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First look at the WCM data from July 2012

September 6th 2012

Ian Kirkman

Data taken night of July 18th 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 ± 1mmD-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 logCan reasonably presume standard 40pC in injection line?

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Measurements

Slide 1

One turn transformer, magnetic core40mm aperture, 100mm length4 equally spaced pick-off points give

reasonably position independent response

Frequency cut-off in beam tube ~ 4.4 GHz

Bandwidth: 15KHz to 4GHz, whichimplies ~40 ps “sigma t” (equates to ~ 94 ps

FWHM response to an infinitely short real pulse)

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Wall current monitor basics(extracted from Jim Crisp presentation, December 2007)

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Therefore not expected to be able to resolve the bunch structure for ananticipated 3-10ps sigma bunch length

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 µsSlide 3 IK 060912

Pulse profiles after background subtraction

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Comments on pulse profiles

Dataset (400000 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 numberLeading edge of the bunch remains reasonably sharpMost of the “spread” occurs behind the leading edgeSmall 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 ≈ 55.359 nsTOF based on mean pulse positions ≈ 55.365 ns(both based on the internal oscilloscope clock, not the RF)

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Pulse height

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• Cleaned-up version of oscilloscope trace• Follows an exponential decay very closely

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

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Pulse integrated area

• “Peaks” below ~ turn 12 are artefacts of fitting and/or WCM slow response• Reasonably flat response for turns 12-170 (~ an 8% drop)

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END

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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............

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