XAPPER Progress & Plans

1. XAPPER Progress & Plans XAPPER 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.

2. The XAPPER experiment will be used tostudy 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. 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. XAPPER Mission

4. XAPPER activities since December 2002 Sample plane Star-pinchplasma Ellipsoidalcondenser

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

6. XAPPER activities since December 2002 Sample plane Star-pinchplasma Ellipsoidalcondenser 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. XAPPER activities since December 2002 Sample plane Star-pinchplasma Ellipsoidalcondenser January-April – Fluence on sample 40x lower than spec

8. XAPPER activities since December 2002 Sample plane Star-pinchplasma Ellipsoidalcondenser 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. XAPPER activities since December 2002 Sample plane Star-pinchplasma Ellipsoidalcondenser 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. 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 Source measurements indicate thatoutput is within 1.4x of specification

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

12. XAPPER activities since December 2002 Sample plane Star-pinchplasma Ellipsoidalcondenser 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. 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 Spot size measurements made with HeNe ~3 mm spot

14. 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) We are removing the condensing optics from the PLEX contract; A combination of LLNL expertise and external vendors will be used

15. 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. XAPPER activities since December 2002 Sample plane Star-pinchplasma Ellipsoidalcondenser February – Question raised if damage could be due to ions.

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

18. 2nd sequence: ~0.13 J/cm2 1st sequence: ~0.19 J/cm2 We have confirmed that damage is being caused by focused x-rays, not stray ions • Sample is ½” diameter Al mirror from Newport (Al on SiO2): • Exposed to 3000 pulses at 8 Hz; tpulse ~40 ns • Translated focusing optic (perpendicular to axis of symmetry) by ~0.9 mm between 1st and 2nd exposure sequences • Observed movement ofdamage spot, indicatingthat damage is caused byx-rays, which are focusedby the condensing optic • Ions, if present, would notbe focused to new spot

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

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

22. We have completed a multi-material versionof ABLATOR; Testing is underway • 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/cm2 • Can actually see plasma burn through Al layer

23. Summary: Source characterization is completed(for now); Ready to start hitting Al samples • 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.

24. Back-up slides

25. Sampleplane Ellipsoidalcondenser Star-pinchplasma PLEX LLC produces a sourcethat meets our needs • Uses a Z-pinch to produce x-rays: • 1 GHz radiofrequency pulse pre-ionizeslow-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/cm2 • Several million pulsesbefore minor maintenance Significant margin for laser-IFE simulations

26. Reticle Phosphorescent material Zr filter (passes 7-17 nm) Incoming x-rays The ellipsoidal condenseris not performing to specification • Specification calls for <3 mm spot size, which provides >7 J/cm2 • Experiments using a phosphorescent disk indicate a large (~1.5 cm) spot • Expected energy appears to be there; will be confirmed with calorimeter experiments OptiCAD spot calculation (with MFSR) CCD image of inner spot

27. Total = 115 MJ Total = 6.1 MJ X-ray fluences in IFE andICF systems will be significant • Direct-drive dry-walls: • Chamber: ~1 J/cm2 • Final optics: ~100 mJ/cm2 • Indirect-drive liquid walls: • Thick-liquid jets: ~1 kJ/cm2 • Wetted wall/vortices:30-80 J/cm2 • NIF ignition targets: • Diagnostic @ 1 m: ~40 J/cm2 • First wall @ 5 m: ~3 J/cm2 • Final optic @ 6.8 m: ~2 J/cm2 Target output calculations (1-D LASNEX) courtesy of John Perkins, LLNL

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

29. The x-ray exposure significantlyreduced the mirror reflectivity • Reflectivity measurement averaged over a5-mm-diameter area centered over obvious damage site NOTE: This mirror looks very different from what an IFE final optic would look like.

30. Result from UCSD X-ray damage: need for rep-rated exposures • 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 Single-shot results are not sufficient

31. Data courtesy of Mark Tillack, University of California at San Diego 532 nm light fluence quoted is normal to beam Single-shot results, (Cont’d.) • Single-shot, laser-induced damage threshold is ~140 J/cm2 • 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

32. Significant damage was found throughout theunshielded region using white-light interferometry • ~250 nm removed over visible damage site • Peak-to-valley removal >500 nm • Considerable pitting throughout unshielded region(concentrated inobvious damage area) • Semi-regular“roughening” observed– seems consistentwith RHEPP results