1. Timing and synchronization at SPARC
M. Bellaveglia
On behalf of the SPARC/X timing, synchronization and LLRF group

2. Summary SPARC general overview Synchronization and timing systems
Phase detection techniques
Feedbacks and PLLs in the system
Two beams synchronization
SPARC future plans
Electrons-photons interaction: SPARC towards LI2FE
LI2FE synchronization
Conclusion

3. SPARC general overview
SEEDING
LASER
PHOTOINJECTOR
UNDULATOR
HHG
DGL
PLASMON-X
THOMSON

4. SPARC general overview

5. LNF Synchronization lab

6. SPARC synchronization system overview
One optical master oscillator
Feedbacks with BW <<1Hz, ≈5kHz and ≈1MHz to synchronize the subsystems
Shot-to-shot (10Hz) analysis for amplitude and phase calculation

7. SPARC timing system overview
Line synchronization
50Hz
PC laser amplification pump
1KHz
RF reference
79.33MHz
Trigger box
1KHz
PC laser oscillator
79.33MHz
Frequency divider
10Hz
RF reference
2856MHz
PC and seeding lasers
Machine trigger
distribution
10Hz
Frequency divider
1KHz
Diagnostics
Input
Output
Electrical
Optical
Transduction
RF triggers

8. Phase detection – standard mixing technique
DtRMS ≈ 55 fs
Sampling
Board
Tested Sampling Boards:
ADLINK 9812: 12-bit, 4-channels, 20 Ms/s
ADLINK 9820: 14-bit, 2-channels, 65 Ms/s
NI PXI 5105: 12-bit, 8-channels, 60 Ms/s
Console application:
Real time base band analysis: phase noise and amplitude measurements
Possibility in choosing waveform analysis

9. Phase detection – Resonant method
DtRMS ≈ 250 fs
2142MHz cavity design to avoid RF interference with accelerating structures
Cavity exited by very short pulses: (i) e.m. field of the beam or (ii) output of a high voltage PD excited by the UV laser
Phase detection is possible using the decay time of some us inside the cavity
250fsRMS time of arrival jitter observed in both the laser and bunch monitor

10. Phase detection – Deflector centroid jitter
SPARC RF deflector
Image of a SPARC bunch vertically streaked on a target
Measurement of the beam centroid vertical jitter
t ≈ 150 fsRMS

11. PLLs - Klystron Fast Phase Lock
Phase shifter
PLL on:
Dt≈77fsRMS
PLL off:
Dt≈630fsRMS
To waveguides
Error amp
From reference
The phase noise introduced at the RF power generation level can be reduced by phase locking the klystron output to the RF reference with an analog loop: same concept as phase loops in CW machines;
Short time available to reach steady state (≈1ms): wideband loop transfer function (≈1 MHz) required.

12. PLLs – Long term drifts correction

13. Two beams synchronization – IR-UV on cathode
IR beam
UV beam
electrons
RF GUN
DEFLECTOR
SCREEN
Experiment to try to modulate the electron beam during the photo emission
Delay line in the IR optical transfer line to synchronize the beams
Coarse synch (same bucket, <360ps): HV photodiode illuminated by the two beams and 5GHz oscilloscope to see the pulses overlap in time
Fine synch (“zero” delay): electron extracted by both the beams and accelerated until the RF deflector

14. Two beams synchronization – IR-UV on cathode

15. Two beams synchronization – FEL seeding
Undulator SR
LASER
SEED
SCREEN

16. Two beams synchronization – FEL seeding
Same approach than the IR+UV experiment
Both the beams are optical and more precisely: (i) the spontaneous radiation of the electron beam and (ii) the seeding laser pulse
Coarse synchronization (about 1ns): photodiode and oscilloscope (500MHz BW is enough)
Tuning the undulator section for spontaneous we were able to see both the signals on the oscilloscope and to overlap the electrical pulses
Also we observed the spectrum of the two beams tuning the spontaneous in the same wavelength range of the seed (400nm)

17. Two beams synchronization – FEL seeding
Fine synchronization: when the coarse synchronization was finished, we tuned the undulator sections to let the electron beam interact with the seed and we slightly moved (5mm) the optical delay line of the seeding laser
We immediately observed the seed amplification at the spectrometer

18. SPARC future plans - SPARC towards LI2FE
SPARC nominal parameters
Electron Beam Energy
155
MeV
RMS normalized transverse emittance
<2
mm-mrad
Bunch Charge
1.1 nC
RMS slice norm. transverse emittance
<1
Repetition rate 10 Hz
RMS total corralated energy spread
0.2 %
Photocathode spot size mm
RMS incorrelated energy spread
0.06
Laser pulse duration (flat top) ps
RMS bunch spot exit
0.4
Laser pulse rise time (10÷90%) 1
RMS bunch exit
Bunch peak current (50% beam)
100 A
SEEDING
LASER
PLASMON-X
FLAME parameters
PHOTOINJECTOR
LASER
Wavelength
800 nm
Compressed pulse energy 5 J
Pulse duration (bandwidth)
30 (80)
fs (nm)
Repetition rate 10 Hz
Energy stability
10%
Pointing stability
<2
urad
THOMSON
HHG
DGL
PHOTOINJECTOR
UNDULATOR

19. SPARC future plans - LI2FE Experiments
Thomson scattering
Requires physical overlapping of SPARC and FLAME beams within the depth of focus of the laser focusing optics.
Experiments: PLASMONX, MAMBO
Request: Δt<1psRMS
Plasma acceleration
SPARC and Flame pulses injected in a gas jet, requires synchronization at the level of the period of the plasma wave.
Experiments: PLASMONX
Request: Δt<100fsRMS

20. SPARC future plans - LI2FE synchronization
FLAME AREA
FLAME oscillator
In 2856MHz
Out 79.33MHz
Current layout
PC laser oscillator is the OMO
Electrical reference distribution
FLAME not yet considered
PC laser
Oscillator
79.33MHz
RF reference
2856MHz
SPARC HALL

21. SPARC future plans - LI2FE synchronization
FLAME AREA
FLAME oscillator
In 2856MHz
Out 79.33MHz
1st solution – electrical distribution
Easiest and quickest
Low cost
Coaxial cable distribution
Possible temperature stabilized cable bundle
Hundreds of femto-seconds performance
PC laser
Oscillator
79.33MHz
RF reference
2856MHz
SPARC HALL

22. SPARC future plans - LI2FE synchronization
FLAME AREA
2nd solution – optical distribution
Fiber laser OMO (Optical Master Oscillator)
Major system modification needed
Higher cost
Fiber links to distribute the signal (active length stabilization)
Optical mixing (cross correlation) for laser clients
Sub-100fs performance
PC laser
Oscillator
79.33MHz
OMO
FLAME oscillator
RF reference
2856MHz
SPARC HALL

23. Conclusion Future plans: electrons-photons interaction
Synchronization system performance
System is inside project specifications
New diagnostic methods developed (BAM, LAM)
e-beam to RF jitter: ≈200 fsRMS
Seeding experiment successful
Future plans: electrons-photons interaction
Possible solutions and relative jitter:
Electrical reference distribution: 100÷200 fsRMS
Optical reference distribution: <100 fsRMS