Impurity Transport in the Edge Transport Barrier of ASDEX Upgrade

H-Mode Discharges

R. Dux, T. Pütterich, M.A. Janzer, R.M. McDermott and the ASDEX Upgrade Team

MPI für Plasmaphysik, EURATOM Assoziation, Garching bei München

R. Dux, JET-E1/2 TF Meeting, Culham, 7.4.2011 - 2

Central tungsten density depends on…

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Central tungsten density depends on…

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W- and C-density pedestal vs. ELM frequ.

Scan in D-puff rate changes ELM frequency

Lower ELM frequency leads to more nW inside pedestal

nC increases less strong with ΔtELM than nW

Need to know inter-ELM transport in ETB to understand effect of ELMs

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Overview

Measurements of the impurity transport in the ETBusing CXRS measurements – Z-dependent

Consequences for transport of W- 1D Transport/Erosion Model for W- results for AUGD and ITER

Summary

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Toroidal edge CXRS system at AUGD

• spatial resolution: 3 mm

• temporal resolution 1.9 ms

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STRAHL

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Scheme of Transport Evaluation

1D-Transport Model

STRAHL

Electron profiles,Geometry, Atomic Data

Fitting procedure

input

Measured impurity profiles

compare

Vary

A1,A2

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Inputs for Modeling the Impurity Transport

Electron profiles and Edge-CXRS during type-I ELMy H-mode

Profiles are adjusted by a two-point model for power balance (i.e. Te =85eV at separatrix)

Analysis in inter-ELM phase

Time [s]

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Model finds good match for impurity profiles

Profiles are well described, except 1ms after ELM (filaments, ELM-model) Pedestal in C6+ is mainly due to pedestal in total C density Separation of v and D possible due to:

(1) modulation by ELM and (2) position of gradient

R. Dux, JET-E1/2 TF Meeting, Culham, 7.4.2011 - 11

Fitted values of v, D and v/D agree with neoclassical transport

D and v are separated, but with relative large uncertainties

v/D is determined well by the gradients and the pedestal height, i.e. pedestal peaking factor

(In equilibrium, w/o sources)

Neoclassical transport (NEOART) is matched for v/D, (NEOART is equivalent to NCLASS)

Neocl. approximation valid for impurities; mostly PS, negligible banana, plateau contribution

97.0

00.1

exp)00.1(

)97.0( pol

pol

drD

v

n

nF

polC

polC

R. Dux, JET-E1/2 TF Meeting, Culham, 7.4.2011 - 12

Neoclassical transport for He, C, Ne and Ar

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Neoclassical transport for He, C, Ne and Ar

Impurity scan gives stronger inward convection for higher charge

Implications: every impurity has a different gradient

W has even higher Z in ETB higher * and collisional diffusion coefficient stronger peaking

R. Dux, JET-E1/2 TF Meeting, Culham, 7.4.2011 - 14

Overview

Measurements of the impurity transport in the ETBusing CXRS measurements – Z-dependent

Consequences for transport of W- 1D Transport/Erosion Model for W- results for AUGD and ITER

Summary

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Model for Radial Transport of Tungsten during ELM cycle

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Modeled W profile evolution during ELM cycle

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Increase of prompt redeposition during ELM:

immediate return to surface during first gyration

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Study dependence of confinement time of W

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Confinement time of W depends on ELM frequency and parallel loss time

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Code results for three AUG H-mode plasmas with f_ELM=50,100 and

200Hz

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ITER: much lower collisional transport due to higher temperature and B-field

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ITER: low W peaking in ETB for relevant ELM frequency range

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Summary

For type-I ELMy H-mode, inter-ELM impurity transport at the barrier is neoclassicalAbsolute values of v and D agreeNeoclassical Z-scaling is observed strong inward pinch

A multi-impurity transport/erosion code was developed combining the transport in the edge barrier and wall erosion including effects of ELMsAUG: consistent description of including all experimental dataimpurity peaking in ETB of ITER very weak for relevant ELM

frequencies

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Outboard limiters most important source

R-sweep modulates outboard W-source

Large divertor source does not play a role

cW reacts strongly to the limiter source

R. Dux et. al., I-6 , PSI 2008, JNM 390-391, 858