XAPPER... it’s here!!!! XAPPER presented by: Jeff Latkowski contributors: S. Reyes, J. Speth, S. Payne, L. J. Perkins, R. Abbott, R. Schmitt (student), W. Meier High Average Power Laser Meeting December 5-6, 2002 Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

Outline Need for rep-rated x-ray exposures XAPPER: Modeling: Source capabilities Source installation & testing Problems with condensing optic Modeling: ABLATOR upgrades/results Topaz/Dyna results LASNEX result for Xe + target Al mirror exposures Near- and long-term plans

Single-shot results are not sufficient Result from UCSD 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, (Cont’d.) Data courtesy of Mark Tillack, University of California at San Diego 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 might be similar Rep-rated x-ray damage studies are needed

General source specifications from PLEX LLC Star-pinch plasma Ellipsoidal condenser Sample plane 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/cm2 Several million pulses before minor maintenance Significant margin for laser-IFE simulations

PLEX LLC delivered the source in October; installation was completed October 31 Sample tray has 5 positions; 1 for photodiode Currently 3 Hz operation; 10 Hz by end CY02 Foil “comb” (below) sits near plasma; greatly reduces debris

An EUV spectrometer, purchased from McPherson, arrived Dec. 2 Up to five samples can, in turn, be rotated into the focused x-ray beam Spectrometer to be mounted vertically using a gantry crane

The ellipsoidal condenser is 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 Incoming x-rays Zr filter (passes 7-17 nm) Phosphorescent material Reticle

ABLATOR is the workhorse of our predictive capability Various updates/improvements have been completed: Introduced direct-drive target spectra for the bare target, as well as the escape spectrum after 6.5 Torr-cm of xenon gas Introduced ability to attenuate IFE x-ray spectra out to distances of more than 6.5 m Added restart capability (read in temperature/enthalpy profile) Added tungsten to materials database Debugged/tested grazing incidence module Additional improvements are planned: Adding stress-strain module Direct input of measured x-ray spectra Addition of ion heating

Escape spectrum through 10 mTorr Xe may differ significantly from bare target ouptut X-rays 6.07 (2%)   Neutrons 279 (70%) Burn ions 52.2 (13%) Debris ions 60.0 (15%) Residual thermal 0.045 (<0.1%) energy Residual burn 1.51 products Laser energy 2.37 absorbed Total out 401 MJ Bare target Target + Xe

Escape spectrum through 10 mTorr Xe may differ significantly from bare target ouptut X-rays 6.07 (2%)   Neutrons 279 (70%) Burn ions 52.2 (13%) Debris ions 60.0 (15%) Residual thermal 0.045 (<0.1%) energy Residual burn 1.51 products Laser energy 2.37 absorbed Total out 401 MJ Bare target Target + Xe LASNEX calculations for 6.5m of 10 mTorr Xe buffer gas (@ 710-8 g/cc  4.610-5 g/cm2) Effect is to trade debris ion (hydro) kinetic energy for increasing x-ray and thermal loads. Secondary x-rays are much softer (peak @ 50-100 eV vs. 3-4 keV for prompt x-rays). Charged particle slowing down models include Li-Petrasso-equivalent formalism (i.e when Vfast-ion ~ Ve, thermal), but not electron collective effects

Escape spectrum through 10 mTorr Xe may differ significantly from bare target ouptut X-rays 51.5 (13%) 6.07 (2%)   Neutrons 279 (70%) 279 (70%) Burn ions 50.9 (13%) 52.2 (13%) Debris ions 4.63 (1%) 60.0 (15%) Residual thermal 13.6 (3%) 0.045 (<0.1%) energy Residual burn 0.35 1.51 products Laser energy 2.37 2.37 absorbed Total out 402 MJ 401 MJ Bare target Target + Xe LASNEX calculations for 6.5m of 10 mTorr Xe buffer gas (@ 710-8 g/cc  4.610-5 g/cm2) Effect is to trade debris ion (hydro) kinetic energy for increasing x-ray and thermal loads. Secondary x-rays are much softer (peak @ 50-100 eV vs. 3-4 keV for prompt x-rays). Charged particle slowing down models include Li-Petrasso-equivalent formalism (i.e when Vfast-ion ~ Ve, thermal), but not electron collective effects

Example use of ABLATOR’s restart capability for an aluminum GIMM 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.

Stress-strain modeling is performed with Topaz/Dyna Thermal stress (and fatigue) is believed to be dominant effect Calculations completed for XAPPER line (113 eV) and tungsten: Set maximum allowable fluence such that ssurf = 50% sy Allowable fluence is ~0.1 J/cm2 Corresponds to a DTsurf of only ~250 K Calculations nearly completed for direct-drive spectrum: Will be used to “dial up a fluence” on XAPPER

A broadband aluminum mirror was exposed Sample details: 1” diameter Al mirror with Pyrex substrate (AL.2 from Newport) MgF2 for oxidation resistance Ta disk covered ½ of sample Exposure details: ~0.1 J/cm2 per pulse at 113 eV 3000 total pulses; 2 Hz; tpulse~40 ns Room-temperature irradiation Calculated DT = 220 K/pulse

A broadband aluminum mirror was exposed Sample details: 1” diameter Al mirror with Pyrex substrate (AL.2 from Newport) MgF2 for oxidation resistance Ta disk covered ½ of sample Exposure details: ~0.1 J/cm2 per pulse at 113 eV 3000 total pulses; 2 Hz; tpulse~40 ns Room-temperature irradiation Calculated DT = 220 K/pulse Shielded side

A broadband aluminum mirror was exposed Sample details: 1” diameter Al mirror with Pyrex substrate (AL.2 from Newport) MgF2 for oxidation resistance Ta disk covered ½ of sample Exposure details: ~0.1 J/cm2 per pulse at 113 eV 3000 total pulses; 2 Hz; tpulse~40 ns Room-temperature irradiation Calculated DT = 220 K/pulse

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

The x-ray exposure significantly reduced the mirror reflectivity Reflectivity measurement averaged over a 5-mm-diameter area centered over obvious damage site

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.

Final Optic Phase I Goals Meet laser induced damage threshold (LIDT) requirements of more than 5 Joules/cm2, in large area optics. Develop a credible final optics design that is resistant to degradation from neutrons, x-rays, gamma rays, debris, contamination, and energetic ions. stiff, lightweight, cooled, neutron transparent substrate 85° Laser UCSD LLNL

Develop a viable first wall concept for a fusion power plant. Chambers Phase I Goals Develop a viable first wall concept for a fusion power plant. Produce a viable “point design” for a fusion power plant Long term material issues are being resolved. UCSD Wisconsin SNL ORNL LLNL Example- Ion exposures on RHEPP

Plans Complete system activation: Enhance diagnostic capabilities: Resolve issues with condensing optic Further diagnose source energy and size Spectral characterization and optimization (EUV spectrometer) Enhance diagnostic capabilities: Procure/install fast optical thermometer (from UCSD) Develop/test/install high-speed laser interferometer Modeling: Add stress-strain model to ABLATOR Sample testing and evaluation: Exposure campaigns for Al, W (variety of forms) Explain effect of energy, number of pulses, fluence, etc. Employ fast thermometer to validate fundamentals of modeling Establish benchmarked code to predict IFE performance of first wall Synergistic effects: Pre- and post-irradiation LIDT for aluminum mirrors Develop synergistic effects plan JFL—11/02 HAPL Mtg.

X-ray fluence is not the correct figure-of-merit Temperature gradients and induced stresses are likely to be most significant effects: Specific energy or energy density (J/g, J/cc) are better measures Can calculate as (J/cc) or (J/g) Expected specific energies from x-ray pulse: Direct-drive IFE: Graphite wall: 160 J/g Tungsten wall: 550 J/g Al optic: 14 J/g SiO2 optic: 30 J/g

X-ray fluences in IFE and ICF 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 Total = 6.1 MJ Total = 115 MJ Target output calculations (1-D LASNEX) courtesy of John Perkins, LLNL