NLC Phase and Timing Distribution System

1
NLC Phase and Timing Distribution System

• Dorel Bernstein, Eugene Cisneros, David Brown,
  Mike Browne, Josef Frisch, Duane Thompson

Josef Frisch
2
Timing System Issues Overview

• System is critical to NLC operation
• System requirements are state of the art.
• Primary risks are technical, system cost is 20M
• RD is underway, first generation prototypes
  being tested.
• Various technical options exist

3
Timing System Functional Requirements

• Provide a time reference for machine triggers
• Trigger timing accuracy lt5 picoseconds
• Trigger step 2.8 or 1.4 nanoseconds (normal
  trigger)
• Provide a phase reference for the accelerator RF
• lt20º X band required 5 picoseconds
• lt0.3º X band desirable 75 femptoseconds
• System length 30 Kilometers ? 1?10-9 stability
  desired
• High reliability required
• Global system ? Machine Protection issues

4
Timing System Technical Issues

• Stability
• Required stability ( 5?10-8) would require
  impractical lt0.01C Temperature stability for
  copper or fiber
• Phase stable fibers would require 0.1C stability
  - still very difficult for multi-kilometer runs
• Desired stability (for 0.3º X-band) is a factor
  of 100 more difficult.
• Need to use feedback to control effective fiber
  length
• Reliability
• This system is critical to all accelerator
  operations
• Global system failure could cause damage due to
  beam energy.
• Need fully redundant system.

5
Timing System Baseline Technical Choices

• Use fiber optics for distribution
• Lower loss than coax
• Lower cost than coax
• Better VSWR available (important for feedback
  scheme)
• Thermal timing coefficient similar (due to index
  change in fiber)
• Noise in fibers much worse than coax for similar
  power
• Fix with local narrow band PLLs
• Machine Protection Each receiver a narrow band
  VCXO PLL
• Remembers phase between pulses - prevents
  sudden global phase shift
• Feedback Scheme
• Use signal reflected from far end of fiber to
  measure phase delay, then adjust laser wavelength
  ?(dispersion)? fiber delay length.
• Requires point to point system (to each sector)

6
Timing Distribution System Block Diagram
7
Redundant Timing Distribution System
8
Timing System Baseline Design / Cost

• Electronics
• Use commercial DFB diode laser (1550nm) with
  temperature tuning for fiber length feedback
• Use standard telecom integrated optics and
  receivers
• Fix phase noise with narrow band phase locked
  loops
• VXI format electronics assumed for costing
• Distribution
• Use standard telecom single mode fiber (SMF28)
• Temperature controlled trench to reduce required
  feedback range
• Full redundant design - single point failure
  resistant
• Costing
• Bottoms up baseline done 20M

9
Timing System RD issues

• System performance requirement is substantially
  beyond current state of the art Stability 40?
  SLAC Drive Line
• System is critical to NLC operation
• Technical questions
• Use of reflected signal for precision phase
  measurement
• Use of thermally tuned laser diodes
• Performance of local PLLs is marginal
• Trench temperature control performance not well
  understood
• Optional designs to be considered
• Length control with additional temperature
  controlled fiber (temperature of additional fiber
  moves in the opposite direction)
• Alternate tunable laser designs

10
Fallback Technology Choices
11
Timing System RD to date

• Demonstration of wavelength control of fiber
  phase length
• Can compensate for a few ?C fiber temperature
• Length change is smooth (but not uniform) at the
  1 X-Band level
• Used Fabry Perot (not Distributed FeedBack)
  laser
• Demonstration of acceptable phase noise through
  fiber
• Phase noise OK with 100Hz PLL (devices available
  at this spec)
• Test used only a 2.2Km fiber - 15Km to be tested
  with new laser
• Full fiber phase transmission prototype under
  construction
• Should allow testing of all critical parameters
• System being debugged Many engineering issues
• interference, VSWR, etc.
• Feedback loop closes - but performance is limited
  by laser bandwidth. (should be fixed with DFB
  laser)

12
Timing System RD Fiber system

• Continue testing of prototype systems
• Demonstrate required performance, or understand
  limitation
• Test alternate designs if prototype fails
• Use temperature controlled additional fiber
• Evaluate precision temperature control of trench
• Evaluate electronic phase shifter
• Use high frequency RF fiber transmission to
  reduce noise
• Test alternate optical systems (special projects
  group)
• Grating tuned, Multi-element DFB, Erbium based,
  etc.
• Communications DWDM laser development is
  applicable
• Evaluate physics limits
• Stimulated Brillouin Scattering significant at
  10mw input
• Polarization effects not well understood
• Transfer technology to Controls prototypes

13
Timing System RD Electronics

• Count down device 8 channel alarm clock
  Options
• Use Programmable logic (e.g. Xilinx) Current
  parts too slow.
• Semi-custom ASIC Solves speed problem but has
  additional design cost.
• Full custom ASIC Can be radiation-hard. Highest
  design cost. current baseline.
• Module / system design
• Fiducial transmission. baseline design
• Possible pattern transmission.
• Module design / prototype
• Control system interface (baseline design is
  VXI)
• Firmware and Software development.
• Most work performed after CDR.

14
Critical RD Milestones

• System functional description January 2000
• Prototype demonstrating minimum required
  performance April 2001
• Laser selection January 2002
• Prototype demonstrating full performance June
  2002
• This is the last significant technical risk item
• Prototype ASIC (if used) tested June 2002
• If an ASIC is not used, then finish prototype
  programmable logic based unit.
• Full prototype system, ready for DFM July 2004

15
Timing System RD Schedule and Costs
16
Timing System Status Summary

• This is a very difficult problem - beyond current
  state of the art.
• Component tests are encouraging for phase noise
• Feedback scheme looks promising - but not yet
  demonstrated
• Prototype system being tested
• Several alternate RD paths if problems develop