Experimental Setup

Results

Effect of Rhenium Addition on Tungsten Fuzz

Formation in Helium Plasmas

Aneeqa Khan1 , Greg De Temmerman2,3 ,Thomas Morgan2 , Paul Mummery1

1 School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, M13 9PL, UK 2 FOM Institute DIFFER, Dutch Institute For Fundamental Energy Research, Association EURATOM-FOM, Trilateral Euregio Cluster, Nieuwegein, Netherlands 3 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046 - 13067 St Paul Lez Durance Cedex , France

Pilot PSI [5]

Magnum PSI [4]

Material Average Temperature

(oC)

Duration (s)

Pure Tungsten

1110 40

990 100

960 200

1270 400

Tungsten-3%

Rhenium

960 40

960 100

930 200

1460 400

Tungsten-5%

Rhenium

970 40

930 100

940 200

1420 400

Table 1: Exposure Conditions

Discs cut from rods of pure tungsten, tungsten 3% rhenium and tungsten 5% rhenium (wt%) were polished to a mirror finish and cleaned in acetone, ethanol

and deionised water. They were then exposed to helium plasmas in Magnum PSI and Pilot PSI for the conditions given in Table 1. The samples highlighted

in purple were exposed in Pilot, and the remaining samples in Magnum.

Introduction

• Tungsten is the candidate material for the divertor in ITER.

• 14MeV neutrons present in ITER will lead to the transmutation of

tungsten to W-3.8at%Re-1.4at%Os following 5 years of operation

[1].

• Exposure of tungsten to helium plasmas at temperatures above

800°C results in fuzzy tungsten [2].

• The helium-induced nanostructure, being very fragile in nature,

could indeed pose severe problems in a fusion reactor in terms of

material losses and dust formation.

• Therefore vital we understand the process of formation.

• Formation of fuzzy tungsten is affected by ion flux, temperature and

exposure time.

• Literature suggests rhenium addition may result in decreased

efficiency of production of helium induced nanostructure [3].

• Addition of rhenium under irradiated condition also results in

increased brittle behavior of tungsten.

• Will the presence of rhenium in tungsten alter the kinetics and the

process of helium induced damage creation?

Pilot

Magnum

Summary/ Further Work References [1] M.R. Gilbert and J.-Ch. Sublet. Neutron-induced transmutation effects in W and W-alloys in a fusion environment. Nuclear Fusion, 51(4):043005,

April 2011.

[2] Y. Ueda, K. Miyata, Y. Ohtsuka, H.T. Lee, M. Fukumoto, S. Brezinsek, J.W. Coenen, a. Kreter, a. Litnovsky,V. Philipps, B. Schweer, G. Sergienko, T.

Hirai, A. Taguchi, Y. Torikai, K. Sugiyama, T. Tanabe, S. Kajita, and N. Ohno. Exposure of tungsten nano-structure to TEXTOR edge plasma. Journal of

Nuclear Materials, 415(1):S92–S95, August 2011.

[3] M. J. Baldwin and R. P. Doerner, “Formation of helium induced nanostructure ‘fuzz’ on various tungsten grades,” J. Nucl. Mater., vol. 404, no. 3, pp.

165–173, Sep. 2010

[4] De Temmerman, G., van den Berg, M. a., Scholten, J., Lof, a., van der Meiden, H. J., van Eck, H. J. N., … Zielinski, J. J. (2013). High heat flux

capabilities of the Magnum-PSI linear plasma device. Fusion Engineering and Design, 88(6-8), 483–487. doi:10.1016/j.fusengdes.2013.05.047

[5] DIFFER. (2014). Pilot-PSI. Available: http://www.differ.nl/research/fusion_physics/psi_experimental/pilot_psi%20. Last accessed 1st June 2014

Acknowledgements to the Leeds EPSRC Nanoscience and Nanotechnology Research Equipment Facilty and Michael Ward for the FIB cross

sections in the Pilot PSI results section.

A disc of each alloy composition was exposed for 400 s at a temperature of approximately 1400 °C to helium plasmas with fluxes of the order of 1024 m-2 s-1 and energies of

30 and 35 eV . The tungsten disc had a diameter of 30mm and the rhenium alloyed discs had diameters of 15mm, All discs were approximately 1 mm thick. Focused Ion

Beam was used to obtain 15 μm length cross sections in the region where the plasma beam hit the surface of the samples. The average depth was determined by taking

depth measurements at 1 μm intervals along the cross sections. There is a small decrease in the depth of the fuzz between pure tungsten and tungsten-3% rhenium. There

is a large decrease in fuzz depth from the 3% to 5% rhenium. Fuzz in pure tungsten is finer than in tungsten-rhenium. This suggests that the rhenium is causing the fuzz to

form more slowly and that an earlier stage of growth is being seen in the rhenium samples.

In this case the observations were the

opposite of those in Pilot. In this experiment

the fuzz appears to be more developed in the

tungsten-5% rhenium samples in comparison

to the 3% rhenium and pure tungsten

samples. Lower magnification SEM images

show the strong grain dependence of fuzz

growth. It can be seen that as the time of

exposure increases, the boundaries between

the grains become less visible as the fuzz

develops. It is known that grain size also

strongly effects the development of fuzz, and

from the low magnification images the grain

size of the pure tungsten seems larger than

the rhenium samples, which may have

affected the fuzz growth. Fuzz growth is well

aligned in early stages, which is clearly

observed in the high magnification SEM

images of the pure tungsten up to 100 s.

Whereas, even at 100 s there is more disorder

in the fuzz observed in the 5% rhenium

sample, and after 200 s, the fuzz is well

developed.

• For 400 s exposures, rhenium seems to inhibit the growth of fuzz.

• For 40-200 s exposures, fuzz grows more quickly in rhenium samples.

• TEM analysis of the fuzz observed in the Pilot samples is required.

• XPS analysis to determine the chemical composition of the surface is needed.

• Development of the mechanical properties of the samples could also be investigated.

• Rhenium does seem to be affecting fuzz growth, but this effect differs between shorter and longer exposure times.

Therefore it would be beneficial to conduct further plasma exposure experiments in order to build up a more

detailed picture.

Flux of order of 1023 m -2 s -1

Flux of order of 1024 m -2 s -1

Cross sections of fuzz in a) pure tungsten, b) tungsten-3% rhenium and c) tungsten-5%

rhenium and d) plot of the variation of fuzz depth and porosity with rhenium concentration for

samples exposed for 400 s at 1400 °C in Pilot PSI.

SEM images of fuzz in a) pure tungsten, b) tungsten-3% rhenium, c) tungsten-5% rhenium

samples to pure helium plasmas at fluxes of the order of 1023 ion·m-2s-1 and energy of 30 eV

Material Average Temperature (oC) Duration (s)

Pure Tungsten 1110 40

990 100

960 200

1270 400

Tungsten-3% Rhenium 960 40

960 100

930 200

1460 400

Tungsten-5% Rhenium 970 40

930 100

940 200

1420 400

0 3 6 10

15

20

0

1

2

3

Po

rosi

ty (

%)

Ave

rage

Fu

zz D

ep

th (

µm

)

Rhenium Concentration (%)

Fuzz Depth Porosity

d)

SEM images at low and high magnifications of tungsten, tungsten-3% rhenium and tungsten-5% rhenium samples exposed for 40, 100 and 200s at approximately 970 °C.

A disc of each alloy composition was exposed for 40,100 and 200 s at a temperature of approximately 970 °C to helium plasmas at fluxes of the order of 1023 m-2 s-1

and energies of 30 eV. The pure tungsten samples were 20mm in diameter and the tungsten-rhenium discs were 15mm in diameter. All the discs were 1mm in thickness, apart from the pure tungsten that was exposed for 40s, which was 0.5mm thick.

a) b) c) a)

b)

c)