1 BROOKHAVEN SCIENCE ASSOCIATES IXS@NSLS-II Workshop, February 7-8, 2008 Inelastic X-ray Scattering at NSLS-II IXS Program, and Current Project Beamline

1 BROOKHAVEN SCIENCE ASSOCIATES

IXS@NSLS-II Workshop, February 7-8, 2008

Inelastic X-ray Scattering at NSLS-II

IXS Program, and Current Project Beamline DesignYong Cai

With contributions by John Hill, Xianrong Huang, Zhong Zhong, Scott Coburn (NSLS-II)Alfred Baron (RIKEN), Yuri Shvyd’ko (APS),

Alex Babkevich and Nigel Boulding (Oxford-Danfysik)IXS@NSLS-II Workshop, February 7-8, 2008



IXS: Current Status

• A powerful (but weak) probe offering energy and momentum resolved information on dynamics and excitations in condensed matter systems

• Practical applications with highly successful state-of-the-art implementation at ESRF, SPring-8 and APS

• Broad areas of applications, including but not limited to the followings: Lattice dynamics – Phonons in solids, vibration modes and relaxation processes in

disordered systems: routinely operational at ~1meV resolution with ~109 photons/sec at ~20keV using symmetric backscattering crystal optics

Charge dynamics – Plasmon in simple metals, complex electronic excitations in strongly correlated systems: best resolution at ~50meV with ~1011 photons/sec at ~10keV for the most demanding experiments

Element specific applications – Chemistry and materials science, materials under extreme conditions of pressure and temperature: x-ray Raman scattering, x-ray emission and absorption spectroscopy by partial fluorescent yield at low resolution (~300meV or lower)



IXS Opportunities at NSLS-II

• Key scientific drivers identified thru community inputs (CDR, user workshops) 0.1-meV scientific case: filling the gap between high and low frequency probes

• Visco-elastic crossover behaviors of disordered systems and fluids• New modes in complex fluids and confined systems• Collective modes in lipid membranes and other biomolecular systems

1-meV scientific case:• Relaxation processes in disordered systems (glasses, fluids, polymers …)• Phonons in single crystals, surfaces, thin films, high pressure systems, small samples• Exotic excitations in strongly correlated systems

10~50-meV (including lower resolution) scientific case:• Non-resonant and resonant inelastic scattering on charge dynamics• X-ray Raman scattering, x-ray emission and absorption spectroscopy by partial

fluorescent yield combined with small beam for small samples of micrometer scale, high pressure, high fields, low and high temperature …

• High flux experiments with low(er) energy resolution



Scientific Mission of the Project Beamline• Develop advanced instrumentation that enables IXS experiments at extremely high

resolution of 0.1 meV at ~10 keV – a key goal for NSLS-II. • Why 10keV, as opposed to 20keV or higher?

Technical merits: higher brightness and flux for NSLS-II Scientific merits: better momentum resolution for a given solid angle, or the same

momentum resolution for larger solid angle Counting efficiency: a complex issue,

sample and optics dependent, requirecareful evaluation

Possible scheme based on highly asymmetric backscattering optics proposed by Yuri Shvyd’ko working at 9.1keV, require considerable R&D(more from Xianrong Huang and Zhong Zhong’s talks)

What are the alternatives?



Specifications and Requirements • Radiation source

Provide flux > 1010 phs/s/0.1meV at 9.1 keV, to provide > 109 phs/s/0.1meV at sample, require beamline overall efficiency > 10%

Essential source size and divergence stability, vibration and thermal stability for achieving the 0.1meV resolution (more from XianRong Huang’s talk)

• Beamline and Endstations Two end stations, one with 0.1meV and the other with 1meV resolution Primary beam energy at 9.1 keV to match scheme for achieving 0.1meV resolution Beam energy tunable over 7~12 keV for added flexibility (e.g., other refractions) Energy scan range: order of 0.1 ~ 1eV, appropriate for the excitations to be studied Momentum resolution: 0.1 ~ 0.4nm-1 at 9.1keV Momentum range: up to 80 nm-1 to cover typical BZ sizes, ~120º at 9.1 keV Spot size: ≤ 10 μm (H) x 5 μm (V), required for high pressure experiment Sample environments: crystal alignment capability, handling of small samples of

micrometer scale, high pressure, low and high temperature (4-800K), …, etc.



Overall Beamline Layout

1.0meV Endstation*

- CDDW HRM (0.7meV)

- CDW Analyzers (0.7meV)

- larger q range (~80nm-1)

* (not in the project scope)

0.1meV Endstation

- CDDW HRM (0.1meV)

- CDW Analyzers (0.1meV)

- 0.1nm-1 q resolution

- limited q range

FOE

- HHL DCM

- VFM / VCM

KBKB

HRMHRM

DCMVFM VCM

Beamline occupies a high-β straight section

R-wall: 28.3m

Walkway: 60.8m



Optical Scheme for 0.1meV

• CDDW mono to achieve 0.1meV with ~100µrad angular acceptance

• Multilayer mirror to achieve 5~10mrad angular acceptance for CDW/CDDW analyzer

~100μradacceptance

< 5:1 focusing

Si(111)

~20μrad divergence

Side viewSi(800)

Si(220)

Si(800)

6 810 104 tan

e

H

E

E

Δθe = ~ 5μrad

E = 9.1keV for Si(800)

ΔE = 0.1 meV, φ = 89.6°



~10 cm

CDDW analyzer with ~0.1mrad acceptance

We hope the beam here is a slightly focused beam with divergence ~0.1mrad and beam height ~50 µm

E = 9.1 keV

We hope the mirror length to be ~10 cm. It can be either a (1) laterally graded multilayer or (2) a parabolically / elliptically bent periodic multilayer

Multilayer Mirror for Analyzer• Requirements:

100:1 demagnification (from 10mrad to 0.1mrad)10mrad angular acceptanceGreater than 50% efficiencyPossibility for parallelization of data collection



Conceptual Beamline Layout

• Multilayer mirror with 100:1 demagnification to provide 10mrad (vertical) angular acceptance for analyzer ~10m arm length



Experimental Floor Layout

25m

~61m + 2m (possibly)

~53m• Space may be sufficient for only one

end station based on current scheme and 10mrad angular acceptance for analyzer

• Another ~8m may be required for a second end station with 5mrad angular acceptance for analyzer, space for mirrors and phase plates

BM line

ID line



Insertion Device

• U20 (IVU), or U14 (SCU) on a high-β straight section Figure of Merit: Flux / meV – provide flux > 1010 phs/s/0.1meV at 9.1 keV

Name U20 U14

Type IVU SCU

Period (mm) 20 14

L (m) 3.0 2.0

No. Periods 150 143

Bmax (T) 0.97 1.68

Kmax 1.81 2.20

Tot. Power (kW)

8.024 16.08

On-axis PD (kW/mrad2)

62.65 103.7

* U20: baseline device



Insertion Device Optimization• Optimize to maximize flux at 9.1keV: magnet period vs length vs minimum gap

Until superconducting devices become an option, the U20-5m seems to be the best option

Basic Undulator Parameters #1 #2 #3 #4 #5Baseline Proposed Proposed Proposed Proposed

Name U20-3m U22-6m U21-4.5m U20-4.5m U20-5mType PMU PMU PMU PMU PMUPeriod (mm) 20 22 21 20 20Length (m) 3 6 4.5 4.5 5No. of Periods 150 272 214 225 250Minimum gap (mm) 5 7.5 7.5 7 7Bpeak (T) 0.969 0.725 0.85 0.88 0.88Keff 1.81 1.4893 1.66671 1.64336 1.64336Minimum 5th harmonic energy, linear mode (eV) 8099.45 9210.20 8518.10 9091.00 9091.00Total power (kW) 8.024 8.955 9.244 9.922 11.02Power density (kW/mrad2) 62.65 84.32 78.15 85.02 94.47

Performance at 9.1keV, 5th harmonic (for 9.3m high-β straight, beta_x=20.8, beta_y=2.94)

Brightness (phs/sec/mrad2/mm2/0.1%BW) 4.68E+20 4.60E+20 4.25E+20 4.90E+20 5.42E+20Total Flux (phs/sec/0.1%BW) 8.00E+14 1.06E+15 1.01E+15 1.20E+15 1.35E+15Brightness ratio with baseline: 1.00 0.98 0.91 1.05 1.16Flux ratio with baseline: 1.00 1.33 1.26 1.50 1.69



Extended Long Straight

• It is possible to obtained one 15m extended long straight by extending one 9.3m high-β straight and shortening two adjacent 6.6m low-β straights of the current lattice• Preliminary solution indicates that it would be possible to put in two U20-5m devices with refocusing

magnet. Potentially more than triple (3.38 times) the flux compared to one U20-3m baseline device• There are accelerator issues (tune shift compensation, radiation shielding) and cost impact.

βx = 18.5, βy = 3.5 for extended LS

βx = 0.8, βy = 0.8 for short straights



Straight Section• High-β straight section (9.3m) is required for a long device

• Additional benefits associated with a high-β compared to a low-β straight section :• Bigger horizontal source size but smaller horizontal divergence, leading to smaller

horizontal photon beam size shorter horizontal mirrors• Lower power load within the central cone of the photon beam delivered to the first optics

heatload is more manageable for first optics, even for two U19 undulators.• Important: Flux within the central cone remains the same!

Photon beam size and power (one U19, at 9.1keV) thru angular aperture of 4(H)x4(V).

Distance, m

K Low-β High-β

Aperture (HxV), μrad2

Beam Size (HxV), mm2

Power, W

Aperture (HxV), μrad2

Beam Size (HxV), mm2

Power, W

30 1.71379.2 x 22.8 2.4 x 0.7

11829.2 x 20.0 1.0 x 0.6

38

30 0.981 65 21



First Optics Enclosure (FOE)• DCM: cryogenic cooled Si(111). • FEA analysis on first crystal of DCM shows < ±5 µrad slope error at 115W heat load• For high-β straights, thermal effect would be less a problem (lower heat load).

Cooled

fixed

mas

k

Bremsst

rahlun

g

collim

ator

Blade B

PM

White b

eam sli

t

DCM

Diamon

d wind

owCooled

flu. s

creen

White b

eam &

Bremsst

rahlun

g stop

Quadra

nt BPM

VFM



Beamline Collimating and Focusing Optics

• Candidate: Bimorph mirrors • Supplied by SESO

• Multiples of 150mm in length

• Each segment can be bent independently (2 electrodes for cylindrical and 4 electrodes for elliptical)

• Bimorph can in principle correct its own tangential polishing slope errors and also correct for tangential errors introduced by other optics

• KB bimorph pair can in principle correct for sagittal and tangential errors

• Small beam size allows short mirrors with small incident angle (2.5mrad) and Si substrate for high reflectivity at 9.1keV



Shadow Ray Tracing with FEA Results

Case Model , LN2 cooled DCM(εx = 0.55nm-rad)

Spot size , μm(No distortion)

Flux, ph/sec (No distortion)

Spot size, μm(W/ distortion)

Flux, ph/s/eV (W/ distortion)

1 Lo-β, K=0.981, 1 U19-3m, 22W 2.0 x 1.8 1.50 x 1013 2.1 x 2.1 1.49 x 1013

2 Hi-β, K=0.981, 1 U19-3m, 7W 7.0 x 1.8 1.49 x 1013 7.0 x 2.0 1.49 x 1013

2a Same as 2, but water cooled 7.0 x 1.8 1.49 x 1013 16 x 7.4 1.51 x 1013

3 Lo-β, K=1.714, 1 U19-3m, 71W 2.0 x 1.9 2.88 x 1013 2.3 x 4.2 2.81 x 1013

3a Same as 3, but hot spot at 125K 2.0 x 1.9 2.88 x 1013 2.1 x 0.5 2.92 x 1013

3b Same as 3, but 2 U19-3m, 115W 2.0 x 2.0 5.80 x 1013 2.9 x 5.9 5.14 x 1013

4 Hi-β, K=1.714, 1 U19-3m, 22W 7.1 x 1.9 2.81 x 1013 7.0 x 3.4 2.79 x 1013



0.1meV Endstation Layout

Features•Pre-focusing (up to 5:1) to reduce length of collimator (C) crystal for 0.1meV HRM •KB mirrors after HRM for micro focusing to ≤ 10(H) x 5(V) μm2

•Temperature scan of energy transfer•Analyzer(s) based on the CDW or CDDW scheme with multi-layer focusing mirror(s) to achieve 10(H)x5(V) mrad2 angular acceptance•High (0.1nm-1) momentum resolution in forward scattering, limited scan range•Extremely clean energy resolution function

Instrument Intensity at Sample

NSLS-II, 3m U19 > 1x109 ph/sec/0.1meV (estimate)

APS, 5m U30 1x109 ph/sec/1meV

SPring-8, 4.5m U32 5x109 ph/sec/1meV



1meV Endstation Layout

Features•Pre-focusing (up to 2:1) to reduce length of collimator (C) crystal for 0.7meV HRM •KB mirrors after HRM for micro focusing to ≤ 10(H) x 5(V) μm2

•Temperature scan of energy transfer•Analyzer(s) based on the CDW or CDDW scheme with multi-layer collimating mirror to achieve 10(H)x5(V) mrad2 angular acceptance•Large momentum scan range (up to 80nm-1) for single crystal studies, require phase plates•Extremely clean energy resolution function

Instrument Intensity at Sample

NSLS-II, 3m U19 > 1x1010 ph/sec/1meV (estimate)

APS, 5m U30 1x109 ph/sec/1meV

SPring-8, 4.5m U32 5x109 ph/sec/1meV

A natural step in achieving 0.1meV resolution



Schedule Summary

• 2008~2011: Design phase, interaction with BAT, actively pursue 0.1meV R&D

• 2011~2013: Construction phase, long lead-time procurements to begin in final design stage

• 2014: Integrated testing phase, to be ready to take beam



Outstanding Issues

• Multiple undulators on extended straight for more flux (depends on AS design)tuning compensation for beam dynamics, heat load on second undulator, cost impact

• CDDW scheme to achieve 0.1meV HRM: Substantial R&D effort required (proof of scheme by end 2010, final design phase)

• Multilayer mirror to achieve 10mrad angular acceptance for CDW / CDDW analyzers: (proof of scheme by early 2010, preliminary design phase)

• Risks with current approach and mitigation strategies:1meV is promising, 0.1meV remains a major challenge, aggressively pursue the R&D and seek alternatives

• Possibility to combine two end stations into one: energy resolution tuning

• Parallel data collection: multiple analyzers, area detector

Your inputs are important!

Documents

1 BROOKHAVEN SCIENCE ASSOCIATES IXS@NSLS-II Workshop, February 7-8, 2008 Inelastic X-ray Scattering at NSLS-II IXS Program, and Current Project Beamline