Dynamic Chamber Armor Behavior in IFE and MFE

1
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 DiegoApril 10, 2002

2
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 RD
• Synergy
• 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

Energy partition for two example targets
Chamber wall
Target micro-explosion
X-rays Fast debris ions Neutrons
4
MFE Operating Conditions
Steady state conditions Load on plasma facing
components dependent on location, e.g. for ITER
However, a number of cyclic off-normal
conditions must be designed for in next step
option - Vertical Displacement Events (VDEs)
- Edge Localized Mode Scenarios
(ELMs) - Disruptions
5
Comparison of IFE and MFE Operating Conditions
for ITER Divertor and NRL Direct Drive Target
Spectra as Example Cases
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 ELMs - Frequency
and energy density are within about one
order of magnitude
6
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 3370C - Melting point of tungsten
3410C
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 (1283C) and high
sputtering yield
Example analysis results for IFE and MFE showed
for C and W armor
7
Example IFE Threat Spectra for 154 MJ NRL Direct
Drive Target
Photons (1)
Debris Ions (16)
These photon and ion spectra used to
calculate energy deposition in armor - 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
Fast Ions (12)
8
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 1s mm - Fast
ions (1-14 Mev) within 10s mm Important to
consider time of flight effects - Photons in sub
ns - Fast ions between 0.2-0.8 ms - Debris
ions between 1-3 ms - Much lower maximum
temperature than for instantaneous energy
deposition case
Ion Power Deposition as a Function of Time for
154 MJ NRL DD Target
Chamber Radius 6 m
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 - Carbon
maximum temperature lt 2000C - Tungsten maximum
temperature lt 3000C (MP3410C) - Some margin
for adjustment of parameters such as target
yield, chamber size, coolant temperature and
gas pressure All the action takes place within
lt 100mm - Separate functions high energy
accommodation in thin armor, structural
function in chamber wall behind
10
Example Analysis of Transient Energy Deposition
on ITER Divertor
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
2. Disruption scenario - Incident plasma
energy of 10 MJ/m2 over 1 ms - Calculations
done with the HEIGHTS package including
vapor shielding effects
11
Example Temperature History of C and W Armor
Subject to Transient ELM Scenario in ITER
Maximum surface temperature is 4200C for CFC
and 6000C 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 mm (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 mm per event) However, the melt
layer thickness is 70 mm Key lifetime issue
for W would be the stability of the melt layer
and the corresponding fractional loss of
melted material
12
Example W Armor Behavior Under MFE Disruption
Conditions
MFE IFE 7000C 2 ms 10 mm
0.1 mm
W Tmax 7200C Time to reach
Tmax 25 ms Melt layer thickness at Tmax
10 mm Max. melt layer thickness 100 mm
Evaporated thickness at Tmax 0.5 mm Max.
evaporated thickness 2 mm Effect of vapor
shielding can be observed Key lifetime issue
based on number of disruptions that must be
accommodated
HEIGHTS calculations
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
13
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)
14
Tritium Inventory in Carbon is a Major Concern

• Operation experience in todays 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. Causeys talk at ISFNT-6)
• - H/C ratio of up to 1
• - Temperature lower than 800 K

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 ELMs and disruptions.
Modeling predictions of tritium retention by
co-deposition with C for ITER - 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 gt570 K - High temperature baking gt
1000 K - Others, (mechnical, local discharges)
15
Major Issues for Dry Wall Armor Include
MFE IFE P P P P
P P P P
P P P
P P
P P
Commonality of Key Armor Issues for IFE and MFE
Allows for Substantial RD Synergy
16
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 RD 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 RD