xapper progress & plans presented by: jeff latkowski xapper team: ryan abbott, steve payne,...

XAPPER Progress & PlansXAPPER Progress & Plans

Presented by: Jeff Latkowski

XAPPER Team: Ryan Abbott, Steve Payne, Susana Reyes, Joel Speth

April 9, 2003

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

XAPPERXAPPER

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The XAPPER experiment will be used toThe XAPPER experiment will be used tostudy damage from rep-rated x-ray exposurestudy damage from rep-rated x-ray exposure

Source built by PLEX LLC; delivered 10/02; operational 11/02; system testing and characterization now complete

Uses rf-initiated star-pinch to generate plasma

Operates with Xe (113 eV), Ar (250-300 eV), N (430 eV)

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XAPPER MissionXAPPER Mission

XAPPER is to perform rep-rated, x-ray exposures to look for “sub-threshold” effects such as roughening and thermomechanical fatigue.

XAPPER provides large doses of soft (100-400 eV) x-rays; Dose is a reasonable figure of merit, not fluence.

XAPPER cannot match exact x-ray spectrum, but it can replicate a selected figure of merit. For example, the peak surface temperature, dose, stress, etc. that would occur in a real IFE system can be matched on XAPPER.

XAPPER will be used in the study of x-ray damage to optics and chamber wall materials.

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XAPPER activities since December 2002XAPPER activities since December 2002

Star-pinchplasma Ellipsoid

alcondenser

Sample plane

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alcondenser

Sample plane

December – Crack in the ceramic within the plasma head. Loss of vacuum, water leak into plasma

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alcondenser

Sample plane

December – Crack in the ceramic within the plasma head. Loss of vacuum, water leak into plasma

Resolution – Replaced ceramic with higher thermal conductivity material; Added epoxy layer as vacuum barrier; Operation to >100,000 pulses (everything from 1-10 Hz) without problem.

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alcondenser

Sample plane

January-April – Fluence on sample 40x lower than spec

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alcondenser

Sample plane


Note: We don’t actually need the full 40x full currently envisioned

experiments – we would be quite happy with a 5x improvement.

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alcondenser

Sample plane


Resolution – Direct source measurements to ensure that problem is with optic, rather than source. Confirmed that source output is adequate.

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Source measurements indicate thatSource measurements indicate thatoutput is within 1.4x of specificationoutput is within 1.4x of specification

Sampled source through foil comb at 23º (rough center of condensing optic, when used)

Source output is ~0.24 J/sr (0.33 expected) Indicates that majority of problem is with

optic

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alcondenser

Sample plane

March-April – Continued problems with second optic.

Incoming x-rays

Zr filter(passes 7-17 nm)

Phosphorescentmaterial

Reticle

CCD imaging of inner spot 1.3 cm

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alcondenser

Sample plane

March-April – Continued problems with second optic.

Resolution – Discussions with internal optics experts. Testing and analysis of current optics. Decision to remove optic from PLEX contract. Internal team to sub-contract mandrels but coat optics internally.

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Spot size measurements made with HeNeSpot size measurements made with HeNe

Tabletop visible (HeNe) spot size measurements suggest error must be a wavelength-dependent effect

Vendors and EUV experts agree that likely explanation is mid-frequency spatial roughness

~3 mm spot

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We are removing the condensing optics from the We are removing the condensing optics from the PLEX contract; A combination of LLNL expertise PLEX contract; A combination of LLNL expertise and external vendors will be usedand external vendors will be used

LLNL’s Materials Science & Technology Division (MSTD) routinely makes collimating optics that far surpass our figuring & roughness specifications

Current plan:– Outside vendor for mandrels (3):

• Roughness specification <1.5 nm RMS• Slope error specification <1 arc-minute

– MSTD to coat optics: C, Pd, Cu, Ni– Should get 4 good optics per mandrel– Total cost: $6-10K/optic

For now, we will switch to study of Al mirrors (we have more than enough fluence for this)

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MSTD has previously produced MSTD has previously produced collimatingcollimating optics that far optics that far exceed our specifications for roughness and slope errorexceed our specifications for roughness and slope error

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X-ray Radial Intensity Distribution

Multiple optics produced from a single mandrel

When measured figure errors (from mandrel) are accounted for, calculations agree well with measured intensities suggests that coating process is not significantly degrading optical quality

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alcondenser

Sample plane

February – Question raised if damage could be due to ions.

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alcondenser

Sample plane

February – Question raised if damage could be due to ions.

Resolution – Conducted simple experiment to verify damage due to x-rays.

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We have confirmed that damage is being We have confirmed that damage is being caused by focused x-rays, not stray ionscaused by focused x-rays, not stray ions

1st sequence: ~0.19 J/cm2

2nd sequence: ~0.13 J/cm2

Sample is ½” diameter Al mirror from Newport (Al on SiO2):– Exposed to 3000 pulses at 8 Hz; pulse ~40 ns– Translated focusing optic (perpendicular to axis of symmetry) by ~0.9

mm between 1st and 2nd exposure sequences

Observed movement ofdamage spot, indicatingthat damage is caused byx-rays, which are focusedby the condensing optic

Ions, if present, would notbe focused to new spot

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Gantry was installed & spectrometer has been Gantry was installed & spectrometer has been mounted/aligned—testing is underwaymounted/aligned—testing is underway

EUV Spectrometer is mounted vertically to intercept x-rays directed upon the pinch axis

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ABLATOR has been used to predict the ABLATOR has been used to predict the time/temperature history of an Al GIMMtime/temperature history of an Al GIMM

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Time (ns)

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ture

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Assumes 99% reflectivity GIMM @ 85Assumes 99% reflectivity GIMM @ 85° and 30 m° and 30 m, 10 mTorr Xe, 1 ns prompt, , 10 mTorr Xe, 1 ns prompt, and 1 and 1 s secondary x-ray pulselengths. Surface zone is 10 nm thick. s secondary x-ray pulselengths. Surface zone is 10 nm thick.

Full 46 MJ assumed for 2Full 46 MJ assumed for 2ndnd x-ray pulse. x-ray pulse.

Secondary x-ray pulse

Prompt x-ray pulse

Laser 30 ns pulse

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Increasing the gas pressure to 50 mTorrIncreasing the gas pressure to 50 mTorrhelps attenuate the x-rayshelps attenuate the x-rays

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Time (ns)

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ture

(K

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Secondary x-ray pulse

Prompt x-ray pulse

Laser 30 ns pulse

Assumes 99% reflectivity GIMM @ 85Assumes 99% reflectivity GIMM @ 85° and 30 m° and 30 m, 50 mTorr Xe, 1 ns prompt, , 50 mTorr Xe, 1 ns prompt, and 1 and 1 s secondary x-ray pulselengths. Surface zone is 10 nm thick. s secondary x-ray pulselengths. Surface zone is 10 nm thick.

Full 46 MJ assumed for 2Full 46 MJ assumed for 2ndnd x-ray pulse. x-ray pulse.

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New version needed to analyze exposure of Newport mirrors (and components such as tungsten armor and dielectric mirrors):– Treatment as single, thin layer (100 nm Al) way too conservative– Treatment as thicker Al layer non-conservative due to high conductivity

Calculation agrees with experimental observations:– Removal of Al at only 0.18 J/cm2

– Can actually see plasma burn through Al layer

We have completed a multi-material versionWe have completed a multi-material versionof ABLATOR; Testing is underwayof ABLATOR; Testing is underway

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Aluminum Fused silica

X-ray pulse off

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Resolve optic issues: outside contractor for mandrels and LLNL-produced coatings

Spectral characterization and tuning (EUV spectrometer)

Enhance diagnostic capabilities:– Fast (<1 ns resolution) photodiode– Procure/install fast optical thermometer (from UCSD)

Add ion heating to ABLATOR

Sample testing and evaluation:– Campaign for Al to begin (actually need to reduce fluence for optics

experiments); return to tungsten once new optics are available– Explain effect of energy, number of pulses, fluence, etc.

Summary: Source characterization is completedSummary: Source characterization is completed(for now); Ready to start hitting Al samples(for now); Ready to start hitting Al samples

Back-up slides

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PLEX LLC produces a sourcePLEX LLC produces a sourcethat meets our needsthat meets our needs

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 pulsesbefore minor maintenance

Star-pinchplasma

Ellipsoidalcondenser

Sampleplane

Significant Significant margin for laser-margin for laser-IFE simulationsIFE simulations

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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; will be confirmed with calorimeter experiments

The ellipsoidal condenserThe ellipsoidal condenseris not performing to specificationis not performing to specification

Incoming x-rays

Zr filter (passes 7-17 nm)Phosphorescent materialReticle

CCD image of inner spot

OptiCAD spot calculation

(with MFSR)

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X-ray fluences in IFE andX-ray fluences in IFE andICF systems will be significantICF 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

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NRL targetHIF target

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/ke

V)

Energy (keV)

Total = 6.1 MJ

Total = 115 MJ

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

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Photodiode signal = 4.1 V (~0.18 J/cm2);3000 pulses @ 8 Hz

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The x-ray exposure significantlyThe x-ray exposure significantlyreduced the mirror reflectivityreduced the mirror reflectivity

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

NOTE: This mirror looks NOTE: This mirror looks very very different from different from what an IFE final optic would look like.what an IFE final optic would look like.

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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

Result from UCSD

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400 MJ TargetGraphite wall @ 8.25 m radius25 mTorr Xe in chamber

154 MJ TargetTungsten wall @ 6.5 m radiusNo gas in chamber

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400 MJ TargetGraphite wall @ 8.25 m radius25 mTorr Xe in chamber

154 MJ TargetTungsten wall @ 6.5 m radiusNo gas in chamber

X-ray damage: need for rep-rated exposuresX-ray damage: need for rep-rated exposures

Single-shot results Single-shot results are not sufficientare not sufficient

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Single-shot results, (Cont’d.)Single-shot results, (Cont’d.)

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 should be quite similar

Rep-rated x-ray damage Rep-rated x-ray damage studies are neededstudies are needed

Data courtesy of Mark Tillack, University of California at San Diego532 nm lightfluence quoted is normal to beam

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

~250 nm removed over visible damage site

Peak-to-valley removal >500 nm

Considerable pitting throughout unshielded region(concentrated inobvious damage area)

Semi-regular“roughening” observed– seems consistentwith RHEPP results

xapper progress & plans presented by: jeff latkowski xapper team: ryan abbott, steve payne,...

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