1 BROOKHAVEN SCIENCE ASSOCIATES 0.1-meV Optics Update Yong Cai Inelastic X-ray Scattering Group Experimental Facilities Division, NSLS-II Experimental

1 BROOKHAVEN SCIENCE ASSOCIATES

0.1-meV Optics Update

Yong CaiInelastic X-ray Scattering Group

Experimental Facilities Division, NSLS-II Experimental Facilities Advisory Committee Meeting

April 23-24, 2009


The IXS Group

• Current Members Xianrong Huang, 0.1 meV crystal optics Marcelo Honnicke, multilayer mirrors for analyzer system Jeff Keister, R&D beamline operation, upgrade and support Zhong Zhong, NSLS D&I 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


Outline

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


Summary of Progress to Date, Issues & Plan

• Major progress in building up the infrastructure to support the R&D programR&D beamline and optics test end station at NSLS (X16A) Crystal fabrication labs (Bldg 703)

• R&D activities have been focused on gaining a better understanding of the technical requirements and challenges of the optics0.1meV crystal opticsMultilayer mirrors

• Issues and planCrystal fabrication capabilities (equipment & staffing)Access to more advanced light source(s) for prototyping

Since last EFAC Meeting (May 5-7, 2008)


0.1meV Crystal Optics

CDW CDDW

2tan2eee

E

E

4ee

E

E

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

• Large angular acceptance (>100 µrad)

• High efficiency (~50%)• Sharp tails (Borrmann

effect), more important than resolution!


Beamline and Spectrometer Optics Layout

~20 μrad Divergence

ΔE of CDW ΔE of CDDW Θe (= 90˚ – φ) 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!

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

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


Comb Crystal Fabrication

• Current approach employed by APS:oCut directly from a monolithic crystal. oPolishing the diffraction surface a major challenge.

• Alternative approach to be explored:oPrepare reference Si(100) surface from a monolithic blockoCut individual fins allowing fine polishing of diffraction

surfaceoAlign individual blocks using reference surface on symmetric

backscattering Si(800) reflectionoMechanical positioning a challenge, but more solvable

As-cut surface roughness 35.4 nm by AFM

Reference surface

Fine polishing

Tilting (rad)

Reference Si(800) reflection

Θ

5mm 100mm


CDDW for 1meV + Channel Cut

Collimated 20rad

5

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

Channel-cut (grazing 7)

• Require incident beam collimated to ≤20 rad no problem for monoanalyzer needs high-precision mirror.

• CC causes ~20% efficiency lossTails sharper than Lorentz


• Lattice homogeneity of the crystal: d/d = ΔE/E ~ 10-8 (0.1 meV/10 keV)

• Temperature uniformity and stability: ΔT ≤ 4 mK (Δd/d = αΔT and thermal coefficient of Si: α=2.5610-6 K-1)

• Surface qualityslope errors (straightness of surface): < 10 µrad, crystal bending (due to mounting or gravity sag): < 0.2 µrad, surface roughness (causes diffused scattering): < 2 nm

• Crystal angular stability: < 0.2 µrad as a result of energy tuning by angular rotation, independent of resolution 0.1 – 1 meV,

• CDW/CDDW analyzer requires 50~100:1 multilayer focusing mirrors for 5~10 mrad acceptance

Other Major Technical Challenges


Angular Stability

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

• This implies also:oAngular vibrations of C,W, D all change , must be stable < 0.2 rad (independent of

targeted energy resolution E)oLattice bending due to gravity sag or mounting changes , so must be < 0.2 rad, for all

C, W, D.


Laterally Graded Multi-layer Mirror

CDW or CDDW

0.2

– 0.

3 m

m

• Design Objectives:Angular acceptance: 5 mrad x 5 mradTo retain a q resolution of 0.01 nm-1

o 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!

o 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)

5 mrad

0.1 mrad

Horizontal Scattering Plane

Strip Detector


z (m

m)

Ideal Mirror Figure

).999971.05100.(451001.84.38

2

2

2

y

xyz

CDW/CDDWSample

Sample – first focus (f1)

• 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!


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(φ) = E0(1-φ2/2)

Montel Optics (collimating)

0.2 m10 m


Other Works Accomplished• Multilayer parameters determined and optimized both for parabolic and

elliptical figures.o Mirror specifications for a non-graded flat surface

Si or B4C layer 1.5 nm, W layer 1.0 nm, 100 bi-layers on Si substrateTheoretical peak reflectivity: 85%

o 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 (δd/d).

• Actively in contact with possible vendors for test mirrors• Test plan using R&D beamline at NSLS developed.

Figure P (mm) Θm (rad) δx (mm) δy (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


First CDW-CDW Test at NSLS

C,W D

• Proof of Principles:o Collimation effect of C crystalo Enhanced Bormann transmission of W

crystalo Most importantly, the dispersion effect of the

D crystalo E = 10 meV achieved, possible causes

being analyzed

Tilting (rad)

ΔE = 10 meV


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 Struble’s first crystalWith help from Shu Cheung


Optics Test End Station

17

• 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 R&D beamline

C/Wcrystal

D crystal in oven


Temperature Control Oven

Room T

Outer Oven, ΔT ≤ 0.5 mK

Inner Oven, ΔT ≤ 0.25 mK

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

~15 hr

D crystal


Dedicated R&D 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 1:1 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!)

SourceMirror(1:1) Mono

R&D beamline assembly

Endstation


Crystal Fabrication LabsEQUIPMENT

X-ray Diffractometer / Blade Saw / Diamond Wire Saw

X-ray Diffractometer / Blade Saw / Diamond Wire Saw

Lapping Machine / Spindle Polisher / CMP PolisherLapping Machine / Spindle Polisher / CMP Polisher

Etching HoodEtching Hood

High-precision dicing saw for Comb crystal

fabrication

High-precision dicing saw for Comb crystal

fabrication

• Two labs being fit out, to be completed in April:Cutting / Lapping Lab major equipments:o Crystal Diffractometer (NSLS equipment)o Mark Blade Saw (NSLS equipment)o Diamond wire saw (delivered)o Lapping machine (delivered)o Strasbaugh Spindle Polisher (rough polishing)

Polishing / Etching Lab major equipments:o ADT dicing saw (delivered)o Strasbaugh CMP polisher (superfine ~ 0.1 nm)o Strasbaugh Spindle Polisher (fine polishing)o 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


Overall Strategy and Near-Term Milestones

CDW/CDDW prototypes 1meV0.5meV0.1meVComb crystals fabrication and testDesign and Develop collimating multilayer mirrors

Overall strategy and timeline:

0.1 meV prototype spectrometer

2009 2010 2011

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


Longer-Term Plan & Milestones

2010• Develop a prototype with 1meV resolution

Strategy 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


Summary

• Excellent progress has been made in establishing the essential infrastructure to support the R&D 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.

Documents

1 BROOKHAVEN SCIENCE ASSOCIATES 0.1-meV Optics Update Yong Cai Inelastic X-ray Scattering Group Experimental Facilities Division, NSLS-II Experimental