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

2 BROOKHAVEN SCIENCE ASSOCIATES 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 ~10 9 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 ~10 11 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)

3 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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

4 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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, require careful 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?

5 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 Specifications and Requirements Radiation source  Provide flux > phs/s/0.1meV at 9.1 keV, to provide > 10 9 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.

6 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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 KB HRM DCM VFM VCM Beamline occupies a high-β straight section R-wall: 28.3m Walkway: 60.8m

7 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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 ~100μrad acceptance < 5:1 focusing Si(111) ~20μrad divergence Side view Si(800) Si(220) Si(800) Δθ e = ~ 5μrad E = 9.1keV for Si(800) Δ E = 0.1 meV, φ = 89.6°

8 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 ~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 acceptance  Greater than 50% efficiency  Possibility for parallelization of data collection

9 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 Conceptual Beamline Layout Multilayer mirror with 100:1 demagnification to provide 10mrad (vertical) angular acceptance for analyzer  ~10m arm length

10 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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

11 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 Insertion Device U20 (IVU), or U14 (SCU) on a high-β straight section Figure of Merit: Flux / meV – provide flux > phs/s/0.1meV at 9.1 keV NameU20U14 TypeIVUSCU Period (mm)2014 L (m) No. Periods B max (T) K max Tot. Power (kW) On-axis PD (kW/mrad 2 ) * U20: baseline device

12 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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#5 BaselineProposed Name U20-3mU22-6mU21-4.5mU20-4.5mU20-5m Type PMU Period (mm) Length (m) No. of Periods Minimum gap (mm) Bpeak (T) Keff Minimum 5th harmonic energy, linear mode (eV) Total power (kW) Power density (kW/mrad 2 ) Performance at 9.1keV, 5th harmonic (for 9.3m high-β straight, beta_x=20.8, beta_y=2.94) Brightness (phs/sec/mrad 2 /mm 2 /0.1%BW) 4.68E E E E E+20 Total Flux (phs/sec/0.1%BW) 8.00E E E E E+15 Brightness ratio with baseline: Flux ratio with baseline:

13 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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. β x = 18.5, β y = 3.5 for extended LS β x = 0.8, β y = 0.8 for short straights

14 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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-βHigh-β Aperture (HxV), μrad 2 Beam Size (HxV), mm 2 Power, W Aperture (HxV), μrad 2 Beam Size (HxV), mm 2 Power, W x x x x

15 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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 mask Bremsstrahlung collimator Blade BPM White beam slit DCM Diamond window Cooled flu. screen White beam & Bremsstrahlung stop Quadrant BPM VFM

16 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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

17 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 Shadow Ray Tracing with FEA Results CaseModel, LN2 cooled DCM (ε x = 0.55nm-rad) Spot size, μm (No distortion) Flux, ph/sec (No distortion) Spot size, μm (W/ distortion) Flux, ph/s/eV (W/ distortion) 1Lo-β, K=0.981, 1 U19-3m, 22W2.0 x x x x Hi-β, K=0.981, 1 U19-3m, 7W7.0 x x x x aSame as 2, but water cooled7.0 x x x x Lo-β, K=1.714, 1 U19-3m, 71W2.0 x x x x aSame as 3, but hot spot at 125K2.0 x x x x bSame as 3, but 2 U19-3m, 115W2.0 x x x x Hi-β, K=1.714, 1 U19-3m, 22W7.1 x x x x 10 13

18 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, meV 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) μm 2 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) mrad 2 angular acceptance High (0.1nm -1 ) momentum resolution in forward scattering, limited scan range Extremely clean energy resolution function InstrumentIntensity at Sample NSLS-II, 3m U19> 1x10 9 ph/sec/0.1meV (estimate) APS, 5m U30 1x10 9 ph/sec/1meV SPring-8, 4.5m U32 5x10 9 ph/sec/1meV

19 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, meV 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) μm 2 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) mrad 2 angular acceptance Large momentum scan range (up to 80nm -1 ) for single crystal studies, require phase plates Extremely clean energy resolution function InstrumentIntensity at Sample NSLS-II, 3m U19> 1x10 10 ph/sec/1meV (estimate) APS, 5m U30 1x10 9 ph/sec/1meV SPring-8, 4.5m U32 5x10 9 ph/sec/1meV A natural step in achieving 0.1meV resolution

20 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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

21 BROOKHAVEN SCIENCE ASSOCIATES Workshop, February 7-8, 2008 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!