1. 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.

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

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

11. Escape spectrum through 10 mTorr Xe may differ significantly from bare target ouptut
X-rays (2%)
Neutrons 279 (70%)
Burn ions (13%)
Debris ions (15%)
Residual thermal (<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 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

12. 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%) (<0.1%)
energy
Residual burn
products
Laser energy
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 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

13. Example use of ABLATOR’s restart capability for an aluminum GIMM
Assumes 99% reflectivity 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.

14. 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

15. 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

16. 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

17. 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

18. 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

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

20. 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.

21. 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

22. 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

23. 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.

24. 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

25. 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: J/cm2
NIF ignition targets:
1 m: ~40 J/cm2
First 5 m: ~3 J/cm2
Final 6.8 m: ~2 J/cm2
Total = 6.1 MJ
Total = 115 MJ
Target output calculations (1-D LASNEX) courtesy of John Perkins, LLNL