IFE Target Fabrication Update

Presented by Jared Hund1

N. Alexander1, J. Bousquet1, Bob Cook1, S. Eddinger, D. Frey1, D. Goodin1, H. Huang, J. Karnes2, R. Luo1, A. Nikroo1, R.

Paguio1, R. Petzoldt1, N. Petta2, N. Ravelo1, K. Saito1, D. Schroen1,

J. Streit2, A. Cheng3, S. Saiedi3

1General Atomics, Inertial Fusion Technology, San Diego, CA2Schafer Corporation, Livermore, CA

3UC San Diego, San Diego, CA

HAPL Workshop

IFT\P2008-012

Since the last HAPL Meeting we have:

• Reduced coating thickness for gas tight capsules – Pinhole free at 15 µm! (63% yield)– Improved from 25 µm (10/31/07)

• Measured the areal density of foam shell with gas tight over coating– Meets specification*

(< 0.3% variation over high modes)

Foam layer: 0.18 mm thickness Divinyl Benzene (DVB) or Resorcinol-Formaldehyde (RF)

DT Vapor

Foam + DT

Thin (300-1200 Å)High Z coating

~ 2

.3 m

m r

ad

10 m CH Overcoat

DT

*Neglecting isolated defects

HAPL Target

Glow Discharge Polymer (GDP) is being used to produce the plastic permeation barrier• The horizontal rotary GDP coater* (“rotocoater”)

has been able to produce gastight HAPL shells– Geometry different than established ICF technique– Produced the best coatings yet– Scalable to mass production

• The shells are tested for gas retention with a cryogenic leak testing technique

*Vermillion et al., Fusion Sci & Tech 51, 791 (2007)

Leak too fast to test at cryo temp

Ugly – viscous flow leak

LN2 temp

Bad – pinhole leak

-22

-20

-18

-16

-14

-12

0

500

1000

1500

2000

2500

3000

T ime (s ec onds )

ln (M

S io

n si

gnal

)

LN2 temp

Good – permeation leak only

Leak too fast to test at cryo temp

Ugly – viscous flow leak

-22

-20

-18

-16

-14

-12

0

200

400

600

800

1000

1200

1400

1600

1800

T ime (s ec onds )

ln (

MS

ion

sign

al)

LN2 temp

Bad – pinhole leak

LN2 temp

Good – permeation leak only

Leak too fast to test at cryo temp

Ugly – viscous flow leak

-22

-20

-18

-16

-14

-12

0 50 100

150

200

250

300

350

400

450

T ime (s ec onds )

ln (

MS

ion

sign

al)

LN2 temp

Bad – pinhole leak

LN2 temp

Good – permeation leak only

Leak too fast to test at cryo temp

Ugly – viscous flow leak

LN2 temp

Bad – pinhole leak

LN2 temp

Good – permeation leak only

T2B H2

RF Coil

Shells VacuumPump

Rotary Union

PlasmaStepperMotor

Changing the background pressure during the GDP coating run affects the outer surface

Background pressure:

500 mtorr 250 mtorr 75 mtorr

Standard condition

• Disadvantages to 250 mtorr coating: • Shells stick together > 2um • Coating rate is reduced to 1/3 of std rate

• Solution: 2 step coating (High/Low background pressure)

The latest capsules have fewer large features

• The latest conditions– Utilized high/low background pressure coating

• 48 hours (1.5 µm) 250 mtorr, finish at 50 mtorr

– More careful techniques to reduce debris• Shell transfer, pyrolysis of chamber

WYKO RMS Surface Roughness

Latest technique (3/08)

11/07 Batch

The smaller range in roughness is due to fewer large defects

*Profiles taken over a 200 x 300 µm patch

The surface roughness evolves as the shells are coated

• Experiment of the evolution of surface roughness in progress

Shells mounted to substrate

Measure surface roughness

Coat w/GDPMeasure surface roughness

Repeat

0

20

40

µm

0 20

40

60µm

0

20

40

µm

0 20

40

60µm

Shell surface starts like this...

... And finishes like this

0.5

0.0

-0.5

µm

0.5

0.0

µm

Bare resorcinol-formaldehyde foam 15 µm of GDP on foam shell

Recent improvements in coatings have decreased the minimum GDP layer for gas retention

0

200

400

600

800

1000

1200

0 10 20 30

GDP coating thickness (um)

D2

Ha

lf lif

e (

sec

)

Pinhole free

Pinholes

Predicted D2permeation rate

50 mtorr background pressure (10/07)

We have reduced the coating thickness for gas tight capsules by

40%!

250 mtorr/ 50 mtorr background pressure (3/08)

Green = pass cryo permeation testBlack = fail cryo permeation test

Current barrier specification: 10 µm

The areal density of shells can be measured by the precision radiography

technique

• X-rays penetrate through 2 walls of shell– Eq: , x is optical depth

• Scintillator converts x-rays into visible light

• System counts every x-ray photon– Noise in counts is

• 16 detectors in two columns• Shell rotates

– Shaft encoder => no cumulative error

1 mm

(16 rows)

2 mm(144 pixels/row)

rotation

detectors

X-ray beam

S.A. EDDINGER, R.B. STEPHENS, H. HUANG, T.J. DRAKE, A. NIKROO, G. FLINT, C.R. BYSTEDT, “Precision X-Ray Optical  Depth Measurements in ICF Shells” Fusion Sci. & Technol. 51, 525 (2007)

xeTT 0

)(

1

counts

The areal density of thick shells have been measured

Areal density specification:

< 0.3% over modes 100 - 500

0.996

0.997

0.998

0.999

1

1.001

1.002

1.003

1.004

1.005

0 45 90 135 180 225 270 315 360

Angle, degrees

Re

lati

ve

Are

al D

en

sit

y

0.991

0.993

0.995

0.997

0.999

1.001

1.003

1.005

0 45 90 135 180 225 270 315 360

Angle, degrees

Re

lati

ve

Are

al D

en

sit

y4.5 mm RF foam shell with 25um GDP overcoating

Large defects

Single Rotation Scan (w/ all 16 traces)

The shells tested meet the areal density specification (neglecting large defects)

Single Rotation Scan (w/ 13 traces)

Conclusion

• We have reduced the GDP coating thickness for gas tight capsules from 25 to 15 um (40%)– Further improvement are possible– Future work: experiments to better

understand mechanism of background pressure/ evolution of coating roughness

• Use this understanding to refine coating parameters