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 PRES Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

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

XAPPER JFL 03/21/06 The original thermometer has not worked for us for a variety of reasons Original system used 200  m fiber with 75 and 40 mm lenses: Gave a 375  m diameter field of view XAPPER has a small spot size of ~440  m 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  m Increased edge temperature to 2450 ºC Reduced field of view cuts signal by 20x, but 46% more solid-angle Overall signal reduction of 14x

XAPPER JFL 03/21/06 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

XAPPER JFL 03/21/06 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 

XAPPER JFL 03/21/06 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.

XAPPER JFL 03/21/06 Original thermometer, (Cont'd.) Use thin sample (<5  m) to keep material hot for "long" time (milliseconds): Sit at lower temperature, lose by T 4 (12-18x) Able to count for ~1ms instead of ~100ns, win big (10 4 x) Unfortunately, the ripples inherent to a thin foil are quite similar to those resulting from surface damage  we immediately see reflected pinch light

XAPPER JFL 03/21/06 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 p/ns in each band Emissivity probably ~0.3 and filters transmission is ~50%, so we have p/ns Uncoated fiber ends (and possibly optics) result in further reductions

XAPPER JFL 03/21/06 We’ve moved to a 6-color pyrometer using 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  m SiO 2 fibers for the two lower ’s and chalcogenide at higher ’s Coated ZnSe lenses for transmission at higher ’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 to 318  m 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)

XAPPER JFL 03/21/06 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 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 vs.

XAPPER JFL 03/21/06 We plan to construct our own, many-color pyrometer tuned to our needs, (Cont'd.) F1 = 62mm / F2 = 62mm / F3 = -35mm EFL 2-3 = 270mm Spot ~100  m L head ~150mm Wavelengths of ~0.5, 1.0, 1.5, 2.0, 2.5, 3.5  m planned. Exact 's TBD pending availability of dichroics and other optics.

XAPPER JFL 03/21/06 Big picture question: Does it make sense to use XAPPER to test optics? Optics are to be driven quite hard: 5 J/cm 2 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 basic scoping studies of damage curves for low number of shots / higher fluences (confirm nothing unusual with soft x-rays, not make predictions for large N) Laser x-rays Debris Ions Burn Ions LIDT data for Al GIMMs at 4   Mark Tillack, UCSD)

XAPPER JFL 03/21/06 XAPPER testing of optics, (Cont’d.) XAPPER can reproduce the peak temperatures and stresses with a fluence of ~22 mJ/cm 2 Would need mJ/cm 2 to replicate temperatures/stresses expected from Mark’s fluences of J/cm 2 (normal to the beam) Ironically, XAPPER will produce longer time-at-temperature than expected in the real case (as opposed to shorter in the chambers work) How should we define “damage” in x-ray exposures?

XAPPER JFL 03/21/06 The meaning of “damage” and “reliability” require more formal and consistent definitions for 10 9 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 10 9 shot reliability mean for optics? - Extremely low probability of initiation allowed - Margin of safety defined

XAPPER JFL 03/21/06 We are developing detailed models that consider availability and reliability over 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

XAPPER JFL 03/21/06 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/cm 2 (versus 1 J/cm 2 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

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

XAPPER JFL 03/21/06 We are now using XMC to design the 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/cm 2 (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

XAPPER JFL 03/21/06 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

Photo credit: Ryan Abbott Pilot: Jeff Latkowski Questions?

Back-up slides

XAPPER JFL 03/21/06 Source designed / built by PLEX LLC Operates with xenon gas pinch to produce eV x-rays Operation possible at up to 10 Hz for millions of pulses Condensing optic Material sample Plasma pinch The XAPPER experiment is used to study damage from rep-rated x-ray exposure

62mm and 150mm lenses Condensing optic Thermometer head Plasma pinch Sample plane

XAPPER JFL 03/21/06 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.