Surface Effects and Retention of Steady State 3He+ Implantation in

Single and Polycrystalline Tungsten

S.J. Zenobia, G.L. Kulcinski, E. Alderson, G. Becerra, B. Cipiti, R. Radel, J. Shea, G. Downing, R. Cao, L. Snead,

R. Noll, and D. Savage

HAPL Meeting-LANL

April 8th, 2008

Fusion Technology Institute

University of Wisconsin-Madison

Progress Since Last Meeting

• Three single-crystalline (SCW) and three polycrystalline (PCW) tungsten specimens were acquired from Dr. Lance Snead and ORNL

• Both SCW and PCW were implanted in the UW IEC device with 30 keV 3He+ to fluences of 5x1016 cm-2 at ~850 °C and 4x1017 and 5x1018 cm-2 at ~1000 °C

• Pre and post-irradiation SEM analysis was done on each sample to diagnose surface morphology changes

• Helium retention fluences and retention ratios were measured in all specimens using 3He(d,p)4He nuclear reaction analysis (NRA)

• Retained He fluence, retention ratios and depth profiles were measured by 3He(n,p)T neutron depth profiling (NDP)

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UW 1.7 MeV

Tandem Accelerator

UW Ion Beam Assisted Analysis Techniques: Elastic Recoil Detection (ERD) & Nuclear Reaction Analysis (NRA)

•Previous work by Radel used the ion beam for ERD analysis of HAPL samples

•Helium retention and depth profile was determined for polycrystalline W between 1018 - 1019 He+/cm2

•O4+ beam only penetrated 130 nm

Tungsten Sample

2 MeV D+ beam

α-particle

p (14.7 MeV)

Solid-State Detector

500 μm Al foil

•NRA uses the 3He(d,p)4He nuclear reaction

•D+ beam easily penetrates the He implanted region

•He retention data was acquired for tungsten samples at implant fluences between 5x1016 – 5x1018 He+/cm2

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NIST Cold Neutron Facility and the Neutron Depth Profiling (NDP) Analysis Technique

•NDP uses a cold neutron source and the 3He(n,p)T nuclear reaction

•Neutrons are ideal for depth profiling and measuring concentration (negligible energy loss)

•He retention for tungsten samples was acquired from Greg Downing at the NIST facility

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Results

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• Morphology changes (SEM)

• Helium retention (NRA, NDP, & ERD)

• Materials viability assessment

Polycrystalline Tungsten Irradiated to 5x1016 3He+/cm2 at ~850 ºC

1 μm

Unirradiated

1 μm

5x1016 cm-2

6

1 μm 1 μm

5x1018 cm-2

1 μm

4x1017 cm-2

Polycrystalline Tungsten Irradiated with 3He+ to 4x1017 and 5x1018 cm-2 at ~1000 ºC

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Single Crystalline Tungsten Irradiated to 5x1016 3He+/cm2 at ~850 ºC

1 μm

Unirradiated

1 μm

5x1016 cm-2

8

1 μm

5x1018 cm-2

Single Crystalline Tungsten Implanted with 3He+ to 4x1017 and 5x1018 cm-2 at ~1000 ºC

1 μm

4x1017 cm-2

Pores

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Comparison of Single & Polycrystalline Tungsten Implanted with 3He+ to 5x1016 cm-2 at ~850 ºC

1 μm 1 μm

Single-crystalline Polycrystalline

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Comparison of Single & Polycrystalline Tungsten Implanted with 3He+ to 4x1017 cm-2 at ~1000 ºC

1 μm 1 μm

Single-crystalline Polycrystalline

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1 μm 1 μm

Single-crystalline Polycrystalline

Comparison of Single & Polycrystalline Tungsten Implanted with 3He+ to 5x1018 cm-2 at ~1000 ºC

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Retained Fluence vs. Implant Fluence

0.01

0.10

1.00

10.00

0.1 1.0 10.0 100.0

Implanted He+ Fluence (1017/cm2)

Ret

ain

ed F

luen

ce (

1017

/cm

2 )

NRA SCW

NRA PCW

NDP SCW

NDP PCW

NRA and NDP Show Retained He Fluence Saturates at ~4x1017 cm-2 in Tungsten

NRA = Nuclear Reaction AnalysisNDP = Neutron Depth Profiling 13

Comparing ERD with NRA & NDP Techniques Confirms Retained He Fluence Does Not Exceed ~4x1017 cm-2 in Tungsten

*R.F. Radel and G.L. Kulcinski (2007)

*

NRA = Nuclear Reaction AnalysisNDP = Neutron Depth ProfilingERD = Elastic Recoil Detection

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Observations on Retained He Fluence in Single and Polycrystalline Tungsten

• Saturation of retained He fluence occurs prior to extensive surface morphology change

• Maximum retained He fluence is observed near 4x1017 cm-2

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Helium Retention Ratio vs. Implant Fluence

0.0

0.2

0.4

0.6

0.8

1.0

0.1 1.0 10.0 100.0

Implanted He+ Fluence (1017/cm2)

Ret

enti

on

Rat

io

NRA SCW

NRA PCW

NDP SCW

NDP PCW

Tungsten’s Helium Retention Ratio Decreases with Increasing Implant Fluences

NRA = Nuclear Reaction AnalysisNDP = Neutron Depth Profiling 16

All Techniques Indicate an Increased Retention Ratio of He in W with Decreasing Implant Fluence

*R.F. Radel and G.L. Kulcinski (2007)

*

NRA = Nuclear Reaction AnalysisNDP = Neutron Depth ProfilingERD = Elastic Recoil Detection

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Observations on the He Retention Ratio in Single and Polycrystalline Tungsten

• Surface damage increases despite a decreasing He retention ratio

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Fluence to Full Power Day Equivalent (FPD) in the Reference HAPL Chamber

2.0 FPD8.5 FPD223 FPD1019 cm-2

0.2 FPD0.9 FPD22.3 FPD1018 cm-2

0.02 FPD0.1 FPD2.2 FPD1017 cm-2

Full He+ Spectrum

10 – 100

keV

10 – 30

keV

*Reference HAPL chamber with 10.5 m radius and 5 Hz duty cycle19

600

700

800

900

1000

1100

1200

1300

1.00E+17 1.00E+18 1.00E+19 1.00E+20

Fluence [He+/cm^2]

Te

mp

era

ture

[C

]

Poly W & W/CCV

Single W

Carbide Foams

W-Re

SiC

CCV

Summary of Examined Materials Viability (Cipiti, Radel, and Zenobia)

Relatively Unaffected

Extensive Surface Damage

PCW

CCV

SiC

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PCW

SiC

CCV

Observations on FW Candidate Materials for the HAPL Chamber

• SCW, W-coated TaC foams, and PCW appear to be the most robust materials

• SiC, velvet materials (examined to date), and W-Re alloys respond poorly to ion implantation

• Abatement of the ion threat spectra is necessary to extend the lifetime of any of the examined materials to practical lifetimes

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Future Work

Carbon Velvet Spikes

Length ~ 1 mm

Diameter (base) ~ 35 μm

Future Work Cont. ?

• Depth profiling analysis for SCW and PCW specimens is currently underway

• Focused ion beam (FIB) milling will be used to determine the penetration depth of pores below the tungsten surface

• Surface erosion and roughness will be measured using optical profilometry to give mass loss estimates

22Photo courtesy of Thad Heltemes - UW

Conclusions

• The threshold for pore formation after 3He+

implantation in both SCW and PCW is observed between 5x1016 - 4x1017 cm-2, becoming extensive by 5x1018 cm-2

• The retained helium fluence in tungsten saturates at ~4x1017 He/cm2

• The He retention ratio in tungsten decreases with increasing implant fluence, showing strong He trapping efficiency at low fluences

• He+ abatement is required to extend the lifetimes of any of the IEC examined materials

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Questions

Samuel ZenobiaUniversity of Wisconsin-Madison1500 Engineering DriveMadison, WI 53706(608) 265-8699zenobia@wisc.edu