Frank Lenkszus

1
ILC Timing Reference Distribution

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

2
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)

3
Key Parameters that Influence Timing
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

5
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
• RD 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)

6
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/ oC
• Primary contributor to temperature coefficient is
  change in refractive index.

7
TELSA Reference Distribution Specifications

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

8
TESLA Features

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

9
TESLA
10
Errors

• Temperature Effects
• Fiber Cable
• FO Tx
• lt 0.1o/oC (_at_1.3 GHz)
• FO Rx
• lt 0.05o/oC (_at_ 1.3 GHz)
• Circulator cross talk
• Should cause only a static phase error therefore
  shouldnt be of concern
• Reflected signal should be of sufficient power.

11
TESLA Component Performance

• Phase detector
• Temperature sensitivity 0.1o/ oC
• Temperature stabilize phase detector?
• Fiber Transmitter
• Temperature sensitivity 0.07o/ oC
• Fiber Receiver
• Temperature sensitivity 0.05o/ oC
• Temperature stabilize fiber receivers?
• Fiber cable
• Measured temperature coefficient 7.5 ppm/ oC
  (expect 10 ppm/ oC)
• 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 gt 40 dB

12
TELSA System Performance

• Integrated system test had problems
• Had to reduce PID P gain to make system stable
• Caused by phase shifter dead-time
• Couldnt run tests for more than 5 -15 hours
  because of software malfunction
• Stability
• Short Term Stability 0.3 psec
• Long Term Stability 2 psec

13
NLC Requirements

• Transmission length 15 km
• Noise 10 sec to 10 kHz lt 0.12 psec RMS
• Stability lt 1 hour /- 1 psec
• Stability Long Term /- 5 psec
• Temperature Stability lt 2x10-8/oC

14
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.

15
NLC Test Setup
16
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 lt 1 hour /- 0.75 psec
• Stability Long Term (1 month) /- 2 psec
• Later report of /- 1 psec
• Temperature Stability lt 10-8/oC

17
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/oC (-10 to 30 oC)
• 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

18
Active Phase Stabilized Link
19
Redundant Reference Transmission with Failover
20
Sector Timing Distribution
21
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 dont 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
• .

22
Local (IntraSector Reference Distribution)
Reference Frish, J. RD for the ILC
Phase/Timing Distribution System, 10/20/04
23
Other Frequencies

• Other generated frequencies will be syncd 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)

24
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

25
Timing Stability Budget

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

26
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

27
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.

28
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.

29
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)

30
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
• RD 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