Master Clock for IceCube

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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
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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.

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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

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Accuracy and Precision

• GPS satellites are synchronized to the US Naval
  Observatory.
• The USNO atomic clocks maintain time to lt
  2x10-15 day-1.
• GPS stability degraded to 4x10-8 second-1 by
  triangulation errors.
• DOM local clocks will display lt 1 x 10-10
  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

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A Commercial Atomic Clock

• Stanford Research Systems PRS-10
• Cost 1500
• High phase-stability quartz oscillator
• Short-term phase-stability 5 x 10-12
• Atomic Rubidium for long time-scale
• Can be disciplined to follow GPS (long-term) if
  the 1 Hz GPS signal is available.

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Rubidium Oscillator Allan Variance

• Figure from http//www.srsys.com/products/PRS10.h
  tm

GTPrzybylski LBNL 10/13/2003
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System Top Level
GPS Clock
Naval Observatory(1.2E-15 drift)
1 pps ASCII time value string
Accurate to 40ns
SRS PRS-10
Master Clock Unit
Fan Out
1pps
Drivers
10 MHz
Slaved Rubidium Oscillator lt1x10-11 jitter
20 MHz PLL
20 MHz
DOM Hub
DOM Hub
3-Twisted Pairs (20 Mhz, 1pps, RS-232)
DOM Hub
GTPrzybylski LBNL 10/13/2003
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Inside the DOM Hub
20 MHz, 1 pps. Time String

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

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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...