short bunches at flash
DESCRIPTION
Short Bunches at FLASH. T. Limberg. Outline. Start-2-End Simulations and a fast Model for Longitudinal Phase Space Simulations Dedicated Benchmark Studies Analysis Machine Set Up for Short Bunches with Subsequent Photon Pulse Length Measurements . FLASH Bunch Compression Scheme. - PowerPoint PPT PresentationTRANSCRIPT
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FELBeamDynamics
FELBeamDynamics
T. Limberg
Short Bunches at FLASH
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Short Bunches at FLASHFELBeamDynamics Outline
Start-2-End Simulations and a fast Model for Longitudinal Phase Space Simulations
Dedicated Benchmark Studies Analysis
Machine Set Up for Short Bunches with Subsequent Photon Pulse Length Measurements
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Short Bunches at FLASHFELBeamDynamics FLASH Bunch Compression Scheme
),,,(
'''
'')'(
393911 ACCACCACCACC
sum
sum
sum AAF
V
V
VChirpBeamEnergy
AACC2/3 , φACC2/335 fs
150 MeV
450 MeV
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Short Bunches at FLASHFELBeamDynamics S2E with 250 pC Bunch Charge (I. Zagorodnov)
Photon Pulse Length (FWHM) : 17 fsNumerically expensive, optimized parameter set
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Short Bunches at FLASHFELBeamDynamics S2E with 100 pC Bunch Charge
Photon Pulse Length (FWHM) : 7 fs
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Short Bunches at FLASHFELBeamDynamics S2E with 20 pC Bunch Charge
Photon Pulse Length (FWHM) : 2 fs
-20 -10 0 10 200
2
4
6
8
10
[a.u]I
GWiP
GWP
[fs]t
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Short Bunches at FLASHFELBeamDynamics E-Bunch Length and Photon Pulse Length
longitudinal position [m] (RMS: 6.37e-006 [m])
horiz
onta
l pos
ition
[m]
(RM
S: 8
.33e
-005
[m])
Top View at Undulator Entrance
-1.5 -1 -0.5 0 0.5 1 1.5
x 10-5
-2
-1
0
1
2
3
x 10-4
0
1000
2000
3000
4000
5000
6000
7000
8000
Photon pulse length can be reduced by:
• transverse offsets• energy offsets• local emittance
blow-up• …
100 pC
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Short Bunches at FLASHFELBeamDynamics Fast Model for longitudinal Phase Space
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Short Bunches at FLASHFELBeamDynamics Bunch Shape after Compression vs. First Linac Section Chirp (500 pC)
120 fs 30 fs 180 fs
ACC1-Phase: 2.51 deg ACC1-Phase: 2.6 deg ACC1-Phase: 2.8 deg
Stability and Tuning Issue
Minimum bunch length limited by non-linearities
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Short Bunches at FLASHFELBeamDynamics Bunch Shape after Compression (100 pC)
15 fs
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Short Bunches at FLASHFELBeamDynamics Study by Helen Edwards et al.
Only BC-2 is on Bunch shape and length as measured with transverse deflecting cavity
(LOLA) vs. ACC1/ACC39 phase
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Short Bunches at FLASHFELBeamDynamics
Longitudinal Phase Space and Profile vs. Energy Chirp (ACC1 phase monitored)
4 deg 5 deg 6 deg
0 deg
7.5 deg
1 deg 2 deg 3 deg)
7 deg
7.5 deg 7.9 deg
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Short Bunches at FLASHFELBeamDynamics Measured and calculated compression factor
(without self-effects)
Small additional chirp and 10% correction of LOLA energy calibration:
r56nom = 178.4 mmoff = 0.18
C
number of measurement(increasing chirp)
M. Dohlus
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Short Bunches at FLASHFELBeamDynamics On crest
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Short Bunches at FLASHFELBeamDynamics Compressed to ca. 50 A
No self-effects
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Short Bunches at FLASHFELBeamDynamics Compressed to ca. 150 A
With self-effects
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Short Bunches at FLASHFELBeamDynamics 1kA Spike
Slope doesn‘t fit
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Short Bunches at FLASHFELBeamDynamics Bunch-Length-Tuning
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Short Bunches at FLASHFELBeamDynamics Bunch-Length-Tuning (differential): 150 pC
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Short Bunches at FLASHFELBeamDynamics Bunch-Length-Tuning: Spectra and Statistics
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Short Bunches at FLASHFELBeamDynamics
Results from another shift block(compiled by S. Schreiber (still preliminary))
> In general good agreement for the short pulses - within a factor of 2
> Larger uncertainties for longer pulses
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Short Bunches at FLASHFELBeamDynamics Tuning Issues
Longitudinal bunch shape changes with pulse train length, but LOLA can take only one bunch
Under study/development: UV Pockels cell
Uncertainty in absolute rf phases Beam Arrival-time Monitors help
rf drifts LLRF hardware and software upgrades improved situation significantly
Instrumentation specified and designed for the original design charge of 1 nC
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Short Bunches at FLASHFELBeamDynamics Peak Current for Short Pulses (Gaussian like)
Charge [pC] Peak Current [kA] E-Bunch <100 fs FWHM
Peak Current [kA] E-Bunch <50 fs FWHM
1000 8.4 16.8
500 4.2 8.4
250 2.1 4.2
100 0.8 1.6
From S2E: At short bunches, peak currents of 2 kA already increase slice emittance.
From SASE Simulations: Peak currents of 1.5 - 2 kA needed for saturation(at least for the shorter wave lengths)
In the charge regime below 250 pC, SASE intensity and very short bunch length should go together
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Short Bunches at FLASHFELBeamDynamics Summary and Remarks
The tools and methods to tune bunch length exist and have passed first tests
Extensive feedback from users about photon beam quality is important
An on-line photon pulse length and pulse shape measurement would be of great help