# Presentation: 323018

## ILC Timing Reference Distribution

- Frank Lenkszus
- Controls Group
- Advanced Photon Source
- Argonne National Lab

- 1/17/2006

## 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)

- 1/17/2006

## 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 |

- 1/17/2006

## Reference Distribution (General)

- Use point-to-point fibers
- Fiber cable has temperature coefficient:  		~10 ppm/ C
- 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

- 1/17/2006

## Prior Work

- TELSA
- “First Generation of Optical Fiber Phase Reference Distribution System for TESLA”, Krzysztof, C., et al, TELSA Report 2005-08
- 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)

- 1/17/2006

## TELSA Requirements

- Requirement: 0.1 Degree phase stability
- Bunch Compressor more stringent: 0.01 degree phase stability
- Dual Redundant fiber transmission to “sectors”
- Sources of Phase Noise
- Master Oscillator
- Fiber Transmission link
- Laser Transmitter
- Temperature variation is the most important source of phase drifts in the long fiber links
- Typical phase length change vs temperature of a fiber optic cable = ~10 ppm/ C
- Primary contributor to temperature coefficient is change in refractive index.

- 1/17/2006

## TELSA Reference Distribution Specifications

- Short Term Stability (phase noise) << 1 ps, (10 fs at XFEL)
- Short term stability (minutes) < 1 ps at RF frequency (0.5 @ 1.3 GHz)
- Long term stability (days) < 10 ps (5.0 @ 1.3 GHz)
- System Length: up to 15 km
- Distributed frequencies 9-2856MHz (Tests done at1.3GHz)
- High Reliability

- 1/17/2006

## TESLA Features

- Use 1550 nm DFB Laser
- Temperature controlled to 25 C
- Use SMF-28 fiber (Corning)
- Loss < 0.22dB/km @  = 1550 nm => 4.4 dB for 20 km fiber
- Phase Shifter
- 5km fiber inside an oven with 30 C temperature range
- Compensates for phase changes induced by 10 C temperature change of 15 km link
- Digital PID controller
- Only PI gains used
- Transmit 1.3 GHz reference

- 1/17/2006

## TESLA

- 1/17/2006

## Errors

- Temperature Effects
- Fiber Cable
- FO Tx
- < 0.1/C (@1.3 GHz)
- FO Rx
-  < 0.05/C (@ 1.3 GHz)
- Circulator cross talk
- Should cause only a static phase error therefore shouldn’t be of concern
- Reflected signal should be of sufficient power.

- 1/17/2006

## TESLA Component Performance

- Phase detector
- Temperature sensitivity ~0.1C
- Temperature stabilize phase detector?
- Fiber Transmitter
- Temperature sensitivity ~0.07C
- Fiber Receiver
- Temperature sensitivity ~0.05C
- Temperature stabilize fiber receivers?
- Fiber cable
- Measured temperature coefficient ~7.5 ppm/ C (expect ~10 ppm/ C)
- Phase Shifter (5 km fiber cable in oven with PID controller)
- Time Constant 20 to 25 minutes
- Rise and fall time 45 +/- 10 minutes (10 to 90%)
- Delay time 5 to 9 minutes (time to reach 10% of maximum value)
- Circulator
- Isolation > 40 dB

- 1/17/2006

## TELSA System Performance

- Integrated system test had problems
- Had to reduce PID P gain to make system stable
- Caused by phase shifter dead-time
- Couldn’t run tests for more than 5 -15 hours because of software malfunction
- Stability
- Short Term Stability 0.3 psec
- Long Term Stability 2 psec

- 1/17/2006

## NLC Requirements

- Transmission length : 	15 km
- Noise 10 sec to 10 kHz: 	< 0.12 psec RMS
- Stability < 1 hour:	+/-  1 psec
- Stability Long Term:	+/- 5 psec
- Temperature Stability:	< 2x10-8/C

- 1/17/2006

## NLC Prototype Features

- Use 1550 nm DFB Laser
- Laser pulsed at 3125 Hz to avoid interference between forward and reflected power.
- Use SMF-28 Single-mode fiber 15 km long
- Phase Shifter
- 6km fiber inside an oven
- Oven continuously cooled by TEC cooler and heated by a wire grid.
- Prototype operated at 375 MHz carrier
- RF signals mixed down to 25 kHz IF and digitized at 200 kHz.
- Phase measured digitally in PC.
- PID  loop implemented in PC to drive phase shifter
- All RF components and optical components were mounted in a temperature controlled oven.
- Test output signal filtered with 100 Hz bandwidth VCXO phase locked loop to reduce broadband noise.

- 1/17/2006

## NLC Test Setup

- 1/17/2006

## NLC Prototype Performance

- System Phase stability: 10 femtosecond per degree C per kilometer
- Phase Noise 0.1Hz to 10 kHz: 	0.25 psec RMS
- Later report of ~0.1 psec
- Stability < 1 hour:		+/-  0.75 psec
- Stability Long Term (1 month) :	+/- 2 psec
- Later report of +/- 1 psec
- Temperature Stability:		< 10-8/C

- 1/17/2006

## Variations

- KEK (“RF Reference Distribtution Using Fibre-Optic Links for KEKB Accelerator”, Natio, T. et al, PAC2001)
- Used Phase Stabilized Optical Fiber (PSOF) : 0.4ppm/C (-10 to 30 C)
- Used WDM (1310 (Forward) and 1550 (Reflected) nm to avoid crosstalk
- Avoids RF chopping
- Distributes 509MHz
- Temperature stabilized phase shifter
- Electronically controlled varactor diodes
- Phase stability: ~ 2 degrees for 4.8 km PSOF cable

- 1/17/2006

## Active Phase Stabilized Link

- 1/17/2006

## Redundant Reference Transmission with Failover

- 1/17/2006

## Sector Timing Distribution

- 1/17/2006

## 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 1⁄2 sector so phase stabilizer not required for each local node.
- Phase Averaging
- Requires directional couplers at each drop point
- .

- 1/17/2006

## Local (IntraSector Reference Distribution)

- Reference: Frish, J. “R+D for the ILC Phase/Timing Distribution System”, 10/20/04

- 1/17/2006

## Other Frequencies

- Other generated frequencies will be sync’d to 5 Hz timing fiducial
- 3.25 MHz	Injector 	(1/400  1.3GHz)
- 500 MHz	DR	(5/13  1.3 GHz)
- 46.3 kHz	Electron (6 km) DR Revolution Clock	(500MHz/Harmonic #)
- 23.15 kHz	Positron (12 km) DR Revolution Clock
- 54 MHz	Lasers     (1/24   1.3 GHz)

- 1/17/2006

## Timing Questions

- Under what conditions should timing cause an MPS trip
- Unrecoverable phase distribution error
- Timing Requirements for Accelerator Components
- Table
- Number, Resolution, Accuracy, Stability, Jitter
- Kickers
- Bpms
- Laser Wire
- Etc
- Timing Requirements for BDS
- Bunch Compressor
- Most stringent timing requirement
- Master Oscillator Specification
- Event System
- Local (sector/ring)
- Global (is this needed)
- Increases fiber plant

- 1/17/2006

## Timing Stability Budget

- Need to develop a stability budget
- Master Oscillator
- Long haul reference distribution
- Bunch Compressor
- All other
- Local (Intra Sector) reference distribution

- 1/17/2006

## Work to be done on Phase Distribution

- Establish stability/phase noise budget
- Master Oscillator
- Long haul distribution
- Local (Intra Sector distribution)
- 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

- 1/17/2006

## Timing Functions

- Master oscillator distribution (1.3 GHz)
- 5 Hz timing fiducial distribution
- Programmable triggers for field hardware
- Mechanism to synchronize software processing to timing events
- Time fiducials for synchronized timestamps for software and hardware events.

- 1/17/2006

## Timing Global Specifications

- Timing Phase locked to RF System
- Stability at the point of RF measurement and control: ~10 picoseconds
- Short Term Stability for Bunch Compressor:  ~100 femtoseconds
- Timing phase reference to be redundant with auto failover
- Timing phase reference distribution will use active phase stabilization
- Phase shifter will be based on fiber in a temperature controlled oven
- Will build on prior work for NLC and TELSA
- Timing phase reference will be distributed via active phase stabilized redundant fibers in star configuration to sectors
- Local distribution will be via coax
- Phase stable coax
- Phase averaging scheme
- Required timing triggers and other frequencies will be developed locally at sector locations from the distributed phase reference.
- 5 Hz timing fiducial will be encoded on timing phase reference by momentary phase shift
- Others have used Amplitude Modulation.

- 1/17/2006

## Timing Global Specifications (Cont.)

- Local timing triggers will be developed by counting down phase reference
- Graded approach to timing trigger generation
- High precision: (pico-second)
- Medium precision (nano-second)
- Low precision (microsecond)

- 1/17/2006

## References

- “First Generation of Optical Fiber Phase Reference Distribution System for TESLA”, Krzysztof, C., et al, TELSA Report 2005-08
- “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
- Larsen, R. S., Technical Systems Configurations – Electrical Subsystem: Instrumentation – Timing, Rev. 1, March 23, 2001

- 1/17/2006