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A bunch compressor design and several X-band FELs. Yipeng Sun, ARD/SLAC 2011-04-13, LCLS-II meeting. Design of two bunch compressors. Magnetic bunch compression. Bunch L phase space. 3-Dip. Chicane. e- source. RF. Dispersive region: chicane, wiggler arc, dogleg etc. - PowerPoint PPT Presentation
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A bunch compressor designand several X-band FELs
Yipeng Sun, ARD/SLAC2011-04-13, LCLS-II meeting
Presentation TitlePage 2
Design of two bunch compressors
Bunch compressionPage 3
Magnetic bunch compression
e- source
Energy modulation (correlation):RF structure, laser, wake field etc.
RF3-Dip. Chicane
Dispersive region:chicane, wigglerarc, dogleg etc.
Bunch L phase space
Different bunch compressors
3(4) dipole chicane, R56 <0, T566 >0achromatic to any order
Wiggler, R56 <0, T566 >0achromatic to any order?
Arc, R56 >0, T566 >0
2-Dip. Dogleg w/ quad+sextupole, R56 >0, T566 tunable
Chicane w/ quadrupole+sextupole, R56 tunable, T566 tunable
NLCTA chicane shape
Bunch compressionPage 5
Dispersion relations
Bunch compressionPage 6
Bunch compressor with dipoles and drifts
Bunch compressionPage 7
General chicane (1)
Bunch compressionPage 8
General chicane (1)
Bunch compressionPage 9
General chicane (2)
Bunch compressionPage 10
General chicane (2)
Presentation TitlePage 11
An FEL withLCLS injector (S-band+X-band
harmonic)Plus X-band Linac2 and Linac3
Presentation TitlePage 12
Scaling
Total length of acceleratorAssume 70% RF in linac
250-10pC
Final bunch length versus bunch charge
Presentation TitlePage 13
Longitudinal wake potential
'long' range
Presentation TitlePage 14
Linac3 length needed for de-chirp after BC2
Presentation TitlePage 15
Accelerator shape (LCLS injector + X-band)
Presentation TitlePage 16
LiTrack, LCLS, 250pC, 3kA
Presentation TitlePage 17
LiTrack, LCLS injector+X-band, 250pC, 3kA
Presentation TitlePage 18
Optics
LCLS
LCLS-Injector + X-band
Presentation TitlePage 19
Elegant simulation, 250 pC, 3 kA (w/ and w/o CSR)
LCLS
LCLS w/o CSR
Presentation TitlePage 20
Elegant simulation, 250 pC, 3 kA
LCLS
LCLS-Injector + X-band (½ R56 in BC2, 0.7 bending angle)
Presentation TitlePage 21
Elegant simulation, 250 pC, 5 kA
LCLS (L3, 30degree)
LCLS-Injector + X-band (½ R56 in BC2, 0.7 bending angle)
Presentation TitlePage 22
Elegant simulation, 250 pC, 5 kA, Projected emittance
LCLS (L3, 30degree)
LCLS-Injector + X-band (½ R56 in BC2, 0.7 bending angle)
Presentation TitlePage 23
Elegant simulation, 250 pC, 5 kA, Trajectory
LCLS (L3, 30degree)
LCLS-Injector + X-band (½ R56 in BC2, 0.7 bending angle)
Presentation TitlePage 24
LCLS-Injector + X-band (0.5 R56 in BC2, 0.7 bending angle), 250 pC, 5 kA
BC1 end BC2 end Linac3 endBC2 entrance
Presentation TitlePage 25
Potential X-band advantage over S-band
• Maintain a flat energy profile when pushing for shorter bunch length and higher peak current (i.e. 6kA at 250pC), due to stronger X-band longitudinal wake in Linac3, to remove energy correlation (chirp); plus possible cancellation of nonlinear chirp between RF, wake and CSR effects.
• Similar or smaller CSR emittance growth in BC2, benefiting from a weaker dipole and a larger energy correlation generated in Linac2 (previous argument)
• Compact (300m vs 1000m, at 14GeV)
• For LCLS, increasing current from 3kA to 6kA requires a smaller L1 phase to generate a longer bunch in ~400m Linac2, so that the L wake chirp is much smaller, and the bunch is compressed more in BC2 with same L2 phase; if keeping similar L1 phase and increasing L2 phase (i.e. from 36d to 37.5), the final energy profile will be very nonlinear.
Presentation TitlePage 26
Elegant simulation, 250 pC, 5 kA
LCLS (L1, 19degree; L2, 36degree; L3, 30degree)
LCLS (L1, 22degree; L2, 37.5degree; L3, 0degree)
Presentation TitlePage 27
An X-band RF based FEL with optics linearization
250 pC
Bunch compressionPage 28
Bunch length after compression
Final coordinate (square)
Minimum lengthMinimum length
Neglect small initial un-correlated energy spread
1st order optimal compression:
2nd order optimal compression:
3rd order optimal compression:
Bunch compressionPage 29
Full compression using optics linearization
1st order dispersion
2nd order dispersion
3rd order dispersion
Bunch compressionPage 30
Minimize CSR (1) short interaction time
New design BC1 (1) first order
B10.2m7 degree
B20.2m3 degree
B30.2m-3 degree
B40.2m-7 degreeQD
QF
R56 = 17 mm
New design BC1 (2) second orderSF1&2 SD1&2 symmetric
K3(SF1) = -K3(SD2)K3(SF2) = -K3(SD1)
T166 = T266 = 0; T566 = 170 mm
Bunch compressionPage 33
Minimize CSR (2) phase space matching
general
x
X’CSR
Large β x
X’CSR
Small β x
X’
CSR
Optimalβ and α
specific
Optimized to minimize CSR impact on emittance
Bunch compressionPage 34
X-band based 2 stage FEL (1) 250pc, 300micron
Presentation TitlePage 35
Final profile at 7GeV (collimation in middle of BC1)
Presentation TitlePage 36
Slice emittance evolution, 250 pC, 6 kA
BC1 entrance BC2 entrance Linac3 endBC1 end
Presentation TitlePage 37
An X-band RF based FEL with normal chicane BC
10 pC
Bunch compressionPage 38
Max bunch length w/o harmonic RF
Bunch compressionPage 39
Bunch compressor and linac design
BC1 BC2 Linac cell
X-band based 2 stage FEL (3) 10pc, 40micron
54 MeV (C. Limborg) 6 GeV
FEL simulation Setup
• FEL at 2 keV , 6 Å (FEL at 8 keV, 1.5 Å)• Electron Charge 10 pC, Centroid Energy 6
GeV, peak current 3 kA with profile as shown in previous slides– S2E file down to undulator entrance
• LCLS Undulator with larger gap lw = 3 cm (1.5 cm); beta-function ~ 15 m
Juhao Wu
Presentation TitlePage 42
FEL performance
Juhao Wu
1.5 angstrom6 angstrom
Bunch compressionPage 43
BC parameters summary
Presentation TitlePage 44
Possible test at NLCTA
Bunch compressionPage 45
Motivation and simulation condition
Motivationo Demonstrate effective bunch compression (5 to 10 times) with x-band RF
Scheme 1: use normal chicane + positive RF chirp (current NLCTA) Scheme 2: use optics w/ higher order dispersion + positive/negative RF
chirp (need to install 4/6 sextupoles in the big chicane)o Investigate tolerances on timing jitter, misalignment etc.; emittance growth
Simulation condition: In Elegant, including transverse and longitudinal wake, coherent synchrotron
radiation (CSR), longitudinal space charge (LSC) and velocity bunching0.5 million macro-particlesFor scheme 1, current operating opticsFor scheme 2, new optics20 pC beam at 5MeV, 0.5ps RMS bunch length, 5e-3 RMS energy spread, 1
m.mrad transverse emittanceBeam energy: 60 MeV at BC1, 120 MeV at BC2
Bunch compressionPage 46
NLCTA optics (current operation)
R56 =-73mm T566 = 111mm R56 =-10mm
T566 = 15mm
Bunch compressionPage 47
Scheme 1 (1) L phase, current and bunch length
Initial
Linac1
BC1
Linac2
BC2
Bunch compressionPage 48
Scheme 1 (2) no compression, on crest
Initial
Linac1
BC1
Linac2
BC2
Bunch compressionPage 49
Scheme 1 (3) 2 stage compress 20 times, end
Bunch compressionPage 50
Scheme 1 (4) effect of timing jitter, near full compression
Timing jitter between laser and RF (assumed same for two RF sections)
On phase + 115 fs (0.5 degree) - 115 fs
Bunch compressionPage 51
Scheme 1 (5) effect of timing jitter, under compression
Timing jitter between laser and RF (assumed same for two RF sections)
On phase + 115 fs (0.5 degree) - 115 fs
Bunch compressionPage 52
Scheme 2 (1) optics
Chicane w/ quadrupole+sextupole, R56 tunable, T566 tunable
6 meters long
Install 4/6 sextupoles in the big chicane
Bunch compressionPage 53
Scheme 2 (2) L phase and current
Bunch compressionPage 54
Scheme 2 (3) 1 stage compress 10 times, end
Bunch compressionPage 55
Scheme 2 (4) Sensitivity to timing jitter
Deviation between analytical formulae and simulation due to:Small difference of beam(RF) parameters being employedCollective effects in simulation
Bunch compressionPage 56
Thank you for your patience!
I would like to thank the following people for their great help and useful discussions:
C. Adolphsen , K. Bane, A. Chao, Y. Cai, Y. Ding, J. England, P. Emma, Z. Huang, C. Limborg, Y. Jiao, Y. Nosochkov, T. Raubenheimer, M. Woodley, W. Wan, J. Wu
Bunch compressionPage 57
Current less sensitive to RF phase jitter
20pC, 80 micron
L =6 m L =9 mrf = -25°
L =330 mrf = -41°
L =550 mrf = -10°
BC-1L =6 m
R56= -36 mm
BC-2L =22 m
R56= -25 mm DL-2L =66 mR56 = 0
DL-1L =12 mR56 0
undulatorL =120 m
6 MeVz 0.83 mm 0.1 %
150 MeVz 0.83 mm 0.10 %
250 MeVz 0.19 mm 1.8 %
4.3 GeVz 0.022 mm 0.76 %
13.6 GeVz 0.022 mm 0.01 %
...existing linac
L0
rfgun
L3L1 X
LhL =0.6 mrf=-160
L2
LCLS
L = 16 mrf = -40°
L = 72 mrf = -40°
L 850 mrf = 0°
BC-2L 14 m
R56= -36 mm
BC-3L 18 m
R56= -11 mm
undulatorL =? m
6 MeVz 2.0 mm 0.1 %
120 MeVz 0.5 mm 2.0 %
375 MeVz 0.1 mm 1.4 %
1.64 GeVz 0.020 mm
0.5 %
20.5 GeVz 0.020 mm 0.01 %
L3L0
LhL =1.4 mrf= -191
rfgun C L1
BC-1L 4 m
R56= -76 mm
L = 8 mrf -22°
L2
TESLA-XFEL
(2003 parameters)
Paul Emma
Energy change + optics (dispersion) (2)Emittance & trajectory (slice)
For sufficiently large slice number, one can assume same energy change in one slice
Change slice emittanceChange slice trajectory
Other terms
CSR energy change + phase rotation (smear)Emittance & trajectory (slice)
For over-compress, CSR-process can be treated as an integral process, with continuing bunch compression (lengthening).
Change slice trajectory & emittance
Negligible