ife chamber walls: requirements, design options, and synergy with mfe plasma facing components

May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components

1

IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components

A. R. Raffray1, D. Haynes2 and F. Najmabadi1

1University of California, San Diego, 458 EBU-II, La Jolla, CA 92093-0417, USA2Fusion Technol. Inst., Univ. of Wisconsin, 1500 Eng. Dr., Madison, WI 53706-1687, USA

PSI-15

Gifu, JapanMay 27, 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

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)


4

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%)


5

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%)


6

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)


7

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


9

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

• Total q’’max on injected target is limited to avoid D-T reaching triple point and possibly causing 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:

l

l

ll

l

t

t

tt

t

n

n

n

n

n

0.0

0.5

1.0

1.5

2.0

2.5

0 2000 4000 6000 8000 10000

Target diameter = 4 mmInjection velocity = 400 m/s

Max. heat flux is at the leadingtarget surface

q'' varies along target surfacebased on DSMC results

Maximum heat flux (W/m2)

24

10

6

Chamber radius (m)

Triplepoint


11

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


12

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


13

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…


14

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


15

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:


16

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


17

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


18

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


19

• 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


20

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


21

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


22

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

ife chamber walls: requirements, design options, and synergy with mfe plasma facing components

Documents

example direct drive

indirect drive target

ife chamber walls

normal operating conditions

target spectra available

mj dd nrl targetenergy10

outlineife chamber

mfe armor