1. ILC Phase Reference Distribution R&D
Frank Lenkszus
Controls Group
Advanced Photon Source
Argonne National Lab
2/8/2006
Frank Lenkszus
Advanced Photon Source

2. Advanced Photon Source
RF Phase Stability
The main technological issue for the RTML is likely to be the required RF system phase stability, which is a few percent of 1 degree of L-band. This phase stability must be maintained for a period which is long enough for a beam-based feedback to determine that an unacceptable phase change has occurred, as indicated by variation in the beam arrival times at the IP; thus, a stability period of a few seconds is probably sufficient. (From the RTML BCD)
2/8/2006
Frank Lenkszus
Advanced Photon Source

3. Key Parameters that Influence Timing
Bunch Compressor Phase Tolerance
0.03 to 0.1 degrees at 1.3 GHz
Inter-linac timing tolerance
100 femto-seconds
0.5 degrees is 1 psec at 1.3 GHz
2/8/2006
Frank Lenkszus
Advanced Photon Source

4. Reference Distribution (General)
Use point-to-point fibers
Fiber cable has temperature coefficient: ~10 ppm/ oC
Fiber dispersion: 10ps/nm/km
Use active phase stabilization for fibers
Dual Redundant system with auto fail-over
Short haul (~500 meters) distribution through conventional coax
Active phase stabilization
Phase average scheme
Phase Stable Coax
2/8/2006
Frank Lenkszus
Advanced Photon Source

5. Advanced Photon Source
Prior Work
TELSA
“First Generation of Optical Fiber Phase Reference Distribution System for TESLA”, Krzysztof, C., et al, TELSA Report
NLC
“A High Stability , Low Noise RF Distribution System”, Frisch, J., et al, Proceedings of 2001 PAC, Chicago, pp 816 – 818
“R&D for the ILC Phase/Timing Distribution System”, Frisch, J. 10/20/04
KEK
KEK (“RF Reference Distribtution Using Fibre-Optic Links for KEKB Accelerator”, Natio, T. et al, PAC2001)
DESY/MIT
“High-Precision Optical Synchronization Systems for X-Ray Free Electron Lasers”, Winter, A et al, Proceedings of the 27th International Free Electron Laser Conference, 8/21/05 – 8/26/05, Stanford CA.
2/8/2006
Frank Lenkszus
Advanced Photon Source

6. Advanced Photon Source
Results of Prior Work
TELSA (15 km cable, 1.3 GHz)
Short Term Stability (~1 minute) 0.3 psec
Long Term Stability (5-15 hours) 2 psec
NLC (15 km cable 375 MHz chopped at 3125 Hz)
System Phase stability: 10 femtosecond per degree C per kilometer
Phase Noise 0.1Hz to 10 kHz: 0.1 psec RMS
Stability < 1 hour: +/ psec
Stability Long Term (1 month) : +/- 1 psec
KEK ( 4.8 km PSOF cable, MHz)
Phase stability: ~ 2 degrees
DESY/MIT (XFEL) (500 meters, 100 MHz repetition rate Mode locked laser, dispersion compensated fiber links)
50 fsec (0.1 Hz to 20 MHz)
2/8/2006
Frank Lenkszus
Advanced Photon Source

7. Active Phase Stabilized Link
2/8/2006
Frank Lenkszus
Advanced Photon Source

8. Redundant Reference Transmission with Failover
2/8/2006
Frank Lenkszus
Advanced Photon Source

9. Advanced Photon Source
Some Timing Issues
Fiber oven phase shifters are large and consume significant power (~ 1kW/fiber)
Chop RF frequency or not – Avoid Circulator cross-talk
NLC chopped at 3125 Hz
TELSA – cross talk constant so don’t worry about it
KEK used WDM (1300/1500 nm)
Bunch Compressor
Required stability at the cavities not demonstrated when transmitted over long distances
Local reference distribution
Active Phase Stabilization
Can we assume temperature stable enough through ½ sector so phase stabilizer not required for each local node.
Phase Averaging
Requires directional couplers at each drop point
Temperature stable Coax .
2/8/2006
Frank Lenkszus
Advanced Photon Source

10. Local (IntraSector Reference Distribution)
Reference: Frish, J. “R+D for the ILC Phase/Timing Distribution System”, 10/20/04
2/8/2006
Frank Lenkszus
Advanced Photon Source

11. Work to be done on Phase Distribution
Establish stability/phase noise budget
Master Oscillator
Long haul distribution
Local (Intra Sector distribution)
(From 1/17/06 LLRF mtg at Fermi) For MO/phase reference distribution/reconstruction and no beam (pilot bunch) spec is:
+/- 0.5 degrees rms (1 over 15 km over “long” time scale
Prototype phase stabilized link building on NLC/TELSA work
Extend prototype to redundant configuration
Develop and test auto failover
Investigate options to distribute phase reference to Bunch Compressors
Failure Effects and Analysis
2/8/2006
Frank Lenkszus
Advanced Photon Source

12. Advanced Photon Source
R&D Proposals
Update Active Phase Stabilization design and prototype
Trench test of fiber system (vs coil in oven)
Evaluate whether to Chop or not Chop.
Prototype Sector Distribution scheme
Evaluate
phase averaging scheme
Issue directional couplers required at each pick crate.
active phase stabilization
Stabilize end to end
Is temperature uniform enough across a sector.
phase stable cable.
Prototype Two-channel phase reference receiver comparator scheme
Is there a credible low-cost way of building a vcxo with sufficient performance?
Evaluate beam derived reference for locking phase reference to beam.
Pursue HOM phase detector scheme.
Investigate different schemes to meet the bunch compressor requirements.
Investigate the wavelength tuneable lasers to replace phase shifters over realistic temperature range.
2/8/2006
Frank Lenkszus
Advanced Photon Source

13. Phase Stabilization R&D
Update Active Phase Stabilization design and prototype
Pick site to install fiber
Want both head and tail ends at same physical location so direct end to end measurements can be made
Full 15 km fiber length is highly desirable
Trench Test?
Can’t control fiber environment
Expensive.
At APS could rap 15 km fiber around SR cable tray (1.1 km)
Integrate with Fermi ILCTA
Chop or not to chop
Select directional coupler with low crosstalk
Prototype in chopping that can be disabled to evaluate performance with and without.
Evaluate effect of chopping on VCXO.
Evaluate low phase noise VCXO’s for receiver end.
2/8/2006
Frank Lenkszus
Advanced Photon Source