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SPS wirescanner measurements present status and issues

SPS wirescanner measurements present status and issues. H. Bartosik - 10.10.2012. Acknowledgements: K. Cornelis , A. Guerrero, G. Iadarola , V. Kain , M. Kuhn, Y. Papaphilippou , J. Ridewood. Operational aspects - Introduction. Operationally only the turn-acquisition mode is used

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SPS wirescanner measurements present status and issues

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  1. SPS wirescanner measurements present status and issues H. Bartosik - 10.10.2012 Acknowledgements: K. Cornelis, A. Guerrero, G. Iadarola, V. Kain, M. Kuhn, Y. Papaphilippou, J. Ridewood

  2. Operational aspects - Introduction • Operationally only the turn-acquisition mode is used • Bunch-by-bunch is very slow and very difficult to setup • Not clear yet if bunch-by-bunch can be used with 50ns on flat top • Range of valid settings for gain and filters not known • To be in linear response of PM • To avoid saturation • Presently overcome by using more or less same settings for LHC beams  comparable • Low resolution of beam profile at flat top • Especially for small 50ns operational LHC beam • Speed of wire cannot be lowered due to high revolution frequency and high intensity

  3. Typical measurements for LHC beam on flat top • Low resolution at flat top • Large scatter in measured emittance • Can combine several measurements (assuming beam is reproducible) • Exploiting the jitter on beam position from shot to shot • Many measurements needed – extensive number of measurements! • Now used in routine operation … 0.97μm 1.30μm 2.01μm

  4. Combined measurements in SPS vs. LHC M. Kuhn • Combination of profiles allows for reproducible measurements • If similar settings are used (typically Filter 4 and 900V PM gain) • Shown measurements correspond to present typical values in operation • Tails can be identified similar to scraper scans • Big discrepancy w.r.t. LHC measurements (round beams!) - due to what? • Range of valid settings for filters and gain not defined (PM saturation) 1.4-1.5μm in LHC in both planes!

  5. New WS application for combined measurements • New application provides possibility to combine single measurements • No bunch-by-bunch capability yet • Same principle using bunch-by-bunch data? (proposed by BI) • Presently studied by Ana • Feasibility for 50ns beam at flat top to be demonstrated! J. Ridewood, V. Kain

  6. Other issues • Presently only WS in 416 available • No possibility to measure both planes at the same time • Measured values using WS in 416 not consistent with LHC • 51995V wire broke during 25ns MD (288x 1.3e11ppb at flat top) • No possibility to measure at flat bottom and flat top in same cycle • Different filters needed - possibility to install 2nd acquisition chain? • Dependence of emittance on beam position • Emittance for different orbit bumps on flat bottom (obtained during WS calibration where linear dependence of beam position was measured!) • Possible explanation for discrepancy w.r.t. LHC measurements? … see SPS logbook 19.07.2012 afternoon

  7. Bunch-by-bunch mode - Introduction • Very useful for MD studies! • For example e-cloud effects as recently in 25ns MD • Would be nice to use in routine operation • Interesting also for “improving resolution” by combining profiles • Present limitations • Number of bunches that can be acquired around 120 • Setting up is very difficult – only for experts • Strong noise on baseline needs to be removed offline (presently) • Saturation of ADC (and maybe also PM? To be checked) • Present (old) wirescanner application is very slow in BbB mode and does not display all emittances in one chart  very tedious and not practical • Scintilatorfor WS in 416 was moved to avoid saturation in BbB mode

  8. Bunch-by-bunch measurements – 25ns beam • Tested with 25ns beam during MD • 4 batches with 1.1e11 ppb on flat top • Maximal filter (7=steel plate) is needed! • ADC is easily saturated (at 16384)! • Subtracting signal from empty slot (offline!!) • Dependence of measurement on PM gain (see Ana) • Optimal settings to be found • Very useful for MDs! • 50ns beam on flat top not tested yet …

  9. Summary and conclusions • Presently only 1 wirescanner per plane available for LHC beams (416) • Discrepancy with respect to LHC (and preinjector) measurements • Dependence of measured emittance on beam position • Range of valid settings not known! • Need measurement campaign to find range of valid settings for gain and filters with operational beam! • Low resolution at flat top • Presently overcome by combining several measurements (turn-acquisition mode) • Possibility of using single measurement in bunch-by-bunch mode for resolving profile is being studied by Ana • Future wirescanners to be installed at large beta functions (independent for each plane!) • Progress with bunch-by-bunch mode • More work to be done on settings, data treatment and also usability of application • 50ns beam at flat top still to be tested with new configuration of WS 416 • Future LHC beams: higher intensity and smaller beam size • 519V recently broke during MD with 25ns beam (1.3e11 ppb on flat top with 288 bunches) • Possibility of installing BSRT for (bunch-by-bunch) measurements on flat top?

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