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XAPPER Update

XAPPER Update. Presented by: Jeff Latkowski XAPPER Team: Ryan Abbott, Brad Bell, and Keith Kanz Special thanks to: Stan Ault HAPL Program Workshop Oak Ridge National Laboratory March 21-22, 2006 UCRL-219931-PRES

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XAPPER Update

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  1. XAPPER Update Presented by: Jeff Latkowski XAPPER Team: Ryan Abbott, Brad Bell, and Keith Kanz Special thanks to: Stan Ault HAPL Program Workshop Oak Ridge National Laboratory March 21-22, 2006 UCRL-219931-PRES Work performed under the auspices of the U. S. Department of Energy byLawrence Livermore National Laboratory under Contract W-7405-Eng-48.

  2. Progress since the last meeting • Thermometer trials and tribulations • Plans for using XAPPER to expose optics JFL 03/21/06

  3. The original thermometer has notworked for us for a variety of reasons • Original system used 200 mm fiber with 75 and 40 mm lenses: • Gave a 375 mm diameter field of view • XAPPER has a small spot size of~440 mm diameter • Gave temperature variations in field of view (a definite no-no for optical pyrometry) • Switched optics to 62 and 150 mm lenses: • Field of view reduced to 83 mm • Increased edge temperature to2450 ºC • Reduced field of view cuts signal by 20x, but 46% more solid-angle • Overall signal reduction of 14x JFL 03/21/06

  4. Original thermometer, (Cont'd.) • Aligning the laser spot to the focused x-ray beam was impossible without manipulation under vacuum  installed two-axis motorized gimbal system • Found a signal! Much celebration!  Movie shows field of view with old thermometer head JFL 03/21/06

  5. Original thermometer, (Cont'd.) • We moved onto a new sample to start collecting real data  signal was gone! • Discovered that the heavily damaged sample had been reflecting pinch light into the thermometer head • Confirming experiment: blocked EUV beam with a plate of glass and still saw same (visible light) signal  JFL 03/21/06

  6. We have tried various fixes • Look for a dead-zone in the spectrum  doesn't appear to be one • Temporal discrimination between pinch and emitted light  pinch light persists too long • Vary angles  not a real option (can’t get shallower angle; blackbody emission is lambertian, so signal would fall rapidly at steeper angles) • Look at the back side of a thin sample  inadequate space All of these options assume that we have a good signal that gets drowned out by reflected pinch light. Instead, we see nothing until the material damages. Suppressing the pinch light won’t fix the underlying problem. JFL 03/21/06

  7. 3500 3000 2500 2000 1500 1000 10-9 10-7 10-5 10-3 10-1 Original thermometer, (Cont'd.) • Use thin sample (<5 mm) to keep material hot for "long" time (milliseconds): • Sit at lower temperature, lose by T4 (12-18x) • Able to count for ~1ms instead of ~100ns, win big (104x) • Unfortunately, the ripples inherent to a thin foil are quite similar to those resulting from surface damage  we immediately see reflected pinch light JFL 03/21/06

  8. Original thermometer, (Cont'd.) • Why doesn’t it work for us? Signal strength is just too low: • 700/800nm aren’t the best wavelengths for our target temperatures; plus, small spread forces narrow bandpass (10 vs. 40nm) filters, further reducing the possible signal • Simple analysis shows that blackbody emission getting to thermometer head (with Lambertian distribution) is only 1400-2100 p/ns in each band • Emissivity probably ~0.3 and filters transmission is ~50%, so we have200-300 p/ns • Uncoated fiber ends (and possibly optics) result in further reductions JFL 03/21/06

  9. We’ve moved to a 6-color pyrometerusing LN-cooled photodiodes • System is borrowed from Stan Ault of LLNL’s B Division – thanks Stan! • System operates with 6 fibers (actually 7 in all) at 1.25, 1.65, 2.11, 2.71, 3.28 and 4.08 mm • SiO2 fibers for the two lower l’s and chalcogenide at higher l’s • Coated ZnSe lenses for transmission at higher l’s and lower Fresnel losses • LN-cooled Kolmar photodiodes with 25ns rise time/50ns fall time • PD’s are set up with pre-amplification circuit • Calibrated with blackbody source (not a ratio-temp lamp like for the old system) • Able to see calibration signal at 700C with lamp with aperture down to318 mm • We have been unable to actually implement in the XAPPER chamber due to very fragile fiber and stiff protective casing • We have operated calibration system near XAPPER while it has been running (electrical noise doesn’t appear to be a problem) JFL 03/21/06

  10. vs. We plan to construct our own, many-color pyrometer tuned to our needs • Use Kolmar’s smaller (0.5mm vs. 1mm) photodiodes to get faster response (7ns rise/~14ns fall) and faster amplifier w/ higher gain • Go to one single crystal sapphire fiber  more signal than with bundle and able to span l range: • In current system, each fiber gets only 1/9 of signal put on bundle • With single fiber, we can afford up to 89% signal loss due to increased fiber attenuation and beamsplitting before signal is as low as it is for current bundle JFL 03/21/06

  11. We plan to construct our own, many-color pyrometer tuned to our needs, (Cont'd.) F1 = 62mm /F2 = 62mm /F3 = -35mm EFL2-3 = 270mm Spot ~100mm Lhead ~150mm Wavelengths of ~0.5, 1.0, 1.5, 2.0, 2.5, 3.5 mm planned. Exact l's TBD pending availability of dichroics and other optics. JFL 03/21/06

  12. Big picture question: Does it makesense to use XAPPER to test optics? • Optics are to be driven quite hard: • 5 J/cm2 in 4 ns gets aluminum very close to its yield strength (or perhaps even beyond) • Variation in shot-to-shot fluence is ~15% • We will overshoot a considerable fraction of the time (probably doesn’t matter  we have same issue for laser damage testing work) • Recommendation: Perform basicscoping studies of damage curvesfor low number of shots / higherfluences (confirm nothing unusualwith soft x-rays, not makepredictions for large N) x-rays Debris Ions Burn Ions Laser LIDT data for Al GIMMs at 4w (Mark Tillack, UCSD) JFL 03/21/06

  13. XAPPER testing of optics, (Cont’d.) • XAPPER can reproduce the peak temperatures and stresses with a fluence of ~22 mJ/cm2 • Would need 22-470 mJ/cm2 to replicate temperatures/stresses expected from Mark’s fluences of 5-100 J/cm2 (normal to the beam) • Ironically, XAPPER will producelonger time-at-temperature thanexpected in the real case (as opposedto shorter in the chambers work) • How should we define “damage”in x-ray exposures? JFL 03/21/06

  14. The meaning of “damage” and “reliability”require more formal and consistentdefinitions for 109 shot systems • Definitions of Damage • - Initiation versus growth • - Coating, surface, bulk damage • Observation of Damage • - In situ versus post analysis • - Microscope, dark field, fluorescence • Damage Testing of Optics • - N on 1, R on 1, S on 1, etc. • - Size of optic tested • - Cleanliness of optics • - Environment of tests • (air, dry nitrogen, vacuum) • - Number of relevant shots • Fabrication of Optics and Coatings • - Bulk purity (contaminants, inhomogeneities) • - Polishing • - Post handling • - Conditioning • Beam characteristics • - Uniformity: constant versus varying • components • - Relevant fluences to real system • - Relevant pulse lengths • - Timescales of noise What does a 109 shot reliability mean for optics? - Extremely low probability of initiation allowed - Margin of safety defined JFL 03/21/06

  15. We are developing detailed modelsthat consider availability and reliabilityover the lifetime of an IFE plant Max of N analysis indicates small change in fluence for a large numbers of shots Bundling/Multiplexing geometries influence availability We think it’s time to gather the “optics” folks and form a working group to exchange ideas and establish similar IFE reliability protocols for testing and analysis JFL 03/21/06

  16. We have begun design of an alternate focusing optic for use on XAPPER • Goal is to provide a larger, flat-top for use in simulating heating of final optics (aluminum GIMMs and silica Fresnels) • Fluence goal is 25 mJ/cm2 (versus1 J/cm2 for tungsten) • Ray tracing capabilities did not appear to be up to the challenge, so we developed our own [XMC]: • Angle-dependent reflectivity • Multiple optic segments & detectors [e.g., artificial CCDs] • Arbitrary orientation of components • User-specified filters Example of a crazy optical system to exercise several XMC features JFL 03/21/06

  17. Using XMC, we have simulatedXAPPER's current optical system • Sensitivity studies have been completed for optic alignment (r, z, q) Radial displacement Axial displacement Zenith tilt These images look very similar to what we actually see on our CCD. This gives us confidence that the code is working properly. JFL 03/21/06

  18. We are now using XMC to designthe new focusing optic • We hope to combine multiple optical segments to provide something resembling a flat top • 10 mJ delivered should be possible • At 50 mJ/cm2 (2x fluence goal), could use spot size of 5 mm diameter • Once optical design is finalized, completed optic could be delivered in 6-8 weeks • Complications: • Fluence measurements will require thinner CCD filters  more expensive, more fragile and subject to pinholes • There’s no hope for an actual temperature measurement  must rely upon modeling and fluence measurements JFL 03/21/06

  19. Future plans • Detailed design, procurement and assembly for the 6-color pyrometer • Additional tungsten exposures: • Goal is many spots on same sample with temperature measurements • Exposure of nanocrystalline tungsten samples • Dr. Snead has promised to provide SiC samples soon • Final design, fabrication and testing for alternate XAPPER optic JFL 03/21/06

  20. Questions? Photo credit: Ryan Abbott Pilot: Jeff Latkowski

  21. Back-up slides

  22. The XAPPER experiment is used to studydamage from rep-rated x-ray exposure • Source designed / built by PLEX LLC • Operates with xenon gas pinch to produce 80-150 eV x-rays • Operation possible at up to 10 Hz for millions of pulses Materialsample Condensingoptic Plasmapinch JFL 03/21/06

  23. Sampleplane 62mm and150mm lenses Thermometerhead Condensingoptic Plasmapinch

  24. XAPPER’s mission is to investigate cyclic fatigue and other “sub-threshold” effects XAPPER is looking for “sub-threshold” (e.g., without melting or ablation) effects such as roughening and thermomechanical fatigue. XAPPER cannot match the x-ray spectrum, but it can replicate a selected figure of merit (e.g., peak surface temperature, dose, stress, etc.). XAPPER is used in the study of x-ray damage to chamber wall materials and will be applied to optics in the near future. Our results to date show some roughening of tungsten, but we do not see anything that would suggest the first wall armor concept would not work. JFL 03/21/06

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