IFSA, Kyoto, Japan, September 2001 1 Dry Chamber Wall Thermo-Mechanical Behavior and Lifetime under IFE Cyclic Energy Deposition A. R. Raffray 1, D. Haynes.

IFSA, Kyoto, Japan, September 2001 1

Dry Chamber Wall Thermo-Mechanical Behavior and Lifetime under IFE Cyclic Energy Deposition

A. R. Raffray1, D. Haynes2, R. R. Peterson2,

M. S. Tillack1, X. Wang1, M. Zaghloul1

1University of California, San Diego, 460 EBU-II, La Jolla, CA 92093-0417, USA2University of Wisconsin, Fusion Technology Institute, 1500 Engineering Drive,

Madison, WI 53706-1687, USA

2nd International Conference on Inertial Fusion Science and Applications

Kyoto, Japan

September 17-21, 2001


Lifetime is a Key Dry Chamber Wall Issue

• Past studies, such as SOMBRERO [1], indicated the need for a protective gas at a significant pressure (e.g. Xe at ~0.5 torr) to prevent unacceptable wall erosion for a carbon chamber wall even for direct-drive targets.

• This creates a formidable challenge for such a design since the presence of a gas would have to also accommodate target and laser requirements.

• Recent studies indicated that only minimal target temperature increase (~1 K) can be tolerated during injection to maintain the required target uniformity for a symmetrical burn. High speed target injection (~100’s m/s) through a background gas could result in higher target temperature deviation due to convection and friction effects [2].

• The presence of a background gas could also lead to laser breakdown depending on the gas density [1].


More Accurate Analyses Were Carried Out to Assess Armor Lifetime and Design Window for Recently Computed Direct and

Indirect Drive Target Spectra

• Until recently, no reasonable design window seemed to exist satisfying the conflicting chamber gas constraints from wall protection on one hand and from the latest target and laser considerations on the other.

• A recent effort as part of the ARIES-IFE program has provided a more detailed assessment of dry chamber wall [6] based on ion and photon spectra from new direct-drive target from NRL [3,4] and indirect drive target from LLNL [4,5]

• Detailed analyses using very fine meshes were performed for both the energy deposition from the photons and ions and the thermal behavior of the wall (ANSYS and BUCKY).

• Photon and ion time of flight effects were included as well as armor melting (for metallic armor) and evaporation.

• C and W flat walls and a C fibrous carpet as an example of an engineered surface were considered in the analyses


X-ray and Charged Particles SpectraNRL Direct-Drive Target [3,4]

1. X-ray (2.14 MJ)

2. Debris ions (24.9 MJ)

3. Fast burn ions (18.1 MJ)(from J. Perkins, LLNL)

3

1

2


X-ray and Charged Particles SpectraHI Indirect-Drive Target [4,5]

1. X-ray (115 MJ)

2. Debris ions (18.1 MJ)

3. Fast burn ions (8.43 MJ)(from J. Perkins, LLNL)

1

10.0E+81.0E+101.0E+111.0E+121.0E+131.0E+141.0E+151.0E+161.0E+171.0E+181.0E+191.0E+201.0E+211.0E+22

1.0E-1 1.0E+0 1.0E+1 1.0E+2 1.0E+3

4HeD T

H Au

Ion Kinetic Energy (keV)

3He

Gd

Fe

Br

Be

210.0E+8

1.0E+10

1.0E+11

1.0E+12

1.0E+13

1.0E+14

1.0E+15

1.0E+16

1.0E+17

1.0E+1 1.0E+2 1.0E+3 1.0E+4 1.0E+5

4He

D

T

H

Ion Kinetic Energy (keV)

3He

γ

N

3


Photon and Ion Attenuation in Carbon and Tungsten for Direct Drive Target Spectra Without Protective Chamber Gas

10.0x103

1.0x105

1.0x106

1.0x107

1.0x108

1.0x109

1.0x1010

1.0x10-6 1.0x10-5 1.0x10-4 1.0x10-3 1.0x10-2

Penetration Depth (m)

Photons, C

Photons, W

Fast ions, C

Fast ions, W

Debri ions, C

Debri ions, W


Photon and Ion Attenuation in Carbon and Tungsten for Indirect Drive Target Spectra for an Example Case Without a Protective

Chamber Gas

10.0x103

1.0x105

1.0x106

1.0x107

1.0x108

1.0x109

1.0x1010

1.0x1011

1.0x1012

1.0x1013

1.0x10-8 1.0x10-7 1.0x10-6 1.0x10-5 1.0x10-4 1.0x10-3 1.0x10-2

Penetration Depth (m)

Photons, C

Photons, W

Fastions, C Fast ions, WDebri

ions, C

Debri ions, W


Photon and Ion Time of Flight Effects Were Taken into Account

Time (ns)

FusionPower(TW)

23 24 25 26 27 28 29 30

10-3

10-2

10-1

100

101

102

103

104

105

106

NRL-DD-43

X-ray Emission from 115 MJ NRL Laser Target

Example Photon Temporal Distribution [1] Debris

Ions

Time20ns 0.2s 1s 2.5s

FastIons

Ph

oton

sEnergy Deposition

Schematic of Temporal Distribution for Photons and Ions Based on Direct Drive Spectrum and 6.5 m Chamber

without a Protective Gas


Sublimation is a Temperature-Dependent Process Increasing Markedly at the Sublimation Point

0.0x100

2.0x108

4.0x108

6.0x108

8.0x108

1.0x109

1.2x109

1.4x109

1500 2000 2500 3000 3500 4000Surface temperature (°C)

1.1x10-2

9.3x10-3

7.3x10-3

5.5x10-3

3.7x10-3

1.8x10-3

0 0.0x100

1.0x106

2.0x106

3.0x106

4.0x106

5.0x106

6.0x106

7.0x106

8.0x106

1.5x103 2.0x103 2.5x103 3.0x103 3.5x103 4.0x103 4.5x103

W surface temperature (°C)

8.8x10-5

7.7x10-5

6.6x10-5

5.5x10-5

4.4x10-5

3.3x10-5

2.2x10-5

1.1x10-5

0

Carbon Latent heat of evaporation = 5.99 x107 J/kg

Sublimation point ~ 3367 °C

Tungsten Latent heat of evaporation = 4.8 x106 J/kg

Melting point ~ 3410 °C

Use evaporation heat flux as a f(T) as surface boundary conditions to include evaporation/sublimation effect in ANSYS calculations


Temperature-Dependent Properties for Carbon and Tungsten Were Used

• C thermal conductivity as a function of temperature for 1 dpa case (see figure)

• C specific heat = 1900 J/kg-K

• W thermal conductivity and specific heat as a function of temperature from ITER material handbook

Calculated thermal conductivity of neutron irradiated MKC-1PH CFC

(L. L. Snead, T. D. Burchell, Carbon Extended Abstracts, 774-775, 1995)


Example Temperature History for Carbon Flat Wall Under Energy Deposition from Direct-Drive Target Spectra Without

Protective Chamber Gas

• Coolant temperature = 500°C

• Chamber radius = 6.5 m

• Maximum temperature = 1530 °C

• Sublimation loss per year = 3x10-13 m (availability=0.85)

Coolant at 500°C3-mm thick Carbon Chamber Wall

EnergyFront

Evaporation heat flux B.C at incident wall

Convection B.C. at coolant wall:h= 10 kW/m2-K


Summary of Thermal and Sublimation Loss Results for Carbon Flat Wall Under Direct Drive Target Spectra

Without Protective Chamber Gas

Coolant Temp. Energy Deposition Maximum Temp. Sublimation Loss Sublimation Loss

(°C) Multiplier (°C) per Shot (m) per Year (m)*

500 1 1530 1.75x10-21 3.31x10-13

800 1 1787 1.19x10-18 2.25x10-10

1000 1 1972 5.3x10-17 1.0x10-8

500 2 2474 6.96x10-14 1.32x10-5

500 3 3429 4.09x10-10 7.73x10-2

* Shot frequency = 6; Plant availability = 0.85

• Encouraging results even for conservative case without chamber gas: sublimation only takes off when energy deposition is increased by a factor of 2-3

• Margin for setting design parameters such as coolant temperature, chamber wall radius, and target yield, and for accounting for uncertainties


Example Temperature History for Tungsten Flat Wall Under Energy Deposition from Direct-Drive Target Spectra Without


• Coolant temperature = 500°C• Chamber radius = 6.5 m• Maximum temperature = 1438 °C

Coolant at 500°C3-mm thick W Chamber Wall

EnergyFront

Evaporation heat flux B.C at incident wall


Key issue for tungsten is to avoid reaching the melting point = 3410°C

W compared to C:• Much shallower energy deposition from photons • Somewhat deeper energy deposition from ions


Summary of Thermal Results for Tungsten Flat Wall for Direct-Drive Target Spectra Without Protective Chamber Gas

Coolant Temp. Energy Deposition Maximum Temp.

(°C) Multiplier (°C)

500 1 1438

800 1 1710

1000 1 1972

500 2 2390

500 3 3207

500 5 5300

• Encouraging results even for conservative case without chamber gas: melting point (3410°C) is not reached even when energy deposition is increased by a factor of 3

• Margin for setting design parameters and accounting for uncertainties


Consider Engineered Surface Configuration for Improved Thermal Performance

• Porous Media- Fiber diameter ~ diffusion

characteristic length for 1 s

- Increase incident surface area per unit cell seeing energy deposition

ESLI Fiber-Infiltrated Substrate (http://www.esli.com)

Large fiber L/d ratio ~100

L

A incident

ncident

fiber= incident sin


Example Thermal Analysis for Fiber Case Under Energy Deposition from NRL Direct-Drive Spectra Without


• Incidence angle = 30°• Porosity = 0.9• Effective fiber separation = 54 m • Sublimation effect not included


Single Carbon Fiber

10m

Coolant at 500°C

1 mm

Temperature Distribution in Fiber Tip at 2.5 s

Max. Temp. = 1318°C


Summary of Thermal Results for Carbon Fibrous Wall Under Energy Deposition from NRL Direct-Drive Spectra

Without Protective Chamber Gas

Porosity Fiber Effective Incidence Maximum Temp. Separation (m) Angle (°) (°C)

0.8 29.6 5 654

0.8 29.6 30 1317

0.8 29.6 45 1624

0.9 54 30 1318

C flat wall as comparison: 1530

• Initial results indicate that for shallow angle of incidence the fiber configuration perform better than a flat plate and would provide more margin (confirmed by recent experimental results)

• Statistical treatment of incidence angle and fiber separation would give a better understanding

Coolant temperature = 500 °CEnergy deposition multiplier = 1


1. Several Erosion Mechanisms Must Be Considered for the Armor in Particular for C [8]

Carbon TungstenErosion:Melting No Yes (MP = 3410°C)Sublimation/evaporation

Yes (SP ~3367°C) Yes

Physical Sputtering Yes (peaks at ~ 1keV)

Yes, high thresholdenergy

Chemical Sputtering Yes (peaks at ~ 0.5keV and 800 K))

No

Radiation EnhancedSublimation

Yes (increasesdramatically with T,peaks at ~ 1 keV)

No

Macroscopic(Brittle) Erosion

Yes (thermal stress +vapor formation)

No

Splashing Erosion No Yes (melt layer)

Tritium Retention:Co-deposition Yes (with cold

surfaces with H/Cratio of up to 1)

No

• Carbon erosion could lead to tritium co-deposition, raising both tritium

inventory and lifetime issues for IFE with a carbon wall. Redeposition/co-deposition requires cold surfaces which would exist in the beam penetration lines and pumping ducts. (For H/C=1, 60 g T per 1m C for R=6.5 m)

• Macroscopic erosion might be a more important lifetime issue than

sputtering and sublimation for IFE operating conditions for high energy ions (>>1 keV)

(From the ARIES Tritium Town Meeting, March 6–7, 2001, Livermore, [9])

• Must Consider Alternate Options for Armor (e.g. refractory metals such as Tungsten)

2. Tritium Co-Deposition is a Major Concern for Carbon Because of Cold Surfaces (Penetration Lines)


Analysis for Indirect Drive Spectra Using BUCKY [7]

• The threat spectrum produced by the indirect drive target differs significantly from that of direct drive targets. The massive hohlraum converts capsule ion and x-ray debris into relatively soft and more potentially damaging x-rays.

• In order for the chamber dry wall armor to survive, some buffer gas MUST be present to absorb the prompt x-rays, re-radiating their energy over a longer period of time.

• To determine the minimum amount of Xe necessary to prevent significant first wall vaporization a series of BUCKY [7] radiative hydrodynamic simulations were conducted.


Example Results from BUCKY for Indirect Drive Spectra for a 6.5 m Radius C Chamber Wall

• Assuming 1 monolayer loss per shot as a measure of acceptable lifetime, the results show that for pre-shot armor temperatures less than ~1000°C, the amount of Xe necessary to protect such a chamber wall is significantly less than the 0.5 torr previously estimated in the SOMBRERO study.

• Unlike the direct-drive laser case, the presence of Xe actually aids in some heavy ion driver beam transport mechanisms, and target heating and injection complications from the presence of the Xe gas are much less important for the massive hohlraum-protected indirect-drive target than for the bare cryogenic direct-drive laser target.

0

500

1000

1500

2000

2500

0 0.1 0.2 0.3 0.4 0.5

Xe Density (Torr)

Pre-Shot Wall Temperature as a Function of Xenon Pressure for Loss of 1 Monolayer of Graphite

Per Shot


Conclusions: Cautious Optimism for IFE Dry Chamber Wall Without Protective Gas

• Very encouraging results were obtained from IFE dry wall analyses based on recent direct drive and indirect drive target spectra.

• The analysis included the key effect of photon and ion time of flight on the energy deposition.

• The results showed that for the direct drive target, a design window exist for C and W armor lifetime even for a case without a protective gas which will greatly help to accommodate target thermal control and laser breakdown requirements while providing some margin for

optimization of design parameters.

• The presence of a protective gas such as xenon is much more important for the indirect-drive spectra but at a much lower pressure than previously considered.

• Several erosion mechanisms exist for C and tritium codepostion on cold surfaces is a key concern. Alternate armor material candidates must be considered (e.g. W or other refractory metals).

• Initial analysis indicates also the benefit of using armor with engineered surface such as a C fibrous carpet. However, other issues must be addressed such as the possibility of coating the

fiber with a refractory to avoid the C problems (in this case), manufacturing and long term integrity.


References

[1] W. R. Meier, et al., OSIRIS and SOMBRERO Inertial Fusion Power Plant Designs: Final Report, WJSA-92-01 (DOE/ER/54100-1), March 1992.

[2] D. T. Goodin et al., Nuclear Fusion 41 (5) May 2001.

[3] S. E. Bodner, et al., Physics of Plasmas 7(6), June 2000, pp. 2298-2301.

[4] http://aries.ucsd.edu/ARIES/WDOCS/ARIES-IFE/SPECTRA/

[5] D. A. Callahan-Miller and M. Tabak, Nuclear Fusion, Vol. 39, No. 7, July 1999.

[6] A. R. Raffray, R. R. Peterson, et al., Assessment of IFE dry chamber walls, to appear in Fusion Engin. & Design.

[7] J.J. MacFarlane, G.A. Moses, R.R. Peterson, BUCKY-1 - A 1-D Radiation Hydrodynamics Code for Simulating Inertial Confinement Fusion High Energy Density Plasmas, UWFDM-984, Univ. of Wisconsin, August1995.

[8] J. Roth, et al., Erosion of graphite due to particle impact,” Nuclear Fusion, 1991.

[9] http://aries.ucsd.edu/LIB/MEETINGS/0103-ARIES-TTM/

http://aries.ucsd.edu/LIB/MEETINGS/0103-ARIES-TTM/







IFSA, Kyoto, Japan, September 2001 1 Dry Chamber Wall Thermo-Mechanical Behavior and Lifetime under IFE Cyclic Energy Deposition A. R. Raffray 1, D. Haynes.

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