Co-deposition of deuterium and impurities in plasma-wall interaction simulators

Marek Rubela, Per Peterssona, Arkadi Kreterb

aAlfvén Laboratory, KTH, Association EURATOM–VR, Stockholm, Sweden

bIEK-4, Forschungszentrum Jülich, Association EURATOM, Jülich, Germany

O U T L I N E •Exposures of carbon-based materials: PISCES-A and PSI-2.

•Surface composition of targets: deuterium and impurity species

•Summary and concluding remarks

Content is a bit archaicbut NOT obsolate

- as long asPWI simulators are

in operation.

PISCES-A (1988)

Experiments

The Aim:

To determine erosion of carbon-based materials:CF222, CF222 + 1m SiC, C+SiC 30% – Schunk GmbH;

CL5890PT – Le Carbonne Lorraine

Exposures:D = 1.15 – 2.81 x 1025 (2 samples 8.8 and 31.8 x 1025)

Target T: 623 – 1200 K

Sample size: disk 25 mm

E. Franconi, M. Rubel and B. Emmoth, Nucl. Fusion 29 (1989) 737.B. Emmoth, M. Rubel and E. Franconi, Nucl. Fusion 30 (1990) 1140.

Ion Beam Analysis

E. Franconi, M. Rubel and B. Emmoth, Nucl. Fusion 29 (1989) 737.B. Emmoth, M. Rubel and E. Franconi, Nucl. Fusion 30 (1990) 1140.

Methods:Rutherford Backscattering Spectroscopy (RBS)

Nuclear Reaction Analysis: 3He(d,p)4He and p(11B,)8Be

Thin layer: 50 nm

Thick layer: 3000 nm

Channel Number

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Deuterium content and distribution

PISCES-A, 1988

Ion Beam Analysis: Impurities

E. Franconi, M. Rubel and B. Emmoth, Nucl. Fusion 29 (1989) 737.B. Emmoth, M. Rubel and E. Franconi, Nucl. Fusion 30 (1990) 1140.

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PISCES-A, 1988

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B

Impurities from plasma generator:

B and La from LaB6 (cathode)Cu (anode)

Erosion from the chamber wall:

Steel components Fe, Ni, Cr

Deuterium and impurities on samples after single exposures

D and impurity content on samples after single exposures.

Exposure Target T (K) D (1015 cm-2) Imp (1015 cm-2)

Single CL5890PT 673 57 30 - 50

CF 222 1023 29 - 39 36 - 81

CFC + SiC film 1200 9 - 15 88 - 340

C + SiC30 1200 4 - 7 53 - 87

C + SiC30 1200 4 - 10 105 - 410

Double C + SiC30 623 - 823 116 - 158 230 - 300

C + SiC30 1023 15 64 - 120

C + SiC30 873 - 1073 135 – 218 300 – 550

8 exposures CL5890PT 623 – 1200 70 - 3500 44 - 10000

More impurities than deuterium.

E. Franconi, M. Rubel and B. Emmoth, Nucl. Fusion 29 (1989) 737.B. Emmoth, M. Rubel and E. Franconi, Nucl. Fusion 30 (1990) 1140.PISCES-A, 1988

Messages

Highly inhomogeneous distribution of species.

Amount of impurities is greater than the deuterium content.

Exposure Target T (K) D (1015 cm-2) Imp (1015 cm-2)

Single CL5890PT 673 57 30 - 50

CF 222 1023 29 - 39 36 - 81

CFC + SiC film 1200 9 - 15 88 - 340

C + SiC30 1200 4 - 7 53 - 87

C + SiC30 1200 4 - 10 105 - 410

Double C + SiC30 623 - 823 116 - 158 230 - 300

C + SiC30 1023 15 64 - 120

C + SiC30 873 - 1073 135 – 218 300 – 550

8 exposures CL5890PT 623 – 1200 70 - 3500 44 - 10000

E. Franconi, M. Rubel and B. Emmoth, Nucl. Fusion 29 (1989) 737.B. Emmoth, M. Rubel and E. Franconi, Nucl. Fusion 30 (1990) 1140.

Deuterium and impurity content on samples: All results.

Ion Beam Analysis: Impurities

E. Franconi, M. Rubel and B. Emmoth, Nucl. Fusion 29 (1989) 737.B. Emmoth, M. Rubel and E. Franconi, Nucl. Fusion 30 (1990) 1140.PISCES-A, 1988

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Spectra recorded in several points on the graphite sample exposed 8 times to plasma.

Distance between points: 5 mm

PISCES-A (2008) Experiment

The Aim:To determine deuterium retention in graphites and CFCs.(NB-41 = CFC, Snecma; ITER reference carbon material; ATJ = graphite)

Exposure:D = 1- 50 x 1025 m-2

Target T: 370 - 820 K

Sample size: disks 25 mm

Number of samples: 3

A. Kreter et al., Phys. Scr. T138 (2009)

PISCES-A (2008): Example of results

D: 152±5 La 3,4

D: 173±5 La 3,5

D: 155±7 La 3,9

D: 126±5 La 4,8

Sample NB41 (B)

Surface concentration of deuterium and lanthanum (1015 cm-2)

NB41 Sample (C) D: 25 x 1015 cm-2

La: 90 x 1015 cm-2

PSI-2 (Berlin, 1998)

PSI-2 (Berlin, 1998) Experiment

The Aim:To determine deuterium retention in NS-31.(NS-31 = CFC with SiC, Snecma)

Exposure:

D = 1.26 x 1025 (5 h, 7x1021 m-2s-1)

Target T: 420 K

Sample size: disk 20 mm

Ion Beam Analysis of NS-31

Channel Number500 750

1.500

0

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Impurities

800

104

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Si

Enhanced Proton Scattering: 1500 keV H+, 1 or 3 mm beam

PSI-2 (Berlin, 1998): NS-31

Channel Number500 750

1.500

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C O

TaLa

Mo

Cu

SiO

C

Si Cu

Mo

Ta La

Messages

Significant amount of co-deposited impurity species originating from the plasma generator.

Not uniform distribution of impurity species on the surfaces in areas located 5-7 mm apart.

Significant difference in the Si content on the surface – very inhomogeneous NS-31 material.

Enhanced Proton Scattering: 1500 keV H+, 1 or 3 mm beam

Summary of Results PSI-2

D: 104 – 152 x 1015 cm-2

B: 46 – 290 x 1015 cm-2

Cu and Ni: 93 – 189 x 1015 cm-2

Mo: 5.0 – 9.0 x 1015 cm-2

La and Ta: 4.2 – 9.9 x 1015 cm-2

Boron and copper (and nickel) are major impurities.

The amount of impurity species exceeds the content of deuterium in the studied surface.

Summary and Concluding Remarks

Plasma generation in PMI simulators is accompanied by erosion of materials from the plasma source and the experimental chamber.

Main impurities are Cu, La, B, Mo, Ni, Ta.These species are co-deposited on the exposed target. Impurity co-deposition is independent on the target Tsurface.

The amount of impurity species usually exceeds the content of deuterium on the studied surface.

Deposition pattern is not homogeneous indicating strong differences in the uniformity of the plasma column.

Summary and Concluding Remarks

It is unreasonable to expect that impurity production can be avoided but the process must be monitored and taken into account when concluding on:

• material erosion (sputter yield changes!);

• fuel retention (surface state plays here crucial role)

• effects of surface modification.

Multiple exposures of targets should probably be avoided unless these are dedicated experiments.

Questions?

Comments?