Abstract:

1. Prospects for IXS at an Energy Recovery LINAC light source Abstract: An Energy Recovery LINAC (ERL) based hard x-ray light source is being planned for construction at Cornell. This 5GeV,100mA facility will generate x-ray beams of unprecedented average spectral brightness. Although it is correct to think of ERL sources as optimized for high coherence and nanobeam science, they can deliver ultra-high spectral flux because the small emittance and energy spread maximize efficient operation of very long, short period undulators [1]. For example focused flux from a 20m ERL ID at 21.75KeV will be more than 100 that from a 3 ID upgrade considered for APS Sector 30 and at 9.1KeV (for CDW/CDDW optics) it would be almost 40 times that of a 5m NSLS-II U20 ID [2].The ERL will enable pushing beyond the horizon of inelastic scattering studies in biology, geology, chemistry and materials science. With a second injector, the Cornell ERL could simultaneously feed an x-ray free electron oscillator (XFELO) [3]. The talk will introduce the ERL, provide an overview of facilities with emphasis on IXS, and focus on new experiments that will become feasible. In particular we can envision: IXS microscopy, selective measurements on single crystals within powder diffraction samples, advances in DAC based high pressure science, and studies of new classes of biological systems. Figure: Cornell ERL plan showing major components and 14 undulator beamlines, with 3 IDs up to 25m. The experimental floor is indicated in pink, while SC Linacs are in yellow. References [1] KD Finkelstein, et.al., J. Phys.Chem. of Solids 66, 2310 (2005). [2] Estimate for 2-d focusing, 50m from source, based on specifications from each facility [3] K-J Kim, Y Shvyd’ko, S Reiche, PRL 100, 244802 (2008).

2. Prospects for IXS at an Energy Recovery LINAC light sourceK.D. Finkelstein, S. M. Gruner, G. Hoffstaetter, D. BilderbackCornell Laboratory for Accelerator-based Sciences & Education (CLASSE) • Outline of talk: • Characteristics of an ERL pertinent to IXS • Opportunity for long undulators: novel designs, beamline engineering • Expected spectral characteristics in comparison to other sources • Expanding the “phase space” for IXS measurements • Niche applications for ERL-based IXS • Summary& invitation For ERL overview please visit poster N4: “The ERL: A Coherent, Hard X-ray Source”

3. Acknowledgements To the entire ERL development team at: Cornell Laboratory for Accelerator-based Sciences & Education (CLASSE) Special thanks for continuing guidance on IXS for future ERL light source: P. Abbamonte, A. Baron, B. Larson, M. McMahon, L. Pollack, K, Shen, Y. Shyvd’ko Thank you to the organizers of this great meeting (IXS-2010) !

4. Characteristics of an ERL pertinent to IXS • ERLs are very flexible: • e- bunch properties determined by injector → short pulses, round beams • Twiss parameters flexible & adjustable → tailor e- trajectory to optimize photons • flexible e- bunch structure & filling pattern → opportunity for FEL beamlines • no separate injection orbit → constant current, very small transverse ID aperture These properties may be compatible with XFELO (at lower rep. rate) Standard run mode, best for IXS FEL capabilities, compatible with routine ERL operation, being explored.

5. ERL opportunities – long undulators, simplify beamline engineering, novel ID designs 1) Smaller dγ/γ & 2d emittance optimum for long undulators: 1000 period undulators should pay big dividends 2) Very narrow harmonics in energy and angle: more ‘useful flux’ thru aperture & higher flux/Watt 3) New ID designs already under development: Prototype “Delta undulator” built and tested (with 50-70MeV electrons) at Accelerator Test Facility - Brookhaven National Laboratory.

6. 1) Undulator harmonic energy width depends on: length (N*λID), e- divergence (ε/β) , electron energy spread (δγ/γ) for K~1, width is approximately*δЕ/Е ~ √[ (1/nN)2 + (2δγ/γ)2 + (γ2(ε/β)/(1 + K2/2))2] n is harmonic number. ERL δγ/γ ~ 20% of storage rings (dominates emittance term) * following Attwood

7. 2) Benefit of narrow harmonics: high ‘useful flux’ & modest power(case of no focusing & combined harmonic power) 18mm period, 25m ERL “delta” ID; 3rd harmonic at 50m 20mm period, 4.5m Spring8 ID; 1st harmonic at 28m (Baron) SPring8 BL35XU for ERL-IXS

8. 3) Novel IDsenabled by small, round e- beam size, no injection orbit Delta ID: fixed gap, fully polarization tunable Fields of Delta: Helical: + 40% Planar: +100% SC - ID: offers higher fields → smaller period &/or wider K-range (realization is challenging!)

9. Average spectral brightness of ERL Delta ID (18mm period, 25m length) relative to existing sources & NSLS-II U20, 3m ID. Calculations based on Table 2 in New Journal of Physics 12, 035011 (2010) (on coherence applications)

10. 3rd harmonic flux-energy tuning range( for 25m long “Delta” ID with 18mm period) Covers full range of energies for high resolution IXS !

11. Where will ERLs shine ? higher spectral flux: boosts count rate from weak scattering systems extends IXS to high Z materials round beam emittance: no drop in brightness with vertical polarization no ‘blind spot’ for scattering near 90 degrees large Q (horizontal scattering geometry) studies at subatomic length scale small ROUND source ideal for high throughput focusing: extends practical range of high pressure studies, IXS microscopy, select single grains within sample brilliance, high peak current (short pulses) & small δE/E are minimal requirements for XFELO, XFEL short pulses might be used to: reduce signal to noise of sample chamber (2ps<->0.6mm)? pump-probe IXS ? Coherent phonons ?

12. Spectral flux: ERL & potential future beamlinesunits:1014 p/s/0.1%bw

13. Expand the “phase space” for IXS measurements By delivering 6 - 12 times more spectral flux, ERLs will make (R)IXS on high Z systems more practical. from - ESRF ID 28 “Primer on IXS” • Ratio of total number of photons (Thomson) scattered to those lost through other processes (predominantly photoelectric absorption) in sample of optimum thickness 1/μas a function of atomic number. (example for 1meV resolution studies).

14. Focused flux (photons/sec/μm2) at resolution specified Think IXS microscope ! • ERL Delta flux calculations for helical mode below 12.4 KeV & planar above. • APS upgrade & Spring8 numbers from table provided by A.Q.R. Baron • NSLS-II based on Feb.2008 workshop & SPECTRA 8.0 calculation. Numbers based on p/s/eV/mm2 50m from source, 2-d focusing at 100:1 (optics accept ½ mm by ½ mm) ALL source sizes based on publishedemittance, beta, and photon energy

15. High Pressure DAC studies • Sample volume Т Asampleis the region of uniform pressure IXS signal • NIXS ~I0(p/s/area) ρТ Asample (∂2σ/∂ΩЕ) ΔΩΔЕ e-μТ • [ρscatterers/volume, absorption coefficient μ , ∂2σ/∂ΩЕ ~ |f(Q)|2 for single species] • IFAsample ~ D2 • and T ~ D then • NIXS~ D3 I0 |f(Q)|2 • D is often [1] inversely proportional to pressure P so, • to obtain comparable signal • I0 ~ P3/ |f(Q)|2 • The ERL delivering 100 times higher I0 (then today’s sources) will enable studies: • at up to 5 times higher pressure (for given |f(Q)| ) • and/or • push frontiers for high pressure studies for low Z materials For example the “holy grail” of low Z materials is hydrogen. The structure has been studied with x-rays to about 30GPa… D [1] A.L.Ruoff, H. Xia, Q. Xia, Rev SciInstrum. 63, 4342 (1992)

16. The phase diagram illustrates how much further we must go to answer fundamental questions about high pressure - temperature phases of hydrogen and some mixtures. Potential for ERL-based pressure studies

17. Build in new science capabilities: using TDS to guide IXS measurements Duel energy resolution monofor switching incident beam between 1eV (for TDS) and 1meV (for IXS). For 1eV downstream (partial blue) crystal of high resolution mono is removed and partial red inserted. For 1 meV measurementsarrangement is reversed. Thermal diffuse scattering (TDS) from silicon (a, b). Model with (c, d) & without (e, f) optical branches [2]. [2] R. Xu, T.C. Chiang, Z Kristallogr. 220, 1009 (2005).

18. Imaging nonequilibrium atomic vibrations with x-ray diffuse scattering M. Trigo, Y. M. Sheu, J. Chen, V. H. Vishwanath, T. Graber, R. Henning & D. A. Reis arXiv:1006.3990v2

19. A similar arrangement might be used to selectively measure oriented single crystals within a powder Possible optical arrangement for IXS DAC studies of crystallites located/oriented by Laue diffraction. High heat load diamond mono (red) passes energy required for IXS. First (thin) diamond is misaligned relative to second for beam transmitted to multilayer mono (blue outline). MML passes full harmonic width (FWHM~60eV) for Laue-alignment of single crystal. Refractive lens (green) focuses beam at DAC. Diamond is realigned to direct beam to high resolution mono (HRM) & last HRM crystal (blue hatched) must be accurately inserted to direct beam along MML beam path.

20. For Alfred:

21. ERL experimental facility: 14 undulatorbeamlines 3 with IDs up to 25m long

22. IXS concept beamline – 25m undulator and 50m for hutches space requirements based on SPring8 BL35XU

23. Potential location for XFEL-Oscillator planned 25m ID

24. Summary and Invitation Where the ERL will shine: high-Z materials, weak scattering (electronic excitations), DAC and micro-sciences, dynamics & phase transitions of liquids and glasses The ERL will potentially support FEL extensions (XFELO ?) WE need your interest and scientific & technical guidance. Please attend workshops to be held at Cornell in June 2011…

25. Example: Soft x-ray SASE FEL (optical length 50m) kick subset of electron bunches from regular ERL beam to FEL line compress to 100fsec pass through special ID (several segments) Yield: x-rays at 1.86KeV (1st H) 100fsec pulses bandwidth 0.12% divergence 9.3urad 3.7e9 photons/pulse (peak brightness ~2e27)

28. Accelerating bunch Returning bunch Energy Recovery Linac A superconducting linac is required for high energy recovery efficiency