IFE Target Fabrication Update Presented by Jared Hund 1 N. Alexander 1, J. Bousquet 1, Bob Cook 1, S. Eddinger, D. Frey 1, D. Goodin 1, H. Huang, J. Karnes 2, R. Luo 1, A. Nikroo 1, R. Paguio 1, R. Petzoldt 1, N. Petta 2, N. Ravelo 1, K. Saito 1, D. Schroen 1, J. Streit 2, A. Cheng 3, S. Saiedi 3 1 General Atomics, Inertial Fusion Technology, San Diego, CA 2 Schafer Corporation, Livermore, CA 3 UC San Diego, San Diego, CA HAPL Workshop IFT\P

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 ( Å) High Z coating ~ 2.3 mm rad 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) T2BT2BH2H2 RF Coil Shells Vacuum Pump Rotary Union Plasma Stepper Motor

Changing the background pressure during the GDP coating run affects the outer surface Background pressure: 500 mtorr250 mtorr75 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/GDP Measure surface roughness Repeat µm µm µm µm Shell surface starts like this And finishes like this µm µm Bare resorcinol-formaldehyde foam15 µm of GDP on foam shell

Recent improvements in coatings have decreased the minimum GDP layer for gas retention 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 test Black = 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 detectorsX-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)

The areal density of thick shells have been measured Areal density specification: < 0.3% over modes 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