Master Clock for IceCube October 21, 2003 Contributors: Jerry Przybylski, Kalle Sulanke, Dave Nygren, Chuck McParland, Bob Stokstad Lawrence Berkeley National Laboratory GTPrzybylski LBNL 10/13/2003

Master Clock Unit (MCU) Status Draft Requirements Document exists now! –Needs more work, will be available soon... The MCU has some conceptual subtlety –Religious debates in progress. Specific Implementation proposals have been made by Sulanke and Przybylski. Working plan is that Sulanke will design and fabricate this subsystem at DESY.

Master Clock Unit: Major Goals Create and distribute stable 20 MHz source to all DOM Hubs in IceCube DAQ. –DOR cards mirror MCU time, calibrate DOMs Link “IceCube Time” to GPS time. –Question: Does IceCube Time  GPS time? Provide robust real-time time verification. –Motivation: detect any error condition in less than 1 sec

Accuracy and Precision GPS satellites are synchronized to the US Naval Observatory. The USNO atomic clocks maintain time to < 2x day -1. GPS stability degraded to ~4x10 -8 second -1 by triangulation errors. DOM local clocks will display < 1 x second -1.  GPS much less stable than DOM local clocks (seconds scale) However, GPS will display better long-term stability (hours scale)  Master Clock unit must employ a source with better short-term stability than GPS, yet must still match long-term GPS time.  Use commercial atomic clock “linked” to GPS over long-term

A Commercial Atomic Clock Stanford Research Systems PRS-10 Cost: ~$1500 High phase-stability quartz oscillator Short-term phase-stability: ~5 x Atomic Rubidium for long time-scale Can be “disciplined” to follow GPS (long- term) if the 1 Hz GPS signal is available.

Rubidium Oscillator Allan Variance Figure from GTPrzybylski LBNL 10/13/2003

System: Top Level GPS Clock 1 pps ASCII time value string DOM Hub SRS PRS MHz PLL Fan Out Accurate to ± 40ns 1pps 20 MHz 3-Twisted Pairs (20 Mhz, 1pps, RS-232) Slaved Rubidium Oscillator <1x jitter Naval Observatory (1.2E-15 drift) 10 MHz Drivers Master Clock Unit GTPrzybylski LBNL 10/13/2003

Inside the DOM Hub DOR card DSB Card CPU From Master Clock Unit 20 MHz (Twisted Pair) 1 Pulse per Second (Twisted Pair) RS-232 Time String (Twisted Pair) 20 MHz, 1 pps. Time String Time String Power Supplies Fans Monitors (Possibly Diskless) GTPrzybylski LBNL 10/13/2003

DSB (DOM hub Service Board - KHS)

Some System Requirements The DOM Hub shall be capable of stand- alone operation, ( use the DSB 20 MHz clock ) –This facilitates many testing activities The IceCube MCU shall be capable of full operation in the absence of GPS data –Could happen, …. IceCube MCU operation shall not require that all DOM Hubs are operational. –Independence of strings during commissioning.

MCU Summary Important to define this subsystem now. –Physics input necessary for requirements. –MCU will be needed for string test at UW. Short term goals: –Requirements Document circulated to Tech board by 15 November 2003 for review. –Requirements Document approved by PO, and accepted by engineering and physics team...