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OUTLINE. ON SOME TIMING JITTER ISSUES FOR THE FERMI  FEL PHOTOINJECTOR LASER SYSTEM Presented by M.B.Danailov Laser Lab, Sincrotrone Trieste danailovm@elettra.trieste.it. Current status of the FERMI project (slides provided by Rene Bakker)

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OUTLINE

ON SOME TIMING JITTER ISSUES FOR THE FERMI  FEL

PHOTOINJECTOR LASER SYSTEM

Presented by M.B.Danailov

Laser Lab, Sincrotrone Trieste

danailovm@elettra.trieste.it

Current status of the FERMI project

(slides provided by Rene Bakker)

Photoinjector laser system and related jitter reduction issues

►required parameters

►main concerns

►near future experiments

SLAC XFEL Short Bunch Measurement and Timing Workshop


ELETTRA

SLAC XFEL Short Bunch Measurement and Timing Workshop


Undulator

Building

(new)

Experimental

User Hall

(new)

1 GeV Linac

(existing)

Booster Synchrotron

(under construction)

Present linac availability:

22 h/day

ELETTRA

2-GeV 3rd generation storage-ring

(existing)

runs presently 3000 h/year,

24 h/day for special studies

FERMI@ELETTRA

SLAC XFEL Short Bunch Measurement and Timing Workshop


FERMI@ELETTRA

  • Key features:

    • Development of a user-facility.

    • Based on existing 1-GeV S-band linac infrastructure.

  • Specifications:

    • Spectral range (2 undulator lines):

      • 100–40nm (12–30eV): FEL-1

      •  40 –10nm(30–124eV):FEL-2

    • Flexible polarization.

    • Seeded operation (SASE as optional).

    • Short pulses (sub-ps  < 100 fs RMS).

    • 50 Hz repetition rate, 1 micro-pulse per macro-pulse.

SLAC XFEL Short Bunch Measurement and Timing Workshop


FERMI@ELETTRA

  • Present status:

    • Funding granted

    • Linac serves as injector for ELETTRA

  • 2005 – 2006:

    • (available for FERMI : 22 h/day)

    • Construction of a new full-energy injector (booster) for ELETTRA

    • Commencement of FEL construction

    • 2007 …………

    • Implementation and use of the linac FEL user-facility

SLAC XFEL Short Bunch Measurement and Timing Workshop


Injector

new

injector

accelerator

S0 – S7

old

injector

RF photo-gun

accelerator

Present Injector

by-pass

FERMI@ELETTRA

SLAC XFEL Short Bunch Measurement and Timing Workshop


bunch compressor

1

bunch compressor

2

new

injector

S0

S1 – S5

S6 – S7

old

injector

linac

linac

linac

BC1

BC2

new

injector

harmonic

cavity

(new)

FERMI@ELETTRA

SLAC XFEL Short Bunch Measurement and Timing Workshop


harmonic

cavity

FEL-1

user stations

new

rf photo-injector

seed

linac

linac

booster

accelerator

BC2

BC1

seed

FEL-2

30 % tunability

FERMI@ELETTRA

SLAC XFEL Short Bunch Measurement and Timing Workshop


  • online diagnostics

  • focused beam

  • direct unfocussed beam

  • monochromatized beam

FEL

synchronized

laser

spontaneous

radiator

photo-cathode

laser

RF

P&P lasers

Master

Oscillator

timing

diagnostics

linac

FEL

feedback

FERMI@ELETTRA

SLAC XFEL Short Bunch Measurement and Timing Workshop


FERMI@ELETTRA

2-Stage High Gain Harmonics Generation

250 nm  50 nm  10 nm

SLAC XFEL Short Bunch Measurement and Timing Workshop


20 ms

~ 2.5 ms

accelerating

field in linac

electron pulse

e.g., 50 ns (20 MHz)

20 ms

~ 2.5 ms

increase of the average brilliance and flux: 40x

FERMI@ELETTRA

SLAC XFEL Short Bunch Measurement and Timing Workshop


FERMI PHOTOINJECTOR LASER

MAIN PARAMETERS

Rep rate: 10 (50) Hz

Pulse duration: 2-10 ps (FWHM), ideal pulse shape: flat-top

Rise-time: 0.5 ps (10-90%)

Spatial profile: top-hat, ~ 1mm 1/e2 radius

Fundamental Wavelength 780-800 nm

UV wavelength (third harmonic) 260-267 nm

Pulse energy (for Cu cathode):

Compressed IR amplifier output – 6 mJ /10mJ

UV after THG crystal- 0.6 mJ/0.75 mJ

UVon the photocathode >0.45 mJ /0.5mJ

Timing stability with respect to RF : < 0.5/0.3 ps RMS

Energy stability : < 4% RMS / <3 %RMS

Stability of the beam position on the photocathode : < 3% 1.5%RMS

SLAC XFEL Short Bunch Measurement and Timing Workshop


Ampl2 (Multi-pass, 50 Hz)

SS

THG

Stab

Pump Laser 2

cr-cor

FERMI PHOTOINJECTOR LASERLAYOUT

REF

Error sig ?

Ampl1

(Regen. , 1 KHz)

ML

Laser

PP

TS

Pump Laser 1

TS: temporal shaping ; PP : pulse picker ; SS – spatial shaping ; Stab – pulse energy stabilization system

cr-cor : cross correlator (SFG intensity -> jitter)

SLAC XFEL Short Bunch Measurement and Timing Workshop


OSCILLATOR JITTER

  • CURRENTLY CHARACTERIZED:

  • 1.Oscillator :

  • - home made mirror dispersion controlled (MDC) Cr:LiSAF laser

  • - Ti:S oscillator with prism dispersion control

  • 2. Phase-locking : Commercial CLX-1100 Timing Stabiliser , based on single band (100 MHz) PL loop , mixer

  • Performance: <200 fs RMS short term stability in noise protected environment

  • Increase to few ps in presence of acoustic noise

  • STRATEGY FOR IMPROVEMENT:

  • 1.Oscillator:

  • MDC Ti:S laser

  • Frequency-doubled Er-doped fiber laser

  • 2.Phase-locking:

  • Use of double band-loop (GHz detector working at harmonic of the rep rate)

  • Digital phase detector based error measurement

SLAC XFEL Short Bunch Measurement and Timing Workshop


FERMI BEAM TRANSPORT SYSTEM

Low vacuum enclosure ?

Relay imaging

Grating

PSD1

T

PSD2

To phase det

  • Open questions:

  • Ray tracing of the transport optics (Relay imaging?)

  • CW pilot beam for fast opt path monitoring

  • - Low vacuum path between laser hutch and gun

Gun

SLAC XFEL Short Bunch Measurement and Timing Workshop


SUMMARY

  • We hope that the stand-by period of FERMI is about to end

  • Timing and synchronization would be crucial for the system

  • Near future tasks on the laser side:

  • ►decision on the femtosecond oscillator type

  • ► further development of digital phase detector based jitter monitoring

  • ►study of diode-pumped regenerative amplifier jitter (cross-correlator based jitter measurement)

  • ► ray tracing of beam transport system

  • ►layout of overall timing system

SLAC XFEL Short Bunch Measurement and Timing Workshop


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