Precision Optical Timing Distribution and Electron Arrival-time
Measurement at XFEL/SPring-8 Yuji OtakeA), Takashi OhshimaA), Hirokazu MaesakaA), Naoyasu HosodaA),
Shinichi Mastubara A) Mituru MusyaB), Kenji Tamasaku A)
A) RIKEN, XFEL Joint Project /SPring-8B) Institute of Laser Science, Univ. of Electro-communications
RIKEN + JASRI
contents
1. Optical time and RF reference system for XFEL/SPring-8.
2. Direct 770nm pump laser activation by a 1540 nm comb laser pulse for the accelerator timing to realize a time jitter with several femto-seconds.
XFEL 8Gev, 0.3 nc, 0.1 nm light(2010, construction finish)
SCSS Test Accelerator250 MeV, 0. 3 nc, 60 nm light
Japan
Korea
Electron Gun Bunch Compressor C‐band Accelerator Undulator
Cavity ΔV/V(%rms) Δφ (deg. rms) Δt (ps rms)238 MHz SHB ± 0.01 ± 0.01 ± 0.12476 MHz Booster ± 0.01 ± 0.02 ± 0.12L-band Cor. Cavity ± 0.03 ± 0.06 ± 0.12L-band APS Cavity ± 0.01 ± 0.06 ± 0.12C-band Cor. Cavity ± 0.1 ± 0.06 ± 0.049S-band Accelerator ± 0.01 ± 0.1 ± 0.09724 C-band Accelerator (up-stream) ± 0.01 ± 0.2 ± 0.097104 C-band Accelerator (Down-stream) ± 0.01 ± 0.5 ± 0.24
rf
BeamThe Crest acceleration Part
OSC e.g. Klystrons
Off-crest acceleration Part
Max.
Tolerance of the Phase & Amplitude of RF Cavities at XFEL/SPring-8
Find perturbations, such as a temperature change, vibration, noise etc.
Reduce/eliminate these perturbations as small as possible.
Design criterion of the timing system for realizing stable SASE generation.
Optical Time Reference System
Carrier Signal Spectrum
Install
Not InstallDeveloped
Within 0.2 K
Optical Time Reference Signal Transmission System
The optical system dose not increase the master oscillator’s noise.
Increase7 fs
Carrier Frequency
Pink: Master Oscillator NoiseBrown : After 500 m Optical Transmission
SSB Noise Spectrum ofEO & OE transmission
Temperature variation around the fiber
Optical Fiber
Glass Wool
Cooling Water
0.5K
T fiber1
T fiber2
T fiber3
Fiber Temperature Control by Water
TrigDelay
IQ Mod.
T fiber1 T fiber2
T fiber3
SCSS test accelerator
C-band klystronMaster OSC
WDM (Wave length Division Multiplex) optical transmission system
Test of Optical Transmission Line using SCSS Test Accelerator
2 weeks
Coaxial Cable Case
Energy fluctuation measured by the rf zero phasing method at the end of the C-band cavity
Case DE DtCoaxial Cable 0.49MeV 138fs (rms)Optical Fiber 0.50MeV 140fs (rms)
Stability of SASE intensityCase mean stdCoaxial Cable 6.17 0.5Optical Fiber 6.20 0.66
(Arbitrary Unit)
Stability of SASE & Beam EnergyOptical Fiber Drive Case
2 hours
1
at E = ~ 120 MeV
When the RF signal was driven by the optical fiber system.
Both of the optical and coaxial cables have the same performance of rf phase and amplitude stability at the SCSS test accelerator.
Including instability at an rf zero phase point, therefore the changes were enhanced.
Optical Fiber Case
Use the 4760 MHz BPM intensity detection cavity
5236MHz
4760MHz
Cavity BPM
Synchronized with acceleration RF
476MHz
TM010 Reference cavity
TM110 Position detection cavity
0o
90o
IQ mixer
0o
90o
I
IQ
Q
BeamThis cavity is placed just before the IDs.
This frequency to prevent the dark current generated by the 5712 MHz accelerator guides.
Performance of Timing System at SCSS Test Accelerator
Beam Time jitter is 46 fs0.54 mV Standard Deviation.Horizontal Scale. 4 ns/div.10 pps Beam Reptation.
12 hours
1 %δE/E
Now, the beam energy stability was improve less than 0.1 % (rms) in the long term (more than half day) by the rf phase feedback control of the cavities (238, 476, 2856 MHz).
R56, 20 mm (BC)Beam energy jitter valueabout 0.06 % (rms)
Results of Beam Arrival Time Jitter Measurements
770 nm Pump Laser Directly Activated by a 1540 nm Comb Laser Pulse
Design criterion to realize a low time jitter fora pump-prove experiment
1.Eliminate electrical synchronization circuits for a pump laser.
2. We only use optical components to pump a 770 nm TiSapphire Laser from a 1540 nm optical master oscillator for the accelerator.
Mode-Lock Laser(Ti Sapphire)
OpticalFiber Line
79.5 MHz Time reference line
RF system: 5712 MHz Klystrons etc
Master Oscillator(Sinusoidal Wave) E/O O/E
Sample
Pump Laser
Our devised & modified part
79.5 MHz rf Signal
XFEL
Present Plan for Pump-Probe Experiments for XFEL/SPring-8
For about 1 km
Devised 770 nm Laser Driven by 1540 nm Comb Laser
Optical comb pulse & its spectrum
5712 MHz Repetition,1ps pulse width
Optical Comb Generator
The laser source (1538 nm) using DFB laser diode in which the light is locked to acetylene absorption spectrum. The frequency stability is almost 10-11 in a frequency region below 10 Hz.
In the optical comb generator, an electro-optic (E/O, LN) crystal is inserted into an optical Fabriot-Periot cavity.The output rf signal of the master oscillator is added into the E/O crystal to generate the comb pulse having a period of the rf signal.
Method to Cull 1540 nm laser pulse train using LN Modulator
1540 nm
Method to Cull 770 nm Comb Laser Pulses using Pockel Cell
60 Hz Signal
Optical Output
LN Modulator
Pockel Cell
Mirror
Mirror
Lens
SHG Crystal
A 60 Hz laser comb pulse train is picked up from 5712MHz comb pulse train
Pulse Culling System
Avalanche Pulser
Experimental Set up for 770 nm Laser System Driven by 1540 nm Laser
Spectrum of the 770 nm laser converted by a PPLN (Periodically Poled Lithium Niobate) crystal. The CW 1500 nm laser light is injected in to the PPLN crystal.
Second Harmonic (770 nm) Generation by PPLN Crystal
5712MHz RF
1540nm Pulse
770nm Pulse
The pulse response of this photo diode is slow, therefore, the pulse width of the 770 nm laser pulse dose not show a true pulse width.
Second Harmonic Generation & Culling 10 Hz Laser Pulse form 5712MHz Comb Laser
We achieved nonlinear amplification of a 50 nm VUV laser with 10 % fluctuation (saturation) at the SCSS test accelerator by using our timing system. This fact shows great possibility to realize XFEL/SPring8.The master oscillator has a sufficient SSB noise level to realize a beam energy stability of 104. The beam energy variation, and the beam time jitter to the acceleration rf, are less than 0.06% (rms) at 120 MeV and 46 fs at the test accelerator.
The 1540 nm & 770 nm laser pulse culling system works well, and the wavelength conversion system from 1540 nm to 770 nm also works well. We will try to drive a TiSapphire regenerative amplifier by the developed system.
Summary
Calculated data
Frequency dividing.Very low-noise power supply.PLL connection between 10 MHz and 2856 MHz sources.
Circuit Diagram & Calculated Noise of Master Oscillator
-160
-150
-140
-130
-120
-110
-100
-90
-80
-70
-60
1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06
Frequency (Hz)
SSB noise Power (dBc)
5712 MHz
5236 MHz
2856 MHz
2380 MHz
476 MHz
238 MHz
Decreases of noise levels at the individual frequencies are proportional to the dividing ratio.
These noise correspond to about 30 fs time jitter with rf pulse modulation (2ms)
SSB Noise Spectra of Master Oscillator
Prototype of Optical Fiber Length Controller
Phase-stabilized optical fiber has a thermal optical length coefficient of 2 ppm/K. The optical length of the fiber moves 1.6 mm/K for 800m.This values corresponds to a phase shift of 11 deg./K and 5.4 ps/K at 5712 MHz, and is not acceptable to employ this method for the X-FEL. Therefore, we developed this fiber length control system.
ExperimentalApparatus
Satisfy the original system performance developed for ALMA. (Controlled it optical length within 3 μm for 25 km.)
Use the 1 km phase stabilized optical fiber cable settled along the circumference of the SPring‐8 ring
1 km FiberError Length Spectrum of Control
Experiment of Fiber Length Control
Timing Control System
IQ modulator rf phase and amplitude control.IQ demodulator detects rf phase and amplitude.
Baseband waveforms are processed by VME high‐speed D/A and A/D converter boards.
Sampling rate: 238 MSPSResolution: 14 bits (D/A) and 12 bits (A/D)
All modules are enclosed in a water‐cooled 19‐inch rack. Regulated within 0.4 K.
To reduce the thermal drift.
DC power is distributed from a low‐noise power supply.
Clean and stable powerSmall heat load for the 19inch rack
26
To check the performance of the optical transmission line,
the stability of SASE intensity andthe energy change cursed by the acceleration field strength change of the Cband accelerator guides by using the zerophase method.
RF BPF
PDundulator
e-beam
Experimental Set-up for Test
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05
Free All V/sqrtHz
Lock Hi All
After Replacing New Fiber Stretcher with Fast Response