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Longitudinal-to-transverse mapping and emittance transfer. Dao Xiang, SLAC June-10-2010 SLAC Accelerator Seminar. Outline. Longitudinal-to-transverse mapping to break the 1 fs time barrier. Longitudinal-to-transverse emittance transfer for storage ring lasing. - PowerPoint PPT Presentation
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Longitudinal-to-transverse mapping and emittance transfer
Dao Xiang, SLAC
June-10-2010
SLAC Accelerator Seminar
2
Outline
Longitudinal-to-transverse mapping to break the 1 fs time barrier
Longitudinal-to-transverse emittance transfer for storage ring lasing
3
Applications of ultrashort electron bunch
Generation of ultrahigh wake field
I. Blumenfeld et al, Nature, 445, 741 (2007)
E167
LCLS
4
Applications of ultrashort electron bunch
Diffraction-before-Destruction
Generation of ultrashort x-ray FEL pulses
R. Neutze et al, Nature, 406, 752 (2000)
5
Compact XFEL
Recent success of using 20 pC electron beam to drive an x-ray FEL at the LCLS has stimulated world-wide interests in using low charge beam (1~20pC) to drive a compact XFEL which delivers ultrashort x-ray pulses (0.1 fs~10 fs).
Y. Ding et al, PRL, 102, 254801 (2009)
How to measure 1 fs bunch?
6
Deflecting cavity
Resolution limited by intrinsic emittance:
Bunch length measurement with a deflecting cavity
7
Deflecting cavity
S band (V=10 MV, Beta=50 m)
Is it possible to overcome the fundamental resolution limit arising from the intrinsic beam divergence/emittance?
LCLS
X band (V=20 MV)
NLCTA
Beam (E=120 MV, Beta=10 m, emittance=8 mm mrad)
X band (V=5 MV, f = 11.424 GHz)
8
Longitudinal-to-transverse mapping
Matrix of an isochronous non-achromatic chicane
Scheme to achieve exact mapping
D. Xiang and W. Wan, PRL, 104, 084803 (2010)
z to x’ x’ to x
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Longitudinal-to-transverse mapping
Transfer matrix of a deflecting cavity
Properly choosing the deflection strength to make
Transfer matrix of the chicane + deflecting cavity
Map z exactly to x’
10
Longitudinal-to-transverse mapping
Final transfer matrix after a parallel-to-point imaging beam line
Map z exactly to x with a magnification ratio
z to x’ x’ to x
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Longitudinal-to-transverse mapping How it works?
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Longitudinal-to-transverse mapping
LCLS over-compression case
13
Longitudinal-to-transverse mapping
LCLS under-compression case
14
Longitudinal-to-transverse mapping
ECHO-7 puzzle
Lasers on Filter in
Turn off either laser does not kill the signal
15
Longitudinal-to-transverse mapping
ECHO-7 puzzle
ECHO phase space HGHG phase space
ECHO current distribution HGHG current distriution
Mu
ltiple b
um
ps p
er wavelen
gth
On
e bu
mp
per w
aveleng
th
16
Longitudinal-to-transverse mapping
ECHO-7 puzzle might be solved by measuring the current
ECHO beam profile HGHG beam profile
ECHO current distribution HGHG current distriution
Mu
ltiple b
um
ps p
er wavelen
gth
On
e bu
mp
per w
aveleng
th
17
Outline
Longitudinal-to-transverse mapping to break the 1 fs time barrier
Longitudinal-to-transverse emittance transfer for storage ring lasing
18
Beam requirement in x-ray FELs
Low geometric emittance
Low energy spread
High peak current
Electron slips back by one radiation wavelength after it travels one undulator period
~1 um emittance with ~1 MeV energy spread and ~kA peak current
19
Storage ring FEL
Beams in storage ring
Large energy spread & Low current
Power gain length at 1nm
PEP-X beam parameters
Low power
Poor transverse coherence
FEL at <1nm is very difficult
20
Current-enhanced SASE (E-SASE) Increase peak current to increase the FEL gain
Suitable for the case when
A. Zholents, PRST-AB, 8, 040701 (2005)
current energy spread
Is it possible to increase the peak current without increasing the energy spread? Violating Liouville’s theorem?
21
Laser assisted emittance tranfer Increase peak current without increasing energy spread
TEM00 laser
Schematic of the laser assisted emittance transfer
TEM01 laser
4-bend chicane Isochronous non-achromatic chicane
Increase peak current Increase peak current
Increase energy spread Increase vertical emittance
E-SASE LAET
22
Laser assisted emittance tranfer
Initial distribution
phase space current
energy spread vertical emittance
23
Laser assisted emittance tranfer
After interaction with the TEM01 laser
phase space current
energy spread vertical emittance
24
Laser assisted emittance tranfer
Final distribution
phase space current
energy spread vertical emittance
25
Laser assisted emittance tranfer
Estimated FEL performances at 1 nm
Gain length:
Peak power:
Limitation
The duration of the current bump is shorter than the slippage length and one needs to frequently use isochronous chicane to shift the radiation to the upstream bumps to sustain the effective interaction
1.8 mm mrad
0.018 mm mrad5.1 MeV
300 A
35 m
~100 kW
26
A technique is proposed to manipulate the beam phase space and rearrange the beam’s x distribution according to its initial z distribution
Summary
The longitudinal-to-transverse mapping technique may allow one to break the 1 fs time barrier in ultrashort bunch length measurement
A technique is proposed to significantly increase the beam current without greatly increasing the energy spread
Thanks!
Many thanks to:
M. Borland, Y. Cai, A. Chao, Y. Ding, P. Emma, Z. Huang, G. Stupakov, M. Woodley, J. Wu and A. Zholents
The laser assisted emittance transfer technique can be used to repartitioning the emittance in 6-D phase space so that one might be able to use the beam from a large storage ring to drive a high-gain FEL.
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