National Synchrotron Light Source II

1. National Synchrotron Light Source II Hard Coherent X-Ray Beamline Lonny Berman EFAC Meeting, October 4th, 2007 with contributions by Alex Babkevich, Nigel Boulding, Scott Coburn, Simon Mochrie, Ian Robinson, Alec Sandy, Lin Yang

2. Scientific Mission • Application of hard (7–20 keV) coherent x-rays to the study of nanoscale dynamics and structure of complex materials • Equilibrium dynamics and fluctuations about the evolution to equilibrium in colloids, polymers, membranes, concentrated proteins, glasses, … • 3-D imaging of microscopic non-crystalline objects such as catalytically active materials, cavities within steel, defect structures in magnetic multilayers, cellular imaging Mark A. Pfeifer, Garth J. Williams, Ivan A. Vartanyants, Ross Harder, and Ian K. Robinson, “Three-dimensional mapping of a deformation field inside a nanocrystal,” Nature 442, 63 (2006) O. G. Shpyrko, E. D. Isaacs, J. M. Logan, Yejun Feng, G. Aeppli, R. Jaramillo, H. C. Kim, T. F. Rosenbaum, P. Zschack, M. Sprung, S. Narayanan, and A. R. Sandy; "Direct measurement of antiferromagnetic domain fluctuations," Nature 447, 68 (2007)

3. Beamline Requirements and Specifications • Coherent flux to supply photons to two different endstations that operate simultaneously, one for x-ray photon correlation spectroscopy (XPCS), one for coherent x-ray diffraction (CXD) • Energy range 7-20 keV using either tunable silicon double crystal monochromator or “pink beam” reflected from mirror • At 8 keV, coherent flux using a Si mono is 6x1012 ph/sec, and tranverse coherence lengths at 25 m from the source are 819 µm vertically and 65 µm horizontally (Ch. 3 of NSLS-II CDR) • Stability • Parasitically fluctuating signals contaminate XPCS time autocorrelation analysis • Parasitically fluctuating signals significantly complicate phase retrieval • Fixed secondary horizontal source intended to improve stability for these experiments • Long small angle XPCS station • “Smart” area detectors likely to have larger pixels than today’s • Long beamline for CXD • High demagnification focusing for CXD and large Q XPCS • Reduced flux density for radiation sensitive samples

4. Overall Beamline Layout CXD endstation 250 m from source XPCS endstation 50 m from source FOE

5. Conceptual Design - Beam Splitting • 2 secondary sources or pinholes in the FOE • Multiplexed operation creates twice as much beamtime • Small horizontal-bounce mirrors used to extract coherent fraction of the beam (in the horizontal) • 2× mirror deflections and long beamline creates sufficient horizontal clearance CHX FOE Beam Splitting Concept - Plan View White beam (WB) Hi-pass filter Pink beam Shutter Slit ½ Slit Mirrors = secondary source or pinhole 12 mrad WB Stop Power-reducing aperture

6. XPCS Beamline Layout endstation enclosure monochromator enclosure

7. CXD Beamline Layout endstation enclosure monochromator enclosure

8. Insertion Device • U19 undulator preferred (unless U14 is available) • High beta straight section • Brighter than APS by a factor of 7 at 10 keV under these conditions (U19, high beta); coherent flux is directly proportional to brightness • Useful upgrade is to add a second undulator in-line 20 m 30 m coherence-defining aperture at sample = 30 µm secondary source = 67 µm undulator source >~ 212 µm Filling of secondary aperture for XPCS beamline can only be accomplished if undulator source width >~ 212 µm, leading to the preference for a high beta straight section.

9. Front End Layout • Front end must include motorized adjustable apertures • Will typically be closed down to an opening no greater than 100 µrad x 100 µrad • Thereafter, separate beams of up to 20 µrad x 20 µrad each need to be extracted for the two beamlines (separation to be done in the FOE)

10. White Beam Components • Water-cooled silicon mirror and monochromator preferred for each beamline, to avoid vibrations associated with a cryo-cooling system (power density is ~100 W/mm2 but power in 20 µrad x 20 µrad is ~30 W) • Finite-element analysis and Shadow ray tracing were carried out (and are still underway) for various cases, involving use of one and two undulators, operating at low K and at high K • The results so far indicate that water-cooled optics will probably be acceptable, although the slope errors will still be noticeable and may have to be compensated using downstream focusing optics • Pink beam capability is preserved into both endstations

11. Specialized Beam Conditioning Optics • Focusing optics will sometimes be used in the two endstations, just before the experimental apparatus • For the XPCS endstation, a vertical focusing mirror (or kinoform lens) is desired to reduce the vertical coherence length in order to match the horizontal coherence length • For the CXD endstation, a two-dimensional focusing system (could be mirror-based, zone-plate-based, refractive-lens-based) is sometimes desired to focus the beam onto a nanometers scale sample

12. XPCS Endstation mirror or refractive lens sample chamber apertures 10 m flight path heavily pixellated area detector with on-board correlator electronics

13. CXD Endstation chamber containing zone plate or refractive lens, apertures, and sample positioner on goniometer possible area detector articulation scheme

14. Requirements Imposed on Conventional Facilities • Exquisite stability, particularly relative stability between the reference point at extraction and the reference point at distant endstation must be achieved. Floor vibration threshold should be same as for the main experimental hall, 25 nm rms for the range of 4-50 Hz. • Importance of relative vibrations between the two buildings is under study through detailed finite element analysis of wave propagation and interaction with the two structures. • Field data measurements from monitoring stations at the desired locations are being gathered to establish spatial variability of vibration environment at the site as well as its correlation characteristics.

15. Outstanding Issues • Several key design decisions still to be made (e.g. choice of focusing optics) • Studies of thermal distortions of optics are still underway • Distant endstation and building design need to be firmed up • Area detector for x-ray photon correlation spectroscopy does not exist and needs a lot of R&D (separately from project) • Instrument for coherent x-ray diffraction does not exist and needs a lot of R&D, particularly in the area of sample registration (to keep the sample always in the same spot in the beam as it is oriented on the diffractometer); XRadia is interested in developing such a system and undertaking the necessary R&D, and is already doing so for Argonne

16. Cost Estimate (Burdened and Escalated) Note: white beam mirrors and slits are in white beam components, downstream monochromators and focusing optics are in beam conditioning optics

17. Alternative Concepts • We are fixed on the design pathway described thus far, based on the CD-1 conceptual design, at least through the CD-2 review • In the course of elaborating the advanced conceptual design, alternative concepts came to mind • We believe that it is important that conventional SAXS should be accommodated in the XPCS endstation, especially because of the large demand for SAXS and the absence of a project beamline to accommodate it • And we also believe that it might be feasible to accommodate the needs of the CXD (out)endstation together with the needs of the hard x-ray nanoprobe (out)endstation through the same single beamline and (out)endstation, providing a route to significant cost savings, albeit requiring extensive re-design and cost estimate revisions of both project beamlines

18. Summary • Two beamlines, each extracting a coherent portion of the beam radiated by an undulator • Deflecting mirrors are used to separate the beams and deliver them to two independent beamlines that can operate simultaneously, one for XPCS and one for CXD • The CXD beamline needs to be long, and a separate building needs to be constructed to accommodate the distant endstation • Lots of R&D challenges that have to be addressed!