presented by: Jeff Latkowski

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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.
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Outline

• Need for rep-rated x-ray exposures
• XAPPER
• 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

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Single-shot results are not sufficient

• 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

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Single-shot results, (Contd.)

• 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
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General source specificationsfrom PLEX LLC

• Uses a Z-pinch to produce x-rays
• 1 GHz radiofrequency pulse pre-ionizeslow-pressur
  e 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
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PLEX LLC delivered the source in
Octoberinstallation was completed October 31

• Sample tray has 5 positions1 for photodiode
• Currently 3 Hz operation10 Hz by end CY02
• Foil comb (below) sits near plasma greatly
  reduces debris

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An EUV spectrometer, purchasedfrom 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

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The ellipsoidal condenseris not performing to
specification

• Specification calls for lt3 mm spot size, which
  provides gt7 J/cm2
• Experiments using a phosphorescent disk indicate
  a large (1.5 cm) spot
• Expected energy appears to be there

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ABLATOR is the workhorseof 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

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Escape spectrum through 10 mTorr Xe may differ
significantly from bare target ouptut
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Escape spectrum through 10 mTorr Xe may differ
significantly from bare target ouptut
LASNEX calculations for 6.5m of 10 mTorr Xe
buffer gas (_at_ 7?10-8 g/cc ? 4.6?10-5
g/cm2) Effect is to trade debrision (hydro)
kinetic energy for increasing x-ray and thermal
loads. Secondary x-rays are much softer (peak _at_
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
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Escape spectrum through 10 mTorr Xe may differ
significantly from bare target ouptut
LASNEX calculations for 6.5m of 10 mTorr Xe
buffer gas (_at_ 7?10-8 g/cc ? 4.6?10-5
g/cm2) Effect is to trade debrision (hydro)
kinetic energy for increasing x-ray and thermal
loads. Secondary x-rays are much softer (peak _at_
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
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Example use of ABLATORs restartcapability for
an aluminum GIMM
Assumes 99 reflectivity GIMM _at_ 85 and 30 m, 10
mTorr Xe, 1 ns prompt, and1 ms secondary x-ray
pulselengths. Surface zone is 10 nm thick. Full
46 MJ assumed for 2nd x-ray pulse.
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Stress-strain modelingis performed with
Topaz/Dyna

• Thermal stress (and fatigue) is believed to be
  dominant effect
• Calculations completed forXAPPER line (113 eV)
  andtungsten
• Set maximum allowable fluencesuch that ssurf
  50 sy
• Allowable fluence is 0.1 J/cm2
• Corresponds to a DTsurf of only250 K
• Calculations nearly completedfor direct-drive
  spectrum
• Will be used to dial up a fluenceon XAPPER

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A broadband aluminummirror 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 tpulse40 ns
• Room-temperature irradiation
• Calculated DT 220 K/pulse

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A broadband aluminummirror 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 tpulse40 ns
• Room-temperature irradiation
• Calculated DT 220 K/pulse

Shielded side
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A broadband aluminummirror 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 tpulse40 ns
• Room-temperature irradiation
• Calculated DT 220 K/pulse

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Significant damage was found throughout
theunshielded region using white-light
interferometry

• 250 nm removed over visible damage site
• Peak-to-valley removal gt500 nm
• Considerable pitting throughout unshielded
  region(concentrated inobvious damage area)
• Semi-regularroughening observed seems
  consistentwith RHEPP results

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The x-ray exposure significantlyreduced the
mirror reflectivity

• Reflectivity measurement averaged over
  a5-mm-diameter area centered over obvious damage
  site

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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.
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Final Optic Phase I Goals

1. Meet laser induced damage threshold (LIDT)
   requirements of more than 5 Joules/cm2, in large
   area optics.
2. Develop a credible final optics design that is
   resistant to degradation from neutrons, x-rays,
   gamma rays, debris, contamination, and energetic
   ions.

UCSD LLNL
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Chambers Phase I Goals

1. Develop a viable first wall concept for a fusion
   power plant.
2. Produce a viable point design for a fusion
   power plant

Long term material issues are being resolved.
UCSD Wisconsin SNL ORNL LLNL UCSD
Example- Ion exposures on RHEPP
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Plans

• Complete system activation
• 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

JFL11/02 HAPL Mtg.
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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

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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/vortices30-80 J/cm2
• NIF ignition targets
• Diagnostic _at_ 1 m 40 J/cm2
• First wall _at_ 5 m 3 J/cm2
• Final optic _at_ 6.8 m 2 J/cm2

Target output calculations (1-D LASNEX) courtesy
of John Perkins, LLNL