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.

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).

Prospects for IXS at an Energy Recovery LINAC light source

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.

Prospects for IXS at an Energy Recovery LINAC light sourceK.D. Finkelstein, S. M. Gruner, G. Hoffstaetter, D. Bilderback

Cornell 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 & invitationFor ERL overview please visit poster N4: “The ERL: A Coherent, Hard X-ray Source”

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) !

Characteristics of an ERL pertinent to IXSERLs 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

Table Error! No text of specified style in document.-1: ERL operating mode target parameters. An electron beam with a 4th set of characteristics for development work is envisioned. Simultaneous with X-ray operation in any of the above modes, a fast kicker will pluck specific bunches out from the main stream at ≤ 10kHz. Bunch charge can be up to 1nC, in which case the geometric emittance (h/v) is simulated to be 2600/37pm for an RMS bunch length of 100fs and a relative energy spread of 2.e-3.

Operating Modes A High Flux

B High Coherence

C - Short Bunch North Arc | South Arc

Energy (GeV) 5 5 5 Current (mA) 100 25 25

Bunch Charge (pC) 77 19 19 Repetition Rate (MHz) 1300 1300 1300

Geom. Emittance (pm) h/v 30 8 120/9 11/9 RMS bunch length (fs) 2000 2000 100 1000

Relative energy spread (1E-3) 0.2 0.2 2

Standard run mode, best for IXS

These properties may be compatible with XFELO

(at lower rep. rate)

FEL capabilities, compatible with routine ERL operation, being explored.

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.

for K~1, width is approximately*

δЕ/Е ~ √[ (1/nN)2 + (2 δγ/γ)2 + (γ2(ε/β)/(1 + K2/2))2 ] n is harmonic number.

1) Undulator harmonic energy width depends on: length (N*λID), e- divergence (ε/β) , electron energy spread (δγ/γ)

0 100 200 300 400 500 600 700 800 900 1000

0.002

0.02

3rd H. fractional energy width

APS condi-tions

ERL hi flux

ERL hi coh

# periods

dE/E

ERL δγ/γ ~ 20% of storage rings (dominates emittance term)

* following Attwood

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

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.22.0E+10

7.0E+10

1.2E+11

1.7E+11

"useful flux" @ 21.75KeV

flux/

meV

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.20

100

200

300

400

500

600

Power through aperture

aperture area (mm2)

Wat

ts

20mm period, 4.5m Spring8 ID; 1st harmonic at 28m (Baron)

for ERL-IXS SPring8 BL35XU

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.21.0E+083.5E+086.0E+088.5E+081.1E+091.4E+091.6E+091.9E+092.1E+092.4E+09

Flux/Watt through aperture

aperature area (mm2)

phot

ons/

sec/

mev

/Wat

t

3) Novel IDs enabled by small, round e- beam size, no injection orbit

Period[mm]Bmax [T] in helical mode Bmax [T] in planar mode

Delta SC Delta SC24 1.0117 1.097 1.431 2.19422 0.9686 1.058 1.37 2.11620 0.9162 1.009 1.296 2.01818 0.8533 0.9497 1.207 1.89916 0.7787 0.8679 1.101 1.736

Fields of Delta:Helical: + 40%Planar: +100%

Delta ID: fixed gap, fully polarization tunable

SC - ID: offers higher fields → smaller period &/or wider K-range (realization is challenging!)

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)

3rd harmonic flux-energy tuning range( for 25m long “Delta” ID with 18mm period)

12000 16000 20000 24000 28000 32000 360001E+13

1E+15

3rd H flux (thru 1mm aperture@50m)

Energy (eV)

phot

ons/

sec/

0.1%

bw

57Fe

Covers full range of energies for high resolution IXS !

higher spectral flux: boosts count rate from weak scattering systemsextends 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 ?

Where will ERLs shine ?

Resolution (meV)

Energy (KeV)

<1 meV (CDW optics)

9.1

6 Si(8 8 8)

15.82

1.5 (1.2) Si(11 11 11)

21.75

0.9 (0.6) Si(13 13 13)

25.7 ERL “Delta” ID λ=18mm, 25m,

1mm aperture @ 50m

118

(helical)

65

(3rd H)

35.4

(3rd H)

33.2

(5th H)

SPring8 BL35XU U20 – 4.5m

0.5 x 1.5mm2 @ 28m

-

18

13

7.3

ESRF ID28 @ 300mA. 3 Revolver IDs

0.6 x 1.6mm2 @ 27m

-

11.2

7.2

5.4

APS Sector 30 100mA.3 x U30 Ids 0.4 x 2mm2 @ 30m

-

-

5.7

3.9

NSLS-II baseline 500mA U20 5m hi-β 0.6 x 1mm2 @ 30m

9.95

1.69

0.07

-

ERL Delta ID flux calculations assume helical mode below 12.4 KeV, planar above. Other numbers are from AQR Baron except SPECTRA 8.0 calculations for NSLS-II based on

IXS@NSLS-II Feb.2008 workshop report by Yong Cai. Aperture size & distance are characteristic for the beamline specified

Spectral flux: ERL & potential future beamlines units: 1014 p/s/0.1%bw

By delivering 6 - 12 times more spectral flux, ERLs will make (R)IXS on high Z systems more practical.

Ratio of total number of photons (Thomson) scattered to those lost through other processes (predominantly photoelectric absorption) in sample of optimum thickness 1/μ as a function of atomic number. (example for 1meV resolution studies).

from - ESRF ID 28 “Primer on IXS”

Expand the “phase space” for IXS measurements

Resolution (meV)Silicon (hkl)

Energy (KeV)

½ (CDDW optics)

9.1

6(8 8 8)15.82

1.5(11 11 11)

21.75

0.9(13 13 13)

25.7

ERL 18mm Delta(20m ID)

9.3x1011 3.7x1012 4.5x1011 1.8x1011

APS Sector 30100mA 3-U30 (7.2m)

- - 3.5 x109 1.2 x109

NSLS-II baseline500mA U20 hi-β

(5m)

2.5 x1010 5.3 x1010 2.33 x108 -

Spring8 BL35XUU20 ID(4.5m)

- 1 x1011 1.32 x1010 3.8 x109

ERL Delta flux calculations for helical mode below 12.4 KeV & planar above. APS upgrade & Spring8 numbers from table provided by A.Q.R. BaronNSLS-II based on Feb.2008 workshop & SPECTRA 8.0 calculation.

Focused flux (photons/sec/μm2) at resolution specified

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 published emittance, beta, and photon energy

Thin

k IX

S m

icro

scop

e !

High Pressure DAC studiesSample volume Т Asample is the region of uniform pressure

IXS signal NIXS ~ I0(p/s/area) ρТ Asample (∂2σ/∂ΩЕ) ΔΩΔЕ e-μТ

[ρ scatterers/volume, absorption coefficient μ , ∂2σ/∂ΩЕ ~ |f(Q)|2 for single species]

IF Asample ~ 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…

[1] A.L.Ruoff, H. Xia, Q. Xia, Rev Sci Instrum. 63, 4342 (1992)

D

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

Present limits in structural studies of hydrogen.

ERL could extend measurement in BOTH P & T!

Potential for ERL-based pressure studies

Build in new science capabilities: using TDS to guide IXS measurements

Duel energy resolution mono for 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 measurements arrangement 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).

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

arXiv:1006.3990v2

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.

Table C-2. Comparative Source Sizes and DivergencesMachine Horiz.

Size (μm)

Horiz. Diverge (μrad)

Vert. Size (μm)

Vert. Diverge (μrad)

ESRF ID13 (4nm, 0.6% coupling)

59 90 8.3 3

APS-A (2.5 nm, 1% coupling)

275 11.3 8.8 2.9

NSLS II (0.5 nm, 2% coupling)

28 19 2.6 3.2

ERL, 25 m undul. hi-flux mode; 30 pm

24.5 6.1 24.5 6.1

ERL, 1 m undulator hi-coher mode; 8 pm

2 4 2 4

For Alfred:

ERL experimental facility:14 undulator beamlines

3 with IDs up to 25m long

IXS concept beamline – 25m undulator and 50m for hutches

space requirements based on SPring8 BL35XU

planned 25m ID

Potential location for XFEL-Oscillator

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…

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)

Energy Recovery Linac

Accelerating bunch Returning bunch A superconducting linac is required for

high energy recovery efficiency