs: adding drifts to JET H-mode pulses
Konz
Simulation of disruption thermal quenches with B2 SOLPS
Wischmeier
SOLPS5 modelling of ohmic plasmas with C13 injection at the top of the machine

21. Dicrepancy in code-experiment comparisons
Detailed comparison between B2.5-EIRENE (SOLPS) edge modelling and experiment shows that the code overestimates plasma density and underestimated electron temperature in the divertor, especially near the strike point position.
The example shown above demonstrates a large discrepancy between simulated and experimental Ha radiation profiles, which is the consequence of the overestimate of the plasma density in the divertor.

22. code-code comparison Edge code benchmarking / ITPA activity
EDGE2D D+C
EDGE2D D
SOLPS
D+C
code-code comparison
Phase I: pure D, no drifts
Phase II: pure D, drifts
Phase III: D+C, no drifts
Phase IV: D+C, drifts
SOLPS-EDGE2D/NIMBUS 
Phase I completed successfully (reported on at PSI 2004)
Phases II and III in progress
SOLPS-UEDGE
Phase I underway
Phase II expected to start soon
Additional code-experiment
JET: SOLPS-EDGE2D/NIMBUS
AUG/D3D: SOLPS-UEDGE
SOLPS
EDGE2D

23. Association Euratom–Tekes
Using MDSplus for SOLPS to ASCOT
2D background (ne, Te, Ti, …) written as MDSplus tree by SOLPS (IPP-Garching) [modelled by Chankin]
 provides input to ASCOT Due to open field lines, special care must be taken with the Monte Carlo collisions
Planned: output of ASCOT to be saved to a MDSplus tree
ITPA standard pedestal MDSplus tree created based on AUG shot (provides the equilibrium data)
ASCOT:
T. Kurki-Suonio, L. Aho-Mantila, J. Heikkinen, V. Hynönen, T. Kiviniemi, A. Salmi, S. Sipilä, V. Tulkki
Distribution of electrons reaching outer target
Association Euratom–Tekes

24. Divertor in-out power asymmetry during ELMs depends
on ion grad-B drift direction T. Eich

25. In-out power asymmetry connected to charge flow asymmetry
charge sign suggests ions to carry excess power
AUG upper SN

26. TW4-TPP-TRIDEP
Humboldt Universität
zu Berlin
W. Bohmeyer
Beginning of the project 08/2004
intermediate report 12/2004
(end 12/2005) prolongated / 2006 *
Main topics:
1. Analysis of Cx Hy mixture produced by chemical erosion
2. Study of the influence of the target temperature
3. Influence of impurities on chemical erosion
IR absorption, QMS, cavities
4. Determination of the balance between deposition and erosion for areas
not exposed directly to the plasma ( ITER pumping duct).
Experiments and ERO-Modelling
density of atomic hydrogen
improvement of experimental data for modelling
(spectroscopic data, cavities,...)
* delayed start of the experiments (reason: no permission to use hydrogen) -

27. CH4 injection into a He-Plasma
Humboldt Uinversität
zu Berlin
CH4 injection into a He-Plasma
2D-CH-emission at 430 nm
7 cm
nozzle
Ne=2*1018 m-3
Ne=1017 m-3
Ne=3*1017 m-3
1.Clear shift from global to local decomposition with increasing el.-density
2.Decomposition and excitation length is not in agreement with atomic data