kwang-je kim anl & u of c& postech workshop on sciences outlook and r&d issues of x-ray...
Post on 13-Jan-2016
215 Views
Preview:
TRANSCRIPT
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
Science Outlook and R&D Issues for an XFELO
4
Ginger Simulation of XFELO Spectrum After 500 Passes (Two Diamond Crystal Cavity, 50 mm and 200mm, R. Lindberg)
Feb 14-15, 2013
Science Outlook and R&D Issues for an XFELO
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
Science Outlook and R&D Issues for an XFELO
6
An XFELO produces fully coherent, temporal as well as transverse, x-ray pulses
Feb 14-15, 2013
Science Outlook and R&D Issues for an XFELO
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
Science Outlook and R&D Issues for an XFELO
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
Science Outlook and R&D Issues for an XFELO
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
Science Outlook and R&D Issues for an XFELO
12Feb 14-15, 2013
Science Outlook and R&D Issues for an XFELO
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
Science Outlook and R&D Issues for an XFELO
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
Science Outlook and R&D Issues for an XFELO
*Technological Institute for Superhard Novel Carbon Materials, Russia
16Feb 14-15, 2013
Science Outlook and R&D Issues for an XFELO
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
Science Outlook and R&D Issues for an XFELO
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
Science Outlook and R&D Issues for an XFELO
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
Science Outlook and R&D Issues for an XFELO
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
top related