Introduction

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

...

The Bunch Charge feedback stablizes the bunch charge of each pulse at the RF gun.  The .  This feedback is a accomplished with a set of two nested feedback loops.  An inner loop, local to the laser system, adjusts the wave-pate angle, and therefore the laser pulse energy, by measuring the laser energy with a Joule meter near the cathode.  An outer loop controls the energy setpoint of the inner loop, based  on 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.  the inner loop is implemented in EPICS on the associated laser IOCs.  The outer loop is a beam-based feedback implemented in Matlab.

DL1 Energy

The DL1 Energy feedback maintains a constant beam energy at DL1.  the x-position reading of BPM13, a measure of relative energy, is used to calculate adjustments to the phase (or 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 spectrometer dump rather than into Sector 21.   In this case, BMPS1 BMPS2 or BPMS3 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 , and BPMS11 are used to measure the relative energy, BL11 is used to measure the relative bunch length.  These measurements are used to adjust the phase (or amplitude?) at L0B and the amplitude and phase of L1-S.  In the case where BL11 is not used, the DL1 + DL2 energy alone may be stablized with this loop.

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. 

...

• Matlab Framework for Feedback Applications
  • read EGU from PVs and display units wherever possible
  • use new event API
  • add limits checking on actuators, states, measurements - inlcuding checking TMIT for validity? see notes o disc. w/Paul
  • add error checking on devices, communications, calculations - need status PVs
• application to collect reference orbit data
• (application to experimentally determine matrix???)

...

• Individual Feedbacks
  • Bunch ChargeEnergy at DL1 Charge
    • gotta get going on this soon!
    • need ICD for toroid
    • need ICD and additional info on inner laser energy loop
  • Energy at DL1 / Spectrometer Dump
    • LLRF questions - need ICD (including PV names and how they work)
    • add control records on LLRF Amp and Phase to lock out users during automated feedback
    • need BPM ICD
  • 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

...