kwang-je kim anl & u of c& postech workshop on sciences outlook and r&d issues of x-ray...

Kwang-Je Kim

ANL & U of C& POSTECH

Workshop on Sciences Outlook and R&D Issues of X-ray FEL Oscillator

February 14-15, 2013

POSCO International Center

Pohang, Korea

Introduction to XFEL-O and Charges to the Workshop

Science Outlook and R&D Issues for an XFELO

2

Free Electron Laser Oscillator

A low-gain device with high Q optical cavity Optical pulse formed over many electron passes Difficult for x-rays

– Electron beam qualities– High-reflectivity normal incidence mirror

Feb 14-15, 2013

Science Outlook and R&D Issues for an XFELO3

X-Ray FEL Oscillator (XFEL-O)

An FEL oscillator is feasible in hard x-ray region by using Bragg mirrors – R. Collela and A. Luccio, 1983; KJK, Y. Shvyd’ko, and S. Reiche, 2008

Tuning is possible with a four mirror configuration– R. M.J.Cotterill, (1968) KJK & Y. Shvyd’ko (2009)

A super-conducting linac with a photo-cathode gun can drive an XFELO

3

Feb 14-15, 2013


4

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

Feb 14-15, 2013


Temporal and spectral evolution of XFELO

5

R.R. Lindberg, K.-J. Kim, Yu. Shvyd’ko, and W.M. Fawley, Phys. Rev. ST-AB. 14, 010701 (2011)

Feb 14-15, 2013


6

An XFELO produces fully coherent, temporal as well as transverse, x-ray pulses

Feb 14-15, 2013


7

Example Parameters Electron beam:

– Energy 6 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, rms energy spread ~ 210-4 – Constant bunch rep rate @ ~1 MHz

Undulator:– Lu= 60 (30) m, lu ~2.0 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 w 25 keV– Bandwidth: /Dw w ~ 1 (5) 10-7 ; rms pulse length = 500 (80) fs– # photons/pulse ~ 1109

– Rep rate ~ a few MHz

8

(..) indicates short-pulse mode for relaxed tolerances

Feb 14-15, 2013

Science Outlook and R&D Issues for an XFELO8

XFELO applications

High resolution spectroscopy

– Inelastic x-ray scattering

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

X-ray photoemission spectroscopy

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

X-ray imaging with nm resolution– Smaller focal spot with the absence of chromatic aberration

Other talks in this workshop

Feb 14-15, 2013


9

An Ultimate X-Ray FEL Facility A grand facility employing XFELOs and high-gain

XFELs can be envisaged in which an XFELO serves as the seed for a high gain amplifier

Feb 14-15, 2013


10

Accelerator Technology Issues Basic configuration: low emittance gun + SCRF Linac Gun

– LCLS low charge operation demonstrated that the beam quality requirements for single pulse can be met

– High rep rate (> MHz) guns have been constructed and are being tested

Cost saving R&D in super-conducting linac– High Q0 (10101011) to save the refrigerator cost

– Solid state RF power

One or more recirculation passes could reduce the cost– Use ERL but in accelerating phase

Feb 14-15, 2013

11

Accelerator technology: Injector

DC gun for ERL(KEK/JAEA, Cornell) and the low frequency RF gun for NGLS will meet the XFELO requirements

Feb 14-15, 2013

N. Nishimori, et al, WEPD51

C. Papadopoulus, et al., MOPD31


12Feb 14-15, 2013


13

6 (7) GeV

3GeV ERLin the first stage XFEL-O in 2nd stage

lrf/2 path-lengthchanger

Using ERL loops for additional acceleration: KEK/JAEA project

Feb 14-15, 2013


14

Challenges for X-ray Optical Elements

Diamond is best: high reflectivity and thermo-mechanical properties– Heat load dynamics: Can DEBragg< 1 meV maintained?

– Radiation damage issues

Stability of optical elements– Angular <10 nr & position< 3 mm @ 1 kHz BW– Precision stages

Surface qualities– Reflectivity and wavefront distortion

Quality of grazing incidence focusing mirrors

Feb 14-15, 2013

15

Reflectivity of TISNCM* Diamond was measured to be >98% at the APS


*Technological Institute for Superhard Novel Carbon Materials, Russia

16Feb 14-15, 2013


16

Grazing Incidence, Curved Mirror

JTEC– Developing a technique combining elastic emission machining

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

– Issue: large difference 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,..

H. Mimura, et. al.

RSI 79, 083104, 2008

Feb 14-15, 2013


17

Further opportunities for an XFELO: Extreme temporal coherence length from sub-mm km108 m(spontaneous emission limit)!

The XFEL-O output pulses are copies of the same circulating intra-cavity pulse

The pulse spacing needs to be stable to maintain a good overlap with electron beams: DT < 3 mm

If the pulse spacing T can be controlled far more accurately, DT <0.01l/c, the spectrum of XFELO output becomes a comb

The extreme-stabilized XFEL-O may establish an x-ray-based length standard and have applications in fundamental physics—quantum gravity, wavefunction collapse of mesoscopic system

Feb 14-15, 2013


18

Cavity stabilization by tying one of the comb lines to a nuclear resonance line(B.W. Adams and K.-J. Kim, to be published)

Feb 14-15, 2013

Find the signal maximum by changing the cavity length ~1 Å and lock to it


19

Charge to Workshop Identify the prospects and importance for sciences

that can be done by XFELO Are there scientific areas not discussed in this

workshop? How can we find them? Identify the technological challenges for

constructing an XFELO, in accelerator and in x-ray optics.

Can the challenges be addressed by an R&D program, say, for 5 years?

Comment on the scientific prospects and technological challenges for an extreme-stabilized XFELO

Feb 14-15, 2013

kwang-je kim anl & u of c& postech workshop on sciences outlook and r&d issues of x-ray...

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