An X-Ray Free Electron Laser Oscillator Kwang-Je Kim ANL & the U of Chicago Claudio Fest Oct. 1-2, 2010 Avalon, CA

An X-Ray Free Electron Laser Oscillator

Kwang-Je Kim

ANL & the U of Chicago

Claudio Fest

Oct. 1-2, 2010 Avalon, CA

Claudio’s Workshops

KJK Catalina Oct 2010

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Claudio’s workshops helped me and others, I am sure, to kick-start my accelerator physics career.Thank you, Claudio!


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Era of Hard X-Ray (1 Å) FEL Commenced in 2009 with the Operation of LCLS (SASE)

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LINAC Coherent Light Source

LCLSProject start 1999

RIKEN/SPring-8 XFEL

2011European XFEL Facility

2014

LCLS August, 2008

2011

LCLS, April 2009

I=500 AI=3000A

April 10, 2009 User experiment September, 2009

•BNP paper in 1984• Claudio’s proposal to use an RF photocathode gun , x~1 , and the SLAC linac

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X-ray FELs beyond LCLS

More facilities– Higher average brightness (Euro XFEL, SCRF)– Compact FELs ( SPring-8)– Coherent soft x-rays with harmonic generation

Options with lighter ( 1-50 pC) bunches with lower emittance ( 0.1 mm-mr)– Atto-second time resolution– meV spectral resolution with an XFELO



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A hard x-ray FEL oscillator (XFELO) will provide full coherence with ultra-pure spectrum

An X-ray pulse is stored in a diamond cavity multi-pass gain & spectral cleaning

Provide transform limited BW ~10-7 meV

Zig-zag path cavity for wavelength tuningOriginally proposed in 1984 by Collela and Luccio and resurrected in 2008

(KJK, S. Reiche, Y. Shvyd’ko, PRL 100, 244802 (2008)

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High reflectivity and narrow Bandwidth with near backscattering from diamond crystals

Photon energy (keV)

Courtesy of Yuri Shvyd’ko


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Representative Parameters

Electron beam: – Energy 7 GeV– Bunch charge ~ 25-50 pC low intensity– Bunch length (rms) 1 (0.1 ps) Peak current 20 (100) A– Normalized rms emittance 0.2 (0.3) mm-mr, energy spread (rms) ~ 210-4 – Constant bunch rep rate @ ~1 MHz

Undulator:– Lu= 60 (30) m,u2.0 cm, K=1.0 – 1.5

Optical cavity:– 2- or 4- diamond crystals and focusing mirrors– Total round trip reflectivity > 85 (50) %

XFELO output:– 5 keV 25 keV– Bandwidth: ~ 1 (5) 10-7 , pulse length (rms) = 500 (80) fs– # photons/pulse ~ 1109

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Blue color in the above indicates short-pulse mode for relaxed tolerances

KJK Catalin

a Oct 201

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Tunable X-ray Cavity

Two crystal scheme – a very limited tuning since

must be kept small

A tunable four crystal scheme– Any interesting spectral region

can be covered by one chosen crystal material

– Simplify the crystal choice Diamond as highest reflectivity & best mechanical and thermal properties

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R. M.J.Cotterill, APL, 403,133 (1968) KJK & Y. Shvyd’ko, PRSTAB (2009)


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XFELO will drastically improve hard x-ray techniques developed at 3rd generation light sources, as well as new applications in areas complementary to SASE

High resolution spectroscopy

– Inelastic x-ray scattering

Mössbauer spectroscopy – 103/pulse, 109/sec Moessbauer s (14.4 keV, 5 neV BW)

X-ray photoemission spectroscopy

– Bulk-sensitive Fermi surface study with HX-TR-AR PES

X-ray imaging with near atomic resolution (~1 nm)– Smaller focal spot with the absence of chromatic aberration

Applications we have not thought of yet!

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XFELO Modeling Analytical (KJK, R. Lindberg)

– Gain calculation, super-mode theory for evolution in optical cavity

GENESIS (S. Reiche) – (x,y) asymmetric, single wavefrontSlow:1 month computing

from noise to saturation!

Reduced 1-D FEL code (R. Lindberg)– Transverse dependence integrated out assuming Gaussian

mode– Fast and reasonable agreement with GINGER and GENSIS

GINGER (W. Fawley)– (x,y) symmetricmuch faster than GENESIS– Implemented a correct crystal response

KJK KEK Dec 21,

2009

Crystal Phase Shift and Cavity Length Detuning Amplitude reflectivity for near

normal incidence x-rays

XFELO works near y~0. The angular spread effect is small

-dependent phase shift

can be corrected by cavity length adjustment

KJK KEK Dec 21,

2009

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2( ) 1 iyr y y i y ie

0

2( )1 H

H H

E Ey

E

( )exp i2

H

H

c

Filtering by crystals expedite and stabilize the development of the ultra-narrow spectrum. Spectrum saturation takes much longer than intensity saturation

KJK KEK Dec 21,

2009

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Ginger Simulation of XFELO Spectrum After 500 Passes (Two Diamond Crystal Cavity, 50 m and 200m, R. Lindberg)


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Technology Development for XFELO

Electron injector Diamond crystal

– Reflectivity– Heat load dynamics

Grazing incidence mirrors Stability of optical elements

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Electron Gun Technologies for XFELO A photo-cathode based injector satisfying XFELO requirements

should be feasible– The LCLS S-band NC RF PC demonstrated ultra-low x

x=0.14 10-6 m, Q=20 pC, fb=120 Hz

– The PITZ L-band NC RF PC may be suitable a pulsed XFELO:

x=0.3-0.4 10-6 m, Q=100 pC, fb=1 MHz, tmacro=800 s, fmacro=10 Hz

– Cornell DC PC for ERL could also work if 750 kV DC voltage can be achieved

x=0.2 10-6 m, Q=20 pC, fb=1.3 GHz, CW

– LBNL 200 MHz, NC RF Gun (CW) (design) could be configured for XFELO application

A thermionic-cathode based injector appears also feasible by modifying the RIKEN/Spring-8 pulsed DC

– RIKEN injector by Togawa and Shintake: 500 kV @ 60 Hz, x=0.6 10-6 m with 3 mm diameter

– Reduce diameter to 1 mm to obtain x=0.2 10-6 m with 1/9 th bunch charge (sufficient for an XFELO)

– Replace DC voltage by 100 MHz RF similar to LBNL

– Reduce the bunch rep rate to a few MHz by pulsed HV on a gate electrode (T. Shintake)

KJK KEK Dec 21,

2009

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Operation of a Gate Electrode ( M. Borland & X. Dong)


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A thermionic cathode may provide a higher stability?


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CeB6 cathode after 20,000 hrs of operation

Laser spot for LCLS gun ( D. Dowells)

KJK KEK Dec 21,

2009

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A possible injector concept for XFELO

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1. Gate electrode HV pulser, 1 MHz, 10 kV, ~3ns. 2. RF cavity with therm ionic cathode, 100 MHz, 1 MV. 3. Solenoid. 4. Quadrupole triplet.5. Chicane. 6. Horizontal jaw slit as an energy filter to select out a 0.5-ns segment in

each rf period. 7. Quadrupole triplet. 8. Short solenoid. 9. Monochromator of the beam energy,

f=600 MHz. 10. Sub-harmonic pre-buncher (velocity bunching), f=300 MHz. 11. Booster linac section, 66 MeV, f=400 MHz. 12. Bunch compressor I. 13. SC linac section, 542 MeV, f=1300 MHz. 14. Bunch

compressor II. 15. Main SC linac, f=1300 MHz

KJK KEK Dec 21,

2009

KJK, HBEB Maui 2009

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X-Ray Optics R&D for XFELO

Diamond crystal– High-reflectivity– Head-load dynamics– Damage issue

Grazing incidence focusing mirror– Reflectivity and phase front quality

Positional and angular stability Advances in these technologies are eagerly sought

after by broader synchrotron radiation community

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Topograpy, R and E data (Sumitomo sample, S. Stoupin & Y. Shvyd’ko)

Optical Properties of HPHT Synthetic Diamond Crystals

Crystal supplier: Element 6, Sumitomo, TISNUM (Moscow)


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Reflectivity and spectral width measurement at APS sector-30 in good agreement with theory

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S. Stoupin, Y. Shyv’dko, A. Cunsolo, A. Said, S. Huang

C(995)

EH=23.765 keV

(Nature Physics 6(2010)196)

Radiation damage issues Power density on crystals is about 4 kW/mm2 ( 21018 photons/s/mm2 @

12.4 keV) ~ 30 times higher than that of the APS undulators Estimate shows that all atoms will be ionized in 250s in the absence of

recombination ( Robin Santra) Various recombination processes may prevent an irreversible damage However, photo-electrons are lost at the surfaces charge build-up

may lead to structural change at the surface Graphitization? Possible remedies

– Isotopically pure 12C crystals, cryogenic temperature

– Attaching a thin conducting layer, e.g. graphene

We plan for a thorough theoretical and experimental study


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Graphitization of a diamond crystal at an APS HHLM ( high heat load monochromator at the APS. The crystal surface became darkened without apparent performance degradation after 1 year of exposure.

KJK KEK Dec 21,

2009

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Heat Load Dynamics As an intracavity x-ray pulse hit crystals, r-dependent temperature rise T

crystal expansion E/E = T (L/L=Is this <10-7? Yes, if cooled to a cryogenic temperature:T< 100K

– Inter-pulse E/E <10-7 due to high thermal-diffusivity– Intra-pulse E/E <10-7 due to <10-7 and if the expansion time < pulse duration (~ps)

Theories suggest the expansion is slow. We will pursue experimental study using laser heating

23S. Stoupin and Y. Shvyd’ko, PRL


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Grazing Incidence, Curved Mirror

JTEC– Developing a technique combining elastic emission machining

(EEM, slow) and electrolytic in-process dressing (ELID, fast) to fabricate a smooth surface to <nm height error and 0.25 mrad figure error

– Issue: large ration in the sagital and meridional depths

– Such mirrors are sought after by “every body” in SR business

Other ways of focusing– Curved crystal surface, CRL,..

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H. Mimura, et. al.

RSI 79, 083104, 2008


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Null-detection FB stabilization at APS Sector 30(S. Stoupin, F. Lenkszus, R. Laird, Y. Shvy’dko, S. Whitcomb,..)

The stability of IC3 signal indicates the angular stabilization of the 3rd crystal pair within 50 nrad is achieved (~1 Hz BW)

(S. Stoupin, F. Lenkszus, R. Laird, Y. Shvy’dko, S. Whitcomb,., RSI, 81, 055108, 2010)

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IC0

IC1 IC2 IC3

IC0

IC1

IC2

IC3

Feedback correction signal

HRM

PZT

Where can an XFELO be implemented?

Euro-XFEL– The length of the macro-pulse ( 1 ms) is sufficient for a

pulsed XFELO ( being studied by J. Rossbach)– Current plan is to use 600 m SCRF linac for 14 GeV with

<E>=23.7 MeV/m. By using the full length of tunnel (720 m) at <E>=10 MeV/m, CW XFELO can be operated @ 7 GeV

Plan for JAEA-KEK ERL includes an XFELO

KJK KEK Dec 21,

2009

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(1) In a straight section of the loop

Beam dump

(2) In an additional single-ended branch

Integration with an ERL light source

From Hajima’s talk at X’ian (Sept. 2009)

Documents

An X-Ray Free Electron Laser Oscillator Kwang-Je Kim ANL & the U of Chicago Claudio Fest Oct. 1-2, 2010 Avalon, CA