Heat and mass transfer in fusion energy
Transcript of Heat and mass transfer in fusion energy
January 25, 2008/ARR 1
Heat and Mass Transfer in Fusion Energy Applications: from the “Very Cold” to the
“Very Hot"
Presented by A. René RaffrayUCSD
SeminarUniversity of California, Los Angeles
Los Angeles, CAJanuary 25, 2008
January 25, 2008/ARR 2
Unique Set of Conditions Associated with Fusion• Realization of fusion energy imposes considerable challenges in the areas of
engineering, physics and material technology.
• This is typified by the heat and mass transfer aspects, which cover a wide range of conditions, from the very cold to the very hot.
• This seminar highlights this wide range of challenges associated with the heat and mass transfer aspects of fusion technology using examples in both the Inertial Fusion Energy (IFE) and the Magnetic Fusion Energy (MFE) Approaches.
Electricity Generator
Targetfactory
Modular LaserArray
Chamber
Schematic of IFE Power Plant (HAPL) ARIES-CS Power Core
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Electricity Generator
Targetfactory
Modular LaserArray
Example of IFE Energy Source Based on Lasers, Direct Drive Targets and Solid Wall Chambers (HAPL)
Target (fabrication at <20K, survival
in chamber during injection)
Chamber conditions(~0.1-1 eV
depending on pre-shot
conditions)
Final optics (+ mirror steering)
Blanket
System (including
power cycle)
Dry wall chamber
(armor must accommodate ion+photon
threat at up to ~2000-3000K)
January 25, 2008/ARR 5
An IFE Target Consists of Multiple Layers with Demanding Fabrication Requirements
Uniformity of DT fuel layer thickness
Inner and outer surface smoothness (order of 1 m)
Example Sector of Spherical Target (HAPL)
• Rep rate of 5-10 Hz leads to ~500,000 targets per day• Mass fabrication production • Need reasonably fast layering technique also to
maintain acceptable tritium inventory
(for target microexplosion physics and thermal radiation shielding)
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In Beta Layering, DT-Fuel moves until Inner Surface is Isothermal
• Volumetric heating (tritium decay) causes sublimation until isothermal condition is reached (beta-layering)
3H --> 3He + ß- + anti-neutrino
(max. ß energy = 18.6 keV)
• Inner surface temperature increases with increasing layer thickness
• Thermal gradient causes fuel to redistribute
• Fuel moves from thicker to thinner region
• Uniform temperature field leads to uniform layer thickness
Uniform temperature field on outer target (TP of DT ~19.79K)
A. J. Martin, Beta energy driven uniform deuterium-tritium ice layer in reactor- size cryogenic inertial fusion targets, J. Vac. Sci. Technol. A6 (3) (1988)
T, PMigration
of fuel
1- D simplification
Tem
pera
ture
Radius
Th
icker
layer
(hott
er)
Th
inn
er
layer
(c
old
er)
Unlayered Target
qDT= 0.05 W/cc
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• Gas stream heats up as the heat from the beta decay is removed from the particles
• Temperature difference causes a non-uniform layer• Temperature variations of helium gas are only slightly
impressed onto fuel• Successful layering will depend on fluidized bed design
– Minimal temperature gradient– Maximum spin and circulation rate of the pellets to provide a
time-averaged isothermal environment
Helium gas: 0.5 atm, <18K>Fuel
Capsule Fuel
Approximate as semi-infinite slabs
Gas T varies 3 mK across capsule
5 Hz target rotation
5 Hz rotational speed lead to acceptable layer uniformity (~1.2%)
Apply dynamic ∆T to static model of fuel layer movement
3 mK local
∆T
GA Has Proposed a Fluidized Bed for Mass Production of IFE Fuel Pellets
LAYERING
Fluidized Bed
Gas Flow
Frit
SPIN
CIRCULATION
Hotter
Cooler
Temperature at an instant
Fuel outer surface varies only 0.008mK
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• STARTING POINT- A fluidized bed has been chosen for mass production
layering of IFE targets (GA)
• Room temperature fluidized bed experiments- For initial observation and characterization of bed
behavior
• Numerical fluidized bed model proposed- Must include particle imbalance
- Validation through theory and experiments
• Experimental water-alcohol layering- Validate layering model - Show proof of principle
• Find optimized parameters for D2 Layering prior to experiment
• END POINT- Successful D2 layering in Mass Production Layering
Experiment (MPLX) (GA)
Plan for GA/UCSD Collaboration on Target Layering
(UCSD/GA)K. Boehm
HiP cell
Fluidized bed
Target Vacuum Pickup
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Desktop Experiment Set-Up to Help Understand Fluidized Bed Behavior Under RT Conditions
• Use unfilled plastic target shells in a nitrogen flow (N2(RT) ~ He(18K)) • Spin rates of unbalanced spheres• One shell was partially filled with whiteout• An unbalanced target needs 2X bed expansion to spin in example case
Fluidized Bed Performance Regular Frit
0
5
10
15
20
25
1.5 2.5 3.5Bed Expansion
Frequency, Hertz
SpinningOffset BallRegular Frit
SpinningFoam BallRegular Frit
CirculatingOffset BallRegular Frit
CirculatingFoam BallRegular Frit
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Surface Degradation is Observed During Fluidization
• A random patch of the target surface is scanned under an SEM for roughening study
• Measurements on (60-40) Au–Pd sputter-coated targets
• Unacceptable Au-Pd layer damage for radiation protection and possibly for target physics requirement
• Need to improve coating process and minimize fluidization time
One patch of the shell analyzed
Au-Pd Surface before Fluidization
Surface after 16 hrs of room temperature fluidization
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Several Parameters Define Window of Operation for Fluidized Bed
Gas Flow≠0
h
Gas Flow=0
h’
• 3 main objectives- Minimize T across bed (~3 mK per target)- Optimize spin and circulation rates at operating point- Preserve surface quality
- Bed expansion ratio:E= h/h’
- Representative of gas speed or mass flow
Crush target
=1.2 =1.5 =2.0 =4.0 =8.0
1 QDT
Surface Damage
FLUID BED CHARACTERISTICS FOR 4.6 mm, 8.8mg CAPSULE
0
20
40
60
80
100
120
140
160
180
200
0 0.5 1 1.5 2
BED GAS PRESSURE (atm)
∆T ACROSS BED
(mK)E=1.2E=1.5E=2.0E=4.0E=8.0
Example operating point:0.5 atmh/h’= 2T=70mK
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Unknowns in Bed Behavior Call for Numerical Analysis
• The behavior of unlayered shells is unknown (unbalanced spheres)
• Experimental observations are restricted to the particles close to the wall
• Tests on the cryogenic apparatus are expensive, time consuming and complex
• Results might be hard to interpret since shells are not easily accessible
• Optimize operating conditions and define narrow window of operation for successful deuterium layering prior to completion of entire setup- gas pressure, flow speed, bed dimensions, additional heating, frit
design, layering time…
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Proposed Numerical Model Consists of Three Parts
• Granular model
• Fluid-Solid interaction
• Layering Model – Thermal/mass transfer
Fluidized Bed Model
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Fluidized Bed ModelPart I: Granular Model
• Discrete Particle Method (DPM)• Motion of individual particles tracked by
computing forces acting on the particles at each time step
• Apply Newton’s second law of motion• Spring – dashpot and/or friction slider
model applied for particle collisions• Limitations: Not developed for
unbalanced spheres
Forces are computed based on relative velocity at contact point
Contact point velocity is
not parallel to wall
Orientation defined by Euler angles
Center of mass Geometrical Center
wall
displacement
wall
Normal Force
Tangential Force
Torque around center of mass
For unbalanced sphere:- Contact forces are a function of relative
velocity at contact point- Depends on the orientation of the particle
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i
ji
sj
sis
ics rss
sss
rrr
rrr
⋅−
−=
bji
Tji
sji
s
jicg oAss ,,,,
rrr⋅−=
bji
Tji
sji A ,,, ωω r
⋅=
sji
s
jicgjis
jicp vsv ,,,,
rrrr+×=ω
s
jcps
icps
cp vvvrrr
−=
( )( ) effs
ncpeffjijisn cvkrrssF ⋅−⋅+−−= ,
rrrr
( )( )stcp
stcps
tcpsn
st
v
vvFF
,
,,,min r
rrr
⋅⋅⋅−= γμ
stot
sicg
si Fs ×= ,
rrτ sb A ττ ⋅=
Equations to Compute Contact Forces in Model
amFrr
⋅=
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛
−−
−−−−
=
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛
bz
by
bx
qqqq
qqqq
qqqq
qqqq
q
q
q
q
ω
ω
ω
0
2
1
0123
1032
2301
3210
3
2
1
0
&
&
&
&
Distance between two sphere centers
Distance between two mass centers
Convert spin into space fixed coordinates
Compute contact point velocity
*Single particle experimental observation to determine parameters such as keff and ceff
Apply Forces to:
amFrr
⋅=
Normal and Tangential Force Component*
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Fluidized Bed ModelPart II: Fluid/Drag Model
• Problem with fluid cell sizes for traditional porous flow model:- Minimum of seven pellets per fluid cell for cell average to work in
control volume method- Not useful to solve fluid equation for 3x4 grid- Choosing a grid size smaller than the shells leads to complication
determining the “average void fraction” around a sphere
• DNS model to resolve flow around each sphere complex, computationally VERY expensive and not warranted for
the purpose of this model
• The most important information we are trying to get is the particle spin and circulation rate
• Experimental observations show, that the spin of the particles is dominantly induced by collisions, not by fluid interaction
• 1-D Lagrangian model to determine void fraction
- Compute the void fraction for each slice of the fluidized bed, bounded by one radius in each direction of the center of each sphere.
- This “region of interest” moves with each particle from time step to time step
- Once the void fraction is known, the drag force can be computed
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Richardson-Zaki Drag Model is Applied Based on Known Void Fraction of Region
( ) 8.3
8.4
6−
⎟⎟⎠
⎞⎜⎜⎝
⎛−= ερρ
π n
tfp
pd u
Ug
df Void Fraction is known
based on 1-D Lagrangian Model
Richardson-Zaki Drag Force for homogeneous fluidized beds:
( )( )25.05.02 832.1_809.3809.3Re Art +−=
( )2
3
f
fpfpgdAr
μ
ρρρ −=
tf
fpt u
d
=ReTerminal Free Fall Velocity is a constant system parameter:
Dellavalle Drag Model to Compute Terminal Free Fall Velocity:
Archimedes Number:
Drag force is added to the total force on the particle at each time step
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Particles need to be spaced apart
Initialize position, velocity and quaternion vectors
Start time stepping
Predictor step
Compute forces based on predicted positions
Compute the resulting pressure drop
Determine bed expansion
Correct positions, velocities and accelerations based on the updated forces
Create time averaged statistics
Write Output every 1000 time steps
Particle – wall collisions
Compute void fraction
Compute drag force
Compute effective weight
Compute force due to particle – particle collisionsLoop over all particles
Proposed Fluidized Bed Model
January 25, 2008/ARR 19
Preliminary Results from Fluidized Bed Model Show Good Qualitative Reproduction of Experimental Results
Exact system parameters need to be determined
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Model Has Been Calibrated through a Series of Runs for Balanced Spheres
6e-05
4e-05
3e-05
2e-05
1e-05
5e-05
0.1 0.2
Time (s)
Total Kinetic Energy in System during Granular Collapse for decreasing time step size
(J)
200 particlesM = 2E-6 KgDiameter = 4 mmK_eff = 1000 N/mC_eff = 0.004 N s/m = 0.0125 N s/m = 0.4I = 5E-12 Kg s^2
Example: Stability and convergence in modeling granular collapse
Next Step: Validation for cases with unbalanced spheres
January 25, 2008/ARR 21
Layering Model
• Compute the redistribution of fuel based on the fluidized bed behavior
• Solve 1-D equations simultaneously:
• This leads to a layering time constant of
• Time step: ~10-5 s for fluidized bed v. ~30-60s for layering
• Based on the time averaged motion and preferential position, we can compute the average temperature/ temperature difference between the thick and the thin side of the shell
⎥⎦
⎤⎢⎣
⎡−=
1
1
2
2
T
P
T
P
lR
C
ICE
diff
ρδ&
Mass Transfer Equation
[ ]fICEICE
ICE hqk
t
hTT ρδδ &&+⎥
⎦
⎤⎢⎣
⎡+⋅=−
1221
Heat Transfer Equation
q
ht fe ′′=
&
Latent heat
Volumetic heating
January 25, 2008/ARR 22
Experimental Demonstration of Layering Proposed Using H2O – IPA Mixture
• Water-alcohol filled shells (freezing point ~240K)
• Fluidized be with cooling stream of N2 or He
• Vol. heat source (IR with bandpass filter or microwave)
• Objectives- Analyze fluidizing behavior for unbalanced shells- Demonstrate target layering process- Investigate the effects of volumetric heating and other bed
parameters on the layering process- Validate layering model
Fluidized Bed
IR- Halogen Light
TOO MUCH HEAT GETS ABSORBED IN FIRST LAYER
TOO TRANSPARENT
Small margin
Room temperatureand pressure
T~240 K in vacuum
Honed copper tubes as waveguides
Bandpass filter
IR halogen lamp
Glass window
Vacuum vessel
Fluidized Bed
Reflective coating to trap radiation
January 25, 2008/ARR 24
The Cryogenic Direct-Drive Target will be Subjected to Challenging Conditions when
Injected into an IFE Chamber
IFE Chamber (R~6-10 m)
Chamber Gas: protective gas (Xe) and/or burn products (D, He)
Chamber wall ~ 1000–1500 K, q’’ rad = 0.2 – 1.2 W/cm2
Target Injection (~100 m/s)
Target Implosion Point
January 25, 2008/ARR 25
Modeling Target Injection Using DS2V
Example Temperature Field Around a Direct Drive Target
- Xe flowing at 400 m/s in the positive x-dir.
- 4000 K stream temperature.
- 3.22x1021 m-3 stream density.
- Sticking coefficient = 0
- Target surface temperature = 18 K
Assumptions• Axially symmetric flow.
• Target is stationary; gas stream velocity to simulate injection.
• Target surface temperature is constant (~18K).
• Sticking coefficient = 0 or 1,
•Accommodation coefficient = 1
• Target doesn’t rotate.
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Thermal Modeling Indicates Limited Gas Density in Chamber to Prevent Target DT Reaching its Triple Point
• For a 16 K target injected at 100 m/s in a 10.5 m chamber, q’’ to reach the TP ~0.5 W/cm2
• Radiation q’’ ~ 0.2 W/cm2 for a 1000K wall and target =0.96
• From DS2V, for a target injected at 100 m/s in 1000 K D2, q’’ = 0.3 W/cm2 for D2 density of ~4 mTorr
• Not much margin left for increases in radiation due to reflectivity change
0.01
0.1
1
10
0.1 1 10Pressure (mTorr)
Heat Flux (W/ sq cm)
T=1000K V=100mpsT=1000K V=400mpsT=4000K V=100mpsT=4000K V=400mps
1-10 m Polymer Shell with Au or Pd Reflective Coating
290 m Solid DT/Foam
190 m Solid DT
DT Vapor Core
~ 4 mm
January 25, 2008/ARR 27
What About the Effect of 3He Nucleation Sites?
electronHeH +→ 23
13
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
x 10-5
0
1
2
3
4
5
6
x 10-6
Tim
e
(delta time =
5 min)
Mole fraction of 3He diffused into the Trap
Radial distance from the center of the trap (m)
Mol
ar f
ract
ion
of
3H
e
• 3He generated into the DT by tritium decay (half life = 12.3 years) could accumulate in clusters and provide nucleation sites
• Time between layering and injection = 4-10 hrs
•• Estimated nucleus radiusEstimated nucleus radius-- 0.4 microns after 4 hrs0.4 microns after 4 hrs-- 1.6 microns after 18 hrs1.6 microns after 18 hrs
• 2-D model to more accurately simulated bubble nucleation and growth
January 25, 2008/ARR 28
2-D Thermal Diffusion Model with Stretched Grid and Bubble Growth
• Bubble grows as fast as heat for the phase change can be delivered to the interface
• As the bubble starts growing, the pressure in the bubble drops even further
• Bubble grows step wise depending on the Bubble grows step wise depending on the gridgrid
• Conservation of energy requires variable Conservation of energy requires variable time stepstime steps
• In order to determine the length of the time In order to determine the length of the time step, the heat flux to the bubble needs to be step, the heat flux to the bubble needs to be computedcomputed
• As the bubble grows from one grid to another, the temperature field is adjusted
Bubble grows radially outward starting somewhere in the domain
⎟⎟⎠
⎞⎜⎜⎝
⎛⋅+⋅=′′
θδδ
δδ T
rr
Tkq
1&
January 25, 2008/ARR 29
Temperature Field Around the Bubble
• Small thermal boundary layer
Time: 4.86 E-6sRadius: 2.94 E-6m
Time: 3.52 E-5sRadius:8.66-6m
Time: 8.53 E-5sRadius:1.09E-5m
Time: 1.47E-4sRadius:1.34E-5m
Time: 2.23E-4sRadius:1.64E-5m
Time: 3.15E-4sRadius:2.00E-5m
January 25, 2008/ARR 30
Comparison with LANL DT Bubble Growth Experimental Observation
•• Two stages of bubble growthTwo stages of bubble growth-- Could be explained by the temperature fieldsCould be explained by the temperature fields
•• Bubble grows into the solid layerBubble grows into the solid layer-- Low strength of DT around triple pointLow strength of DT around triple point
•• Small bubbles nucleate later but grow fast for a Small bubbles nucleate later but grow fast for a longer longer period of timeperiod of time
-- Higher superheat requiredHigher superheat required
-- Higher surrounding temperature results in a faster Higher surrounding temperature results in a faster growthgrowth
Comparing Bubble Growth (LANL experiments and numerical simulation)
0.0E+00
2.0E-05
4.0E-05
6.0E-05
8.0E-05
1.0E-04
1.2E-04
1.4E-04
0 0.02 0.04 0.06 0.08 0.1 0.12
time (seconds)
bubble diameter (meters)
bubble T=18K, p=22 000Pa, R_min=1.6E-6m
meltlayer heat flux =1W/cm 2̂
LANL BUBBLE UPPER
LANL BUBBLE LOWER
bubble T= 18K, p =22 000Pa, R_min = 4E-7m
January 25, 2008/ARR 31
• Melt layer around the target does not violate symmetry requirements• Bubbles do violate symmetry• Nucleus of a certain size present in the DT• Temporal separation of melt layer occurrence and bubble nucleation• If melt layer acceptable for target physics requirement and limiting criterion based
on bubble growth, possibility of significant impact on target and chamber design- Increase heat flux by a factor of 3-10
Applying Model to Characterize Target Design Limitations
January 25, 2008/ARR 33
What are the Threats on the Chamber Wall?
• X-ray, ion and neutron fluxes to the chamber wall several times per second.
• Neutron flux penetrates deeper and not an issue for armor.
• Need to develop armor that can accommodate X-ray and (more importantly) ion threats.
Target micro-explosion
Chamber wall
X-rays Fast & debris ions Neutrons
Direct Drive
Target (MJ) X-rays
4.94 (1.3%)
Neutrons
274.3 (74.7%)
Gammas
0.017 (0.005%)
Burn Product Fast Ions
47.14 (12%)
Debris Ions Kinetic Energy
40.71 (16%)
Total
367.1
Example energy partitioning for 350 MJ-class direct drive target
(HAPL reference from J. Perkins, Oct. 2005)
January 25, 2008/ARR 34
Ion and Photon Threat Spectra Cover Appreciable Energy Ranges
• Example spectra for 350 MJ-class direct drive target (HAPL reference, J. Perkins, Oct. 2005).
January 25, 2008/ARR 35
Ion Power Deposition Occurs in a Very Thin Armor Region (~m’s) over a Few s
• Example case for 10.75 m chamber without protective gas to avoid target survival and placement issues.• Only thin armor region sees large energy deposition and temperature transients (next slide).• 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 (similar to MFE).• W chosen as preferred armor material (high-temperature capability, no tritium concern).• Armor lifetime is a key issue and is the focus of the R&D in this area.
Coolant
FSW
q
January 25, 2008/ARR 36
Temperature History and Gradient for W Armor in a 10.75 m Chamber Subject to the 350 MJ-Class Baseline Target Threat
Spectra (from HAPL)• 1-mm W on 3.5 mm FS at 580 °C.• No chamber gas.• Time-of-flight spreading of ion energy deposition results in much lower temperature
rise than assumption of instantaneous energy deposition.• Peak temperature ~2400°C.
January 25, 2008/ARR 37
Impact of Threat Spectra on 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.
• Because the exact IFE ion and X-ray threat spectra on the armor cannot be duplicated at present, experiments are performed in simulation facilities as part of the HAPL program:- Ions (RHEPP@SNL).
- Laser (Dragonfire@UCSD).- Fatigue testing of the W/FS bond in ORNL infrared facility.- He management is addressed by conducting implantation experiments (UNC, UW)
along with modeling of He behavior in tungsten (UCLA).
AblationDepth
T or T
No net ablation, but surface roughening
Threshold for ablation
Threshold for roughening
Net Ablation
January 25, 2008/ARR 38
Long Term Exposure Experiments Suggest Roughening Threshold and Temperature Dependence for W, for example:
• Results from the RHEPP ion beam facility at SNL (0.8-1.6 MeV) indicates roughening threshold for powder metallurgy W (PM W) at ~ 1 J/cm2 at RT. - some improvement with heated W samples.- single crystal W better.- rhenium (Re) and Re/W alloy much better.
• Does roughening matter if it does saturate and does not lead to armor failure? Probably not.• Additional testing and diagnostics needed for confirmation of initial experimental indications on
saturation and threshold for W armor. • For HAPL, as an initial armor survival constraint from these early results, a temperature limit of
2400°C was assumed for the W armor (e.g. corresponding to a RHEPP fluence of ~1.2 J/cm2).
• Results from Dragonfire laser testing facility at UCSD (YAG laser, 10 Hz) with W (~3000°C) indicate possible roughening saturation after ~105 shots.
• Also, PM W behavior seems to depend more on T than T.11A, 200mJ, 773K, Max: 3,000K (~2,200K T)
103 shots 105 shots104 shots
January 25, 2008/ARR 39
Another Major Issue is Ion Implantation Effect on W
• He retention and surface blistering characteristics of W
• Carbide formation and change of thermophysical properties of surface
• R&D activities as part of HAPL program include:
• He implantation/anneal cycle experiment(UNC/ORNL)
- ~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 of implanted ion behavior including bubble formation and
behavior (HEROS code at UCLA)
• He ion irradiation of W at 800 °C shows significant surface damage at modest exposure
• Need better understanding (including pulse effect and net mass loss)
• Possibility of porous material to enhance release and relieve thermal stress
January 25, 2008/ARR 40
0
1
2
3
4
5
6
1.0E+15 1.0E+16 1.0E+17 1.0E+18 1.0E+19 1.0E+20
Dose per He implantation (ions/m2)
Effective Diffusion Activation Energy ( eV)
Single crystalPolycrystalline
IFE Case ~5 x 1016 atoms/m2
1 MeV He Implantation and Release in W (UNC)
• He retention in W decreases drastically when a given He dose is spread over an increasing number of pulses, each one followed by W annealing to 2000°C • Simple diffusion model suggests values of
effective activation energy as a function of dose• Results suggest porous material with 50-100 nm microstructure would keep at% of retained He in W to a few %
- Vacuum plasma spray porous W with ~10-100 nm microstructure (PPI/UCSD).
January 25, 2008/ARR 41
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
e
Yield (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
• Desirable to avoid protective chamber gas based on target survival and injection considerations
• Large chamber maintained as baseline for HAPL
• Possibility of advanced chambers explored, in particular use of magnetic intervention to stir away the ions and help achieve a more compact chamber
January 25, 2008/ARR 43
The Divertor Challenge in MFE: How to Accommodate the Heat and Particle Fluxes
ARIES-CS Compact Stellarator Concept as example of MFE Device
• Provide region for ion neutralization and fusion ash pumping
• W armor considered for power plant application
- high temperature capability - relatively high sputtering threshold
• Provide region for ion neutralization and fusion ash pumping
• W armor considered for power plant application
- high temperature capability - relatively high sputtering threshold
Field line tracing model to estimate
divertor heat flux for ARIES-CS
January 25, 2008/ARR 44
ARIES-CS Divertor Design
• UCSD/FZK collaboration• Design for a max. q’’ of at least 10 MW/m2 • He coolant and tungsten-alloys as structural material and for armor• Previous concepts include:
• UCSD/FZK collaboration• Design for a max. q’’ of at least 10 MW/m2 • He coolant and tungsten-alloys as structural material and for armor• Previous concepts include:
• Build on the W cap design and explore possibility of a new mid-size configuration with good q’’ accommodation potential, reasonably simple (and credible) manufacturing
Cooling finger with W caps (~1-2 cm) (FZK):- minimize use of W as structural material - accommodate higher q’’- many small units (~105-106)required, raising
reliability and maintenance concerns
Plate configuration (~ 1m) (FZK):-fewer units ~100-1000-not well suited for thermal gradient accommodation
January 25, 2008/ARR 45
T-Tube Divertor Concept (also applicable to Tokamaks)
• W allow cartridge inside outer tube• Cooling with discrete or continuous jets• W armor layer• Graded transition connection from W alloy to FS
manifold to reduce differential thermal expansion and stress
• W allow cartridge inside outer tube• Cooling with discrete or continuous jets• W armor layer• Graded transition connection from W alloy to FS
manifold to reduce differential thermal expansion and stress W alloy
outer tube
W alloy inner cartridge
W armor
January 25, 2008/ARR 46
Set Tube Length for Acceptable Deflection
• Deflection <0.2 mm for L=10 cm and D = 1.5 cm• Deflection <0.2 mm for L=10 cm and D = 1.5 cm
January 25, 2008/ARR 47
Excellent Thermal-Hydraulic Performance• Results from and FLUENT (CFD) and CFX indicates that for q’’ = 10 MW/m2:
- High jet heat transfer coefficient- W alloy temperature within ~600-1300°C (assumed ductility andrecrystallization limits, but
requires further material development)
• Results confirmed through dedicatedexperiments at Georgia Tech.
• Results from and FLUENT (CFD) and CFX indicates that for q’’ = 10 MW/m2:- High jet heat transfer coefficient- W alloy temperature within ~600-1300°C (assumed ductility andrecrystallization limits, but
requires further material development)
• Results confirmed through dedicatedexperiments at Georgia Tech.
Example Case:• Jet slot width = 0.4 mm• Jet-wall-spacing = 1.2-1.6 mm• Specific mass flow = 2.12 g/cm2 • Mass flow per tube = 48 g• P = 10 MPa, P ~ 0.1 MPa•T ~ 90 K for q’’ = 10 MW/m2
• THe ~ 605 - 695°C
January 25, 2008/ARR 48
Design Optimized for Reasonable Stresses
• Results from ANSYS for q’’ = 10 MW/m2:- Maximum thermal stress ~ 370 MPa
• Graded transition connection from W alloy to FS manifold results in acceptable stresses
• Results from ANSYS for q’’ = 10 MW/m2:- Maximum thermal stress ~ 370 MPa
• Graded transition connection from W alloy to FS manifold results in acceptable stresses
th,max ~ 370 MPa
January 25, 2008/ARR 49
Divertor Unit Cell Design Allows for Assembly in Manifolding Units and Integration in Plates of
Required Sizes• T-tubes assembled in a manifold unit.• Typical divertor target plate (~1m x ~1 m) consists of a number of manifold
units.
Details of T-tube manifolding to keep FS manifold structure within its temperature limit
January 25, 2008/ARR 50
Fabrication Method Being Investigated at Plasma Processes Inc. (PPI, Huntsville, AL)
• Vacuum Plasma Spray (VPS) posible• New EL-Form process method preferred
- High temperature electroforming based on electrodeposition of compact layers of metals onto a mandrel of the desired shape. - Deposits >99% of theoretical density as deposited- Avoid possible shrinkage linked with long term post-processing sintering or HIPing
• Vacuum Plasma Spray (VPS) posible• New EL-Form process method preferred
- High temperature electroforming based on electrodeposition of compact layers of metals onto a mandrel of the desired shape. - Deposits >99% of theoretical density as deposited- Avoid possible shrinkage linked with long term post-processing sintering or HIPing
• Co-axial tube successfully manufactured as part of SBIR I effort
• Prototypical geometry + heat flux testing as part of Phase II
January 25, 2008/ARR 51
Only Very Few Off-Normal Events Could be Allowed in a Fusion Power Plant
• Disruptions can result in heat loads on the divertor (ITER, 6-25 MJ/m2 over ~1.5-3 ms)• Melting and evaporation would occur• Very few such events allowed (cannot shut down the power plant + armor lifetime)
• Disruptions can result in heat loads on the divertor (ITER, 6-25 MJ/m2 over ~1.5-3 ms)• Melting and evaporation would occur• Very few such events allowed (cannot shut down the power plant + armor lifetime)
Temperature History of W Divertor Armor Under 3 MJ/m2 over 3 ms Disruption Heat Load
(3 mm W armor, 2 mm W tube thickness; q''=10MW/m2; h =20 kW/m2-K)
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
0.0E+00 1.0E-03 2.0E-03 3.0E-03 4.0E-03 5.0E-03 6.0E-03
Time (s)
Temperature (°C)
Tmax,WTcool
Divertor W Phase Change Thickness Following 3 MJ/m2 over 3 ms
Disruption Heat Load (3 mm W armor, 2 mm W tube thickness
q''=10MW/m2; h =20 kW/m2-K)
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
0.0E+00 1.0E-03 2.0E-03 3.0E-03 4.0E-03 5.0E-03 6.0E-03 7.0E-03 8.0E-03 9.0E-03 1.0E-02
Time (s)
W Phase Change Thickness (m)
W Evaporated LayerW Melt Layer
Maximum W Armor Phase Change Thickness as a Function of Energy Density for Example Disruption Case over Deposition Times of 1 and 3 ms
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
0 1 2 3 4 5 6
Energy Density (MJ/m2)
Maximum Phase Change
Thickness (m)
Evap. for 1 ms
Evap. for 3ms
Melt for 1 ms
Melt for 3 ms
Poly. (Evap. for 1 ms)
Poly. (Evap. for 3ms)
2-mm W alloy3-mm W armor
Heh = 20 kW/m2-KT = 700°C
Energy Deposition
January 25, 2008/ARR 52
Summary
• Realization of fusion energy imposes considerable demands in the areas of engineering, physics and material technology, as typified by the heat and mass transfer aspects, which cover a wide range of conditions, from the very cold to the very hot, e.g.:
- IFE target: < 20K
- IFE pre-shot chamber environment: ~1000-10000 K
- IFE chamber wall: ~1500-3000 K
- MFE divertor normal/off-normal conditions: ~1500/4000 K
• Exciting challenges
• Much progress toward credible solutions but more work needs to be done.