Max-Planck-Institut für Plasmaphysik Report from IPP Garching on work related to the EU PWI Task Force: Oct 2005- 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

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

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

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

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

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

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

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

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)

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 2001-2004 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 2001-2004 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 2004-5 Largest erosion at strike points, both for carbon and tungsten Erosion of carbon 10-20 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

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 10 from 2004/2005 to 2005/2006  Outboard limiters are main carbon source

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

Statements on plasma flow H.-W.Müller

Shot resolved gas balance in ASDEX Upgrade Volker Rohde

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.

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 (Wolfgang.Jacob@ipp.mpg.de) Planned work: investigation of possible scavenging action of N in laboratory plasmas using cavity probes © Thomas Schwarz-Selinger, October 2006

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

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.

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.

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

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.

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

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 17151 (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

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

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

TW4-TPP-TRIDEP Humboldt Universität zu Berlin W. Bohmeyer Beginning of the project 08/2004 intermediate report 12/2004 (end 12/2005) prolongated 06 / 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) -

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