Dry-Wall Target Chambers for Direct-Drive Laser Fusion

Laser IFE WorkshopLaser IFE WorkshopFebruary 6-7, 2001February 6-7, 2001

Naval Research LaboratoryNaval Research Laboratory

Gerald L. Kulcinski, Robert R. Peterson and Donald A. Haynes

presenting for the staff of the Fusion Technology Institute

University of Wisconsin-Madison

Program Plan for the Design of Dry-Wall Target Chambers for Direct Drive Laser Fusion-U. of Wisconsin (WBS 3.1-3)

Overall Objective…………..Integrated direct drive fusion chamber concept

FY 01 Deliverables……… 1. Calculate threat spectra to first wall and assess methods to eliminate wall ablation.

2. Identify injection conditions that will allow several direct drive targets to survive to thermal environment inside the chambers.

3. Design blanket and shielding to protect critical components.

4. Incorporate innovative concepts into previous designs.

Relevance of Deliverables NIF-Wall survival (1,3), Safety (3)

DP/NNSA-Reaction products, opacity modeling (1)

Energy-IFE Power Plants (1,2,3,4)

FY01 Funding $500 k

Threat Spectra

Threat Spectra

New Chamber Blanket Design

New Chamber Blanket Design

FW Response

FW Response

Target Heating

Target Heating

Shielding of Critical Components

Shielding of Critical Components

50 %

20 %

30 %

Previous WorkPrevious Work

Incorporate into Improved Chamber Design

Incorporate into Improved Chamber Design

Elements of UW FY 01-02 Research on Dry Wall Target Chambers for Direct Drive Laser Fusion

MF A M J J A S DO N J

Chronology of UW Work on Dry Wall Laser Chambers

Threat Spectra and Target HeatingThreat Spectra and Target Heating

Blanket/FW Design and ShieldingBlanket/FW Design and Shielding

Incorporate into Improved Chamber Design

Incorporate into Improved Chamber Design

Threat Spectra and Target Heating

Robert Peterson Donald Haynes Igor Golovkin Greg Moses Elsayed Mogahed Igor Sviatoslavsky Paul Wilson John Santarius Gerald Kulcinski

Threat Spectra and Target Heating

Robert Peterson Donald Haynes Igor Golovkin Greg Moses Elsayed Mogahed Igor Sviatoslavsky Paul Wilson John Santarius Gerald Kulcinski

Improved Chamber Design

Igor Sviatoslavsky Mohamed Sawan Robert Peterson Gerald Kulcinski

Improved Chamber Design

Igor Sviatoslavsky Mohamed Sawan Robert Peterson Gerald Kulcinski

Chamber Design and Shielding

Mohamed Sawan Laila El-Guebaly Doug Henderson Hesham Khater Elsayed Mogahed Igor Sviatoslavsky Gerald Kulcinski

Chamber Design and Shielding

Mohamed Sawan Laila El-Guebaly Doug Henderson Hesham Khater Elsayed Mogahed Igor Sviatoslavsky Gerald Kulcinski

Key Personnel for FY01-02 Work on Laser Fusion Chambers-University of Wisconsin

Target Output and First Wall Calculations for Laser Fusion Chambers

US-Japan Workshop on Laser FusionUS-Japan Workshop on Laser FusionJanuary 25-27, 2001January 25-27, 2001

Lawrence Livermore National LaboratoryLawrence Livermore National Laboratory

Robert R. Peterson, Donald A. Haynes and Igor E. Golovkin

University of Wisconsin-MadisonFusion Technology Institute

Objective of Present Study

• To understand if the recent NRL direct drive target design can survive in a SOMBRERO-type dry wall chamber (no vaporization of C-C composite)

• To investigate the degree to which the Xe fill gas could be reduced to lower the aerodynamic frictional heating of direct drive targets.

• Apply latest analysis methods and explore the possibility of innovative injection techniques in dry wall chambers

Roadmap to Calculate IFE Wall/Target Survival Conditions

NRL

Sombrero

Target

Output

BUCKY

Gas

Protection

Gas

Species

Gas

DensityRadius

OpacityEOSOPA IONMIX

BUCKY

First Wall

T(t)

Twall

Material

BUCKY

First Wall Vaporization?

Target

Injection

no

yesBUCKY

Friction

T4

Velocity

Distance in Chamber

Straight

Tube

T > 1.5 K?

Chamber Works!

no

ANSYS

yes

NRL

Sombrero

Target

Output

Gas

Protection

First Wall

T(t) Vaporization?

Gas

Species

Gas

DensityRadius Twall

T > 1.5 K?

Chamber Works!

Friction

T4

Velocity

Target

Injection

Distance in Chamber

Straight

Tube

MaterialOpacity

BUCKY

EOSOPA IONMIX

BUCKY BUCKY BUCKY

no

yes

yes

no

ANSYS

First Wall Erosion and Target Heating During Injection are Competing Concerns in Direct-Drive Laser Fusion Dry-Wall Target Chambers

Chamber Physics Critical Issues Involve Target Output, Gas

Behavior and First Wall Response

Design,Fabrication,

Output Simulations,(Output Experiments)

Design,Fabrication,

Output Simulations,(Output Experiments)

Gas Opacities,Radiation Transport,

Rad-Hydro Simulations

Gas Opacities,Radiation Transport,

Rad-Hydro Simulations

Wall Properties,Neutron Damage,

Near-Vapor Behavior,Thermal Stresses

Wall Properties,Neutron Damage,

Near-Vapor Behavior,Thermal Stresses

X-rays,Ion Debris,Neutrons

Thermal Radiation,

Shock

Target Output Gas Behavior Wall Response

UW uses the BUCKY 1-D Radiation-Hydrodynamics Code to Simulate Target, Gas Behavior and Wall Response.

• 1-D Lagrangian MHD (spherical, cylindrical or slab).

BUCKY, a Flexible 1-D Lagrangian Radiation-Hydrodynamics Code; Useful in Predicting Target Output and Target Chamber

Dynamics

• Thermal conduction with diffusion.

• Applied electrical current with magnetic field and pressure calculation.

• Equilibrium electrical conductivities

• Radiation transport with multi-group flux-limited diffusion, method of short characteristics, and variable Eddington.

• Non-LTE CRE line transport.• Opacities and equations of state from EOSOPA or SESAME.

BUCKY, a Flexible 1-D Lagrangian Radiation-Hydrodynamics Code; Useful in Predicting Target Output and Target Chamber

Dynamics

• Thermonuclear burn (DT,DD,DHe3) with in-flight reactions.

• Fusion product transport; time-dependent charged particle tracking, neutron energy deposition.

• Applied energy sources: time and energy dependent ions, electrons, x-rays and lasers (normal incidence only).

• Moderate energy density physics: melting, vaporization, and thermal conduction in solids and liquids.

• Benchmarking: x-ray burn-through and shock experiments on Nova and Omega, x-ray vaporization, RHEPP melting and vaporization, PBFA-II K emission, …

• Platforms: UNIX, PC, MAC

Direct-Drive Targets Under Consideration Have Different Output

DT Vapor

DT Fuel

Foam + DT

1 CH + 300 Å Au

0.265g/cc

0.25 g/cc1.50 mm

1.69 mm

1.95 mm

DT Vapor

DT Fuel

Foam + DT

1 CH

0.265g/cc

0.25 g/cc1.22 mm

1.44 mm

1.62 mm

Direct-drive Laser Targets

CH

SOMBRERO (1990) NRL (1999) NRL (1999)

Laser Energy: 1.3 MJLaser Type: KrFGain: 127Yield: 165 MJ

Laser Energy: 1.6 MJLaser Type: KrFGain: 108Yield: 173 MJ

Laser Energy: 4 MJLaser Type: KrFGain: 100Yield: 400 MJ

Debris Ions 94 keV D - 5.81 MJ141 keV T - 8.72 MJ138 keV H - 9.24 MJ188 keV He - 4.49 MJ 1600 keV C - 55.24 MJTotal - 83.24 MJ per shot

Standard Direct-Drive Radiation Tailored-Wetted Foam Wetted Foam

DT Vapor

DT Fuel3.0 mm

2.7 mm2.5 mm

Spectra:•Calculated with BUCKY•Calculated by NRL•Calculated with Lasnex

Spectra:•Not Yet Calculated

The energy partition and spectra for SOMBRERO were supplied by DOEand need to be calculated.

Time (ns)

Po

sitio

n(m

m)

0 0.5 1 1.5 21.9

1.925

1.95

1.975

2

2.025

2.05

2.075

2.1

NRL DD-3515 Au zones

Laser

Au

CH

DT-wetted Foam

Laser Quickly Burns though 300 Ǻ Au and Radiatively Pre-Heats the Ablator

•Close-up of laser burning through thin gold and plastic shells of NRL target

•Gold and plastic are hot and rapidly rarifying, probably not in local thermodynamic equilibrium.

•Gold is expanding at 75 km/s from laser blow-off.

Time (ns)

Po

sitio

n(c

m)

0 10 20 300

0.1

0.2

0.3

0.4

0.5

NRL DD-43

Au

CH

DT-wetted foam

DT

Implosion, Burn and Explosion of NRL Radiation Smoothed Direct-Drive Laser Fusion Target

•22% of DT ice is burned; NRL and LLNL get about 32 %, though peak R (LLNL) and bang time (NRL) do agree.

•This calculation yielded 115 MJ; another, 200 MJ

•Very little DT in wetted foam is burned.

•Other yields would be achieved with further tuning.

•Target expands at a few time 108 cm/s and radiates.

Ion Spectrum for NRL Radiation Pre-Heated Target Depends on Yield

Ion Energy (eV)

Nu

mb

er

of

Ion

s

103 104 105 106 107 108 1091016

1017

1018

1019

1020 DTHCAuHe

NRL-DD-43

Ion Spectrum from 115 MJ NRL Laser Target

Wetted Foam

Plastic

Au

DT Ice

DT Gas

SOMBRERO

Ion Energy (eV)

Nu

mb

er

of

Ion

s

103 104 105 106 107 108 1091016

1017

1018

1019

1020 DTHCAuHe

NRL-DD-49

Ion Spectrum from 160 MJ NRL Laser Target

Wetted Foam

Plastic

Au

DT Ice

DT Gas

SOMBRERO

•The particle energy of each species in each zone is then calculated as mv2/2 on the final time step of the BUCKY run. This time is late enough that the ion energies are unchanging. The numbers of ions of each species in each zone are plotted against ion energy.•The spectra from direct fusion product D, T, H, He3, and He4 are calculated by BUCKY but they don’t make it out of the target.•The ion spectra is more energetic for 200 MJ yield

Ion Spectrum for 115 MJ Yield NRL Target Ion Spectrum for 200 MJ Yield NRL Target

Open collimator LOS 1/2 8” from Z

Pin Hole Camera10 degrees tilt to center. 9” from center of camera hole plate to blast shield.

L I D

CR39 film measures ion energy through damage track lengths.

Z-pinch x-ray source

Ion Spectrum Experiments on Z are in Progress to Validate Target Output Calculations

SHOT # 603 06/26/00 16:13

Damage by ions

Z X-rays

CR39detector

Ablator Material

Concept

Ion track analysis and supporting BUCKY simulations are in progress.

X-ray Spectra from Targets is Changed by High Z Components and Yield

•X-ray spectra are converted to sums of 3 black-body spectra.

•Time-dependant spectra are in Gaussian pulses with 1 ns half-widths and are used in chamber simulations.

• Time-integrated fluences are shown for 115 MJ and 200 MJ NRL and 400 MJ SOMBRERO.

•The presence of Au in the NRL targets adds emission in spectral region above a few keV.

•At higher yield the Au is more important.

Photon Energy (eV)

No

rma

lize

dX

-ra

yF

lue

nce

101 102 103 104 105 10610-7

10-6

10-5

10-4

10-3

10-2

10-1

160 MJ115 MJSOMBRERO

NRL-DD-43NRL-DD-49

X-ray Spectrum from 115 MJ and 160 MJ NRL and SOMBRERO Laser Targets

Time (ns)

X-r

ay

Po

we

r(T

W/c

m2)

0 10 20 3010-1

100

101

102

103

NRL-DD-43

X-ray Emission from 115 MJ NRL Laser Target

NRL 116 MJ

NRL 200 MJ

SOMBRERO 400 MJ

The threat spectrum can be thought of as arising from three contributions: fast x-rays, unstopped ions, and

re-radiated x-rays

Some debris ions are deposited in chamber gas, which re-radiates the energy in the form of soft x-rays

The x-rays directly released by the target are, for Xe at the pressures contemplated for the DD target, almost all absorbed by the wall.

Some debris ions are absorbed directly in the wall.

The wall (or armor) reacts

to these insults in a

manner largely

determined by it’s

thermal conductivity and stopping

power.

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

1e-8 1e-7 1e-6 1e-5 1e-4 1e-3

Time (s)

Wa

ll S

urfa

ce T

em

pe

ratu

re (

C)

Prompt X-rays 9MJ

Ions absorbed by the wall (1.2MJ)+Re-radiated

energy (27MJ)

For example, the first wall does not vaporize for the SOMBRERO target in a 6.5m radius chamber filled with 0.1 torr Xe and a wall equilibrium temperature of 1450C.

•The separation in time of the insults from the prompt x-ray, the ions, and the re-radiated x-rays is crucial to the survival of the wall.

•The Xe serves to absorb the vast majority of the ion energy and almost half of the prompt x-rays and slowly re-radiates the absorbed energy at a rate determined by the Plank emission opacity of the Xe.

For the current calculations, IONMIX has been used to generate Non-LTE Xe opacity tables

Xe Average charge state, n_i = 1e16/cc

0

10

20

30

40

50

0.1 1 10 100 1000 10000Electron Temperature (eV)

Ave

rage

Cha

rge

Sta

te

IONMIX

LTE

EOSOPA (LTE) / IONMIX COMPARISON: Xe 1e16/cc

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04

Photon Energy (eV)

Ro

sse

lan

d G

rou

p O

pa

city

(cm

^2/g

)

IONMIX 1 eV

EOSOPA 1 eV

IONMIX 100 eV

EOSOPC 100 eV

•Xe gas at or below 0.5 Torr in Density is not in LTE.

•The Xe opacity can differ substantially between LTE (EOSOPC) and Non-LTE (IONMIX).•IONMIX opacities are used in this study.

•Non LTE (IONMIX) ionization is substantially below the LTE (Saha) ionization.

A scan of Xe density holding the first wall equilibrium temperature fixed at 1450C was performed to examine the onset of vaporization.

SOMBRERO TARGET in 6.5m C Chamber, Equilibrium Wall Temperature of 1450C

2500

2600

2700

2800

2900

3000

3100

3200

0.05 0.06 0.07 0.08 0.09 0.1

Xe Density (Torr)

Tem

pera

utre

(C

)

1st Peak T_wall (C)

2nd Peak T_wall (C)

T_sublimination att_vap

Initial SublimationTemperature (C)

Direct Energy Deposition on Wall, SOMBRERO Target in 6.5m C Chamber, Equilibrium Wall Temperature of 1450C

0

2

4

6

8

10

12

14

0.05 0.06 0.07 0.08 0.09 0.1

Xe Density (Torr)

Ene

rgy

(MJ)

or

Ma

ss (

g) X-ray EnergyDeposited in Wall(MJ)

Ion EnergyDeposited in Wall(MJ)

Amount Vaporized(g)

•For the SOMBRERO target in a 6.5m graphite chamber, the prompt x-rays are the major threat.

•Even at 0.05 Torr Xe, 78MJ of the 83MJ of ion energy is absorbed by the gas, slowly re-radiated to contribute to the second peak in temperature.

•The sublimation threshold occurs when the prompt x-rays loading is above 1.88 J/cm2 for x-rays with the SOMBRERO spectrum, for this equilibrium wall temperature.

0

20

40

60

80

100

120

SOMBRERO NRL 400MJ "NRL"

No

n-n

eutr

on

ic T

arg

et O

utp

ut

(MJ) IONS

X-rays

The SOMBRERO and NRL targets differ significantly in yield, partitioning, and spectra. These differences lead to very

different target chamber dynamics.

•Even if the NRL spectra are scaled up by the ratio of the total yields (400/165), it poses considerably less threat to the target chamber.

• It has fewer of the dangerous, prompt x-rays and a different ion spectrum.

• For instance, the first wall survives at conditions where the SOMBRERO target vaporizes 6.7g of wall material per shot. (This assumes that the energy is increased by increasing the flux, and not the shape, of the spectra..)

Surface Temperature as a Function of Time, 0.05 Torr Xe, T_equilibrium = 1450C

1400

1800

2200

2600

3000

3400

1.00E-08 1.00E-07 1.00E-06 1.00E-05

Time (s)T

em

pe

ratu

re (

C)

SOMBRERO SCALED NRL

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

0.1 1 10 100 1000

Photon Energy (keV)

X-r

ay

Sp

ect

rum

(J/

keV

)

SCALED NRL (5.6MJ X-rays)

SOMBRERO (22.5MJ X-rays)

Detail: Carbon and deuterium deposition and X-ray spectra for SOMBRERO and Scaled NRL Targets in 6.5m Radius C Chamber

SOMBRERO

1.E+14

1.E+15

1.E+16

1.E+17

1.E+18

1.E+19

1.E+20

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00

Depth (cm)

Num

ber

of D

epos

ited

Ions

D Hydro

C Hydro

Scaled NRL

1.E+14

1.E+15

1.E+16

1.E+17

1.E+18

1.E+19

1.E+20

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00

Depth (cm)

Num

ber

of D

epos

ited

Ions

D_Hydro

C_Hydro

D_Knockon

The spectra differ primarily due to the Au and knock-ons in the NRL spectrum and the 55MJ of 1.6MeV C ions in the SOMBRERO spectrum. The NRL knock-ons heat the 1st mm of the wall volumetrically.

Xe density is 50 mtorr and wall temperature is 1450 ° C.

A C-C Target Chamber Can Survive, with Proper Gas Protection and Wall Temperature

0

500

1000

1500

2000

2500

3000

3500

0 0.1 0.2 0.3 0.4 0.5 0.6

Xe Density (Torr)

Max

.Equ

ilibr

ium

Wal

l Tem

p. to

Avo

id

Vap

oriz

atio

n (C

)

SOMBRERO Target

NRL Target

Chamber Radius of 6.5m

•A series of BUCKY calculations have been performed of the response of a 6.5 m radius graphite wall to the explosions of SOMBRERO and NRL targets. Time-of-flight dispersion of debris ions is important, especially for low gas density.

•The gas density and equilibrium wall temperature have been varied to find the highest wall temperature that avoids vaporization at a given gas density.

•Vaporization is defined as more than one mono-layer of mass loss from the surface per shot.

•The use of Xe gas to absorb and re-emit target energy increases the allowable wall temperature substantially.

NRL

Sombrero

Target

Output

Gas

Protection

First Wall

T(t) Vaporization?

Gas

Species

Gas

DensityRadius Twall

T > 1.5 K?

Chamber Works!

Friction

T4

Velocity

Target

Injection

Distance in Chamber

Straight

Tube

MaterialOpacity

BUCKY

EOSOPA IONMIX

BUCKY BUCKY BUCKY

no

yes

yes

no

ANSYS

First Wall Erosion and Target Heating During Injection are Competing Concerns in Direct-Drive Laser Fusion Dry-Wall Target Chambers

Target Injection for Laser Fusion Chambers

US-Japan Workshop on Laser FusionUS-Japan Workshop on Laser FusionJanuary 25-27, 2001January 25-27, 2001

Lawrence Livermore National LaboratoryLawrence Livermore National Laboratory

G.L. Kulcinski, E. A. Mogahed, and I. N. Sviatoslavsky

University of Wisconsin-MadisonFusion Technology Institute

Assumptions For NRL Target Heating Calculations

• Injection velocity = 400 m/s

• Target spectral reflectivity = 99%

• Transport distance in chamber = 2 m (tube)• Thermal diffusivity of CH @ 18 K = 0.009 cm2/s

• T at DT/CH interface < 1.5 K

• Tumbling target (symmetric heat transfer)

The HeatFlux

Absorbed inthe OuterSurface ofthe Target

Depends onthe FW

Temperatureand theTarget

Emissivity 0.001

0.01

0.1

1

10

100

600 800 1000 1200 1400 1600 1800

Thermal Radiation Heat FluxAbsorbed by the Target

Ra

dia

tio

n H

ea

t F

lux

Ab

so

rbe

d (

W/c

m2)

First Wall Temperature (K)

Emissivity of the First Wall (Carbon) = 0.8

Target Reflectivity = 0.00.2 0.40.6

0.8

0.90.95

0.99

The Heat Flux Due to Aerodynamic Friction on the Target Outer Shell is Strongly Dependant on the Chamber Gas Density and the

Velocity of the Target.

0.01

0.10

1.00

10.00

200 250 300 350 400

Surface Heat Flux Due to Friction for a 4 mm Target

Su

rfa

ce

He

at

Flu

x D

ue

to

Fri

cti

on

(W

/cm

2)

Target Speed (m/s)

0.0001 Torr

0.0005 Torr

0.001 Torr

0.005 Torr

0.01 Torr

0.05 Torr

0.1 Torr

0.5 Torr

1 Torr of Xe gas

After Eckert and McAdams

0.0002 Torr

Frictional Heat Flux for a 4 mm Diameter Target

0.01

0.10

1.00

10.00

200 250 300 350 400

Surface Heat Flux Due to Friction for a 6 mm Target

Su

rfa

ce

He

at

Flu

x D

ue

to

Fri

cti

on

(W

/cm

2)

Target Speed (m/s)

0.0001 Torr

0.0005 Torr

0.001 Torr

0.005 Torr

0.01 Torr

0.05 Torr

0.1 Torr

0.5 Torr

1 Torr of Xe gas

After Eckert and McAdams

0.0002 Torr

Frictional Heat Flux for a 6 mm Diameter Target

UW has started the use of a 2-D Monte-Carlo Hydrodynamics Code from Sandia to Model Frictional Target Heating

This calculation was performed with the Icarus code by Tim Bartel of SNL.

Since the collisional mean-free-path is the same order as the target size, a detailed calculation is needed.

Angle from Target Equator (degrees)

Pre

ssu

re(P

a)

-60 -30 0 30 600

2

4

6

8

10

12

14

16

18

20

Monte-Carlo Frictional Heating Calculation

Xe density = 3.2 1014 cm-3 (0.009 Torr)

T = 1500 K

mfp = 2.2 mm

Sound speed = 364 m/s

Target diameter = 4 mm

Injection speed = 400 m/s

-.0006 0 .0006 0012 -.0012 Axial Distance from Target Center (m)Angle from Target Equator (degrees)

Su

rfa

ceH

ea

tF

lux

(W/c

m2)

-90 -60 -30 0 30 60 900

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8Xe density = 3.21014 cm-3

T = 1500 Kmfp = 2.2 mmSound speed = 364 m/sTarget diameter = 4 mm

Monte-Carlo Frictional Heating Calculation

Xe density = 3.2 1014 cm-3 (0.009 Torr)

T = 1500 K

mfp = 2.2 mm

Sound speed = 364 m/s

Target diameter = 4 mm

Injection speed = 400 m/s

Monte-Carlo Frictional Heating Calculation

-.0006 0 .0006 0012 -.0012 Axial Distance from Target Center (m)

The Heat Flux Due to Aerodynamic Friction on the Target Outer Shell is Strongly Dependant on the Chamber Gas Density and the

Velocity of the Target.

0.01

0.10

1.00

10.00

200 250 300 350 400

Surface Heat Flux Due to Friction for a 4 mm Target

Su

rfa

ce

He

at

Flu

x D

ue

to

Fri

cti

on

(W

/cm

2)

Target Speed (m/s)

0.0001 Torr

0.0005 Torr

0.001 Torr

0.005 Torr

0.01 Torr

0.05 Torr

0.1 Torr

0.5 Torr

1 Torr of Xe gas

After Eckert and McAdams

0.0002 Torr

Frictional Heat Flux for a 4 mm Diameter Target

0.01

0.10

1.00

10.00

200 250 300 350 400

Surface Heat Flux Due to Friction for a 6 mm Target

Su

rfa

ce

He

at

Flu

x D

ue

to

Fri

cti

on

(W

/cm

2)

Target Speed (m/s)

0.0001 Torr

0.0005 Torr

0.001 Torr

0.005 Torr

0.01 Torr

0.05 Torr

0.1 Torr

0.5 Torr

1 Torr of Xe gas

After Eckert and McAdams

0.0002 Torr

Frictional Heat Flux for a 6 mm Diameter Target

Max

Ave

CROSS-SECTION OF SOMBRERO CHAMBER

The Target Injection Tube Protects the Target from Thermal Damage During Injection

• A target injection tube extends from the top of the chamber to within 2 meters of the chamber center.

• It consists of a tungsten core which is He gas cooled in a closed cycle cooling system.

• The tungsten core is surrounded by a carbon double tube assembly cooled by Xe gas, extending 0.5m beyond the tungsten core.

• The Xe gas after cooling the carbon tube enters the chamber replenishing the chamber buffer gas.

• The tungsten core is stationary, but, the carbon tube is slowly moved forward at the rate at which the carbon evaporates.

• The target is shielded from high temperature radiation from the first wall, and by tube differential pumping avoids frictional heating with the buffer gas along most of its trajectory.

GraphiteTungsten

Thick. = 0.3 cm

Thick. = 0.2 cm

Thick. = 0.3 cm

Thick. = 0.3 cm

Outer Diameter = 5 cmInner Diameter = 1 cm

Inner Diameter = 2.4 cm

Cross-Section of the Target Injection Tube

Section B-B

Graphite

Section A-A

86420.001

.01

.1

1

10

Pressure Profile in Target Injection Tube as a

Function of Distance from Chamber Center

Distance Along Injection Tube (m)

Gas P

ressu

re P

rofi

le in

Tu

be (

torr

)

Target Injection Tube Chamber Center

Molecular flow regimeThroughput 8e-5 torr l/s.cm2Pumping speed 34 cm3/s

TARGET INJECTION TUBE DETAILS

PARAMETERS OF TARGET INJECTION TUBE Material ID (cm) OD (cm) t (cm)

Inner W tube W 1.0 1.6 0.3Outer W tube W 2.4 3.0 0.3Coolant Flow area He 1.6 2.4 0.4Inner Graphite tube C 3.0 3.4 0.2Outer Graphite tube C 4.4 5.0 0.3Coolant Flow area Xe 3.4 4.4 0.5

THERMAL HYDRAULIC PARAMETERS OF TARGET INJECTION TUBE

W tube coolant He gasLength of W tube(m) 4.0Nuclear heating in W tube (Kw) 86.0He gas pressure (atm) 80.0Inlet temperature (K) 77Outlet temperature (K) 300He gas velocity (m/s) 21Average temperature of inner W wall (K) 250Graphite tube coolant XeLength of tube (m) 4.5Nuclear heating in graphite tube (Kw) 48.0Radiant heating in graphite tube (Kw) 30.0Xe gas pressure (atm) 10Inlet temperature (K) 300Outlet temperature (K) 1174Xe gas velocity (m/s) 81Average temperature of inner graphite tube (K) 1000

A

A B

B

GraphiteTungsten

Thick. = 0.3 cm

Thick. = 0.2 cm

Thick. = 0.3 cm

Thick. = 0.3 cm

Outer Diameter = 5 cmInner Diameter = 1 cm

Inner Diameter = 2.4 cm

Cross-Section of the Target Injection Tube

Section B-B

Graphite

Section A-A

The Neutron Irradiated Thermal Conductivity of Graphite at 1-2 dpa Approaches the Unirradiated Value at High Temperatures

0

10

20

30

40

50

60

70

80

90

100

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Irradiation and Test Temperature-°C

% o

f U

nir

radia

ted V

alu

e

A-05 CX-2002U

N-112 DMS-678Source: Bonal and Wu, Phys Scripta, T64, 1996

First Wall Temperature Transient Range(First Few Microns)-Sombrero-91

400 600 800 1000 1200 1400

Irradiation Temperature, oC

40

30

20

10

3

2

1

0

x 1022

AXZ 5Q1

AXZ 5Q1

AXZ 5Q1

AXF 8Q1

AXF 8Q1

AXF 8Q1

LOWER BOUND

AXF

GRAPHNOL N3M

Bounds from Kasten et al.

Data from Kennedy et al.

POCO Grades

CSF

GILSOCARBON

PGA

The Useful Lifetime of Graphite is a Functionof the Neutron Irradiation Temperature

Birch & Brocklehurst, 1987

Fusion Technology Institute • University of Wisconsin

Region Excluded due to Radiation Damage Accumulation

0

500

1000

1500

2000

2500

3000

3500

0 0.1 0.2 0.3 0.4 0.5 0.6

Xe Density (Torr)

Ma

x.

Eq

uil

ibri

um

Wa

ll T

em

p.

to A

vo

id

Va

po

riza

tio

n (

C)

SOMBRERO WALL ConstraintNRL WALL ConstraintSOMBRERO TARGET (200 m/s, 6.5m, 0.2 Reflectivity)NRL TARGET (400 m/s, 2m, 0.99 Reflectivity)NRL TARGET (400 m/s, 6.5m, 0.99 Reflectivity)

Chamber radius of 6.5mTumbling Target

It is Difficult to Find an Operational Regime for the NRL Target in a Dry-Wall Chamber

(Assuming 1.5 K Fuel Temperature Rise)

160 MJ

400 MJ

Chamber radius of 6.5 mTumbling target

Survivability of Targets and C-C First Walls in SOMBRERO Dry Wall

Chamber with No Fill Gas

Target

First Wall

SOMBRERO

NRL

Yes(TFW<2,100 °C)

Yes(if TFW<1,600 °C)

No(evaporation, unless TFW < RT)

Yes(if TFW<1,500 °C)

Survivability of Targets and C-C First Walls in SOMBRERO Dry Wall

Chamber with 0.1 Torr Xe Fill Gas

Target First Wall

SOMBRERO

NRL

Yes(if TFW<2,100 °C)

No(frictional heating, TFW << RT)

Yes(TFW<1,600°C)

No Solution(TFW<< RT))

Survivability of Targets and C-C First Walls in SOMBRERO Dry Wall

Chamber with 0.01 Torr Xe Fill Gas

Target

First Wall

SOMBRERO

NRL

Yes(TFW<2,100 °C)

Yes(if TFW<1,600 °C)

No(evaporation, unless TFW < RT)

Yes(if TFW<1,600 °C)

Parametric Studies for Laser Chamber Analysis, Feb. to Oct. 2001

• Targets NRL-ref, SOMBRERO, NRL-400

• Temp Rise in DT, K 1.5, 5, 10

• Target Reflectivity 0.2, 0.9, 0.99

• Injection Velocity, m/s 200, 400

• Distance Target Exposed, m 2, 6.5, 8

• FW Material C-C, SiC, W

• Cavity Gas Xe, Kr

• Gas Pressure, Torr 0, 0.01, 0.1

FY 2001 | FY 2002 | FY 2003 | FY 2004 | FY 2005 |

FY 2001 | FY 2002 | FY 2003 | FY 2004 | FY 2005 |

Laser Dry-Wall Chamber Program Plan

Power Plant Point Design

Imbed Two Chamber Designs into Sombrero Reference

Scope New Ref Design

Full Analysis of Improved Dry Wall Ref. Design

Experimental Validation of Materials

Establish operational parameters for FW/Blk

Test Thermal Life & PrepareIrr. Capsules

Begin First Material Radiation Damage Studies

Experimental Results On Radiation Damage of Chamber Materials

Chamber Clearing

Test time to damp cavity gas

Define Cavity Gas Dynamics

Experiment on Target Injection in Hot Turbulent Dilute Gas

Reestablish Baseline Target InjectionParameters

Establish Operating Windows (sufficient for 1,000 MWe)

Target Spectra Exp. & Survival

Incorporate New Target Designs

Experiments on Target Heating

New Target Survival Criteria

Safety and Environment

Establish Allowable Inventory & Release

Experiments on T2 & Radioisotope Release

Design Basis Accident Analysis