ILE, OsakaConcept and preliminary experiment on

protection of final optics in wet-wall laser fusion reactor

T. Norimatsu, K. Nagai, T. Yamanaka and Y. Izawa

Presented at Japan-US Workshop on Power Plant Studies and

Related Advanced Technologies, Oct 9, 2003, San Diego USA

ILE, Osaka

Introduction

• In a laser fusion reactor with a wet wall, the critical issue is protection of the final optics, especially from neutral metal vapor.

• Following each laser shot, more than 20 kg of liquid metal evaporates in a reactor of 5 m radius.

• We are going to use a set of rotating shutters having different rotational speeds to block the major portion of the blast wave from the opposite inner surface.

• However, some neutral vapor (9mg/shot) will enter the beam duct, possibly contaminating the final optics and promoting erosion of the surface by laser-induced plasma.

ILE, Osaka

Cascade reactor for fast ignition scheme

• New Koyo has a cascade flow of LiPb to provide fresh, cold surface to obtain quick pumping. The reactor has a hybrid structure to simplify the LiPb flow. The distance between the ceiling and the firing position is set to balance the ablation with condensation.

Thermal out put 400 MJRep-rate 3 Hz

Non condensable gas

Target Injector

Compression beam

LiPb

Ignition beam

ILE, Osaka

In wet-wall reactor, protection of final optics from neutralized particles seems most critical.

• Neutron damage can be reduced by locating the optics 30 m apart.

• Alpha particles and ions can be removed by a Magnetic field.

• Ablated metal from inner surface can be shielded by rotary shutters.

583.27ns583.59ns

583.63ns583.68ns583.72ns

1016

1017

1018

1019

1020

1021

1022

1023

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Nu

mb

er d

en

sity

(cm

-3)

Position (m)

1500m/s

NeutronsDistance > 30 m

particles Ions

Electro magnetAblated neutral gas

Rotary shutters Neutralized energetic particles

Q u ic k T ime ý Ç ²G IF ê L í£ É v É ç É O É â É ÄÇ ™Ç ± Ç Ã É s É N É ` É É Ç ¾å ©Ç È Ç …Ç Õ ïK ó v Ç Ç Å B

Q u ic k T ime ý Ç ²G IF ê L í£ É v É ç É O É â É ÄÇ ™Ç ± Ç Ã É s É N É ` É É Ç ¾å ©Ç È Ç …Ç Õ ïK ó v Ç Ç Å B

Q u ic k T ime ý Ç ²G IF ê L í£ É v É ç É O É â É ÄÇ ™Ç ± Ç Ã É s É N É ` É É Ç ¾å ©Ç È Ç …Ç Õ ïK ó v Ç Ç Å B

The speed of blast wave is estimated to be 1500 m/s.

ILE, Osaka

Protection scheme of final optics by rotary shutters

0.05Torr Xe or H2

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The dimension and the rotational speed of the first shutter seem acceptable.

Mode BeamNumber

LaserEnergy

kJ / beam

Beamdiameter

(m)

Portdiameter

(cm)

Diameterof shutter

(m)

Rotarionalspeed of

first shutter(rps)

Centraligintion 32 125 1 17 1 21.65

Fastignition

Compression32

25 0.5 10 0.5 25.47

Heating1 70 4 60 2 38.21

30 m5 m

Rotary shutter

Port diameter

Beam diameter

350 mm 200 mm

1000 mm

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Timing chart for blast wave and rotary shutters

1 m s

2nd shot2nd shot3rd shot

4th shot

1s1 0 s 1 0 0 s 10ms 1 0 0ms

2nd shutter 14Hz

3rd shutter 3Hz

1st shutter 28Hz

Target injectionMiss fired target

1st bluster wave from the wall

v=3,000m/s @20,000K

v=1500 m/s

Charged particlies from plasma 1～2 μ s

Neutron, alpha, x-rays 10～20 ns

Blaster waves

1000

1500

2000

Tem

pe

ratr

ue

o

f in

ne

r s

urf

ac

e (

K)

Open

Open

Open

2500

500

ILE, Osaka

To experimentally simulate Pb vapor diffusion in a beam duct, an electro furnace to make glass shells was employed.

ILE, Osaka

Basic characteristics of furnace

20

0

40

0

60

0

80

0

10

00

12

00

14

00

0

50

100

150

16

00

Temperature (K)

0.1Torr H2

P=１ Torr ? Pb vapor

Cf. MP. of Pb = 600 K

0

200

400

600

800

1000

1200

0

5

10

15

20

0 20 40 60 80 100 120

Operation history

Temperature (C) Mass of Pb (g)

Tem

pe

ratu

re (

C)

Ma

ss

of P

b (g

)

Time (min)

ILE, Osaka

A lot of Pb particles, drops of dew, was observed on the surface of a quartz rod during a H2 10 Torr, 1400K, 1hr operation.

• To simulate diffusion of Pb vapor from wet-wall-reactor to the final optics, 25 g Pb was evaporated.• No deposition of Pb at areas of T > 800K and T< 600K.• A lot of Pb particles ranging < 300 mm at the area of 650K < T < 750K.

20

0

40

0

60

0

80

0

10

00

12

00

14

00

0

5 0

1 0 0

1 5 0

16

00

Temperature (K)

5mm

Quartz rod

0.1Torr H2

P=0.1 Torr ? Pb vapor

5mm

Cf. MP. of Pb = 600 K

ILE, Osaka

Many Pb particles ranging 0.1 to 30 m were deposited on the bottom of furnace filled with 10 Torr H2.

Top view

Cross sectional view

100 m

1 m

Pb deposition area

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Lead deposited on the 500K to 800K surface during a H2 0.1 Torr, 1400K, 1hr run. No dew on the bottom rod.

• To simulate diffusion of Pb vapor from wet-wall-reactor to the final optics, 14 g Pb was evaporated.• No deposition of Pb at bottom area of T > 800K and T< 600K and at top area of T > 750K and T<

500K. Hydrogen gas flow from bottom to top carried the Pb vapor toward colder region.

5mm

Quartz rod

0.1Torr H2

P=0.1 Torr ? Pb vapor

5mm

200

400

600

800

10

00

12

00

14

00

16

00

Vacuum

ILE, Osaka

No deposition of Pb was observed on witness plate in 0.1 Torr H2.

0

20

40

60

80

100

0 200 400 600 800 1000 1200

No increase in absorption was obserbed.

Glass substrateTopBottom

Tra

ns

mit

tan

ce

(%

)

Wavelength (nm)

Pb deposition area

It seems that Pb vapor condenses on cold surface before forming aerosol.

3 cm

50 cm

1400K

800K

300K

500K

Pb vapor rich

H2

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Deposition area moved inward during a H2 0.1 Torr, 780K, 1hr run. But no deposition on witness plate

• 9.5 g of Pb (1/3 of previous case) was evaporated during 1hr run.

• Deposition area moved inward.

• No drop of dew was observed.

• No deposition on bottom

• This result indicates that contamination of final optics can be avoided if the first bluster wave is blocked.

5mm

Quartz rod

0.1Torr H2

P=0.0001 Torr ? Pb vapor

5mm

No deposition on witness plates

ILE, Osaka

For simplification, theoretical value of Diffusion constant for Pb was used instead of LiPb.

2

Pv

mkT

12

2

2 8

6

kTD

n m

522865( ) (23.23 4.09 10 )P T EXP T

T

0.0001

0.001

0.01

0.1

1

10

100

1000

700 800 900 1000 1100 1200 1300

鉛蒸気圧フィット

Vapor pressure (Pa)

Temperature

y = exp(m1-m2/x+m3*m0)エラー値3.057123.234m1 1817.822865m2

0.001302-4.093e-05m3 NA0.0092075カイ２乗NA1R

Vapor pressure of Pb

Theoretical diffusion constant

Saturated evaporation rate

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No deposition on >800K area can be explained by re-evaporation.

• Distribution of Pb vapor in the duct is dominated by wall temperature.(Left) No deposition at >800K can be explained by re-evaporation.(Right)

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The speed of vapor at beam inlet is estimated to be 100 m/s.

• When the shutter opens, a radial gas flow still develops due to cryogenic effect of the camber wall.

• The LiPb vapor pressure is estimated to be <0.05 Torr.

• In the next calculation, 0.1 Torr, 100 m/s were used for safety.

Y. Kozaki et al, Presented at IAEA FEC

ILE, Osaka

Pb vapor whose initial speed of 100 m/s can not reach final optics in 0.1 Torr buffer gas.

• The velocity of Pb vapor decreases to 30 m/s before the amplitude of deformation exceeds the thickness of Pb vapor. The vapor enters into the duct by 6m.

0.5m

100m/s

100m/s 30m/s

ILE, Osaka

Summary

• In a future laser fusion reactor, final optics at the end of 30m-long beam duct can be protected from metal vapor using a rotary shutter and 0.1 Torr hydrogen gas.

The vapor (v=100m/s) will stop within 6m.

• When the hydrogen gas in the duct is sufficiently low, ( 0.5 Torr for 3 cm diameter duct, 0.05Torr for 30cm duct), formation of Pb aerosol seems to be not very serious.

ILE, Osaka

Remaining issue

• Synchronization of target injection with rotary shutter. Since it is quite difficult to change rotating speed of the shutter disk, target injection must synchronize with the open timing of the shutter.

For example, v=200+/-1 m/s

• Chamber clearanceBecause of thermal radiation transfer, blast wave becomes cold before it reach the chamber center resulting rot of particles when it collides at the chamber center.

ILE, Osaka

Rotary shutters impose sever accuracy for the injection velocity.

• Fire timing of the target and open time of the rotary shutters must be synchronized with accuracy of 0.2 ms.

• This requires the injection velocity of 200 +/-2 m/s.

1 m

0.2 m

52 m/s

0.35 m

Laser beam

Laser port

1st rotary shutter 24 Hz, 1440rpm

Allowable jitter, 5% of port radius