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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
"FillingPatternDiagnostics - EPICS 2010 BNL"