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Introduction

Feedback systems are to be prototyped in Matlab for the first commissioning of the LCLS system in early 2007.   There are six feedback systems to be tested in the first commissioning run.  A description of each feedback follows.

Bunch Charge

The Bunch Charge feedback stablizes the bunch charge of each pulse at the RF gun.  The total bunch charge measurement of the toroid IM01, near the RF gun, is used to calculate adjustments to the laser intensity at the cathode.

DL1 Energy

The DL1 Energy feedback maintains a constant beam energy at DL1.  the x-position reading of BPM13 is used to calculate adjustments to the amplitude of the klystron L0B.

Energy at the Spec. Dump

The Spectrometer Dump Energy feedback loop is identical to the DL1 Energy loop, except it is used when the beam is directed to the SDUMP rather than into Sector 21.   In this case, BMPS1 x-position is used to measure the relative energy.

DL1 Energy + BC1 Energy + Bunch Length

The BC1 location along the linac requires both energy and bunch length stabilization.   This feedback loop will include the energy at DL1 as well, so that the energy feedback from RF gun through and beyond BC1 work together as a single loop.  BPM13, BPMS11 are used to measure the relative energy, BL11 is used to measure the relative bunch length.  These measurements are used to adjust the amplitude at L0B and the amplitude and phase of L1-S.

Injector Launch

The Injector Launch feedback is required to stabilize the trajectory of the beam as it enters the linac at Sector 21.  The x-position and y-position measurements of BPM9 through BPM15 will be used to calculate adjustments to the desired B-field of the XCO4 / YCO4 and XCO7 /YC07 corrector magnets.  This feedback attempts to stabilize the states: x-position, x-angle, y-position, y-angle of the beam. 

RF phase of Transverse Deflecting Cavity

This feedback is used to stabilize the phase of the beam with respect to the RF field of the cavity.  This feedback is used only during a Bunch Length Measurement and is integrated into the Bunch Length Measurement application. 

References

Requirements and Design

User Guide

Schedule

The Feedback Prototyping project includes several sub-projects. A task list and schedule is (will be...) included for each:

  • Matlab Framework for Feedback Applications
    • use new event API
    • add limits checking on actuators, states, measurements - inlcuding checking TMIT for validity? see notes
    • add error checking on devices, communications, calculations
  • application to collect reference orbit data
  • (application to experimentally determine matrix???)
  • soft IOC for stored Feedback data and dynamic setpoints
  • soft IOC simulator to generate data for feedback testing
    • add simulation of user controls for LLRF
    • add calc of real BPM x-position values, replace virtual energy device for Energy feedbacks
    • add calc of real BL11 reading, replace virtual current device for Energy / Bunch length feedback
  • Individual Feedbacks
    • Bunch ChargeEnergy at DL1
      • gotta get going on this soon!
    • Energy at Spectrometer Dump
      • LLRF questions
      • add control records on LLRF Amp and Phase to lock out users during automated feedback
    • DL1 Energy + BC1 Energy + Bunch Length
      •  need to use IM01 to calc Bunch Lenght values (along with BL11 reading)
      • where to get calibration constant C for BL11/ IM01 calcs
    • Injector Launch
      • test Paul's latest optimization algorithm with latest simulator BPM values and noise levels
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