26pC04

ional Conference on Plasma-facing materials and components for fusion application, Aix-en-Provence, France, May 18-22nd, 2015

Application of laser ultrasonics for plasma material interaction studies
thod forin-situ materialc in fusion devices
Lee Heun Tae、大宅諒、伊庭野健造、上田良夫
H.T. Lee, M. Oya, K. Ibano, Y. Ueda

. Ibano and Y. Ueda

大阪大学大学院工学研究科
Graduate School of Engineering, Osaka University

versity, Suita, Osaka, 565-0871, Japan

1. Introduction
acoustic emission during crack propagation,
There is a critical need in the plasma material
experiments were performed in-vacuo with 30µm thick W specimens. Here the Nd: YAG laserinteraction field for an in-situ and non-contact
method for material characterization andwas used to generate ablation force that
health monitoring of installed components. To
resulted in crack propagation while theaddress this need, our proposed approach is tovibrometer was used to measure the acoustic"Laserultrasonicmethodcanperformmany of the standard ultrasonic testing
utilize laser ultrasonics [1] as a plasma-facing
emission generated when the crack propagated.
but remotely
non-contact- suitablefor use in hostile environment. We
component
diagnosticbyforfusion devices.
A
3. Results
short havepulsedhighlighted
laser resultsin generationof withsomeof our work
W-materials examining:elastic waves in the ultrasonic range due to
Typical time trace of the surface displacement
Wave velocity
thermo-elastic
expansionmeasurements:
or ablation. Theseat the epicenter measured at the back surface
waves aresubsequently
detectedusing
alaserof a waves
polycrystal(PCW) sample is• Longitudinal and shear waves (surface
alsotungstenpossible)
vibrometer.
Bothand bulk
can gauging.
shown in Fig. 1. It was found that the• Useof surface
such waves
forwaves
thicknessbe generated and detected to measure surface
longitudinal wave velocity depends weakly on
and bulk
properties,
respectively.
The material
deuterium retention, and grain size differences
Elastic
property
determination:
thickness, mechanical properties, and stresses
in the µm range. However, ultra fine-grained W• Local elastic properties can be determinedfrom wave speeds
can be deduced from analysis of the time tracewith grain sizes in the order of a few hundred•Grosselastic
properties
canbe
determined
analysisof the detected waves. Here we focus on: (1) thenm resultedfrom
in anvibration
increase inmodal
the wavevelocity.
determination of sound wave velocities inYoung’s modulus is derived from the measured
varioustungstenwhich (e.g.
are required
wave velocities.
Next, heating
it was foundthat crack"In-situ
ionmaterials
implantation
H or He loading)/ in-vacuo
apparatus
for thickness gauging of W components, and (2)propagation generates lamb waves or guided
coming online to test in-situ material’swaves.
response
under ion/ heat loading
determination of acoustic emission during
A shift towards shorter time scales ofcapable ofinobtaining
bothbulklower
propertychanges.
scientificthe
crack propagation
W as a firststepsurface
towards andthefrequencyparts(i.e.
indicated
quantifying
fracture
toughnessunder fusionbasisWfor
material
monitoringdata) distance to the source was decreasing (i.e. crack
relevant conditions.
propagation towards detection point).

Summaryhes:

tructurents
ngsd iseels).

ound
hat
grity

18
Setup 2.1 Experimental

12.0

Photodiode signal [V]Displacement [nm]Displacement (nm)

500
400

105 mJ

50.2

0.30.40.50.60.7

1000-200-300-101Time (µs)

50Standard 5 Mhz contact
ultrasonic transducer

0-50

0.0

0.1

200-100-400

5 mJ

-100

00.0

Velocity (mm/s)

300

Velocity (mm/s)

Displacement (nm)wavelkading

Photodiode Signal (a.u)

PCW
Increasing
excitation
Longitudinal (L)A Q-switched Nd: YAG laser
at 1064
nm (15(1 mm thick)
12
laser
power
results
inwave arrival
ns FWHM) is focused to ~0.1 mm diameter on0shift from thermoelastic
1.5
various W
specimens which
generateelastic
to ablation
regime6-1waves in the ultrasonic range by thermo-elastic
expansion0 or ablation. These waves are
1.0-2
subsequently detected using a commerciallyavailable-6 He-Ne laser (633.8 nm) vibrometer-3
0.5
head and decoder from Polytec which measures
Shear (S)-12
the change in surface displacement andwave arrival
-4velocity.-18
The displacement is determined by the0.00200
400
600
0.0 of the0.5
1.01.5phase shift
backscatteredprobe
beam2.0
Setup 2Time [ns]Time (µs) are based on
while the30 velocity measurements
the Doppler Wave
effect. Wavevelocityexperiments
Fig. 1: Surface ofdisplacement
the epicenter
Characterization
wave sourceatgeneration
generation
17 mJ
25
were performed
in air with laser energy < 20 bymeasured
attheback
surfaceofPCW
sample.
pulsed laser (Broadband signal)
mJ. The sourceanddetection
laserswere17 mJ
300
Pulse response
20~ Thermal diffusion
delay time of opposite
positioned directly
one another,
250 C.B. Scruby, R. J. Dewhurst, D. A. Hutchins,[1]timescale
electronics ~150 ns
200
sandwichedby the W specimen of interest(i.e.
andS. B. Palmer,
8 mJ J. Appl. Phys. 51, 6210 (1980)
158 mJ
150e inepicenter configuration). For detecting of100

0.2

0.4

0.6

Time (µs)

0.81.0