Fabrication of spherical Cu-oleate targets

using emulsion method

Yuki IWASA1* iwasa-y@ile.osaka-u.ac.jp

Kohei YAMANOI1, Kana FUJIOKA1, Seungho LEE1, Shohei SAKATA1,

Hiroshi SAWADA1,2, Akira YAO1, Akifumi YOGO1, Hideo NAGATOMO1,

Shinsuke FUJIOKA1 and Takayoshi NORIMATSU1

1 Institute of Laser Engineering, Osaka, Japan

2 Department of Physics, University of Nevada Reno, USA

* JSPS Research Fellow

22nd Target Fabrication Meeting @ Las Vegas, Nevada 2017 Mar. 12 -16

Summary

• Cu-containg spherical targets were fabricated with emulsion method

for fast ignition experiment.

• The Cu-oleate microsphere contents ~1 at. %, and Cu-ions were

distributed homogenously in the microsphere.

• 200-μm diameter microsphere showed good sphericity of 0.97.

Although the microspheres have 1-μm deep defects, the defects

had no significant effect on the areal density.

• These Cu-oleate spherical targets were used in magnetized fast

ignition experiment. The targets enabled to visualize the energy

transfer of laser-induced electron beam.2/15

Magnetized fast ignition with sphere

target was designed for FIREX.

Fast Ignition REalization Experiment (FIREX)

• Core heating with laser-induced electron beam

• To heat up Ti > 5 keV

• Heating efficiency ~1.6 % @ 2013*

Improvement of heating efficiency

• compression => Spherical target

• divergence angle => guiding w/ strong B-field

3/15*Y. Arikawa, et al.,J. Phys. Conf. Ser. 688 (2016) 12004.

B-field

previous design

new design

4/15

500 um 200 um

shell sphere

maximum density high low

hydrodynamic instability large small

Morphological requirement high low

Morphological requirement of target is

relaxed by using solid sphere.

Using spherical target

• Compression with spherically converging shock

• More hydrodynamically stable than shell implosion

~1 at% Cu-containing sphere was

required to visualize heated region.

Fast ignition experiment with Cu-containing target

• Cu-Kα imaging with ~1 at.% Cu-doped shell targets*

• Visualization of heated region

• Estimation of Te by x-ray spectroscopy

Requirement of Cu-containing sphere

• Cu contents : ~1 at. %

• 200-μm solid sphere

• Low-Z composition

5/15* L.C. Jarrott, et al., Nat. Phys. advance on (2016) 1–7.

CVD method* => difficult to fabricate “sphere”

Emulsion method

• Cu(II)-oleate (C17H33COO)2Cu

be solvable to organic solvent

contain Cu 0.93 at.% ideally

compose by low Z material

Microspheres were fabricated by

emulsion method with Cu(II)-oleate.

6/15

Solution of Cu-oleate

Cu-oleate (C17H33COO)2Cu

*A. Nikroo, et. al, Fusion Sci. Technol. 45 (2004) 144–147.

Cu(II)-oleate

Fabrication of spherical Cu-oleate

microsphere with O/W emulsion method

1. Droplet generation: glass capillary based microfluidic device*

• oil: Cu-oleate solution 7 wt %

• water: PVA aqueous solution 5 wt% + NaCl 5g/L

2. solvent removal in PVA for 2-3 days

3. washing with diluted water

Droplet generation with microfluidic device

Cu-oleate microspheres

7/15*A.S. Utada, et. al, Science, 308 (2005) 537–541.

Cu concentration were preserved

through emulsion method.

• Unexpected reduction of Cu ions to water/oil phase

• ICP-AES measurement

1. Preparation of Cu-oleate microspheres

2. Dissolving Cu ions with nitric acid (HNO3)

3. Measuring concentration of sample solution

4. Evaluation the Cu contents

• Cu contents 9.7 wt. % => nearly equal to ideal contents 10.1 wt% (0.9at%)

8/15

HNO3 aqHNO3 aq

Cu2+

Cu2+Cu2+

ICP-AES

Cu ions were distributed uniformly in

the microsphere from EDS mapping.SEM-EDS measurement

• Sample: Cu-oleate embedded in polymer

• Mapping Cu-Lα detection (green dots)

• Intensity profile along radius (center => serface)

9/15-100 -80 -60 -40 -20 0 20 40

0.0

0.5

1.0

1.5

2.0

2.5

Inte

nsi

ty (

arb

.un

its)

Position (m)

Microsphere Polymer

Cu-Lα detection (green dots) Integrated intensity profile

Microsphere

Polymer

The microsphere showed good sphericity.

• Radial profile from optical images

• 𝐒 = 𝟏 −𝑹𝒎𝒂𝒙−𝑹𝒎𝒊𝒏

𝑹𝒂𝒗𝒆

𝑹𝒂𝒗𝒆: 102.6 μm

𝑹𝒎𝒂𝒙: 103.5 μm

𝑹𝒎𝒊𝒏: 100.6 μm

• Sphericity S >0.97

• Similar value were obtained from

other spheres

angular profile of sphere

10/15

1-μm depth “defect” were observed

on the surface.

• Surface observation with laser microscope

• Defects were found on entire surface

• Property of defect• depth : ~1 μm

• size : 5–20 μm (mode 30-120)

• RMS 0.8 μm

11/15

40.0 μm

30.0 μm

-5

5

0

(μm)

50 μm

Cu-oleate targets with defects can achieve

an areal density similar to ideal sphere.

Compression simulation

• 2-D hydrodynamic simulation PINOCO*

• 200 μm Cu-oleate sphere w/ or w/o defects (fabricated or ideal sphere)

• 2ω, 12 beams, 250J/beam

• Maximum areal density

• w/ defects (real target) : 0.070 g cm-2

• w/o defects (ideal sphere): 0.069 g cm-2

• No major difference were observed

• Attenuation in high mode (>40) **

12/15

Areal density during compression

*H. Nagatomo, et. al, J. Plasma Phys. 72 (2006) 791.

**M. Murakami, et. al, Phys. Plasmas. 22 (2015) 1–10.

1.0 1.2 1.4 1.6 1.80.00

0.02

0.04

0.06

0.08

0.10 Cu-oleate microsphere with defects

Ideal Cu-oleate microsphere

Are

al d

en

sity

R (

g c

m-2)

Time (ns)

Cu-oleate targets enable to visualize

energy transfer of fast electrons

• Succeed to visualize heated area

• Guiding electron w/ B-field

• Te evaluation from x-ray energy spectroscopy => Te ~ 1.7 keV

w/ B-field

13/15

w/o B-field

S. Sakata, et. al, to be submitted.

Cu-Kα images of heated region w/ or w/o B-field

Cu (II) olate

sphere attached

Au hollow cone

LFEX

Au

cone

summary

• Cu-containg sphere targets were fabricated with emulsion method.

• The Cu-oleate microsphere contents ~1 at. %, and Cu-ions were

distributed homogenously in the microsphere.

• 200-μm diameter microsphere showed good sphericity of 0.97.

Although the microspheres have 1-μm deep defects, the defects

had no significant effect on the areal density.

• These Cu-oleate spherical targets were used in fast ignition

experiment. The targets enabled to visualize the energy transfer of

laser-induced electron beam.

14/15

Acknowledgement

15/15

This work was supported by the Japan Society for the Promotion of

Science (JSPS) through the Grants-in-Aid for JSPS Research Fellow Grant

Number 15J00902 and by the National Institute for Fusion Science (NIFS)

through the NIFS Collaborative Research Program Project Number

NIFS12KUGK057. Y. Iwasa is a JSPS Research Fellow. The authors are

also very grateful to the members of the Target Fabrication Group of ILE.

16/15

200um

There are some good surface condition sphere

vacuum 50℃10 min 100 min

cooling R.T. cooling R.T.

Improvement of surface quality by melting