0.1-meV Optics Update

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0.1-meV Optics Update
Yong Cai Inelastic X-ray Scattering
GroupExperimental Facilities Division, NSLS-II
Experimental Facilities Advisory Committee
Meeting April 23-24, 2009
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The IXS Group

• Current Members
• Xianrong Huang, 0.1 meV crystal optics
• Marcelo Honnicke, multilayer mirrors for analyzer
  system
• Jeff Keister, RD beamline operation, upgrade and
  support
• Zhong Zhong, NSLS DI beamline spokesperson (M)
• Scott Coburn, engineering design (50)
• Leo Reffi, mechanical design (on loan from design
  group)
• Bill Struble, crystal cutting and lab support
• Yong Cai, IXS beamline, group leader
• Future Members (per staffing plan)
• Postdoctoral Fellow (Crystal fabrication, optics
  testing, etc.) offer accepted, to start around
  June 1
• Scientific Associate (Crystal fabrication lab)
  Searching
• Beamline Scientist (IXS beamline) - Searching

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Outline

• Summary of progress to date, issues plan
• Current optical scheme and technical challenges
• Near-term milestones and longer-term plan
• Summary

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Summary of Progress to Date, Issues Plan
Since last EFAC Meeting (May 5-7, 2008)

• Major progress in building up the infrastructure
  to support the RD program
• RD beamline and optics test end station at NSLS
  (X16A)
• Crystal fabrication labs (Bldg 703)
• RD activities have been focused on gaining a
  better understanding of the technical
  requirements and challenges of the optics
• 0.1meV crystal optics
• Multilayer mirrors
• Issues and plan
• Crystal fabrication capabilities (equipment
  staffing)
• Access to more advanced light source(s) for
  prototyping

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0.1meV Crystal Optics

• CDW and CDDW optics schemes at 9.1 keV proposed
  by Yu. Shvydko, verified by our dynamical theory
  calculations (Xianrong Huang)

CDW
CDDW

• Large angular acceptance (gt100 µrad)
• High efficiency (50)
• Sharp tails (Borrmann effect), more important
  than resolution!

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Beamline and Spectrometer Optics Layout
20 µrad Divergence

• Major parameters determined and verified for E
  9.13 keV, ??e 5 µrad, and h 0.5 mm

?E of CDW ?E of CDDW Te ( 90 f) Length of D
2 meV 1 meV 4.5 120 mm
0.7 meV 0.3 meV 1.5 380 mm
0.2 meV 0.1 meV 0.4 1400 mm!

• Comb crystal proposed by Yu. Shvydko a possible
  solution to the long D crystal length, but a
  major challenge to fabricate (in progress)

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Comb Crystal Fabrication

• Current approach employed by APS
• Cut directly from a monolithic crystal.
• Polishing the diffraction surface a major
  challenge.
• Alternative approach to be explored
• Prepare reference Si(100) surface from a
  monolithic block
• Cut individual fins allowing fine polishing of
  diffraction surface
• Align individual blocks using reference surface
  on symmetric backscattering Si(800) reflection
• Mechanical positioning a challenge, but more
  solvable

As-cut surface roughness 35.4 nm by AFM
Reference Si(800) reflection
Fine polishing
T
Reference surface
100mm
5mm
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CDDW for 1meV Channel Cut

Channel-cut (grazing 7?)

• No need for long D crystal
• Switchable between 0.1 and 1 meV

• Require incident beam collimated to 20 ?rad no
  problem for monoanalyzer needs high-precision
  mirror.
• CC causes 20 efficiency loss

Tails sharper than Lorentz
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Other Major Technical Challenges

• Lattice homogeneity of the crystal ?d/d ?E/E
  10-8 (0.1 meV/10 keV)
• Temperature uniformity and stability ?T 4 mK
  (?d/d a?T and thermal coefficient of Si
  a2.56?10-6 K-1)
• Surface qualityslope errors (straightness of
  surface) lt 10 µrad, crystal bending (due to
  mounting or gravity sag) lt 0.2 µrad, surface
  roughness (causes diffused scattering) lt 2 nm
• Crystal angular stability lt 0.2 µrad as a
  result of energy tuning by angular rotation,
  independent of resolution 0.1 1 meV,
• CDW/CDDW analyzer requires 501001 multilayer
  focusing mirrors for 510 mrad acceptance

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Angular Stability

• Energy Tuning by D crystal rotation ? Tuning
  rate 0.07 meV/µrad

• This implies also
• Angular vibrations of C,W, D all change ?, must
  be stable lt 0.2 ?rad (independent of targeted
  energy resolution ?E)
• Lattice bending due to gravity sag or mounting
  changes ?, so must be lt 0.2 ?rad, for all C, W,
  D.

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Laterally Graded Multi-layer Mirror
0.2 0.3 mm
CDW or CDDW

• Design Objectives
• Angular acceptance 5 mrad x 5 mrad
• To retain a q resolution of 0.01 nm-1
• Corresponding to 0.1 mrad in horizontal
  acceptance at 9.1 keV or 20 µm transverse width
  at 200 mm from source. Possible solution use
  area detector!
• Laterally projected source size due to sample
  thickness may be a limiting factor, but not a
  severe problem due to lessen q resolution
  required at higher q. (0.1 mrad 20 µm projected
  source size at 200mm)

Strip Detector
0.1 mrad
5 mrad
Horizontal Scattering Plane
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Ideal Mirror Figure

• Parabolic ellipsoid (focusing collimator)
• Horizontal collimation to 0.1 mrad or better is
  required in order to retain the q resolution!
• Vertical focusing (up to 0.1 mrad) to minimize D
  crystal length for analyzer, but may limit the
  horizontal q resolution at low q.
• Vertical collimation to less than 20 µrad may
  allow the use of 2nd channel cut for resolution
  switching between 0.1 and 1 meV for the analyzer,
  and/or possible energy dispersive and q resolved
  detection in the vertical direction with an area
  detector
• A real challenge to make!

Sample first focus (f1)
Sample
CDW/CDDW
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Alternative Mirror Configurations

• A single toroidal mirror to approximate the ideal
  surface
• Montel optics parabolic (collimator) in a double
  bounce geometry (involving beam inversion of L-R
  and U-D)
• KB configuration
• A single mirror only for vertical
  focusing/collimating
• Horizontal angular acceptance of C crystal
  3mrad!Horizontal energy dispersion of D crystal
  E(f) E0(1-f2/2)

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Other Works Accomplished

• Multilayer parameters determined and optimized
  both for parabolic and elliptical figures.
• Mirror specifications for a non-graded flat
  surfaceSi or B4C layer 1.5 nm, W layer 1.0 nm,
  100 bi-layers on Si substrateTheoretical peak
  reflectivity 85
• Figure specifications
• In-house ray-tracing codes developed to examine
  performance of the multilayer mirrors including
  effects of slope error, roughness, and interlayer
  thickness fluctuation (dd/d).
• Actively in contact with possible vendors for
  test mirrors
• Test plan using RD beamline at NSLS developed.

Figure P (mm) Tm (rad) dx (mm) dy (mm) d1 (nm) d2 (nm)
Parabolic 0.30796 0.02775 36.17 1.002 2.3495 2.5710
Elliptical 0.30193 0.02775 35.94 0.953 2.3513 2.5683
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First CDW-CDW Test at NSLS

• Proof of Principles
• Collimation effect of C crystal
• Enhanced Bormann transmission of W crystal
• Most importantly, the dispersion effect of the D
  crystal
• ?E 10 meV achieved, possible causes being
  analyzed

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New CDW-CDW Test

• Aim for a more controlled study of the optics to
  understand conditions to achieve the targeted
  energy resolution.
• Verify sharp tail in resolution function with new
  optical path
• New C/W crystal to minimize strain

Bill Strubles first crystal With help from Shu
Cheung
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Optics Test End Station
D crystal in oven
C/Wcrystal

• Current components designed to test CDW-CDW
  scheme with temperature control ovens
• Include a double-crystal diffraction / imaging
  stage for characterizing crystal quality
• Flexible and adaptable for other schemes (e.g.,
  CDDW, comb crystals, )
• Most components fabricated and assembled, and
  being installed on RD beamline

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Temperature Control Oven
Room T
D crystal
Outer Oven, ?T 0.5 mK
Inner Oven, ?T 0.25 mK
15 hr

• First oven tests passive controlling on both
  inner (45 C) and outer (35 C) ovens.
• Excellent stability uniformity to be tested.

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Dedicated RD Beamline at NSLS

• An existing PRT beamline, revived after major
  clean-up and repair effort of shielding, vacuum,
  safety and user interlock, beamline and
  endstation control, to allow initial testing of
  0.1 meV resolution optics
• Existing beamline optics (a 11 focusing mirror
  and a DCM) found to be functional but required
  optimization, to be upgraded within 6-12 months.
• Beamline granted operation status since April 10,
  2009 after beamline review and readiness
  walkthrough. (took just 1 year from inception to
  operation, but still a lot of work!)

Endstation
Mirror(11)
Source
Mono
RD beamline assembly
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Crystal Fabrication Labs
EQUIPMENT

• Two labs being fit out, to be completed in April
• Cutting / Lapping Lab major equipments
• Crystal Diffractometer (NSLS equipment)
• Mark Blade Saw (NSLS equipment)
• Diamond wire saw (delivered)
• Lapping machine (delivered)
• Strasbaugh Spindle Polisher (rough polishing)
• Polishing / Etching Lab major equipments
• ADT dicing saw (delivered)
• Strasbaugh CMP polisher (superfine 0.1 nm)
• Strasbaugh Spindle Polisher (fine polishing)
• Chemical etching hood and wet bench
• Partial operation in April
• Need to consolidate fabrication equipment and
  streamline fabrication process
• Too few staff with expertise in polishing and
  etching

X-ray Diffractometer / Blade Saw / Diamond Wire
Saw
Lapping Machine / Spindle Polisher / CMP
Polisher
High-precision dicing saw for Comb crystal
fabrication
Etching Hood
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Overall Strategy and Near-Term Milestones
Overall strategy and timeline
2009
2010
2011
CDW/CDDW prototypes 1meV?0.5meV?0.1meV Comb
crystals fabrication and test Design and Develop
collimating multilayer mirrors
0.1 meV prototype spectrometer
Date Item Status
June 2009 Actual measurement of the resolution function for CDW scheme. Looking for a sharper tail may be more important than the actual resolution. Still on schedule, waiting on completion of end station. Key areas to watch new control system, ovens test, X16A mirror and mono.
Sept 2009 Fabrication and testing of first comb crystal cut for 1meV. Energy resolution and efficiency measured. Still on schedule, need to push for bldg 703 labs. Hire of scientific associate to fill knowhow gap (etching and polishing). Short-term outsourcing
Sept 2009 Fabrication and testing of multilayer mirror. Demonstrate required specs can be met. In progress, potential road block the on-time delivery of mirror
Nov 2009 Demonstration of the CDDW/CDDW scheme (beam pass thru all optics) Area to watch, continue investigation of alternative schemes
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Longer-Term Plan Milestones

• 2010
• Develop a prototype with 1meV resolutionStrategy
  being considered a Partner User Proposal with
  APS for Sector 30
• Demonstration experiments on Plexiglas with 1meV
  resolution (real test of energy resolution and
  tail by scattering rather than diffraction)
• Full work on CDDW prototype to test 0.5 meV
  resolution (with comb crystals), including
  detailed exploration of crystal quality (defects,
  impurities, inhomogeneities), fabrication issues.
• Test and improve collimating/focusing multilayer
  mirrors
• Seek alternative approaches if encounter
  unexpected showstoppers
• 2011
• Test and improve analyzer optics with multilayer
  mirrors
• Full work on CDDW prototype to test 0.1 meV
  resolution (with comb crystals)
• Finalize design

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Summary

• Excellent progress has been made in establishing
  the essential infrastructure to support the RD
  program.
• Initial test results of the asymmetric dispersion
  optics prove the working principles of the
  optics.
• Key technical challenges to achieve the 0.1meV
  resolution for both the monochromator and
  analyzer are now well understood and being
  addressed.
• Need to streamline crystal fabrication capability
  within the NSLS-II project, and for prototyping a
  1meV resolution instrument.
• A modified approach with intermediate staged
  goals may be necessary for the development of the
  IXS beamline.