IFE Dry Chamber Wall Designs

1
IFE Dry Chamber Wall Designs

• A. R. Raffray and F. Najmabadi
• University of California, San Diego
• Laser IFE Materials Working Group
  MeetingUniversity of California, Santa
  BarbaraAugust 30, 2001
• For more info, please visit the ARIES web site
  http//aries.ucsd.edu/ARIES/

2
Outline of Presentation

• Dry Chamber Wall Design
• Must satisfy conflicting requirements set by
  operation and performance of different components
  
• Dry Chamber Wall Options
• Armor is Key Region - Blanket design can be
  adapted from MFE blankets
• Candidate Armor Materials and Configurations
• C, W, Engineered surface (fibrous surface),
  others
• Example thermal analyses
• Key Material Issues
• Use of very thin armor on structural material to
  separate energy accommodation function from
  structural function
• Surface and near-surface properties under pulsed
  conditions (ion and neutron fluxes and fluence)
• Armor fabrication and bonding
• Erosion
• Armor lifetime and need for in-situ repair
• Tritium retention issues
• Must consider other armor options besides C
• Must prioritize material RD - make the most of
  information from MFE and focus on key IFE issues

3
Requirements from Several Components and
Processes Must be Balanced in Evolving IFE
Chamber Design
Tout
Laser Driver
HX to Power Cycle
Target Injection
Tin
4
Target Thermal Control Requirements on Wall
Temperature and Chamber Gas Pressure

• Analysis of design window for successful
  injection of direct and indirect drive targets in
  a gas-filled chamber (e.g., Xe)
• No major constraints for indirect-drive
  targets.
• Narrow design window for direct-drive targets
• (Pressure lt 50 mTorr, Wall temperature lt 700 C)

5
Laser Beam Propagation and Breakdown Sets
Requirement on the Chamber Gas Pressure for a
Given Laser Intensity
The chamber environment following a target
explosion contains a hot, turbulent gas which
will interact with subsequent laser pulses.
Gas breakdown may occur in the vicinity of the
target where the beam is focused. A better
understanding of the degree of gas ionization and
the effects on beam propagation is needed (under
study at UCSD).
6
Outline of Presentation

• Dry Chamber Wall Design
• Must satisfy conflicting requirements set by
  operation and performance of different components
  
• Dry Chamber Wall Options
• Armor is Key Region - Blanket design can be
  adapted from MFE blankets
• Candidate Armor Materials and Configurations
• C, W, Engineered surface (fibrous surface),
  others
• Example thermal analyses
• Key Material Issues
• Use of very thin armor on structural material to
  separate energy accommodation function from
  structural function
• Surface and near-surface properties under pulsed
  conditions (ion and neutron fluxes and fluence)
• Armor fabrication and bonding
• Erosion
• Armor lifetime and need for in-situ repair
• Tritium retention issues
• Must consider other armor options besides C
• Must prioritize material RD - make the most of
  information from MFE and focus on key IFE issues

7
Armor is Key RegionAll the Action Takes Place
within 0.1-0.2 mm of Surface
Photon and ion energy deposition falls by 1-2
orders of magnitude within 0.1 mm of
surface Because of thermal capacity of
armor, FW structure experiences much more
uniform q and quasi steady-state temperature
Most of neutrons deposited in the back where
blanket and coolant temperature will be at
quasi steady state due to thermal capacity
effect Focus IFE effort on armor design and
material issues Blanket design can be adapted
from MFE blankets
Depth (mm) 0 0.02 1 3 Typic
al T Swing (C) 1000 300 10 1
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Example of Adapting an MFE Blanket Design to IFE
Variation of ARIES-AT blanket High
performance blanket with possibility of adjusting
wall temperature to satisfy target thermal
control requirement Simple, low pressure design
with SiCf/SiC structure and Pb-17Li coolant and
breeder. Innovative design leads to high
Pb-17Li outlet temperature (1100oC) while
keeping SiCf/SiC structure temperature below
1000oC leading to a high thermal efficiency of
55. Plausible manufacturing technique. Very
low afterheat. Class C waste by a wide
margin. Modular blanket for ease of replacement.
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Candidate Dry Chamber Armor Materials
Carbon (considered for SOMBRERO) - High
temperature capability - Key tritium retention
issue (in particular co-deposition) - Radiation
effects on properties - Erosion (several
mechanisms effects of IFE conditions - pulsed
operation, radiation...) - Fabrication -
Bonded layer or integrated with structural
material? - Safety Tungsten Other
Refractories - Melting concern - Fabrication/bon
ding and integrity under IFE conditions Enginee
red Surface to Increase Effective Incident
Area - e.g. C fibrous carpet - With C, still
tritium retention issue - Possibility of coating
fiber with W - Requirement on fiber thermal
conductivity - negative effect of neutron
irradiation Others?
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Example Temperature History for Tungsten Flat
Wall Under Energy Deposition from NRL
Direct-Drive Spectra Including Time-of-Flight
Effects

• Temp. variation mostly in thin armor region
• Key issue for tungsten is to avoid reaching the
  melting point 3410C
• Significant margin for design optimization
• Similar margin for C slab

• Coolant temperature 500C
• Chamber radius 6.5 m
• Maximum temperature 1438 C

Armor surface
20mm depth
Coolant
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Consider Engineered Surface Configuration for
Improved Thermal Performance
Porous Media - Carbon considered as example
but could also be coated with W - Fiber
diameter diffusion characteristic length
for 1 ms - Increase incident surface area per
unit cell seeing energy deposition
jincident
Aincident
L
jfiber jincident sin q
Q
ESLI Fiber-Infiltrated Substrate Large fiber L/d
ratio 100
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Example Thermal Analysis for Fiber Case
Incidence angle 30 Porosity
0.9 Effective fiber separation 54 mm
Sublimation effect not included
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Summary of Thermal Results for Carbon Fibrous
Wall without Protective Gas
Coolant temperature 500 C Energy deposition
multiplier 1
Porosity Fiber Effective Incidence Maximum
Temp. Separation (mm) Angle
() (C) 0.8 29.6
5 654 0.8 29.6
30 1317 0.8 29.6
45 1624 0.9 54 30 1318
C flat wall as comparison
1530
Initial results indicate that for shallow angle
of incidence the fiber configuration perform
better than a flat plate and would provide more
margin (confirmed by initial results from
RHEPP/MAP facility on ESLI sample) Optimization
study is under way
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Outline of Presentation

• Dry Chamber Wall Design
• Must satisfy conflicting requirements set by
  operation and performance of different components
  
• Dry Chamber Wall Options
• Armor is Key Region - Blanket design can be
  adapted from MFE blankets
• Candidate Armor Materials and Configurations
• C, W, Engineered surface (fibrous surface),
  others
• Example thermal analyses
• Key Material Issues
• Use of very thin armor on structural material to
  separate energy accommodation function from
  structural function
• Surface and near-surface properties under pulsed
  conditions (ion and neutron fluxes and fluence)
• Armor fabrication and bonding
• Erosion
• Armor lifetime and need for in-situ repair
• Tritium retention issues
• Must consider other armor options besides C
• Must prioritize material RD - make the most of
  information from MFE and focus on key IFE issues

15
Armor Material Issues
Armor material does not need to be the same as
structural material - Actually, separating
energy accommodation function from structural
function is beneficial - Focus on surface and
near-surface properties under pulsed conditions
(ion and neutron fluxes and fluence) Armor
fabrication and bonding - Integrity - Ability
to accommodate pulsed operation
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Armor Erosion
Lifetime is a Key issue for Armor - Even
erosion of one atomic layer per shot results in
cm erosion per year - Need to better understand
molecular surface processes - Need to evolve
in-situ repair process - Several erosion
mechanisms in particular for carbon - Major
uncertainties in estimating sublimation based on
vapor pressure for carbon because of difficulty
of predicting atomic cluster size of sublimating
carbon
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1. Several Erosion Mechanisms Must Be Considered
for the Armor
2. Tritium Co-Deposition is a Major Concern for
Carbon Because of Cold Surfaces (Penetration
Lines)
From the ARIES Tritium Town Meeting (March 67,
2001, Livermore (IFE/MFE Discussion
Session) (http//joy.ucsd.edu/MEETINGS/0103-ARIES
-TTM/) Carbon erosion could lead to tritium
co- deposition, raising both tritium inventory
and lifetime issues for IFE with a carbon
wall. Redeposition/co-deposition requires
cold surfaces which would exist in the beam
penetration lines and pumping ducts. (For
H/C1, 60 g T per 1mm C for R6.5 m)
Macroscopic erosion might be a more important
lifetime issue than sputtering and sublimation
for IFE operating conditions for high
energy ions (gtgt1 keV) RD effort should be
prioritized
Must Consider Alternate Options for Armor (e.g.
W)
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Conditions Assumed for ITER ELMs, VDEs and
Disruptions Compared to Conditions Associated
with a Typical Direct Drive Target IFE (latest
NRL target)
We should make the most of existing RD in MFE
area (and other areas) since conditions can be
similar within 1-1.5 order of magnitude (ELMs
vs IFE) Contact established and initial meeting
with Dr. G. Federici (ITER, Garching), Prof. H.
Bolt (IPP, Garching (ASDEX)) and Dr. B. Schedler
(Plansee, Austria)
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Summary of some key points from discussion with
Plansee (Austrian manufacturer of
refractory-based material) to discuss their
experience from MFE and its possible application
to IFE
Contact person Dr. Bertram Schedler
I. Testing of W and W/Rhenium Samples Fatigue
tests of 107 cycles at a maximum temperature of
1000C with a 150Hz rotating anode were
performed on W and W/rhenium alloy samples.
Microcracks induced by stress relief were
observed on the surface. These tests
indicated that adding 5-10 of rhenium to W would
provide better resistance against cracking, but
at the expense of lower thermal conductivity.
Also, rhenium can be added to W to increase
thermal expansion coefficient if required by
thermal expansion mismatch at bond with CFC (or
SiC but SiC thermal expansion coefficient is
close to that of W). A porous structure
(5-20 porosity) might help diffuse the stresses
by small propagation of micro cracks without
catastrophic damage.
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Summary of some key points from discussion with
Plansee (Austrian manufacturer of
refractory-based material) to discuss their
experience from MFE and its possible application
to IFE
II. Fabrication procedures Physical Vapor
Deposition (atomic deposition from sputtering)
provides a highly dense non-columnar deposit of
pure W and pure rhenium on CFC. Typical
thicknesses would be about 25-120 microns.
Higher thicknesses are possible but takes a long
time and are not attractive economically.
PVD process could also be used for W and rhenium
on SiC/SiC (CVD could also be used at
650C) Vacuum plasma spraying could be used
for higher thicknesses (200-500 microns). PVD
coating survived up to 12 MW/m2 at the Jülich
facility (sweeping e-beam)
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Summary of some key points from discussion with
Plansee (Austrian manufacturer of
refractory-based material) to discuss their
experience from MFE and its possible application
to IFE
III. W Bonding to C and/or SiC A key problem
with W bonding to C (or SiC) is carbide formation
at interface between W and C (or SiC). It would
lower the thermal conductivity and reduce
ductility. For example at 1400C over 5 hours,
10-20 microns of WC was formed at the
interface. One improvement is to avoid
carbide formation by using a thick W layer to
maintain low enough temperature at the interface
(lt900C), or by multilayer coating (about 5
microns of rhenium/W multilayers) to prevent
diffusion of carbon to W interface (patented
process from Plansee) SiCf/SiC is preferred
to CFC mostly based on its oxidation protection
as compared to CFC (700C) SiC and W are
not stable at high temperature. They form a WSi
eutectic with 10 W in Si which melts at 1400C
(much lower than pure W 3410C). 0.7-22 of C
in W also reduces the melting point to
2710C. To avoid eutectic melting the
interface SiC/W temperature should be maintained
lt 1300C. However, diffusion reaction forming
brittle intermetallic phase of WSi and possible
carbide formation would still occur, necessating
the use of a diffusion barrier.
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Summary of some key points from discussion with
Plansee (Austrian manufacturer of
refractory-based material) to discuss their
experience from MFE and its possible application
to IFE
IV. Behavior under IFE Conditions It is very
difficult to predict the thermo-mechanical
behavior of a thin tungsten layer on SiCf/SiC
or CFC under the cyclic nature of IFE operation
(1500-2000C peak temperature, 10Hz) and
under the high energy ( 100 keV) ion flux and
neutron fluence expected. General interest
in follow-on meetings on an ad-hoc basis
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Concluding Remarks
HAPL material RD should focus on issues
specific to inertial fusion - Final
Optics - Armor - Pulsed neutron-irradiation
effects Developing a dry wall chamber
requires a coordinated effort - Engineering
- Design integration - Material Armor
RD - Maximize information from and synergy
with MFE effort on PFC armor - Also use MFE
data base on blanket and structural material
- Prioritize RD - Focus on feasibility
issues first - Develop in-situ repair
processes - C tritium retention issue (if this
cannot be solved, other issues are
irrelevant) - W armor Fabrication/bonding of W
layer on structural material cyclic testing of
mock up