ARIES-IFE Chamber Engineering Activities

June 18, 2002 A. R. Raffray, et al., ARIES-IFE Chamber Engineering Activities, IAEA Meeting, San Diego

1

ARIES-IFE Chamber Engineering Activities

A. R. Raffray1, F. Najmabadi1 and the ARIES Team

1University of California, San Diego, 458 EBU-II, La Jolla, CA 92093-0417, USA

Second IAEA Technical Meeting on Physics and Technology of Inertial Fusion Energy Targets and Chambers

San Diego, California

June 17-19, 2002


2

Outline

• IFE chamber operating conditions– Comparison with MFE

• Dry Walls (major focus of presentation)– Design operating windows

– Critical issues and required R&D

– Synergy with MFE

• Wetted Walls – Example analysis and critical issues

• Concluding Remarks


3

Objectives:

Analyze & assess integrated and self-consistent IFE chamber concepts

Understand trade-offs and identify design windows for promising concepts. The research is not aimed at developing a point design.

Approach:

Advanced target designs from NRL (laser-driven direct drive) and LLNL (Heavy-ion-driven indirect-drive) are used as references.

To make progress, we divided the activity based on three classes of chambers:• Dry wall chambers;• Solid wall chambers protected with a “sacrificial zone” (such as liquid

films); • Thick liquid walls.

We research these classes of chambers in series with the entire team focusing on each.

ARIES Integrated IFE Chamber Analysis and Assessment Research Is An Exploration Study


4

IFE Operating Conditions

• Cyclic with repetition rate of ~1-10 Hz • Target injection (direct drive or indirect drive)

• Driver firing (laser or heavy ion beam)

• Microexplosion

• Large fluxes of photons, neutrons, fast ions, debris ions toward the wall

- possible attenuation by chamber gas

Target micro-explosion

Chamber wall

X-rays Fast & debris ions Neutrons

Example of Direct-Drive Target (NRL) (preferred option for coupling with laser driver)

DT Vapor0.3 mg/cc

DT Fuel

CH Foam + DT

1 m CH +300 Å Au

.195 cm

.150 cm

.169 cm

CH foam = 20 mg/cc

Example of Indirect-Drive Target (LLNL/LBLL) (preferred option for coupling with heavy ion beam driver)


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Energy Partitioning and Photon Spectra for Example Direct Drive and Indirect Drive Targets

NRL DirectDrive Target(MJ)

HI IndirectDrive Target(MJ)

X-rays 2.14 (1%) 115 (25%)

Neutrons 109 (71%) 316 (69%)

Gammas 0.005 (0.003%) 0.36 (0.1%)

Burn ProductFast Ions

18.1 (12%) 8.43 (2%)

Debris IonsKinetic Energy

24.9 (16%) 18.1 (4%)

ResidualThermal Energy

0.013 0.57

Total 154 458

Energy Partitions for Example Direct Drive and Indirect Drive Targets

Photon Spectra for Example Direct Drive and Indirect Drive Targets

• Much higher X-ray energy for indirect drive target case (but with softer spectrum)

• More details on target spectra available on ARIES Web site: http://aries.ucsd.edu/ARIES/

(25%)

(1%)


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Example IFE Ion Spectra

10.0E+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+18

1.0E+19

1.0E-1 1.0E+0 1.0E+1 1.0E+2 1.0E+3 1.0E+4 1.0E+5

4HeD

TH

Au

Ion Kinetic Energy (keV)

3He

12C

10.0E+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

N


3He

γ

Debris Ions (16%)

Fast Ions (12%)

154 MJ NRL Direct Drive Target 458 MJ Indirect Drive Target

10.0E+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


3He

γ

N

Fast Ions (2%)

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


3He

Gd

Fe

Br

Be

Debris Ions (4%)


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There are Similarities Between IFE and MFE Armor Operating Conditions e.g. ITER Divertor and 154 MJ NRL Direct Drive Target Spectra Case

• Although base operating conditions of IFE (cyclic) and MFE (steady state goal) are fundamentally different, there is an interesting commonality between IFE operating conditions and MFE off-normal operating conditions, in particular ELM’s - Frequency, energy

density and particle fluxes are within about one order of

magnitude

• Assess performance of chamber dry wall option under these direct-drive target conditions

ITER Type-I

ELM’s

ITER VDE’s ITER

Disruption

thermal

quench

Typical IFE

Operation

(154 MJ DD

NRL target)

Energy 10-12 MJ ~ 50 MJ/m2 100-350 MJ ~ 0.1 MJ/m2

Affected

area 5-10 m2† A few m2† ~10 m2†

Chamber wall

(R~5-10 m)

Location Surface (near

divertor strike

points)

Surface/bulk Surface (near

divertor strike

points)

bulk (~m’s)

Time ≥200 µs ~ 0.3 s ~ 1 ms ~ 1-3 s

Max.

Temperature

Melting/

sublimation

Melting/

sublimation

Melting/

sublimation

~ 2000-3000°C

(for d rywal )l

Frequency F ewHz ~ 1 per 100

cycles

~ 1 per 10

cycles

~ 10 Hz

Base

Temperature

≥ 500°C ~ 200°C 200-1000°C ~ >700°C

Particle

fluxes ~1023 m-2s-1

† large uncertainties exist

~1024 m-2s-1(peak under normal operation)


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Candidate Dry Chamber Armor Materials Must Have High Temperature Capability and Good Thermal Properties for

Accommodating Energy Deposition and Providing Required Lifetime

• Carbon and refractory metals (e.g. tungsten) considered - Reasonably high thermal conductivity at high temperature (~100-200 W/m-K)

- Sublimation temperature of carbon ~ 3370°C

- Melting point of tungsten ~3410°C

• In addition, possibility of an engineered surface to provide better accommodation of high energy deposition is considered- e.g. ESLI carbon fiber carpet showed good

performance under ion beam testing at SNL (~5 J/cm2 with no visible damage)

• Example analysis results for C and W armor for NRL 154 MJ direct drive target case


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10.0x103

1.0x105

1.0x106

1.0x107

1.0x108

1.0x109

1.0x1010

1.0x1011

1.0x1012

1.0x1013

1.0x1014

1.0x10-7 1.0x10-6 1.0x10-5 1.0x10-4

4HeD

T

P

Au

Time (s)

3He

12C

1x106

1x107

1x108

1x109

1x1010

1x1011

1x10-8 1x10-7 1x10-6 1x10-5 1x10-4 1x10-3 1x10-2

Debris ions,W

Fast ions, C

Photons, W

Photons, C

Fast ions, W

Penetration depth (m)

Energy Deposition as a Function of PenetrationDepth for 154 MJ NRL DD Target

Debris ions, CC density = 2000 kg/m3

W density = 19,350 kg/m3

Energy Deposition as a Function of Penetration Depth for 154 MJ NRL DD Target

Ion Power Deposition as a Function of Time for 154 MJ NRL DD Target

Chamber Radius = 6 m

• Penetration range in armor dependent on ion energy level- Debris ions (~20-400 kev) deposit most of their energies within m’s- Fast ions (~1-14 Mev) within 10’s m

• Important to consider time of flight effects (spreading energy deposition over time)- Photons in sub ns- Fast ions between ~0.2-0.8 s- Debris ions between ~ 1-3 s- Much lower maximum temperature than for instantaneous energy deposition case

Characteristics of the Target Spectra Strongly Impact Chamber Wall Thermo-Mechanical Response


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Temperature History of C and W Armor Subject to 154MJ Direct Drive Target Spectra with No Protective Gas

• For a case without protective gas:- Tungsten Tmax < 3000°C (MP=3410°C)- Some margin for adjustment of

parameters such as target yield, Rchambe, Tcoolant, Pgas

- Similar results for C (Tmax < 2000°C)

• All the action takes place within<100m- Separate functions: high energy

accommodation in thin armor, structural function in chamber wall behind

- Focus IFE effort on armor; can use MFE blanket

200

600

1000

1400

1800

2200

2600

3000

Surface

1 micron

5 microns

10 microns

100 microns

Time (s)

3-mm Tungsten slab

Density = 19350 kg/m3

Coolant Temp. = 500°C

h =10 kW/m2-K154 MJ DD Target Spectra

Coolant at 500°C

3-mm thick Chamber Wall

EnergyFront

h= 10 kW/m2-K


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Target Injection Requirements Impose Constraints on Pre-Shot Chamber Gas Conditions

llll

l

l

ll

t

t

tt

t

t tt

n

n

n

n

n n n

n

0.0

0.5

1.0

1.5

2.0

2.5

0 5000 10000 15000 20000

Target diameter = 4 mmInjection velocity = 400 m/sTarget temperature = 18 K

Max. heat flux is at the leadingtarget surface

q'' varies along target surface

Maximum heat flux (W/m2)

24156

Chamber radius (m)Triplepoint

• Total q’’max on injected target is limited to avoid D-T reaching critical point and local micro-explosion instability

• For a direct drive target injected at 400 m/s in a 6 m chamber, q’’max <~6000 W/m2

- Max. q’’rad from the wall = 6000 W/m2 for Twall = 545 K- Example combinations of TXe and Pxe resulting in a max. q’’condens. = 6000 W/m2

- Tgas=1000 K and PXe = 8 mtorr- TXe = 4000 K and PXe = 2.5 mtorr

- Narrow design window for direct drive target- Need more thermally robust target

• No major constraint for indirect drive targets (well insulated by hohlraum)

1x101

1x102

1x103

1x104

1x105

1x106

0.1 1 10 100

1000K

4000K

Max. heat flux is at the leading target surface

Xe temp.

Condensation coefficient x Pressure at RT (mtorr) (σc x )P

q''max - for D T to

reach triple point for Rchamb 6 of m

. and injection vel of400 /m s:


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Example Design Window for Direct-Drive Dry-Wall Chambers

Thermal design windowDetailed target emissionsTransport in the chamber

including time-of-flight spreadingTransient thermal analysis of

chamber wallNo gas is necessary

Laser propagation design window(?)

Experiments on NIKE

Target injection design windowHeating of target by radiation,

friction and condensationConstraints:

Limited rise in temperature Acceptable stresses in DT ice

Need more thermally robust target


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In addition to Vaporization, Other Erosion Processes are of Concern in Particular for Carbon

Chemical SputteringRadiation Enhanced Sublimation- Increases with temperature

Physical sputtering- Not temperature-dependent - Peaks with ion energies of ~1kev

(from J. Roth, et al., “Erosion of Graphite due to Particle Impact,” Nuclear Fusion, 1991)

Plots illustrating relative importance of C erosion mechanisms for example IFE case(154 MJ NRL DD target,HEIGHTS code, ANL)

- RES and chemical sputtering lower than sublimation for this case but quite

significant also

- Physical sputtering is less important than other mechanisms

- Increased erosion with debris ions as compared to fast ions

Rchamber = 6.5 m

CFC-2002U


14

Tritium Inventory in Carbon is a Major Concern

• Operation experience in today’s tokamaks strongly indicates that both MFE and IFE devices with carbon armor will accumulate tritium by co-deposition with the eroded carbon in relatively cold areas (e.g. R. Causey’s ISFNT-6 presentation)

- H/C ratio of up to 1

- Temperature lower than ~800 K

• Source of carbon in IFE

- From armor C dry wall (even one molecular layer lost per shot results in cm’s of C lost per year)

- From target (but much smaller amount)

• Redeposition area in IFE- C armor at high temperature (~2000°C)

- However, penetration lines for driver and target injection would be much colder

• If C is to be used, techniques must be developed for removal of co-deposited T- Baking, mechanical, local discharges…


15

Major Issues for Dry Wall Armor Include:

Commonality of Key Armor Issues for IFE and MFE Allows for Substantial R&D Synergy

Carbon

• Erosion- Microscopic erosion (RES, Chemical and Physical Sputtering)

- Macroscopic Erosion (Brittle fracture)

• Tritium inventory - Co-deposition

Refractory metal (e.g. Tungsten)

• Melt layer stability and splashing

• Material behavior at higher temperature

- e.g. roughening due to local stress relief (possible ratcheting effect)

- Possible relief by allowing melting? - quality of resolidified material

Carbon and Tungsten

• He implantation leading to failure (1 to 1 ratio in ~100 days for 1 m implantation depth)- In particular for W (poor diffusion of He)

- Need high temperature or very fine porous structure

• Fabrication/bonding (integrity of bond during operation)

Search for alternate armor material and configurations

In-situ repair to minimize downtime for repair• Cannot guarantee lifetime

MFE IFE


16

Major Issues for Wetted Wall Chambers

Key processes: Condensation Aerosol formation and behavior Thin film dynamics or thick jet

hydraulics

Chamber clearing requirements:• Vapor pressure and temperature

• Aerosol concentration and size

• Condensation trap in pumping lineInjection from the back

Condensation

Evaporation

Pg

Tg

Film flow

Photons

Ions

In-flight condensation

Wetted film loss:• Energy deposition by photon/ion • Evaporation (including explosive boiling)

Thin film re-establishment:• Recondensation• Coverage: hot spots, film flow instability,

geometry effects• Fresh injection: supply method (method,

location)

Thick wall re-establishment:• Recondensation• Hydraulics (jet or thick liquid film

reestablishment around pocket)• Coverage - need to create penetration windows

for driver and target; effect of flow instability

Wall protection:


17

Processes Leading to Vapor/Liquid Ejection Following High Energy Deposition Over Short Time Scale

Energy Deposition &

Transient Heat Transport

Induced Thermal- Spikes

Mechanical Response

Phase Transitions

•Stresses and Strains and Hydrodynamic Motion•Fractures and Spall

• Surface Vaporization•Heterogeneous Nucleation•Homogeneous Nucleation (Phase Explosion)

Material Removal Processes

Expansion, Cooling and

Condensation

Surface Vaporization

Phase Explosion Liquid/Vapor

Mixture

Spall Fractures

Liquid

FilmX-Rays

Fast Ions

Slow Ions

Impulse

Impulse

σy

σx

σz


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High Photon Heating Rate Could Lead to Explosive Boiling

Photon-like heating rate

Ion-like heating rate

• Effect of free surface vaporization is reduced for very high for heating rate (photon-like)

• Vaporization into heterogeneous nuclei is also very low for high heating rate

• Rapid boiling involving homogeneous nucleation leads to superheating to a metastable liquid state

• The metastable liquid has an excess free energy, so it decomposes explosively into liquid and vapor phases.

- As T/Ttc increases past 0.9, Becker-Döhring theory of nucleation

indicate an avalanche-like and explosive growth of nucleation rate (by 20-30 orders of magnitude)

From K. Song and X. Xu, Applied Surface Science 127-129 (1998) 111-116


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Phase Explosion from Photon Energy Deposition Would Provide a Source Term for Aerosol Formation in Chamber

Example Results from Volumetric Model with Phase

Explosion in Pb Film• Liquid and vapor mixture evolved by phase explosion shown by shaded area

- ~0.5 m with quality >~0.8

• Could be higher depending on behavior of 2-phase region behind

• Initial source for aerosol formation

EEsensiblesensible = Energy density required for the material to reach the saturation temperature = Energy density required for the material to reach the saturation temperature

E E ( 0.9 Ttc )= Energy density required heat the material to 0.9 T= Energy density required heat the material to 0.9 Tcriticalcritical

Et = Total evaporation energy (= Esensible + E Evaporation)

Assumed ablated Pb vapor pressure = 1000 torr


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• Spherical chamber with a radius of 6.5 m

• Surrounded by liquid Pb wall

• Spectra from 458 MJ Indirect Drive Target0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5

Radial Position (m)

Region 1Region 2

Region 3Region 4

Analysis* of Aerosol Formation and Behavior

10 3

10 5

10 7

10 9

10 11

10 13

10 15

0.1 1 10

anp_reg1_kal_data

100 µs

500 µs

1000 µs

5000 µs

10000 µs

50000 µs

100000 µs

Number Concentration (#/m

3)

Particle Diameter (µm)

10 3

10 5

10 7

10 9

10 11

10 13

10 15

0.1 1 10

anp_reg4_kal_data

100 µs

500 µs

1000 µs

5000 µs

10000 µs

50000 µs

100000 µs

Particle Diameter (µm)

Number Concentration (#/m

3)

Region 1Region 4

• From this example calculations, significant aerosol particles present after 0.1 s • ~109 droplets/m3 with sizes of 1-10 m in Region 1

• This could significantly affect target injection (approximate limits: 50 nm limit for direct drive and about 1 m for tracking) and driver firing and necessitate additional chamber clearance actions

• More detailed analysis under way (aerosol behavior + target and driver requirements)

* From P. Sharpe’s calculations, INEEL


21

Film Condensation Rate Would Affect the Pre-Shot Chamber Conditions for a Thin Liquid Film Configuration

• Characteristic time to clear chamber, tchar, based on condensation rates and Pb inventory for given conditions

• For higher Pvap (>10 Pa for assumed conditions), tchar is independent of Pvap

• As Pvap decreases and approaches Psat, tchar increases substantially

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

1x100 1x101 1x102 1x103 1x1043x104

Vapor Pressure (Pa)

Pb:Film temperature = 1000KFilm Psat = 1.1 Pa

Vapor velocity = 0

Vapor Temp. (K)

1200

10,000

5000

2000

ƒƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ

æ

ææ æ æ æ æ æ æ æ æ

ø

ø ø ø ø ø ø ø ø ø ø

”

” ” ” ” ” ” ” ” ” ”

0

0.02

0.04

0.06

0.08

0.1

0.12

1x100 1x101 1x102 1x103 1x104 1x105 1x106

Vapor pressure (Pa)

ƒ

æ

ø

”

Pb film temperature = 1000KFilm Psat = 1.1 Pa

Vapor velocity = 0Chamber radius = 5 m

Vapor Temp.

10,000 K

5000 K

2000 K

1200 K

• Typically, IFE rep rate ~ 1–10

• Time between shots ~ 0.1–1 s

• Pvap prior to next shot could be up to 10 x Psat

Example Analysis of Pb Vapor Film Condensation in a 10-m Diameter Chamber


22

Analysis & Experiments of Liquid Film Dynamics and Thick Liquid Wall Hydraulics Are On-going

2-D & 3-D Simulations of liquid lead injection normal to the chamber first wall using an immersed-boundary method (Georgia Tech.)

• Onset of the first droplet formation

• Whether the film "drips" before the next fusion event

• Lead film thicknesses of 0.1 - 0.5 mm; injection velocities of 0.01 - 1 cm/s;

• Inverted surfaces inclined from 0 to 45° with respect to the horizontal

Experiments on high-speed water films on downward-facing surfaces, representing liquid injection tangential to the first wall (Georgia Tech.)

• Reattachment of liquid films around cylindrical penetrations typical of beam and injection port

Experiments and modeling of thick liquid jet formation and behavior (UCB, UCLA)

• Understand behavior of thick liquid jet and formation of pocket and required penetration space

• Preferred fluid candidate is FLiBe

These issues and activities are relevant to both IFE and MFE


23

Concluding Remarks

• Very challenging conditions for chamber wall armor in IFE

• Different armor materials and configurations are being developed

- Dry wall option

- Wetted wall options

- Similarity between MFE and IFE materials

• Some key issues remain and are being addressed by ongoing R&D effort

- Many common issues between MFE and IFE chamber armor

• Very beneficial to: - develop and pursue healthy interaction between IFE and MFE

communities

- make the most of synergy between MFE and IFE chamber armor R&D

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ARIES-IFE Chamber Engineering Activities

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