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Acronyms

Term

Description

AC

Alternate Current

ATCA

Advanced Telecommunications Computing Architecture

CPU

Central Processing Unit

EPICS

Experimental Physics and Industrial Control System

FPGA

Field Programmable Gate Array

IOC

Input Output Controller

LCLS

Linac Coherent Light Source

MDL

Main Drive Line

MO

Master Oscillator

NC

Normal-Conducting

RF

Radio Frequency

SC

Super-Conducting

SHM

Shelf Manager

VMTG

VME-based Master Trigger Generator

Objective

The main objective of this project is to be able to use subsystems built for the LCLS-I reference frequencies with the LCLS-II beam.  The beneficiaries include XTCAV, STCAV and possibly others.  In order to do that, the 476MHz Master Oscillator (MO) signal for LCLS-I should be replaced with a new 476MHz source locked to the LCLS-II Master Oscillator, with the latter operating at 162.5MHz.

Requirements

The requirements for this project are listed below.

  1. Generate a 476MHz RF reference in Sector-2 to use with XTCAV.  The RF reference will have similar jitter characteristics as the LCLS-II Master Oscillator.
  2. Transmit a 476MHz RF reference to Sector-10 to replace the LCLS-I Master Oscillator.  The new RF reference will have similar jitter characteristics as the existing LCLS-I Master Oscillator.
  3. Align the triggerring of the Super-Conducting (SC) & Normal-Conducting (NC) timing systems for XTCAV to operate at 120Hz.
  4. Merge the NC event timing onto the SC event timing. 

Timing System Description

The 476MHz MO provides an RF source to the timing system.  This signal is combined with a 360Hz signal derived from the 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 output is thus synchronized with the 476MHz MO --via a 71kHz RF signal-- and it triggers the fiducial generator at 360Hz.  The 360Hz output of the fiducial generator is amplitude-modulated onto the original 476MHz signal (hence 2.78ms between peaks and with a 476MHz frequency) and is propagated down the Main Drive Line (MDL).  The aforementioned trigger generation occurs in Sector-10 in its entirety and then gets propagated to other sectors and buildings.


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

Linac Locking Description


RF Distribution


References

Timing for LCLS

Timing_Note_Nov2023.pdf

Linac Locking Review

Linac Locking Review.pdf


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