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. Raffray 1 , D. Haynes 2 and F. Najmabadi 1 1 University of California, San Diego, 458 EBU-II, La Jolla, CA 92093-0417, USA 2 Fusion Technol. Inst., Univ. of Wisconsin, 1500 Eng. Dr., Madison, WI 53706-1687, USA PSI-15 Gifu, Japan May 27, 2002
22
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IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components. A. R. Raffray 1 , D. Haynes 2 and F. Najmabadi 1 1 University of California, San Diego, 458 EBU-II, La Jolla, CA 92093-0417, USA - PowerPoint PPT Presentation
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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)
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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%)
May 27, 2002 A. R. Raffray, et al., 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
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)
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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…
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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,
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
• 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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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
May 27, 2002 A. R. Raffray, et al., IFE Chamber Walls: Requirements, Design Options, and Synergy with MFE Plasma Facing Components
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