1. XAPPER Progress & Plans Presented by: Jeff Latkowski XAPPER Team: Ryan Abbott, Steve Payne, Susana Reyes, Joel Speth April 9, 2003 Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. XAPPER

2. JFL—4/03 HAPL The XAPPER experiment will be used to study damage from rep-rated x-ray exposure  Source built by PLEX LLC; delivered 10/02; operational 11/02; system testing and characterization now complete  Uses rf-initiated star-pinch to generate plasma  Operates with Xe (113 eV), Ar (250-300 eV), N (430 eV)

3. JFL—4/03 HAPL XAPPER Mission  XAPPER is to perform rep-rated, x-ray exposures to look for “sub-threshold” effects such as roughening and thermomechanical fatigue.  XAPPER provides large doses of soft (100-400 eV) x-rays; Dose is a reasonable figure of merit, not fluence.  XAPPER cannot match exact x-ray spectrum, but it can replicate a selected figure of merit. For example, the peak surface temperature, dose, stress, etc. that would occur in a real IFE system can be matched on XAPPER.  XAPPER will be used in the study of x-ray damage to optics and chamber wall materials.

4. JFL—4/03 HAPL XAPPER activities since December 2002 Star-pinchplasma Ellipsoidalcondenser Sample plane

5. JFL—4/03 HAPL XAPPER activities since December 2002 Star-pinchplasma Ellipsoidalcondenser Sample plane December – Crack in the ceramic within the plasma head. Loss of vacuum, water leak into plasma

6. JFL—4/03 HAPL XAPPER activities since December 2002 Star-pinchplasma Ellipsoidalcondenser Sample plane December – Crack in the ceramic within the plasma head. Loss of vacuum, water leak into plasma Resolution – Replaced ceramic with higher thermal conductivity material; Added epoxy layer as vacuum barrier; Operation to >100,000 pulses (everything from 1-10 Hz) without problem.

7. JFL—4/03 HAPL XAPPER activities since December 2002 Star-pinchplasma Ellipsoidalcondenser Sample plane January-April – Fluence on sample 40x lower than spec

8. JFL—4/03 HAPL XAPPER activities since December 2002 Star-pinchplasma Ellipsoidalcondenser Sample plane January-April – Fluence on sample 40x lower than spec Note: We don’t actually need the full 40x full currently envisioned experiments – we would be quite happy with a 5x improvement.

9. JFL—4/03 HAPL XAPPER activities since December 2002 Star-pinchplasma Ellipsoidalcondenser Sample plane January-April – Fluence on sample 40x lower than spec Resolution – Direct source measurements to ensure that problem is with optic, rather than source. Confirmed that source output is adequate.

10. JFL—4/03 HAPL Source measurements indicate that output is within 1.4x of specification  Sampled source through foil comb at 23º (rough center of condensing optic, when used)  Source output is ~0.24 J/sr (0.33 expected)  Indicates that majority of problem is with optic

11. JFL—4/03 HAPL XAPPER activities since December 2002 Star-pinchplasma Ellipsoidalcondenser Sample plane March-April – Continued problems with second optic. Incoming x-rays Zr filter (passes 7-17 nm) Phosphorescent material Reticle CCD imaging of inner spot 1.3 cm

12. JFL—4/03 HAPL XAPPER activities since December 2002 Star-pinchplasma Ellipsoidalcondenser Sample plane March-April – Continued problems with second optic. Resolution – Discussions with internal optics experts. Testing and analysis of current optics. Decision to remove optic from PLEX contract. Internal team to sub-contract mandrels but coat optics internally.

13. JFL—4/03 HAPL Spot size measurements made with HeNe  Tabletop visible (HeNe) spot size measurements suggest error must be a wavelength-dependent effect  Vendors and EUV experts agree that likely explanation is mid-frequency spatial roughness ~3 mm spot

14. JFL—4/03 HAPL We are removing the condensing optics from the PLEX contract; A combination of LLNL expertise and external vendors will be used  LLNL’s Materials Science & Technology Division (MSTD) routinely makes collimating optics that far surpass our figuring & roughness specifications  Current plan: –Outside vendor for mandrels (3): Roughness specification <1.5 nm RMS Slope error specification <1 arc-minute –MSTD to coat optics: C, Pd, Cu, Ni –Should get  4 good optics per mandrel –Total cost: $6-10K/optic  For now, we will switch to study of Al mirrors (we have more than enough fluence for this)

15. JFL—4/03 HAPL MSTD has previously produced collimating optics that far exceed our specifications for roughness and slope error Multiple optics produced from a single mandrel When measured figure errors (from mandrel) are accounted for, calculations agree well with measured intensities  suggests that coating process is not significantly degrading optical quality

16. JFL—4/03 HAPL XAPPER activities since December 2002 Star-pinchplasma Ellipsoidalcondenser Sample plane February – Question raised if damage could be due to ions.

17. JFL—4/03 HAPL XAPPER activities since December 2002 Star-pinchplasma Ellipsoidalcondenser Sample plane February – Question raised if damage could be due to ions. Resolution – Conducted simple experiment to verify damage due to x-rays.

18. JFL—4/03 HAPL We have confirmed that damage is being caused by focused x-rays, not stray ions 1 st sequence: ~0.19 J/cm 2 2 nd sequence: ~0.13 J/cm 2  Sample is ½” diameter Al mirror from Newport (Al on SiO 2 ): –Exposed to 3000 pulses at 8 Hz;  pulse ~40 ns –Translated focusing optic (perpendicular to axis of symmetry) by ~0.9 mm between 1 st and 2 nd exposure sequences  Observed movement of damage spot, indicating that damage is caused by x-rays, which are focused by the condensing optic  Ions, if present, would not be focused to new spot

19. JFL—4/03 HAPL Gantry was installed & spectrometer has been mounted/aligned—testing is underway EUV Spectrometer is mounted vertically to intercept x-rays directed upon the pinch axis

20. JFL—4/03 HAPL ABLATOR has been used to predict the time/temperature history of an Al GIMM Assumes 99% reflectivity GIMM @ 85° and 30 m, 10 mTorr Xe, 1 ns prompt, and 1  s secondary x-ray pulselengths. Surface zone is 10 nm thick. Full 46 MJ assumed for 2 nd x-ray pulse. Secondary x-ray pulse Prompt x-ray pulse Laser 30 ns pulse

21. JFL—4/03 HAPL Increasing the gas pressure to 50 mTorr helps attenuate the x-rays Secondary x-ray pulse Prompt x-ray pulse Laser 30 ns pulse Assumes 99% reflectivity GIMM @ 85° and 30 m, 50 mTorr Xe, 1 ns prompt, and 1  s secondary x-ray pulselengths. Surface zone is 10 nm thick. Full 46 MJ assumed for 2 nd x-ray pulse.

22. JFL—4/03 HAPL  New version needed to analyze exposure of Newport mirrors (and components such as tungsten armor and dielectric mirrors): –Treatment as single, thin layer (100 nm Al) way too conservative –Treatment as thicker Al layer non-conservative due to high conductivity  Calculation agrees with experimental observations: –Removal of Al at only 0.18 J/cm 2 –Can actually see plasma burn through Al layer We have completed a multi-material version of ABLATOR; Testing is underway

23. JFL—4/03 HAPL  Resolve optic issues: outside contractor for mandrels and LLNL-produced coatings  Spectral characterization and tuning (EUV spectrometer)  Enhance diagnostic capabilities: –Fast (<1 ns resolution) photodiode –Procure/install fast optical thermometer (from UCSD)  Add ion heating to ABLATOR  Sample testing and evaluation: –Campaign for Al to begin (actually need to reduce fluence for optics experiments); return to tungsten once new optics are available –Explain effect of energy, number of pulses, fluence, etc. Summary: Source characterization is completed (for now); Ready to start hitting Al samples

24. Back-up slides

25. JFL—4/03 HAPL PLEX LLC produces a source that meets our needs  Uses a Z-pinch to produce x-rays: –1 GHz radiofrequency pulse pre-ionizes low-pressure gas fill –Pinch initiated by ~100 kA from thyratrons –Operation single shot mode up to 10 Hz  Operation with Xe (11 nm, 113 eV): –70% of output at 113 eV (tunable) –3 mm diameter spot –Fluence of ≥7 J/cm 2  Several million pulses before minor maintenance Star-pinchplasma Ellipsoidalcondenser Sampleplane Significant margin for laser- IFE simulations

26. JFL—4/03 HAPL  Specification calls for 7 J/cm 2  Experiments using a phosphorescent disk indicate a large (~1.5 cm) spot  Expected energy appears to be there; will be confirmed with calorimeter experiments The ellipsoidal condenser is not performing to specification Incoming x-rays Zr filter (passes 7-17 nm) Phosphorescent material Reticle CCD image of inner spot OptiCAD spot calculation (with MFSR)

27. JFL—4/03 HAPL X-ray fluences in IFE and ICF systems will be significant  Direct-drive dry-walls: –Chamber: ~1 J/cm 2 –Final optics: ~100 mJ/cm 2  Indirect-drive liquid walls: –Thick-liquid jets: ~1 kJ/cm 2 –Wetted wall/vortices: 30-80 J/cm 2  NIF ignition targets: –Diagnostic @ 1 m: ~40 J/cm 2 –First wall @ 5 m: ~3 J/cm 2 –Final optic @ 6.8 m: ~2 J/cm 2 Total = 6.1 MJ Total = 115 MJ Target output calculations (1-D LASNEX) courtesy of John Perkins, LLNL

28. JFL—4/03 HAPL Photodiode signal = 4.1 V (~0.18 J/cm2); 3000 pulses @ 8 Hz

29. JFL—4/03 HAPL The x-ray exposure significantly reduced the mirror reflectivity  Reflectivity measurement averaged over a 5-mm-diameter area centered over obvious damage site NOTE: This mirror looks very different from what an IFE final optic would look like.

30. JFL—4/03 HAPL  Design can provide systems that avoid significant single- shot damage  Single-shot results are not adequate; miss: –Thermal fatigue –Surface roughening (RHEPP results, UW analyses) –Difficult to assess very small ablation levels  Analyses need to consider multi-shot effects; rep-rated exposures are needed Result from UCSD X-ray damage: need for rep-rated exposures Single-shot results are not sufficient

31. JFL—4/03 HAPL Single-shot results, (Cont’d.)  Single-shot, laser-induced damage threshold is ~140 J/cm 2  Multiple-shot operation is only safe at a small fraction (~40%?) of the single-shot threshold  Gradual optical degradation explained (ref: Ghoniem) as roughening caused by migration of dislocation line defects  While length scales will differ (eV vs. keV), laser/x-ray physics should be quite similar Rep-rated x-ray damage studies are needed Data courtesy of Mark Tillack, University of California at San Diego 532 nm light fluence quoted is normal to beam

32. JFL—4/03 HAPL Significant damage was found throughout the unshielded region using white-light interferometry  ~250 nm removed over visible damage site  Peak-to-valley removal >500 nm  Considerable pitting throughout unshielded region (concentrated in obvious damage area)  Semi-regular “roughening” observed – seems consistent with RHEPP results