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IK 060912 Slide 0 First look at the WCM data from July 2012 September 6 th 2012 Ian Kirkman.

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Presentation on theme: "IK 060912 Slide 0 First look at the WCM data from July 2012 September 6 th 2012 Ian Kirkman."— Presentation transcript:

1 IK Slide 0 First look at the WCM data from July 2012 September 6 th 2012 Ian Kirkman

2 Data taken night of July 18 th 2012 Multiple turns established. Wall current monitor in ring (located in cell 37) monitored from ACR using emmascope3 Whole series of response matrix measurements made: F-14 moving by ± 1mm D-14 moving by ± 1mm (relative to standard offsets of all quads = +2mm) But data shown here taken with F-14 and D-14 at standard +2mm offset Effective momentum = 18.1 MeV/c Bunch charge not recorded in the log Can reasonably presume standard 40pC in injection line? IK Measurements Slide 1

3 One turn transformer, magnetic core 40mm aperture, 100mm length 4 equally spaced pick-off points give reasonably position independent response Frequency cut-off in beam tube ~ 4.4 GHz Bandwidth: 15KHz to 4GHz, which implies ~40 ps “sigma t” (equates to ~ 94 ps FWHM response to an infinitely short real pulse) IK Wall current monitor basics (extracted from Jim Crisp presentation, December 2007) Slide 2 Therefore not expected to be able to resolve the bunch structure for an anticipated 3-10ps sigma bunch length

4 WCM oscilloscope trace LeCroy ‘scope “emmascope3”; 40 GS/s sampling rate Ξ 25 ps interval between points WCM “sits on” long background due to septum pickup WCM also suffers from significant Kicker 1 pickup noise for 1st dozen or so turns, plus ringing after that This shows 177 turns over 10 µs Slide 3IK

5 Pulse profiles after background subtraction Slide 4 IK

6 Comments on pulse profiles Dataset ( points) split into 177 files and each separately background subtracted Consistent reduction in the peak signal from first to last turn (~ factor of 10) Consistent broadening of the WCM pulse from first to last turn (~ factor of 10) Asymmetric pulse shapes, getting more asymmetric with turn number Leading edge of the bunch remains reasonably sharp Most of the “spread” occurs behind the leading edge Small pre-pulse about 350 ps in front of the main pulse ?? By turn 170 have full pulse width at base of ~ 5 ns (10% of the orbit) This is ~ 200 digitised points, can pulse shape can easily be resolved TOF based on leading edge ≈ ns TOF based on mean pulse positions ≈ ns (both based on the internal oscilloscope clock, not the RF) Slide 5IK

7 Pulse height Slide 6IK Cleaned-up version of oscilloscope trace Follows an exponential decay very closely

8 Pulse FWHM Good overall fit to linear increase turns < 10, FWHM flattens out at ~175 ps, and WCM appears not to be fast enough for initial bunch length of σ =10 ps, this implies WCM response function σ ≈ 70 ps cf Jim Crisp value (2007) of σ = 40ps for 4GHz cut-off Slide 7IK

9 Pulse integrated area “Peaks” below ~ turn 12 are artefacts of fitting and/or WCM slow response Reasonably flat response for turns (~ an 8% drop) Slide 8IK

10 END IK Slide 9

11 More work Calibrate WCMs properly against the BPMs / Faraday cup (?) Check WCM linearity Look at WCM pulse in the EMMA injection line : Repeatability Width cf pulse seen in ring cell 37 (WCMs too slow) Total charge (relative) Momentum spread Suggestions IK Slide 10


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