Timing System R+D for the NLC Josef Frisch

NLC and PEPII Phase and Timing Requirements (approximate)

Why do we need high stability (10ps) triggers? ● BPM pickoffs typically produce a few x100ps pulse (button) or pair of pulses (stripline). If a gated integrator or sampler could be triggered with ~10ps resolution it would make a very simple and low noise BPM. ● Streak cameras, laser wires, etc. could also use high stability trigger timing.

Timing and Phase Distribution ● Timing requirements for NLC are sufficiently tight that active stabilization is needed ● Easiest to use RF phase distribution system for timing ● A fiducial is placed on the RF at 120 or 360Hz) and triggers are generated by counting RF cycles after this fiducial

NLC and PEPII Upgrade ● Technology developed for NLC timing system is applicable to PEPII. ● PEPII requirements much looser – Easier Phase / timing stability – Fewer units required (less cost sensitivity) ● PEPII Ring turn clock will different design – Also needed for NLC damping rings.

Timing Distribution Technologies ● Both copper cable and fiber optics have similar phase coefficients with temperature ~2x10 -5 /°C – Fiber coefficient due to change in index – NLC Would require °C stability: Tough! – PEPII needs.02 °C. (Still not easy) ● Need to use feedback ● Fiber preferred over Copper due to lower loss, better VSWR, and lower cost. – Radiation sensitivity must be considered – Use fiber for long haul, coax in tunnel.

NLC Timing System ● Point to point fiber system (~50 drops for NLC) ● Laser modulated by RF carrier ● Measure transmission fiber length using light reflected from far end of fiber ● Adjust length using fiber spool in oven in series with main fiber

RF Distribution Test System

1 Month, 10 °C Temperature Step 1ps

Performance test for 1 month 1ps

Redundant Architecture ● Want single point failure immune system, but do not want full duplication. ● Sudden phase shift of a sector could cause a large energy excursion - possibly damaging the accelerator. ● Redundancy built into the system topology.

Redundant Fiber System Note: local oscillators in each "crate" prevent sudden changes in sector phase.

Phase Distribution System Status ● Test system meets NLC requirements for phase stability and phase noise ● Fault tolerant system architecture developed – Single point failure resistant ● Fiducial electronics tested, but not used with fiber system. ● Next generation system being developed for PEPII.

Use of Tunable Lasers for Fiber Phase Length Control ● A wavelength tunable laser could replace the fiber /oven. – Wavelength tuning coupled with dispersion (typical 20ps/nm/Km) will provide adjustable delay. – Thermal shift ~2x10 -5 / 0 C or 100ps/km/ 0 C – Need 5nm/ 0 C, or about 50nm total. ● DWDM 1550nm band is ~30nm wide. ● Expect commercial lasers soon!

Changes From Prototype ● Embedded intelligence, rather than external Windows PC. ● Surface mount components to replace connectorized components. ● System to consist of rack mount RF / Optical module and rack mount oven module. ● Temperature stabilization may not be needed for PEPII performance.

Open Design Issues ● Digital vs Analog: Where to convert? – Digital: Use Digital down converters, fast ADCs, fast math in programmable logic – Analog: Everything up to the ADC for the slow feedback loops is analog ● Control system interface: – OK light? – Full support as EPICS micro? ● Single controller, or multiple controllers.

What Does a Future System Look Like? ● All logic on single chip, either PLD, or possibly custom ASIC. – Need 714MHz logic for NLC - few years. ● May integrate CPU with logic, or use micro. ● Still want some analog components: Mixers, amplifiers,etc. – "Cell phone" type components cheap and small