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FillingPatternDiagnostics - EPICS 2010 BNL

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					                                             Wir schaffen Wissen – heute für morgen



                          Paul Scherrer Institut
                          Timo Korhonen
                          Filling Pattern Diagnostics and Feedback at SLS


EPICS Meeting, BNL 2010
         Introduction

•History
   – SLS started with routine top-up operation soon after
      initial commissioning. The first top-up control
      application was quite primitive
        • Simple sequential filling
        • Caused often a very uneven filling – bad for stability
   – Second approach: use a free BPM pickup
        • Tricky to work with phase changes
        • Single bucket resolution was poor
   – Finally decided to use avalanche photodiodes after a
      bending magnet port
        • Better resolution and stability
        • Readout system was an oscilloscope
            – Sampling rate was insufficient
            – Sometimes decided to “go fishing”...
   – We wanted to have something better and more stable...

                                                         EPICS Meeting, BNL, 10/11/10
            The application
•The application has been presented in a
EPICS meetings earlier (eg. 2008 @
Legnaro, Italy)
    – Babak Kalantari is the author –
       contact him for details
•This presentation concentrates on the
measurement system
•Any arbitrary filling pattern can be defined
    – Machine is filled to that pattern and
       kept there
    – However, not all patterns are feasible
        • RF disturbances etc.


                                                Filling pattern control has
                                                a remarkable effect on orbit
                                                feedback performance
                                                                   EPICS Meeting, BNL, 10/11/10
               PSI, 27.11.09
EPICS Meeting, BNL, 10/11/10
             Measurement instrument
•ADC board custom designed by Micro-Research
Finland
     – VME format
     – 2 AT84AD001B Dual 8-bit 1 Gsps ADCs
         • 4 channels in total
     – Integrated event receiver (not in use now
       due to problems in prototype version)
     – Two FPGAs
         • One for EVR & interfaces
         • One for ADC handling and
           applications
     – SDRAM slot for long samples (not in use)




                                                   EPICS Meeting, BNL, 10/11/10
               PSI, 27.11.09
EPICS Meeting, BNL, 10/11/10
           Measurement result
•Upper graph: compressed pattern
for one turn (480 buckets)
•Lower graph: zoom into one
bucket
•240 points for 2 ns
     – 120 GSPS equivalent
•However: APD rise time (about
160 ps) is longer than the SLS
bucket length
     – Our application needs only
       the integrated charge

                                    APD behaves like a low-pass filter:
                                    Bunch appears wider than it really is – but the
                                    area scales linearly to bunch charge


                                                                    EPICS Meeting, BNL, 10/11/10
            Measurement to control
•After the measurement, we have a big waveform
         • 480 * 240 points
    – This has to be processed to get the bunch charge
         • Not as straightforward as it might seem
             – Phase matching required
             – Where exactly does one bucket start?
         • Basic process: when starting with an empty machine, fill a
           single bucket and measure
             – Find where the peak charge is and center
         • Has to be monitored for RF phase changes
             – These change the position of bunches related to machine
               clock (RF)
    – After phase matching, integrate the points to get bunch charges



                                                              EPICS Meeting, BNL, 10/11/10
                Another application of the same board
•500 MHz data acquisition
     – a.k.a. Single photon counting
     – Also uses an avalance photodiode
     – Very low photon intensities measured at a high rate (thus 500 MHz)
     – Customized firmware to discriminate and count
     – Counted values become pixels in a picture (or movie frame)




                                                                            EPICS Meeting, BNL, 10/11/10
                                                                                                               Ch 0:
      sample            Rstripline     element            date                                                 (91004002_a.png)

PJ(VII)-Mem_Ch3_4      15,1 Ω        Q5_1500_B1        04.10.2009   Co (784.5 eV)
                                                                                             excitation frequency: 250MHz
Co layer of a Ni80Fe20 (40nm) / Cu (2.8nm) / Co (40nm)                                       excitation power: ~60mW
lateral dimensions (1.5 x 1.5)µm2                                                            magnetic flux density: ~1mT

         Phase = 0°                              Phase = 45°                        Phase = 90°                     Phase = 135°




        Phase = 180°                         Phase = 225°                           Phase = 270°                    Phase = 315°




                                                                                                                               PSI, 27.11.09
                                                                                                                EPICS Meeting, BNL, 10/11/10
                   GIF-Movie – please start the presentation




Co layer of a Ni80Fe20 (40nm) / Cu (2.8nm) / Co (40nm)   excitation frequency: 250MHz
lateral dimensions (1.5 x 1.5)µm2                        excitation power: ~60mW
                                                         magnetic flux density: ~1mT




                                                                                         PSI, 27.11.09
                                                                          EPICS Meeting, BNL, 10/11/10
            Status
•Application is in routine operation since 3 years
        • Rock-solid
             – No more problems with over-filled buckets
             – Required operator interventions (re-calibrate, etc.) very
               rare
        • There would be a lot of room to enhance
             – But it works, so priority is low
             – One seldom hears from the users (except when there is
               an apparent problem)
             – Measurement process could be optimized
                  » But speed is not an issue for this application
        • Has a big effect on beam stability




                                                                 EPICS Meeting, BNL, 10/11/10
           Issues
•We are still using the prototype ADC
   – Works without problems, but would be nice to have a production
      version
•The application could be enhanced in many ways
   – If we only had the time to work on it
•There would be many other applications
   – If we only had the time to work on them
•Small dilemma with the future versions (what to ask for)
   – Just finalize the current design or
   – Upgrade the components
        • Would mean development work
             – For Jukka (MRF) and
             – For us (test & re-commission)
        • Would bring new possibilities


                                                            EPICS Meeting, BNL, 10/11/10
Acknowledgements
Micro-Research (ADC design). Diagnostics group (APD setup).




                                                              EPICS Meeting, BNL, 10/11/10

				
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