IFE Dry Chamber Wall Designs - University of California ...aries.ucsd.edu/raffray/presentations/Workshops/Las_Mat_UCSB_Aug01... · much more uniform q’’ and quasi ... structure

August 30, 2001 A. R. Raffray, IFE Dry Chamber Wall Designs 1

IFE Dry Chamber Wall Designs

A. R. Raffray and F. NajmabadiUniversity of California, San Diego

Laser IFE Materials Working Group MeetingUniversity of California, Santa Barbara

August 30, 2001

For more info, please visit the ARIES web site:http://aries.ucsd.edu/ARIES/


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 R&D - make the most of information from MFE and focus on key IFE issues


Requirements from Several Components and ProcessesMust be Balanced in Evolving IFE Chamber Design

LaserDriver

Tout

Target Injection

Tin

HX to Power Cycle

Coolant Temperature

• Cycle efficiency

• Target thermal control• Wall lifetime

ChamberGas

Pressure

• Wall lifetime

• Target thermal control• Laser breakdown• Chamber clearing

Chamber Size

• Wall lifetime

• Capital cost

Laser Energy,Gain,

Rep. Rate

• Power production

• Material temperature constraint• Chamber clearing


Target Thermal Control Requirements on Wall Temperature andChamber Gas Pressure

• Analysis of design window for successful injection of direct andindirect 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 < ~50 mTorr, Wall temperature < 700 °C)


Laser Beam Propagation and Breakdown Sets Requirement on theChamber Gas Pressure for a Given Laser Intensity

• The chamberenvironment following atarget explosion containsa hot, turbulent gas whichwill interact withsubsequent laser pulses.

• Gas breakdown mayoccur in the vicinity of thetarget where the beam isfocused.

• A better understanding ofthe degree of gasionization and the effectson beam propagation isneeded (under study atUCSD).

1E+09

1E+10

1E+11

1E+12

1E+13

1 10 100 1000 10000

Pressure (Torr)

Rosen 1987 (1/3 um, 15 ns)

Murray 1977 (1/4 um, 20 ns)

Turcu 1997 (1/4 um, 18 ns, Kr)

Alcock 1972 (1/3 um, 8 ns)

Buscher PRL 1965 (1/3 um, 20 ns)

Gower 1981 (1/4 um, 10 ns)Sombrero












Armor is Key RegionAll the Action Takes Place within 0.1-0.2 mm of Surface

Photon and Ion Attenuations in C and W Slabsfrom NRL Direct Drive Target Spectra (154 MJ)

• 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 steadystate due to thermal capacity effect

• Focus IFE effort on armor design and material issues

• Blanket design can be adapted fromMFE blankets

Depth (mm): 0 0.02 1 3Typical T Swing (°C): ~1000 ~300 ~10 ~1

Coolant

~ 0.1 mm Armor

3-5 mm

StructuralMaterial


Example of Adapting an MFE Blanket Design to IFE

Blanket & First Wall Segment• Variation of ARIES-AT blanket• High performance blanket with possibility

of adjusting wall temperature to satisfytarget thermal control requirement

• Simple, low pressure design with SiCf/SiCstructure and Pb-17Li coolant andbreeder.

• Innovative design leads to high Pb-17Lioutlet temperature (~1100oC) whilekeeping SiCf/SiC structure temperaturebelow 1000oC leading to a high thermalefficiency of ~ 55%.

• Plausible manufacturing technique.

• Very low afterheat.

• Class C waste by a wide margin.

• Modular blanket for ease of replacement.


• 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/bonding and integrity under IFE conditions

• Engineered 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?

Candidate Dry Chamber Armor Materials


Example Temperature History for Tungsten Flat Wall UnderEnergy Deposition from NRL Direct-Drive Spectra Including

Time-of-Flight Effects

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

Armor surface

20µm depth Coolant

• Temp. variation mostly in thin armorregion

• Key issue for tungsten is to avoidreaching the melting point = 3410°C

• Significant margin for designoptimization

• Similar margin for C slab

Coolant at 500°C3-mm thick WChamber Wall

EnergyFront

Evaporation heatflux B.C atincident wall

Convection B.C. atcoolant wall:h= 10 kW/m2-K


Consider Engineered Surface Configuration forImproved Thermal Performance

• Porous Media- Carbon considered as example but

could also be coated with W- Fiber diameter ~ diffusion

characteristic length for 1 µs- Increase incident surface area per

unit cell seeing energy deposition

ESLI Fiber-Infiltrated Substrate

Large fiber Łd ratio ~100

L

Aincident

Θ

ϕincident

ϕfiber= ϕincident sin θ


Example Thermal Analysis for Fiber Case

• Incidence angle = 30°• Porosity = 0.9• Effective fiber separation = 54 µm • Sublimation effect not included

Convection B.C.at coolant wall:h= 10 kW/m2-K

Single CarbonFiber

10µm

Coolant at 500°C

1 mm

TemperatureDistribution inFiber Tip at 2.5 µs

Max. Temp.= 1318°C


Summary of Thermal Results for Carbon FibrousWall without Protective Gas

Porosity Fiber Effective Incidence Maximum Temp.Separation (µm) 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 configurationperform 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

Coolant temperature = 500 °C; Energy deposition multiplier = 1












Armor Material Issues

• Armor material does not need to be the same as structuralmaterial- 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


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 sublimatingcarbon


1. Several Erosion Mechanisms Must Be Considered for the Armor

Carbon Tungsten

Erosion:

Melting No Yes (MP = 3410°C)

Sublimation/

evaporation

Yes (SP ~3367°C) Yes

Physical Sputtering Yes (peaks at ~ 1

keV)

Yes, high threshold

energy

Chemical Sputtering Yes (peaks at ~ 0.5

keV and 800 K))

No

Radiation Enhanced

Sublimation

Yes (increases

dramatically with T,

peaks at ~ 1 keV)

No

Macroscopic

(Brittle) Erosion

Yes (thermal stress +

vapor formation)

No

Splashing Erosion No Yes (melt layer)

Tritium Retention:

Co-deposition Yes (with cold

surfaces with H/C

ratio of up to 1)

No

From the ARIES Tritium TownMeeting (March 6–7, 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/C=1, 60 g T per 1µm C for R=6.5 m)

• Macroscopic erosion might be a more important lifetime issue than sputtering and sublimation for IFE operating conditions for high energy ions (>>1 keV)

• R&D effort should be prioritized

• Must Consider Alternate Options for Armor (e.g. W)

2. Tritium Co-Deposition is a Major Concern for Carbon Because of ColdSurfaces (Penetration Lines)


Conditions Assumed for ITER ELM’s, VDE’s andDisruptions Compared to Conditions Associated with a

Typical Direct Drive Target IFE (latest NRL target)ITER Type-I

ELM’s

ITER VDE’s ITER

Disruptions

Typical IFE

Operation

(direct-drive

NRL target)

Energy <1 MJ/m2 ~ 50 MJ/m2 ~ 10 MJ/m2 ~ 0.1 MJ/m2

Location Surface near div.

strike points

surface surface bulk (~µm’s)

Time 100-1000 µs ~ 0.3 s ~ 1 ms ~ 1-3 µs

Max.

Temperature

melting/

sublimation

points

melting/

sublimation

points

melting/

sublimation

points

~ 1500-2000°C

(for dry wall)

Frequency Few Hz ~ 1 per 100

cycles

~ 1 per 10

cycles

~ 10 Hz

Base

Temperature

200-1000°C ~ 100°C ~ 100°C ~ >500°C

• We should make the most of existing R&D in MFE area (and other areas) sinceconditions can be similar within ~1-1.5 order of magnitude (ELM’s 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)


Summary of some key points from discussion with Plansee(Austrian manufacturer of refractory-based material) to discusstheir experience from MFE and its possible application to IFE

I. Testing of W and W/Rhenium Samples

• Fatigue tests of 107 cycles at a maximum temperature of ~1000°C 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 resistanceagainst cracking, but at the expense of lower thermal conductivity.

• Also, rhenium can be added to W to increase thermal expansion coefficient if required bythermal 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 propagationof micro cracks without catastrophic damage.

Contact person: Dr. Bertram Schedler



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 beabout 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 ~650°C)

• 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)



III. W Bonding to C and/or SiC

• A key problem with W bonding to C (or SiC) is carbide formation at interface between Wand C (or SiC). It would lower the thermal conductivity and reduce ductility. For exampleat 1400°C 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 lowenough temperature at the interface (<900°C), 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 toCFC (~700°C)

• SiC and W are not stable at high temperature. They form a WSi eutectic with 10% W in Si which melts at 1400°C (much lower than pure W ~ 3410°C). 0.7-22% of C in W also reduces the melting point to ~2710°C.

• To avoid eutectic melting the interface SiC/W temperature should be maintained< ~1300°C. However, diffusion reaction forming brittle intermetallic phase of WSi and possible carbide formation would still occur, necessating the use of a diffusion barrier.



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 (~1500-2000°C 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


ConcludingRemarks

• HAPL material R&D 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 R&D- Maximize information from and synergy with MFE effort on PFC armor

- Also use MFE data base on blanket and structural material

- Prioritize R&D- 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

Documents

IFE Dry Chamber Wall Designs - University of California ...aries.ucsd.edu/raffray/presentations/Workshops/Las_Mat_UCSB_Aug01... · much more uniform q’’ and quasi ... structure