Dynamic Chamber Armor Behavior in IFE and MFE
A. R. Raffray1, G. Federici2, A. Hassanein3, D. Haynes4
1University
of California, San Diego, 458 EBU-II, La Jolla, CA 92093-0417, USA
2ITER Garching Joint Work Site, Boltzmannstr. 2, 85748 Garching, Germany.
3Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA
4Fusion Technol. Inst., Univ. of Wisconsin, 1500 Eng. Dr., Madison, WI 53706-1687, USA
ISFNT-6
San Diego
April 10, 2002
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
1
Outline
• Chamber armor operating conditions
– MFE and IFE
– Comparison
• Candidate armor materials
– Focus on dry walls for this presentation
– Properties and characteristics
• Example analysis for dry walls
– IFE
– MFE
• Critical issues and required R&D
– Synergy
• Concluding Remarks
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
2
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
Chamber
wall
Target
microexplosion
Energy partition for two
example targets
X-rays
NRL Direct
Drive Target
(MJ)
2.14 (1%)
HI Indirect
Drive Target
(MJ)
115 (25%)
Neutrons
109 (71%)
316 (69%)
Gammas
0.005 (0.003%) 0.36 (0.1%)
Burn Product
Fast Ions
Debris Ions
Kinetic Energy
Residual
Thermal Energy
Total
18.1 (12%)
8.43 (2%)
24.9 (16%)
18.1 (4%)
0.013
0.57
154
458
X-rays
Fast & debris ions
Neutrons
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
3
MFE Operating Conditions
• Steady state conditions
• Load on plasma facing components dependent
on location,
e.g. for ITER:
Peak surface heat flux
(MW/m2)
First wall
0.5
Limiter
0.5 (~8 for ~100s)
Baffle
3
Divertor target
~10
Lifetime
(No. of cycles)
30000
30000 (5000)
3000-10000
3000-10000
• However, a number of cyclic off-normal conditions must be designed for in
next step option
- Vertical Displacement Events (VDE’s)
- Edge Localized Mode Scenarios (ELM’s)
- Disruptions
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
4
Comparison of IFE and MFE Operating Conditions for ITER
Divertor and NRL Direct Drive Target Spectra as Example Cases
ITER
• Although base operating
conditions of IFE and MFE
are fundamentally different,
there is an interesting
commonality between IFE
operating conditions and
MFE off-normal operating
conditions, in particular
ELM’s
- Frequency and energy
density are within about one
order of magnitude
Type-I ITER VDE’s
ELM’s
Energy
10-12 MJ
~ 50 MJ/m2
ITER
Typical
Disruption
Operation
therma l
(154 MJ DD
quench
NRL targe t)
100-350 MJ
~ 0.1 MJ/m2
Affected
IFE
Chamber wa ll
area
5-10 m2†
A few m2†
~10 m2†
Location
Surfa ce (near Surfa ce/bulk
Surfa ce (near bul k (~m’s)
divertor strike
divertor strike
points)
points)
(R~5-10 m)
Time
•200 µs
~ 0.3 s
~ 1 ms
~ 1-3 s
Max.
Melting/
Melting/
Melting/
~ 2000-3000 °C
Temperature sublim ation
sublim ation
sublim ation
(for dry wall)
Frequency
~ 1 per 100 ~ 1 per 10 ~ 10 Hz
Base
Few Hz
•500°C
cycles
cycles
~ 200°C
200-1000°C
~ >700°C
Temperature
Part icle
fluxes
~1024 m-2s-1(peak under normal operation)
~1023 m-2s-1
† large un certainties exist
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
5
Candidate Chamber Armor Materials Must Have High
Temperature Capability and Good Thermal Properties
• Carbon and refractory metals (e.g. tungsten) considered for both IFE and
MFE
- 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, IFE considers possibility of an
engineered surface to provide better
accommodation of high energy deposition
- e.g. ESLI carbon fiber carpet showed good
performance under ion beam testing at SNL
(~5 J/cm2 with no visible damage)
• Beryllium considered for moderately loaded first wall of ITER
- However, not compatible with commercial reactor operation because of its low
melting point (1283°C) and high sputtering yield
• Example analysis results for IFE and MFE showed for C and W armor
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
6
No. of Ions per Unit Energy (#/keV)
Example IFE Threat Spectra for 154 MJ NRL Direct Drive Target
No. of Ions per Unit Energy (#/keV)
Photons (1%)
1.0E+17
N
4
He
1.0E+16
1.0E+19
1.0E+18
4
He
H
1.0E+16
3
1.0E+15
1.0E+14
T
He
12C
1.0E+13
Au
1.0E+12
1.0E+11
Debris Ions (16%)
1.0E+10
10.0E+8
1.0E-1
1.0E+0
1.0E+1
1.0E+2
1.0E+3
1.0E+4
• These photon and ion spectra used to
calculate energy deposition in armor
D
1.0E+14
T
1.0E+13
3
He
Fast Ions (12%)
-
H
1.0E+12

-
1.0E+10
10.0E+8
1.0E+1
1.0E+2
1.0E+3
1.0E+4
1.0E+5
For ions, tabulated data from SRIM used
for input for ion stopping power as a
function of energy
For photons, overall attenuation
coefficient as a function of energy used
Ion Kinetic Energy (keV)
April 10, 2002
1.0E+5
Ion Kinetic Energy (keV)
1.0E+15
1.0E+11
D
1.0E+17
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
7
Spatial and Temporal Profiles of Volumetric Energy Deposition
in C and W for Direct Drive Target Spectra
• Penetration range in armor dependent on ion energy level
-
Debris ions (~20-400 kev) deposit most of their energies within 1’s m
Fast ions (~1-14 Mev) within 10’s m
• Important to consider time of flight effects
- 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
Energy Deposition as a Function of Penetration
Ion Power Deposition as a Function of Time for
Depth for 154 MJ NRL DD Target
154 MJ NRL DD Target
Chamber Radius = 6 m
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
8
Temperature History of C and W Armor Subject to 154MJ
Direct Drive Target Spectra with No Protective Gas
3000
2000
Surface
1800
800
-18
600
Time (s)
Coolant
at 500°C
Energy
Front
m
1.0x10 -5
9.0x10-6
1.0x10-6
400
0.0x100
1.0x10 -5
9.0x10-6
8.0x10 -6
7.0x10-6
6.0x10 -6
5.0x10-6
4.0x10 -6
3.0x10-6
2.0x10 -6
1.0x10-6
0.0x100
200
Sublimation Loss = 9x10
7.0x10-6
600
3-mm Carbon Slab
Density= 2000 kg/m3
Coolant Temperature = 500°C
h =10 kW/m2-K
154 MJ DD Target Spectra
1000
6.0x10 -6
1000
1200
5.0x10-6
3-mm Tungsten slab
Density = 19350 kg/m3
Coolant Temp. = 500°C
h =10 kW/m2-K
154 MJ DD Target Spectra
100 microns
4.0x10 -6
1400
10 microns
1400
3.0x10-6
100 microns
1800
5 microns
1600
10 microns
Temperature (¡C)
Temperature (¡C)
5 microns
2200
1 micron
8.0x10 -6
1 micron
2.0x10 -6
2600
Surface
Time (s)
• For a case without protective gas:
-
Carbon maximum temperature < 2000°C
Tungsten maximum temperature < 3000°C (MP=3410°C)
Some margin for adjustment of parameters such as target
yield, chamber size, coolant temperature and gas pressure
• All the action takes place within < 100m
3-mm thick
Chamber Wall
April 10, 2002
h= 10 kW/m2-K
Separate functions: high energy accommodation in thin
armor, structural function in chamber wall behind
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
9
Example Analysis of Transient Energy Deposition on ITER
Divertor
q’’(W/m2)
1. Type I ELM scenario
- Initial condition based on design heat flux
of 10 MW/m2
- Energy fluence of 1 MJ/m2 over 0.2 ms
- Calculations done with the RACLETTE
code neglecting any vapor shielding effect
5000
10
0.2 ms
t
2. Disruption scenario
- Incident plasma energy of 10 MJ/m2 over 1 ms
- Calculations done with the HEIGHTS
package including vapor shielding effects
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
10
Example Temperature History of C and W Armor Subject to
Transient ELM Scenario in ITER
•
•
•
•
•
•
Maximum surface temperature is ~4200˚C for CFC and ~6000˚C for W
Temperature drops to the initial value in about 10 ms ( no temperature ratcheting effect for
ELM frequencies of ~ 1-2 Hz)
Sublimated CFC thickness is ~5 m (this limits the number of ELMs with such energy
densities that can be tolerated in ITER)
Evaporated thickness in the case of W is lower (~1 m per event)
However, the melt layer thickness is ~ 70 m
Key lifetime issue for W would be the stability of the melt layer and the corresponding
fractional loss of melted material
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
11
•
•
•
•
•
•
W Tmax
Time to reach Tmax
Melt layer thickness at Tmax
Max. melt layer thickness
Evaporated thickness at Tmax
Max. evaporated thickness
MFE
~ 7200°C
~ 25 s
~ 10 m
~ 100 m
~ 0.5 m
~ 2 m
Surface Temperature, K
Example W Armor Behavior Under MFE Disruption
Conditions
IFE
~ 7000°C
~ 2 s
~ 10 m
~ 0.1 m
1000
8000
Tungsten
7000
10 MJ/m
1 ms
6000
HEIGHTS calculations
2
B = 5 T,  = 2
100
0
T
s
5000
Melted Thickness ( m)
4000
10
3000
1
2000
• Effect of vapor shielding can be observed
• Key lifetime issue based on number of disruptions
that must be accommodated
Vaporization Thickness (
0.1
0
0
10
10
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
10
2
10
3
Temperature (°C)
6000
5000
3-mm Tungsten slab
Density = 19350 kg/m3
Coolant Temp. = 500°C
h =10 kW/m2-K
401 MJ DD Target Spectra
Melt layer = 7.3 m
Evap. loss = 0.08 m
4000
3000
2000
No protective gas
1000
0
1.0x10-7
April 10, 2002
1
Time, s
7000
• Interesting comparison: MFE case under
disruption and example IFE case with no
protective gas for high yield (401 MJ)NRL
DD target spectra to illustrate armor
behavior under respective threats
- IFE case is for illustration
- Protective gas will be used (e.g. ~80 mtorr
of Xe at RT) to spread out over time energy
deposition on armor
m)
1000
1.0x10-6
Time (s)
1.0x10-5
12
Other Erosion Processes are of Concern in Particular
for Carbon
Chemical Sputtering
Radiation Enhanced Sublimation
- Increases with temperature
Physical sputtering
- Not temperature-dependent
- Peaks with ion energies of ~ 1 kev
(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 spectra)
Rchamber = 6.5 m
CFC-2002U
April 10, 2002
- 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
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
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 (such as in penetration lines) (R. Causey’s talk at ISFNT-6)
H/C ratio of up to 1
Temperature lower than ~800 K
600
Tritium codeposition (g-T)
-
• Carbon is currently chosen in ITER to clad the
divertor target near the strike points because of
its greater resilience to excessive heat loads
during ELM’s and disruptions.
• Modeling predictions of tritium retention by
co-deposition with C for ITER
JET
equivalent
5 g/
pulse
ITER-FEAT
400
In-vessel limit
modeling predictions
Brooks et al.,
2-5 g-T / pulse
2 g/pulse
200
- The inventory limit (shown by double line) is
predicted to be reached in approximately 100 pulses
• If C is to be used, techniques must be developed
for removal of co-deposited T
- Baking with oxygen atmosphere at >570 K
- High temperature baking > 1000 K
- Others, (mechnical, local discharges…)
April 10, 2002
10 g/
pulse
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
1 g/pulse
0
0
50
100
150
Number of ITER pulses, 400 sec. each
14
200
Major Issues for Dry Wall Armor Include:
Carbon
MFE
IFE
P P
• Erosion
- Microscopic erosion (RES, Chemical and Physical Sputtering)
- Macroscopic Erosion (Brittle fracture)
• Tritium inventory
P P
- 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
P P
P P
Carbon and Tungsten
• He implantation leading to failure (1 to 1 ratio in ~100 days for 1 m implantation depth)
P
- 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
P P
P P
P P
Commonality of Key Armor Issues for IFE and MFE Allows for
Substantial R&D Synergy
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
15
Concluding Remarks
• Challenging conditions for chamber wall armor in both IFE and MFE
- Overlap between IFE conditions and some MFE off-normal events
• Different armor materials and configurations are being developed
- 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
chamber communities
- make the most of synergy between MFE and IFE Chamber Armor
R&D
April 10, 2002
A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE
16