Setting up ASTA UED LLRF for 120 Hz operation

ASTA UED derives its timing from LCLS EVG timing system.

LCLS EVG has the event code '40' for 120 Hz operation on beamcode 0 for LCLS.



The masks for the event code 40 have been setup to exclude time slots 2,3,5 and 6 with the exclusion mask of 0x36 in Modifier 2.

Thus time slots 1,4  alone are active.

Each time slot corresponds to 60 Hz. Thus the three active time slots support 3*60Hz = 180 Hz operation.

Event modifier bits for 40 are as below.

The VME Master IOC-AS01-RF01 has looks for the above patterns.

    1. It provides pattern matching in two time slots for 120 Hz operation, instead of three time slots for 180 Hz.
    2.  Event code 40 has been added to the default set of events and visible in AS01 EVR RF01 Trigger Diags panel

  1. Setting up 120 Hz timing:
    1. Navigate to astahome->Event/ASTA->LLRF->Experts->RF01 Triggers...
    2. This brings up the 'AS01 EVR RF01 Trigger Diags' panel as shown in figure above.
    3. Enable the IRQ button in the row corresponding to 40. You will see the 'Rate' PV corresponding to this row display '120.0'

  2. Before switching from 180 Hz to 120 Hz operation, first disable Gun LLRF Feedbacks:



  3. Setup the UED Gun LLRF feedback rate to 120 Hz:
    1. Bring up the PAU screen by clicking on 'PAU AS01 Gun' towards the bottom left of above VME panel.
      1. Ensure 'Activate PAU' button is 'ON'.
      2. Ensure Beam code for all the four data slots DS0,DS1,DS2 an DS3 are '0'. This corresponds to LCLS beamcode.
      3. Set the Time slot for DS0 to '4' and for DS1 to '1'. These correspond to the two included time slots TS1 and TS4.
      4. The last two data slots are not included in the feedback loop - so it does not matter what it is set to. Leave them at '4' and '1' respectively.
      5. For each time slot corresponding to a data slot, there are two sets of patterns.
        1. The first row of patterns are modifier bits that provides inclusion. The second row provides exclusion.
        2. Set the exclusion masks for 'Mod. 2' for DS0 and DS1 to 0x36 and DS2 and DS3 to  '0xffffff'. This excludes TS2,TS3,TS5 and TS6 timeslots.
      6. If you would like 60 Hz feedback operation, set DS1 Mod 2 exculsion mask also to '0xffffff'. This is how it is shown in figure below.
      7. All other modifier bits for all data slots should be set to 0.
      8. Change the Pipeline Index to '2' (from '1').
      9. Increase the 'Delay (usec)' from '850' to '970'.
      10. The 'Callback call rate (Hz):' field should show 120.00 after these changes. This means feedback is operating at 120 Hz.




  4. Navigate to astahome->RF/Global->Gun->Mux for PDES
    1. This brings up the 'GUN:AS01:1:PDES' panel.
    2. Ensure 'Fast Feedback' is 'OFF'

  5. Navigate to astahome->RF/Global->Gun->Mux for ADES
    1. This brings up the 'GUN:AS01:1:ADES' panel.
    2. Ensure 'Fast Feedback' is 'OFF'.
      Note: We will use the 'Offset' fields to compensate for some more of the data slot specific timeslot jitter.
      This is under investigation and for future.
      For now ensure all the four Offset PVs are 0.0


  6. Setup the PAC trigger rate to 120Hz.
    1. TTB13 'GUN PAC Control' is the trigger for the Gun PAC. 
      Disable the button corresponding to column '13' in whichever row it is enabled
      Enable the button corresponding in row corresponding to Event Code '40' column '13'.
      Ensure that only the button corresponding to to the '40' is enabled and all others are disabled under column 13.
    2. The SSSB trigger from the PAC output. Thus, if the PAC triggers at 120 Hz, so will the SSSB.

  7. The Modulator is triggered by TTB3 'MOD TRIG Control'.
    1. Disable the button corresponding to column '3' in whichever row it is enabled
      Enable the button corresponding in row corresponding to Event Code '40' column '3'.
      Ensure that only the button corresponding to to the '40' is enabled and all others are disabled under column 3.

  8. Setup the PAD trigger rate to 180 Hz.
    1. TTB11 'GUN PAD Control' is the trigger for the Gun PAD. 
      Disable the button corresponding to column '11' in whichever row it is enabled
      Enable the button corresponding in row corresponding to Event Code '40' column '11'.
      Ensure that only the button corresponding to to the '40' is enabled and all others are disabled under column 11.



  9. Now enable the LLRF Gun feedback loops:

If the PAU has been configured correctly two of the four dataslots (DS0, DS1)  should be updating. This shows that the feedback is working at 120 Hz.

Navigate to astahome->RF/Global->Gun->PatternAware:



  • No labels