HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 1 Progress Towards Realization of a Laser IFE Solid Wall Chamber A.R. Raffray 1, J. Blanchard 2, J. Latkowski.

May 22-27, 2005 ISFNT-7, Tokyo, Japan

1

HAPL

Progress Towards Realization of a Laser IFE Solid Wall Chamber

A.R. Raffray1, J. Blanchard2, J. Latkowski3, F. Najmabadi1, T. Renk4, J. Sethian5, S. Sharafat6, L. Snead7 ,

and the HAPL Team

1University of California, San Diego, 460 EBU-II, La Jolla, CA 90093-0438, USA2University of Wisconsin, Fusion Technology Institute, Madison, WI 53706, USA

3Lawrence Livermore National Laboratory, Livermore, CA 94550, USA 4Sandia National Laboratories, Albuquerque, NM 87185, USA

5Naval Research Laboratory, Washington, DC, USA6University of California Los Angeles, Los Angeles, CA, USA

7Oak Ridge National Laboratory, PO Box 2008, MS-6169, Oak Ridge, TN, USA

ISFNT-7Tokyo, Japan

May 22-27, 2005


2

HAPL

Outline

• HAPL Program Overview

• Dry Wall Chamber Configuration

• Key Issue: Wall Survival

• R&D Effort

- Experiments

- Modeling

• Conclusions


3

HAPL

IFE Chamber Studies in US

• ARIES-IFE study concluded a couple of years ago- focused on evolving parameter design space - laser and heavy ion drivers- direct and indirect-drive targets- dry wall, wetted wall and thick liquid wall chambers - results reported at several conferences and most recently in special

issue of Fusion Science & Technology (November 2004)

• Termination of effort on heavy ion, indirect-drive target, thick liquid wall chamber studies (HYLIFE)

• Currently IFE technology is funded through the following two programs:

- HAPL study (multi-year, multi-institution effort led by NRL)

- Z-pinch study (starting last year, led by SNL)


4

HAPL

Electricity Generator

Targetfactory

Modular LaserArray

• Modular, separable parts: lowers cost of development AND improvements

• Conceptually simple: spherical targets, passive chambers

• Builds on significant progress in US Inertial Confinement Fusion Program

The HAPL Program Aims at Developing a New Energy Source: IFE Based on Lasers, Direct Drive Targets and Solid Wall Chambers

Target injection, (survival and

tracking)

Chamber conditions (physics)

Final optics (+ mirror steering)

Blanket (make the most of MFE design and R&D info)

System (including

power cycle)

Dry wall chamber

(armor must accommodate ion+photon threat and

provide required lifetime)


5

HAPL

Chamber Wall Must Accommodate Threat Spectra from Direct Drive Target

1x10-1

1x100

1x101

1x102

1x103

1x104

1x105

1x106

1x10-3

1x10-2

1x10-1

1x100

1x101

1x102

1x103

X-ray Output (J/keV)

Photon Energy (keV)

Ion Threat Spectra

Photon Threat Spectra

Example 154 MJ direct drive target (350 MJ target also considered)


6

HAPL

Power Deposition Occurs in a Very Thin Armor Region

0

500

1000

1500

2000

2500

3000

3500

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

1x10-3

1x10-2

Time (s)

1-mm Tungsten armor

Density = 19350 kg/m

3

2.5 mm FS layer

Coolant Temp. = 500°C

h =10 kW/m

2

-K

154 MJ DD Target Spectra

R

chamber

= 6.5 m

Rep rate = 10

Distance from

the W surface:

0

10 μ m

1 μ m

5 μ m

100 μ m

1000 μ m

q

FS

Coolant

W Armor

Example power deposition profile in W armor for 154 MJ direct drive target and 6.5 m

chamber radius

• Only thin armor region sees huge temperature transients

• This led to the configuration choice of a thin armor layer (~ 1 mm) on a FS substrate

• Blanket at the back sees quasi steady state (can make use of MFE effort)

• W chosen as preferred armor material (high-temperature capability, no tritium concern)

• However, lifetime is a key issue and is the focus of the R&D in this area

Example temperature history at different spatial location in W armor


7

HAPL

W Armor Lifetime • Several possible mechanisms could lead to premature

armor failure:- ablation- melting (is it allowable?)- surface roughening & fatigue (due to cyclic thermal stresses)- accumulation of implanted helium- fatigue failure of the armor/substrate bond

• R&D effort includes modeling and experimental testing of the armor thermo-mechanical behavior.

AblationDepth

T or T

Net AblationNo net ablation,

but surface roughening

Threshold for ablation

Threshold for roughening

• Because the exact IFE ion and X-ray threat spectra on the armor cannot be duplicated at present, experiments are performed in simulation facilities:- Ions (RHEPP)- X-ray(XAPPER and Z)

- Laser (Dragonfire)- Fatigue testing of the W/FS bond in ORNL infrared facility (initial results show good adhesion of 0.1 mm W diffusion bonded or plasma-sprayed on FS after 1000’s of thermal cycle pulses). - He management is addressed by conducting implantation experiments (ORNL) along with

modeling of He behavior in tungsten (UCLA).

• The possibility of utilizing an engineered porous armor is also considered to help in enhancing the transport of implanted helium and in accommodating thermal stresses.


8

HAPL

RHEPP Ion Beam Facility (SNL) • Ion beam with energy of up to 800 keV for singly-

charged He ions, and up to 1.6 MeV for doubly-charged N ions with a pulse-width of 100-300ns.

• Energy within the range expected for IFE but pulse-width shorter than few s expected for IFE.

• Uncertainty includes variation in cycle to cycle energy deposition of up to about ±50% and lack of real-time diagnosis (e.g. temp. measurement).

• Result interpretation must consider RHEPP energy deposition characteristics as compared to IFE (i.e melting of a W sample requires ~ 2 J/cm2 in RHEPP but more than 4 times this fluence in IFE)

• Surface roughening measured by 1-D profilometry (DekTak).

• Studies have focused on determining the roughening thresholds for different armor sample materials at different base temperatures.


9

HAPL

Observations from RHEPP Experimental Results• Roughening threshold for powder metallurgy W

(PM W) ~ 1 J/cm2 at RT- Heating the PM W reduces the roughening and

possibly increases the threshold but with additional pulses (up to 1000), the roughness reaches the level of the RT sample.

• Single crystal W shows less roughening than PM W, and possibly higher threshold.

• Rhenium (Re) and Re/W alloy show much better resistance to roughening than W.

• Roughening seems to increase linearly with the number of pulses at a given ion fluence. It also increases with the fluence per pulse.

• Roughening trends seem independent of the predicted W surface Tmelt (~3410°C at a fluence of ~ 2-2.5 J/cm2) perhaps because of very short melt duration (<150 ns).

• Does roughening saturate?- Needs to verified by testing over more prototypic number of pulses and less variation in energy

deposition (e.g. testing in a rapid cyclic heat load facility such as with a laser).


10

HAPL

XAPPER X-Ray Facility (LLNL) • XAPPER is based upon an extreme ultraviolet (EUV) X-ray

source designed and built by PLEX LLC using a plasma pinch as source .

• An ellipsoidal focusing optic is used to increase the per-shot X-ray fluence to ~1 J/cm2 over a spot size of ~ 1 mm.

• The X-ray spectra show energy around 100 eV, ~ one order of magnitude lower than the typical IFE X-ray energy, but the attainable fluence for the given spectra is sufficient to reproduce the peak temperature of the W armor under the IFE spectra (with melt occurring at a fluence of about 1-1.2 J/cm2).

• However, the time deposition of the energy is short, of the order ~0.01 s compared to the ~1 s in the IFE case (governed by the time of flight of ions).

• Samples can be irradiated with up to 105-106 pulses (the latter requiring about 28 hrs of continuous testing).


11

HAPL

Observations from Initial XAPPER Results

• Initial results suggest that there may be a roughening threshold (somewhat higher for single crystal W than for PM W).

• Further experiments are needed to understand better whether the roughening increases linearly with number of pulses and also whether it saturates after a number of cycles.

• One major improvement is the future installation of an optical thermometer (from UCSD) to measure the surface temperature.


12

HAPL

Single Shot Testing in Z Machine (SNL)

• Z can provide up to 10 keV X-rays.

• W samples (single crystal, powder metallurgy and chemical vapor deposition) exposed to various fluences.

• The results showed no melting below a fluence of 1.3 J/cm2.

• Heated samples (600°C) were exposed to fluences of 0.27 and 0.9 J/cm2, and surfaces examined with 2-dimensional VEECO profilometry:- The surface appearance of the polycrystalline samples, i.e. the PM W and CVD W, is

different from the SC W, with an indicated roughening threshold between 0.3 and 0.9 J/cm2.

- The SC sample showed no evidence of roughening at 0.9 J/cm2, indicating a higher roughening threshold for SC W than for the other polycrystalline W samples.

0

0.27

0.9

Fluence(J/cm2) SC W PM W CVD W


13

HAPL

Dragonfire Laser Facility (UCSD)

• The samples are heated using a YAG laser with a rep rate of 10 Hz. The high rep-rate of the laser allows testing to 105-106 cycles.

• Modeling has shown the possibility to simulate the IFE W armor surface temperature temporal and spatial to some extent) temperature profiles by adjusting the laser pulse.

• A high-speed optical thermometer was developed to measure the real-time temperature of sample surface with ns resolution.

• Additional diagnostics, such as QMS & RGA to measure and characterize per-shot ejecta and constituents are to be installed.

• A high-temperature sample holder is included to allow testing at prototypical “equilibrium” temperature.


14

HAPL

Initial Dragonfire Results

• It seems that the samples evolve at two different time scales:- Defect planes appear at low shot counts (~103 shots) - Individual "nuggets" (with higher roughness) appear over the high shot counts (~105 shots).

• Samples at the higher base temperature show less damage. For example for 1,000 shots and a T of ~2,500°C, a sample at 500°C base temperature shows almost no damage whereas a RT sample shows clear damage.

• This is also seen with higher shot counts but the difference between the two samples is less marked.

• Future effort will help to understand better these preliminary observations and to observe the effect of testing with higher shot counts on sample roughening.

530mJ (~2500oC T), RT

103 shots 104 shots 105 shots

530mJ (~2500oC T), 500oC

103 shots 104 shots 105 shots


15

HAPL

Example of Modeling Performed to Better Understand the W Thermal Stress Behavior and Crack Initiation and Growth

• ANSYS calculations of the stress intensities for crack depths ranging from 15 m to 150 m (and spacing of 1 mm)

- The stress intensity falls from ~10 MPa-m1/2 for the 15 m crack to ~2.6 MPa-m1/2 for the 150 m

crack, and to zero for deeper cracks with smaller spacings.

- This indicates that cracks that initiate at the surface may stop before reaching the armor/steel interface (within ~100 m from the surface).

- Limited fracture mechanics data for thin tungsten films make prediction of fracture behavior is

difficult (must rely on experiments).

Coolant

FSW

q• High cycle fatigue in FS substrate- Data for F82H indicate lifetime >106 cycles for stress amplitudes of ~400 MPa

- Data from other steels (such as 12Cr-2W FS) indicate lifetime over 108 cycles (HAPL level) at stress amplitudes ~300 MPa at 400 °C

- Hence, there seems to be margin in the steel stress levels since the tensile stresses in a typical HAPL cycle are not as high as the compressive

stresses, whereas the tests are done with a mean stress of 0.


16

HAPL

He Studies Focused on Investigating He Retention and Surface Blistering Characteristics of W

• Goal is to determine if He retention can be mitigated by the pulsed nature of He implantation in combination with the high temperature spikes within the IFE reactor

• Experimental activities:- He implantation/anneal cycle experiment(ORNL+UNC)

- ~850°C base T, ~1.3 MeV He, pulsed implantation and anneals at 2000°C over ~ 1000 cycles to fluences of ~1020 He/m2

- He + D implantation in IEC facility (UW)- ~800°C base T, ~10-100 keV ion, pulsed

implantation to fluences of ~1022 He/m2

• Modeling activities:- HEROS code (UCLA)

• Engineered material also considered to enhance He release and provide stress relief- W foam (Ultramet/UCLA)- Vacuum plasma spray porous W with ~10-100 nm

microstructure (PPI/UCSD)


17

HAPL

IFE Conditions May Mitigate He Retention Effect

• He retention decreases drastically when a given He dose is spread over an increasing number of pulses, each one followed by W annealing to 2000°C, to the extent that there would be no He retention below a certain He dose per pulse.

• For SC, this threshold would be ~ 1016 ions/m2 per shot (lower for PC W)

• This threshold is still too low as the IFE He dose per shot is ~1017 ions/m2.

• However, for the IFE case the W armor surface temperature would be closer to 2400°C which would significantly increase the He mobility and should increase the per-shot threshold.

• Thus, the trends are very promising but more R&D is required to make a better assessment of He behavior in the IFE case.


18

HAPL

Required PXe as a Function of Yield to Maintain TW,max<2400°C for 1800 MW Fusion Power and Different Rchamber

0

10

20

30

40

50

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350 400 450

Xe

Pre

ssu

re (

@S

T)

(mto

rr)

Rep

etit

ion

Rat

eYield (MJ)

3.5 mm FSTcoolant=572°C

h=67 kW/m2-K

chamber60 40

1 mm WR (m)5.7

6.5

7

8

10

Armor Survival Constraints Impact the Overall IFE Chamber Design and Operation

• W temperature limit of 2400°C assumed for illustration purposes (~1.2 J/cm2 roughening threshold from RHEPP results)

• Limit to be revisited as R&D data become available

• Example chamber parameters for 0 gas pressure:- Yield = 350 MJ; R=10.5 m; Rep. rate ~ 5 for 1750 MW fusion

• Integrated IFE chamber design under way

• Desirable to avoid protective chamber gas based on target survival and injection considerations


19

HAPL

Conclusions (I) • The HAPL program is aimed at developing Laser IFE based on a

laser driver, direct drive targets and a solid wall chamber.

• The design and R&D effort in the chamber and material area is focused toward the key issues affecting the W/FS armor/FW survival under the ion and photon threat spectra.

• Initial testing of armor thermal response have been performed in a range of facilities.- Possible threshold for armor roughening, which needs to be fully

characterized for IFE conditions.- To be determined is whether roughening saturates after a number of

cycles or whether it leads to mass loss.- Generally, single crystal W shows less roughening than powder-met W,

and W-Re alloy shows much better resistance to roughening than W; - Armor samples at a higher base temperature tend to show less damage

(as compared to room temperature samples)


20

HAPL

Conclusions (II) • Initial results from fatigue testing of the W/FS bond indicate good adhesion of

the coating (no spalling). Long term thermal stability studies are under way.

• Modeling studies indicate the possibility of cracks initiating at the armor surface but propagating to < 100 m from the surface. Castellating the armor would help accommodate the stresses and reduce crack propagation concerns.

• There seems to be a significant margin in the FS stress levels to accommodate the cyclic stress without crack formation in the FS substrate.

• Initial results indicate that there might be a He flux per shot threshold below which the implanted He will be released during the temperature excursion. This threshold is lower for single crystal W as compared to powder met W. Future modeling and experimental effort should help to better understand this effect under IFE prototypical conditions.

• Overall, although some major issues still need to be resolved, results are encouraging for the possibility of utilizing a W-armored chamber. The major chamber armor and wall issues have been identified and are being addressed through a combination of modeling and experimental R&D.

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 1 Progress Towards Realization of a Laser IFE Solid Wall Chamber A.R. Raffray 1, J. Blanchard 2, J. Latkowski.

Documents

chamber wall

usa isfnt

laser ife solid wall

w armor slide

wetted wall

hapl team

mj direct drive target

mj target