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In LCLS-I, the 476MHz MO provides an RF source to the timing system.  This signal is combined with a 360Hz signal derived from a sequencer chassis (i.e. derives a 360Hz signal coincident with the zero crossings from the 3-phase AC power line).  The 476MHz and the 360Hz signals are routed to the inputs of the VME-based Master Trigger Generator (VMTG).  The VMTG samples a 71.4kHz signal (a sub-harmonic of LCLS-I & LCLS-II MO frequencies) and generates a 360Hz fiducial that is aligned with the 71.4KHz signal.

(Fiducial Generation - Borrowed from Timing for LCLS slide deck - , see References section below)

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With Linac Locking, the above 476MHz LCLS-I Master Oscillator gets replaced by a new RF reference that is phase-locked to the LCLS-II Master Oscillator (located in Sector-2) and transmitted to Sector-10 via an RF-over-Fiber (RFoF) connection.  Lastly, the alignment of the triggers between SC and NC timing is done in Sector-20.

RF Distribution Overview

Linac locking is a portion of the RF distribution network that aims to support LCLS-I timing generation and distribution.  See diagram below for the big picture.

(RF Distribution Network - Borrowed from Linac Locking Review slide deck - , see References section below)

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As of the date this documentation was produced, the work to meet the first three requirements is almost complete and is currently undergoing verification.  The fourth requirements requirement has been deferred to be tackled at a later date.

RF Source Generation

For a better idea on how the 476MHz is generated in Sector-2, there's documentation in place that describes related IOCs and existing hardware to accomplish this.  See the link below for more details.

Linac Locking - PLL SIM IOCs [sioc-sys0-ms07 & sioc-sys0-ms08]

RF Transmission

For the transmission of the RF signal from Sector-2 to Sector-10, the reader is encouraged to refer to the documentation for the RFoF IOC.

Linac Locking - RFoF Telnet IOC [sioc-sys0-ms11]

Trigger Alignment

For Trigger Alignment, see the section describing the corresponding IOC.

Linac Locking - Trigger Alignment IOC [sioc-sys0-ms12]

References

Timing for LCLS

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