Annual High-Z /Metal PFC SEWG Meeting, Ljubljana 1-2 October 2009 Studies of Plasma-Wall...

Annual High-Z /Metal PFC SEWG Meeting, Ljubljana 1-2 October 2009

Studies of Plasma-Wall Interactions

Post mortem characterization of exposed tungsten PFCs (TEXTOR and AUG) with various microscopic

and analytical techniques

Association IPPLM / EURATOM, PolandElżbieta Fortuna-Zaleśna, Joanna Zdunek, Witold Zieliński, Mariusz Andrzejczuk, Marcin Pisarek,

Tomasz Płociński, Stanisław Szpilewicz, Marcin Rasiński

Presented by Lukasz Ciupinski

Association

EURATOM-IPPLMWarsaw University of Technology


Research Activities

• I. Post mortem analysis of tungsten coated tiles from the divertor strike point region of ASDEX-Upgrade

– Examinations of deposits present at tungsten coatings

– Examinations of „bubble like” formations present in the small cavities of tungsten coating

• II. Examinations of Langmuir probe from TEXTOR tokamak

Outline


I. Post mortem analysis of tungsten coated tiles from the divertor strike point region of ASDEX-Upgrade

Material

9 samples from 2 divertor strike point tiles:

Element 01b/1 from the outer strike point region, coated with a 200 µm W VPS layer

Element 04/1 from the inner strike point region, coated with ~4 µm W

Experimental

• Tiles installed from 4 o 10/07• No boronization performed• All PFCs tungsten coated

In 2009 we continued TEM examinations of deposits developed at these tiles and bubble-like formations present at the surface of tungsten coating (exploring FIB technique).

K. Sugiyama at al. Deuterium inventory in the full tungsten divertor of ASDEX Upgrade


Surface morphology of the inner divertor strike point tile [2008 results]

Typical surface topography:•Compact, glassy-like layer of deposit•Dust particles•Re-melted tungsten layer•Stratified character of deposit

50 m 50 m

deposit

disclosed tungsten coating

50 m 10 m

The results obtained in 2008 revealed at the coated surface of the inner divertor strike point tile a thick, compact, glassy-like deposit with good adhesion and integrity.


Surface morphology of the outer divertor strike point tile [2008 results]

50 m 25 m

100 m

Typical surface topography:• Dust particles• Eroded areas• Bubble-like formations

In the case of outer strike point region large areas subjected to erosion were revealed by SEM observations. In the small cavities of the coating, the „bubble-like” formations were observed.

10 m


XPS examinations (ESCALAB 210) [2008 results]

Name Tile 1 Tile 2

At.%

C 37.6 35.2

W 18.9 34.6

O 39.4 28.5

N 2.2 1.1

Fe 1.3 0.2

Na 1.6 0.4

The main constituents of surface layers are carbon, tungsten and oxygen.

Tile1 (Element 01b/1) - outer strike point region

• Tungsten is present in the deposit in the form of oxides, elemental tungsten, carbides and wolframates. Oxides and wolframates dominate. The fraction of metallic form and carbides amounts to 5.4 at.% (about 1/3 of tungsten fraction).

• Most of carbon is present in the form of hydrocarbons and graphite. Only insignificant amount (less than 2 at.%) is present in the form of carbides.

Tile2 (Element 04/1)- inner strike point region

• The fraction of tungsten in an elemental form and carbides is comparable with oxidised forms [3:2].

• The significant fraction of carbon is present in the form of carbides and/or isolated carbon.

Chemical composition of surface layers

The XPS examinations revealed that the main constituents of the deposits were carbon (35at. %), tungsten (20-35at.%) and oxygen (30-40at.%). Nitrogen and iron were present at the level of 1at. %.


tile

W coating

deposit

W protection mask

BF-STEM and HRSEM images of FIB specimen

A deposit was revealed at the surface of the tungsten coating, up to 1.5 µm thick.

This deposit has a stratified structure, with sublayers differing in thickness, structure and chemical composition. Their thickness varies in the range from 10 to 50 nanometers. They have diversified structure: chained, striped or doted form.

The deposited material is compact, however, seldom voids are present.

IA. TEM/HRSEM investigations of the structure of deposit present at the coating of the inner divertor strike point tile


The observations in TE mode together with EDS analyses reveal that the sublayers differ in the chemical composition. There are layers enriched in tungsten and oxygen alternating with carbon containing ones. Additionally, it was observed that the part of deposit closer to the coating surface was richer in carbon in the comparison to the external one.

Distributions of W, O, C and Fe along the lines shown in the upper images

W protection mask

W coating

W C

O C O

W

Fe


TEM image of deposit and corresponding diffraction pattern

SAD investigation showed that the deposit was amorphous.

IA. TEM/HRSEM investigations of the structure of deposit present at the coating of the inner divertor strike point tile


•A thin layer of deposit was revealed (on average 60 nm).

•The adhesion of the deposit is good. Locally, small pores, up to 400 nm long.

•Some small dust flakes at the coating surface.

Note: The specimen for STEM/TEM observations was cut from a small cavity of the coating, in the region were “blister-like” formations were observed.

IB. TEM/HRSEM investigations of the structure of deposit present at the coating of the outer divertor strike point tile

HRSEM images of FIB specimen of the deposit

dust

W protection mask

deposit

W coating


STEM images of deposit

The morphology of the deposit reveals three sublayers, the internal and external are similar, whereas the central one is different. The interfaces between particular sublayers are diluted.

The DF images prove that the sublayers differ in the chemical composition. The outer and inner sublayers contain more light elements in comparison to the central one.

Having in mind the XPS results, it can be concluded that the outer and inner sublayers contain a lot of hydrocarbons, whereas the central zone is rich in tungsten/tungsten compounds.

IB. TEM/HRSEM investigations of the structure of deposit present at the coating of the outer divertor strike point tile


IC. Examinations of bubble like formations present in the small cavities of tungsten coating

The “bubble-like“ formations were observed at the surface of outer strike point divertor tile, on sample #2 (from the private flux region) and sample #3 (from the strike point region).

Most of the tile surface was subjected to erosion.

The “bubble-like“ formations were observed in small cavities of the coating.

Images of examinated sample surfaces (#2 left and #3 right)

10 m

5 m


FIB images of bubble-like formations cross-section

Cross-sections through the „bubble-like” formations revealed voids.

During cutting, blisters collapsing was observed. This suggests these are gas blisters.

IC. Examinations of bubble like formations present in the small cavities of tungsten coating


Experimental

The surface of the W Langmuir probe after exposure in TEXTOR tokamak was investigated by scanning electron microscopy (SEM). During experimental campaign the tip of the probe partially melted, evidence of this event is visible in the form of re-melted tungsten droplet.

II. Examinations of Langmuir probe from TEXTOR

SEM images of the probe surface (scratches)

1 mm 500 m


At the surface of the probe the fine flattened droplets, often with characteristic dendrite-like structure, up to 150 µm in diameter were observed.

The EDS measurements revealed they were rich in aluminum and oxygen.

The alumina was also detected in small crevices/discontinuities of tungsten surface.

100 m

1 mm 50 m

re-melted part of the probe



1. In the overheated region, adjacent to the re-melted part of the probe the material (tungsten) re-crystallized.

2. In the analyzed region (area with alumina particles) the probe surface was locally lightly re-melted.

3. No evidence of blisters formation was found

10 m

500 m 20 m

1 2

3



Poster presentation E. Fortuna-Zalesna et al. “Plasma induced surface modification in the divertor strike point region of ASDEX Upgrade”, PFMC 12

Article M. Mayer et al. “Tungsten erosion and redeposition in the all-tungsten divertor of ASDEX Upgrade“ submitted for PFMC 12.

Deliverables


Thank you for your kind attention


Activities proposed for 2010

• WP10-PWI-03-01-xx-01/IPPLM_Poland (Dust generation in present devices)– Characterization of dust collected in EU machines (AUG and TEXTOR): TEM, SEM,

XPS, AES, BET etc.

• WP10-PWI-04-02-xx-01/IPPLM_Poland (Characterisation of outer and inner divertor erosion as well as the migration of impurities from main chamber to divertor and inside the divertor)

– Characterization of exposed AUG divertor outer strike point tiles (PVD, 10 µm W on 3 µm Mo) with various microscopic and analytical techniques.

• WP10-PWI-05-01-xx-01/IPPLM_Poland (PWI in a full-W device)– Polycrystalline W, physical vapor deposited W (ASDEX Upgrade type) and plasma-

sprayed W samples (ASDEX Upgrade type) will be irradiated at the IPP laboratory devices Hochstromquelle and PlaQ by deuterium and helium ions. Surface morphology changes, such as formation of nanostructures, blisters or foam-like structures on the irradiated samples, will be investigated by high-resolution scanning electron microscopy (HR-SEM), focused ion beam cross-sectioning (FIB), and transmission electron microscopy (TEM) at WUT

Annual High-Z /Metal PFC SEWG Meeting, Ljubljana 1-2 October 2009 Studies of Plasma-Wall...

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