Status of SPARC synchronization system and possible upgrades M. Bellaveglia On behalf of the LNF timing, synchronization and LLRF group

SUMMARY SPARC present synchronization system Some option to enhance the system without the transition to the optical distribution Future development and requirements Study of an optical synchronization system with cost estimation Conclusion

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

Phase detection – standard mixing technique Sampling Board DtRMS ≈ 55 fs 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 Phase detection resolution ≈40fs

PLLs - Laser and RF phase lock Electro-opto-mechanical PLL: BW limited to some kHz (piezo-crystal maximum frequency) It locks the laser oscillator repetition rate (79.33MHz=RF/36) to a stable Reference Master Oscillator (RMO) to keep the main frequency constant in time Full electronic PLL: BW measured in lab ≈1MHz We have chosen to use this system architecture to bypass the laser Synchrolock and overcome the PLL bandwidth limitation problem The main oscillator of the system is presently the photo- cathode laser oscillator

How the Synchrolock works Stepper motor, coarse positioning Laser oscillator cavity 12.6ns Galvo motor low freq. correction 79.33MHz From RMO Piezo motor high freq. correction Synchrolock board Motor drivers Fundamental loop @79.33MHz EO transducer and active filtering Frequency x9 Harmonic loop @714MHz

Upgrading the Synchrolock New harmonic loop phase detection Actual scheme: Active frequency x9 multiplier and active filtering after photo detection -> high electronic noise 714MHz phase comparison -> low resolution Reference lock limited to <300fsRMS rms of relative jitter New scheme (1k€ to 5k€): Phase comparison at higher frequency -> higher resolution, locking performance <100fsRMS Interface with motors to be studied (level of signals, interconnections, changing motor drivers?…) Simpler upgrade to optical phase detection

Comparison with FLAME oscillator PLL We measured the performance of the FLAME IR oscillator in terms of phase noise at the manufacturer site and after the installation at LNF High frequency (high resolution) phase comparison directly at 2856MHz We measured with Agilent SSA E5052A an absolute phase noise of about 130fs We measured phase noise relative to the RF reference less than 90fs

PLLs – Klystron intra-pulse phase lock PLL on: Dt<70fsRMS PLL off: Dt≈630fsRMS Phase noise is introduced at the RF power generation level (klystron) It can be reduced by phase locking the klystron output to the RF reference with an analog loop (like in CW RF in storage rings); Very short time available to reach steady state (in case of SLED ≈1ms): wideband loop transfer function (≈1 MHz) required.

RF gun feeding system upgrade Gun accelerating gradient increased by increasing the RF pulse level and shortening its duration Unfortunately the PLL to compress the phase noise introduced by klystron needs 1us to set up correctly To maintain the Klystron PLL performance the RF pulse has been amplitude modulated: in the first 3us the RF level is kept as low as possible to make the PLL working the RF is brought to the maximum level in the last 0.8us

PLLs - Slow drifts compesation Temp. Phase

Measurements on system performance Phase noise detection resolution: <50fsRMS Linac RF devices phase noise (standard phase detection): 40÷100 fsRMS Photo-cathode LAM measured time jitter (resonant monitor): ≈250fsRMS (resolution problem) e-bunch time jitter BAM (bunch arrival resonant monitor): ≈250fsRMS RF deflector centroid jitter (image analysis): ≈150fsRMS

Upgrading the resonant monitor Use of a Mach-Zender 10GHz EO modulator Already purchased and tested in the synch-lab

Electron-photon bunch synchronization Most strict requirement for laser PWFA with external injection SPARC and Flame pulses injected in a gas jet (or capillar), requires synchronization at the level of the period of the plasma wave. Request: Δt<100fsRMS 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

SPARC-FLAME synchronization FLAME AREA FLAME oscillator In 2856MHz Out 79.33MHz Next future solution: Coaxial cable distribution Easiest and quickest Low cost Possible temperature stabilized cable bundle 100fsRMS laser-to-RF synchronization Requires PC Synchrolock upgrade Present phase detection resolution ≈40fs PC laser Oscillator 79.33MHz RF reference 2856MHz SPARC HALL

Enhanced synchronization FLAME AREA Optical synchronization Fiber laser OMO Major system modification needed Higher cost Fiber stabilized links to distribute the signal Possible optical mixing for laser clients Sub-100fsRMS laser-to-RF synchronization FLAME laser oscillator PC laser oscillator SPARC HALL OMO fiber laser oscillator RF synthesizer

Upgrading to optical synchronization

Reference Master Oscillator Used to long term stabilize OMO frequency avoiding slow drifts No extreme performances needed Choice of commercial product (jitter <50fs from 10Hz to 10kHz) Already tested and installed at SPARC

Reference signal generation Phase noise of an Optical Master Oscillator (OMO) from 1kHz to 10MHz is <5fsRMS Quotation from MENLO Systems (excluded RMO)

Reference signal distribution Point-to-point distribution with a jitter <10fsRMS Quotation from MENLO Systems (excluded RMO) Possibilily to avoid one of the links installing the dedicated rack in the PC laser clean room Possibility to avoid both the links using special temperature drifts insensitive fibers Special fibers available from OFS (Optical division of FURUKAWA ELECTRIC CO., LTD.) Prices are: without jacket (FA-KF5062) 13.5 k€/km (675€ for 50m) with jacket (FA-KC4108B) 64.9 k€/km (3245€ for 50m) cable bundle ≈200k€/km

Optical phase detection for laser clients Phase detection resolution in the range of attoseconds Client locks in the worst case with a jitter well below 50fsRMS We are testing a dummy setup in the synch-lab Presently we are limitated in the measurement by the low laser power available Quotation from MENLO

Conclusions Coaxial cable distribution: Can be upgraded to ≈100fsRMS between the electron and the photon beams PC laser Synchrolock should be upgraded Resonant monitor should be upgraded Optical reference distribution (locking sub-systems with <50fsRMS jitter): It is mandatory in case of LPWA acceleration with external e-bunch injection It is already developed and installed by MENLO systems in FERMI@ELETTRA Total quotation from MENLO systems (SMF28 fibers excluded): We can choose to use the special fiber from Furukawa instead of the actively stabilized fiber links from MENLO In this case can yield to a total system cost of ≈245k€ (included fibers for sub-systems interconnection)