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BEAM INSTRUMENTATION OF RELEVANCE FOR

LUMINOSITY DETERMINATION

LHC Lumi Days – 01/03/2012 Jean-Jacques Gras on behalf of

the CERN Beam Instrumentation Group

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Presentation Overview

This presentation will focus on the developments foreseen in the near future on Beam Instrumentation of relevance for luminosity determination.

n.b.: Alex will cover the BRAN in the next talk.

Beam Current Measurements

Beam Profile Measurements

Beam Position Measurements

Conclusions

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Beam Current via DCCT

• As demonstrated yesterday by Colin (see conclusions below), our 2011 objective for an absolute accuracy below 1% of our DCCT in all conditions has been more than achieved.

• As explained, our remaining main source of error is now linked to our ADC bins. Work in progress (see next slide) and looks extremely promising

• We also have to convince ourselves in the lab during 2012 that the DCCT will perform as well with nominal 25ns beams.

P. Odier, S. Thoulet, M. Ludwig, L. Jensen

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Beam Current via DCCT

• In addition to some uncertainty on the calibration, our poor ADC bin (12 bits) is also giving some artefact on the measurement like it is shown on the top picture.

• This can be explained by a combination of ADC bin, noise and acquisition averaging. See the demo (n.b. you must install first the CDF Player to enjoy it)

• Bottom picture shows the results of our 24 bits ADC during this time.

• This board is still under commissioning but it can already be used during VdM scans.

12 bits ADC

24 bits ADC

P. Odier, S. Thoulet, M. Ludwig, L. Jensen

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Beam Current via DCCT

• The results of this 24 bit ADC board are really promising.

• Let’s look in details on this 01/11/2011 fill where some studies on UFO happened

• These UFO’s seen by this ADC. Some more than in Logbook.

• We are currently studying plugging lifetime on this device to (see below)

P. Odier, S. Thoulet, M. Ludwig, L. Jensen

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Beam Current via Fast BCTs

• As demonstrated yesterday by Massi (see conclusions below), FBCT provided accurate measurements during 2011 VdM scans but we start seeing systematic effects at the permil level.

• We identified the weakest part of our system to be the monitor itself, which suffer from bunch length and position dependence.

• Our priority this this will be to assess a other monitor technology: Integrating Current Transformers

D. Belohrad, M. Ludwig, L. Jensen

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Beam Current via Fast BCTs: ICT Plans

April: production of two ICTs, laboratory tests, winding of the cores.

April TS: installation in the tunnel instead of one system B FBCT,

May onwards: tests and performance assessments

If OK, produce monitors for LS1

D. Belohrad, M. Ludwig, L. Jensen

Split into to 2 parts allow installation

without vacuum intervention.Final version

would be a in 1 piece.

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Beam Current via WCM

Work is on-going to improve overall frequency response of system

We will assess this new algorithm on PS and LHC monitors and eventually use them as another input during vdM scans

We hope to achieve with this a relative accuracy below the 1% level.

Beam Current via Sync. Light (LDM-BSRA) Basic Principle:

Charge particules produce light when they are bent by a magnetic field. This look simple but for many reasons, it is not! and our optical bench is quite crowded to try to cope with all abberations and requirements.It has to host the Abort Gap and Longitudinal Density Monitors in addition to our Profile Monitors

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Beam Current via LDM

Proton/Ion beam

Slow camera (BSRTS)

Fast camera (BSRTF)

Abort Gap Monitor(AGM)

Long. Density Monitor (LDM)

Optical delay line

TDC

RF timingNetwork

Neutral filters

Color filters90 %

10 %

60 %40 %

10 %90 %

In the tunnel, it looks like ->

As explained by Adam yesterday, our main issues with the LDM are:• Our dependence on beam

position• The difficulty to evaluate the

debunched beam population

Beam Current via LDM Method:

Single photon counting with synchrotron light Avalanche photodiode detector 50 ps resolution TDC

APD

TDC

synchrotron light

LHC turn clock

Electrical pulse

Arrival time

filter

Longitudinal Bunch Shape

Adam Jeff, Andrea Boccardi, Enrico Bravin and Rhodri for the animation

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Beam Current via LDM: Emittance/Alignment

Dependence2011 Set Up

Focused light from BSRT

APD

APD acceptance

Transverse profile

APD acceptance

Our APD has a small acceptance w.r.t. incoming beam size.

Alignment variations (from undulor to D3 or due to beam motion) can modify the transmission.

This also introduces a dependence on beam size.

Adam Jeff, Andrea Boccardi, Enrico Bravin

x10

-3

x10-3

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Beam Current via LDM: Emittance/Alignment

Dependence2012 Test Set Up on B1

APD acceptance

Profiles after diffusion

Spot size after diffuser ~ independent of beam size -> emittance dependence reduced

But we lose a lot of light!

Adam Jeff, Andrea Boccardi, Enrico Bravin

APD

Light from BSRT

Diffuser

x1

0

-3

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Beam Current via LDM: Emittance/Alignment

Dependence2012 Test Set Up on B1

APD acceptance

Profile after diffusion

Spot size after diffuser ~ independent of beam size -> emittance dependence reduced

Good coupling efficiency, plenty of light!

Adam Jeff, Andrea Boccardi, Enrico Bravin

Light from BSRT

Diffuser

x1

0

-3

APD

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Beam Current via LDM

We will also investigate in 2012 if the Abort Gap could help us to define the amount of debunched beam we may neglect with the current algorithm used to evaluate ghost charges.

0.35

0.30

0.25

0.20

-11.25 -8.75 -6.25 -3.75 -1.25 1.25 3.75 6.25 8.75 11.25Time (ns)

Adam Jeff, Andrea Boccardi, Enrico Bravin

?

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Beam Emittances via BSRT

Fedrico Rocarolo, Aurelie Rabiller, Enrico Bravin, Ana Guerrero

• Diffraction• Depth of field• Extended source• Camera resolution

sPSF:

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Beam Emittances via BSRT

Not so Good - B2 H @ 3.5 TeV● Single correction factor doesn’t

work for both small & big bunches

● Indicates scaling factor in addition to correction in quadrature

Actions 2012: Understand sources of errors Improve the optical line wherever possible Publish corrected sigmas within error of ±10% at injection & top energy

(and possibly corresponding emittances) Move front-end software to new LINUX PC to allow quicker processing

and acquire bunch by bunch profiles a factor 10 faster

Fedrico Rocarolo, Aurelie Rabiller, Enrico Bravin, Ana Guerrero

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Beam Emittances via BWSMain 2011 Issue : noise on B1 signal (Source investigated during several technical stops but not identified) has been fixed :

We systematically acquire a dummy bunch in abort gap Subtract this baseline from the real bunch signal Tested in MD3 & successfully applied for subsequent operation

BWS will remain the reference for beam emittance measurements (up to 5e12 p at 3.5 TeV, 2.5e13p at 450 GeV)

Ana Guerrero, Jonathan Emery

Before and After

Correction

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Beam Position at BPMSWBoth beams in the same pipe

Leads to cross-talk between the beams Isolation is only ~20dB (factor 10) – difficult to improve

Main signal perturbed by parasitic signal from other beam System can trigger on other beam (displaced at these locations) falsifying average orbit

Solution Use synchronous mode - orbit calculated from single bunch (firmware

deployed) Needs mask configured for filling pattern & BPM location (underway)

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Beam Position at BPMSW• The eratic behavior of the BPMSW should disappear with the implementation of the synchronous orbit.• We expect noise below 10 microns on these BPMSW but they will still suffer from our overall temperature dependence, which we plan to significantly reduce during LS1

DT = 1°C

Eva Calvo, Rhodri Jones, Lars Jensen

Prototype temperature controlled racks currently under test.Achieved stability <1°C over 3 day periodThe remaining 50μm variation is under investigation

Currently

∆T +/- 5°C

∆x

200μ

m

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Conclusions & AcknowledgmentsWe would like to take this opportunity to again thank you for:

Your trust in our capacity and will to serve you well Your patience Your help (especially the BCNWG and in particular Colin and

Gabriel) in analyzing our instrument results Your very demanding requirements and gentle pressure,

which significantly speeded up our progress on understanding our systems

We were happy to hear yesterday that the bad news is that other sources of uncertainties can not rest in peace behind Beam Instrumentation’s ones anymore.But we’ll try to keep the current momentum and continue to progress on all these instruments until we feel we reached their full potential.

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Beam Current via Fast BCTs: ICT Principe

When the beam passes, the beam charge is first stored into the capacitor storage, then read away using high permeability toroid.

Two time constants involved: 1 from beam passing to

capacitor storage (Tbeam) 1 from readout (Treadout )Output charge independent of

beam position and length but Tbeam has to be smaller than Treadout

D. Belohrad, M. Ludwig, L. Jensen