1. Summary of SPARC first-phase operations
Daniele Filippetto
on behalf of SPARC team

2. Outlines Layout (12/06) Laser and cathode Synhcronization
Diagnostic and system commissioning
Best results
Conclusions

3. RF: Waveguide and gun conditioning successful
Conditioning time~2 weeks
Eacc~120MV/m
Ekin=5.6MeV (e-)

4. High complexity system!!
Laser:
High complexity system!!
oscillator
pumps
amplifiers
Harmonics
generator
UV stretcher
Pulse shaper
Daily optimization is required

5. Sparc hall: Faraday cup ICT Beam dump Spectrometer Magnets E-meter
cross

6. Operation days: RF and timing systems; RF conditioning Beam operation
Flat pulse
Beam
operation
Gauss pulse
Installation &
characterization LC
mask
Transfer
Line install.
New
stretcher
Normal
incidence
Diagnostics
development
Flat top
studies

7. Layout
Laser and cathode operations
Synhcronization systems
Diagnostic overview and system commissioning
Best results
Conclusions

8. Longitudinal pulse shaping: two stages
Minimum rise time of 3 ps
with the dazzler only
How to increase the
Steepness: simulations

9. Two stages pulse shaping:results
With the DAZZLER and the UV stretcher allow to easily change the pulse length and the time shape
During the run it was achieved rise time down to ps
15 ps pulse
Gaussian pulse
10 ps pulse
6 ps pulse

10. Transfer line and imaging:
Circular beam at cathode (>98%)
Front tilt compensation (< 200 fs)
Work for different spot sizes.
High energy losses: 65%
Sensitive to lens position (±1 mm)
Difficult to be measured
Poor transverse uniformity
A grating parallel to the cathode was employed to diffract the beam at 72°. A lens was used to compensate the chromatism at the image plane.
72° incidence
90° incidence
Better uniformity and lower losses
A mirror in vacuum is required

11. New laser diagnostic: FESCA 200
Sub-ps resolution streak camera has been recently installed at LNF
The measured resolution is about 200 fs in the IR and 500 In the UV
Flat top UV measurements
A short IR pulse was used as reference in
jitter corrected multiple image-acquisistion
IR beam UV
pulse

12. 1nC electron bunch with 50 μJ laser energy (~6*10^13 photons @ 266nm)
Quantum efficiency optimization:
Laser cleaning with 10 μJ and 100 μm spot size diameter.
Mean QE increased from ^-5 to 10^-4
Improved uniformity over a 4 mm square region
1nC electron bunch with 50 μJ laser energy (~6*10^13 266nm)

13. Layout
Laser and cathode operations
Synhcronization systems
Diagnostic overview and system commissioning
Best results
Conclusions

14. Time jitter maximum acceptable values: - SPARC phase I (achieved):
Synchronization:
Time jitter maximum acceptable values:
- SPARC phase I (achieved):
± 2ps between the Laser pulse and the Linac RF
(RF gun mainly)
- SPARC phase II (on the way):
± 0.5ps between the Laser pulse and the Linac RF
(RF gun and RF compressor mainly)
- and next-generation experiments (under study):
± 0.1ps control of the bunch longitudinal position
Synchronization strategy
Laser to RF synchronization:
1-5kHz bandwith piezo-electro-optical feedback (Synchrolock)
Standard laser IR oscillator time jitter measurement
Innovative UV pulse single shot
time arrival measurement
RF to RF synchronization:
Feedback loops
Signal demodulation to monitor the phase of the fields in the RF structures along the machine

15. RF to RF synchronization
Slow feedback (BW<<1Hz):
Correction of the temperature drifts in the waveguides
Motorized phase shifters
0.25ps RMS time jitter measured in the gun (with fast feedback off)
Fast feedback (BW~1MHz):
Correction performed inside a single 4µs klystron
pulse
Electronic phase shifters
230fs open loop time jitter
23fs closed loop time jitter

16. Laser to RF synchronization

17. 10Hz final amplified pulse measurement (best result is 400fs)
Agilent SSA (absolute) measurements
SPARC monitor system (relative to RF)
350fs RMS
10Hz final amplified pulse measurement
(best result is 400fs)
New cavity filter used to reject the noise
coming from high power RF structures
79.3MHz oscillator measurement (very good agreement with SSA)

18. Layout
Laser and cathode operations
Synhcronization systems
Diagnostic overview and system commissioning
Best results
Conclusions

19. Diagnostic overview
60 cm: faraday cup to measure the charge at gun exit, and
Cromox screen to see and center the beam;
cm: E-meter (slits cross, Yag and CCD cross);
Emittance, beam envelope, beam parameters
as function of trnsv. coordinates;
270 cm :aerogel + streak camera; beam length;
cm :FODO;
370 cm : dipole;
400 cm : spectrometer cross (Yag+ CCD) ; E & ΔE meas.
440 cm : ICT (beam charge)
Image of streaked light from
Aerogel (UCLA collaboration)
T=12 ps }
prepare the beam to E & ΔE meas.

20. Envelope automatic measure
The emittance-meter moves and stops in several (15-30) positions. Several images are collected at each point, and an algorithm calculates the RMS parameters and the error bars.

21. Emittance automatic measure
an automated emittance scan has been developed, making use of the centroids
and rms calculated from envelope scan.
30 images each slit position
13 slit positions each z position (sampling the beam with σ/2 step width)
30 z positions
11700 images & ~450 motor movements each ε evolution measurement
The high measurement resolution allows to precisely reconstruct not only the
second moment but the entire transverse trace space distribution (x-x’ or y-y’)

22. Data analysis
It has been the first time of direct emittance evolution measurements and
experimental study of dynamical behaviour
Problems:
Need to know exactly the percent
of charge used to calculate di emitt. (haloes estimation)
Same cut for emitt. meas. at different positions
High sensitivity needed to measure small fluctuations
As result of collaboration between experimental & BD groups
3 independent alghoritms were developed for emittance calculations:
Alg. based on single image analysis and data extrapolation;
Alg. Based on trace space plot filtering;
Genetic alg. fitting 8 different ellispes with same centers, maximizing the
(Intensity/Area) function;
All the procedures have been compared with the simulations, and they showed a
Very good agreement

23. Examples of measurements:

24. Layout
Laser and cathode operations
Synhcronization systems
Diagnostic overview and system commissioning
Best results
Conclusions

25. T= 5.6 MeV, I= 92 A, n = 1.6 m ==> B= 7x1013 A/m2
charge
0.83 nC
pulse length (FWHM)
8.9 ps
rise time
2.6 ps
rms spot size
0.36 mm
RF phase (-max)
-8°

26. phase space - simulation and measurements

27. Flat-top Vs Gaussian pulse shape
charge
0.74 nC
pulse length (FWHM)
8.7 ps
rise time
2.6 ps
rms spot size
0.31 mm
RF phase (-max)
-8°

28. The double minimum experimental evidence
charge
0.5 nC
pulse length (FWHM)
5 ps
rise time
1.5 ps
rms spot size
0.45 mm
RF phase (-max)
+12°
Emittance scan as function of B in a fixed point
Isol=198 A

29. Energy spread evolution along the drift
Demonstr. of negligible WF effect due to the bellows
Isolation of longitudinal space charge eff.
Study of longitudinal dynamics for different charges,
RF phases and pulse lengths

30. Conclusions
Commissioning of the system
Flat top generation with UV pulses
Nominal beam parameters
Good agreement with simulations
Phase space evolution
Energy spread evolution
Flat top Vs Gaussian
Emittance oscillation