introduction to beam instrumentation cas 2013 trondheim , norway 18 th – 29 th august , 2013

Slide 1

Introduction toBeam InstrumentationCAS 2013Trondheim, Norway18th 29th August, 2013

Dr. Rhodri JonesHead of the CERN Beam Instrumentation Group

Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

1What do we mean by beam instrumentation?The eyes of the machine operators i.e. the instruments that observe beam behaviourAn accelerator can never be better than the instruments measuring its performance!What does work in beam instrumentation entail?Design, construction & operation of instruments to observe particle beamsR&D to find new or improve existing techniques to fulfill new requirementsA combination of the following disciplinesApplied & Accelerator Physics; Mechanical, Electronic & Software EngineeringA fascinating field of work!What beam parameters do we measure?Beam PositionHorizontal and vertical throughout the acceleratorBeam Intensity (& lifetime measurement for a storage ring/collider)Bunch-by-bunch charge and total circulating currentBeam LossEspecially important for superconducting machinesBeam profilesTransverse and longitudinal distributionCollision rate / Luminosity (for colliders)Measure of how well the beams are overlapped at the collision point

IntroductionDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

2More MeasurementsMachine ChromaticityMachine TuneQFQFQFQDQDSFSFSFSDSDSpread in the Machine Tune due to Particle Energy SpreadControlled by Sextupole magnetsCharacteristic Frequencyof the Magnetic LatticeGiven by the strength of theQuadrupole magnetsOptics Analogy:Achromatic incident light[Spread in particle energy]Lens[Quadrupole]Focal length isenergy dependentDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

3The Typical InstrumentsBeam Positionelectrostatic or electromagnetic pick-ups and related electronicsBeam Intensitybeam current transformersBeam Profilesecondary emission grids and screenswire scannerssynchrotron light monitorsionisation and luminescence monitorsfemtosecond diagnostics for ultra short bunchesBeam Lossionisation chambers or pin diodesMachine Tune and Chromaticityin diagnostics section of tomorrowLuminosityin diagnostics section of tomorrow Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

4Measuring Beam Position The Principle-----++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-+++--+-++--+--++-+-------+++++-+++--+-++--+--++-+-------++++-+++--+-++--+--++-Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

Wall Current Monitor The Principle-----+++++-+++--+-++--+--++-+--+-------++++-+++--+-++--+--++-V+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++Ceramic Insert+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

Wall Current Monitor Beam Response

LIBVRCFrequencyResponse00

IBDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

Electrostatic Monitor The Principle-----++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-+++--+-++--+--++-+-------++++-+++--+-++--+-+-------++++-+++--+-++--+--++-+-V-------Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

Electrostatic Monitor Beam ResponseVBVRCFrequency (Hz)Response (V)00

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

Electrostatic Monitor The Principle-----+++++-+++--+-++--+--++-+-------++++-+++--+-++--+-+-------++++-+++--+-++--+--++-+-V--------+++++--+-+-+-+----+++-++-+--+-+-----+++-++--+-------+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

Electrostatic Pick-up Button Low cost most popular Non-linearrequires correction algorithmwhen beam is off-centreFor Button with Capacitance Ce & Characteristic Impedance R0

Transfer Impedance:

Lower Corner Frequency:

Area Ar


11

Frequency (Hz)Response (V)00

A Real Example The LHC ButtonDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

12Standard BPMs give intensity signals which need to be subtracted to obtain a difference which is then proportional to positionDifficult to do electronically without some of the intensity information leaking throughWhen looking for small differences this leakage can dominate the measurementTypically 40-80dB (100 to 10000 in V) rejection tens micron resolution for typical aperturesSolution cavity BPMs allowing sub micron resolutionDesign the detector to collect only the difference signalDipole Mode TM11 proportional to position & shifted in frequency with respect to monopole mode

Improving the Precision forNext Generation Accelerators

f / GHzU / VFrequency DomainTM01TM11TM02U~QU~QrU~Q

Courtesy of D. Lipka,DESY, Hamburg

TM01TM11TM02Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

13Obtain signal using waveguides that only couple to dipole modeFurther suppression of monopole mode

Prototype BPM for ILC Final FocusRequired resolution of 2nm (yes nano!) in a 612mm diameter beam pipeAchieved World Record (so far!) resolution of 8.7nm at ATF2 (KEK, Japan)Todays State of the Art BPMs

Monopole ModeDipole ModeCourtesy of D. Lipka,DESY, Hamburg

Courtesy of D. Lipka & Y. HondaDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

14Accuracy mechanical and electromagnetic errors electronic componentsResolutionStability over timeSensitivity and Dynamic RangeAcquisition Time measurement time repetition timeLinearity aperture & intensityRadiation tolerance

Criteria for Electronics Choice -so called Processor ElectronicsDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

15Processing System FamiliesD I G I T I Z E Rturn by turnno turn by turnLegend: / Single channel

Wide Band

Narrow bandNormaliserProcessorActiveCircuitryHeterodynePOS = (A-B)

SynchronousDetectionAutomaticGain Controlon SMultiplexedPassiveNormalisationPOS = [log(A/B)] = [log(A)-log(B)] DifferentialAmplifierLogarithmic AmplifiersIndividualTreatmentLimiter,Dt to Ampl.Amplitudeto TimePOS = [A/B] POS = [ATN(A/B)] Amplitudeto Phase.Limiter,f to Ampl.POS = D / S HeterodyneHybridD / SHomodyneDetectionElectrodesA, BDirectDigitisationPOS = D / S Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

16Linearity Comparison


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AB1.5nsB + 1.5nsABBeamAmplitude to Time NormalisationSplitterDelay linesCombinerPick-upDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

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ABAmplitude to Time NormalisationA + (B + 1.5ns)

ABB + (A + 1.5ns)Dt depends on positionDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

19BPM Acquisition ElectronicsAmplitude to Time NormaliserAdvantages

Fast normalisation (< 25ns)bunch to bunch measurementSignal dynamic independent of the number of bunchesInput dynamic range ~45 dBNo need for gain selectionReduced number of channelsnormalisation at the front-end~10 dB compression of the position dynamic due to the recombination of signalsIndependent of external timingTime encoding allows fibre optic transmission to be used

Limitations

Currently reserved for beams with empty RF buckets between bunches e.g.LHC 400MHz RF but 25ns spacing1 bunch every 10 buckets filledTight time adjustment requiredNo Intensity informationPropagation delay stability and switching time uncertainty are the limiting performance factors


What one can do with such a SystemUsed in the CERN-SPS for electron cloud & instability studies


21The Typical InstrumentsBeam Positionelectrostatic or electromagnetic pick-ups and related electronicsBeam Intensitybeam current transformersBeam Profilesecondary emission grids and screenswire scannerssynchrotron light monitorsionisation and luminescence monitorsFemtosecond diagnostics for ultra short bunchesBeam Lossionisation chambers or pin diodesMachine Tunes and Chromacititiesin diagnostics section of tomorrowLuminosityin diagnostics section of tomorrow Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

22Current TransformersBeam current

Magnetic fieldriroFields are very low

Capture magnetic field lines with cores of highrelative permeability

(CoFe based amorphous alloy Vitrovac: r= 105)wN Turn winding

Transformer Inductance


23CSRBeam signalTransformer output signal

Winding of N turns and Inductance L

The Active AC transformerRFRLAttIBULDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

24Fast Beam Current Transformer500MHz BandwidthLow droop (< 0.2%/ms)

BEAMImageCurrentCeramic Gap80nm Ti Coating20W to improveimpedance1:40 PassiveTransformerCalibration windingDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

25Acquisition Electronics

FBCT Signal after 200m of CableIntegrator OutputData taken on LHC type beams at the CERN-SPS25ns


26What one can do with such a System

Bad RF Capture of a single LHC Batch in the SPS (72 bunches)Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

27The DC transformerBIAC transformers can be extended to very low frequency but not to DC ( no dI/dt ! )

DC measurement is required in storage rings

To do this: Take advantage of non-linear magnetisation curve Use 2 identical cores modulated with opposite polaritiesDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

28DCCT Principle Case 1: no beamIBModulation Current - Core 1Modulation Current - Core 2IMtHysteresis loopof modulator coresDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

29DCCT Principle Case 1: no beamIB

VtdB/dt - Core 1 (V1)dB/dt - Core 2 (V2)Output voltage = V1 V2Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

30DCCT Principle Case 2: with beamBeam Current IBVt IBOutput signal is at TWICEthe modulation frequencydB/dt - Core 1 (V1)dB/dt - Core 2 (V2)Output voltage = V1 V2IBDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

31Zero Flux DCCT SchematicBeamCompensation current Ifeedback = - IbeamModulatorV = R IbeamPower supplyRSynchronousdetectorVa - VbVbVaDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

32The Typical InstrumentsBeam Positionelectrostatic or electromagnetic pick-ups and related electronicsBeam Intensitybeam current transformersBeam Profilesecondary emission grids and screenswire scannerssynchrotron light monitorsionisation and luminescence monitorsfemtosecond diagnostics for ultra short bunchesBeam Lossionisation chambers or pin diodesMachine Tunes and Chromacititiesin diagnostics section of tomorrowLuminosityin diagnostics section of tomorrow Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

33Secondary Emission (SEM) GridsWhen the beam passes through secondary electrons are ejected from the wires

The liberated electrons are removed using a polarisation voltage

The current flowing back onto the wires is measured

One amplifier/ADC chain is used for each wire


34Profiles from SEM grids

Charge density measured from each wire gives a projection of the beam profile in either horizontal or vertical plane

Resolution is given by distance between wires

Used only in low energy linacs and transfer lines as heating is too great for circulating beams


35Wire ScannersA thin wire is moved across the beamhas to move fast to avoid excessive heating of the wire and/or beam lossDetectionSecondary particle shower detected outside the vacuum chamber using a scintillator/photo-multiplier assemblySecondary emission current detected as for SEM grids Correlating wire position with detected signal gives the beam profile

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


36OTR ScreenMirrorIntensifier -CCDBeamBeam Profile Monitoring using Screens

LensExit windowOptical Transition RadiationRadiation emitted when a charged particle beam goes through the interface of 2 media with different dielectric constantssurface phenomenon allows the use of very thin screens (~10mm)Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

37Beam Profile Monitoring using ScreensScreen Types Luminescence Screensdestructive (thick) but work during setting-up with low intensities Optical Transition Radiation (OTR) screensmuch less destructive (thin) but require higher intensity


38Beam Profile Monitoring using ScreensUsual configurationCombine several screens in one housing e.g.Al2O3 luminescent screen for setting-up with low intensityThin (~10um) Ti OTR screen for high intensity measurementsCarbon OTR screen for very high intensity operationAdvantages compared to SEM grids allows analogue camera or CCD acquisition gives two dimensional information high resolution: ~ 400 x 300 = 120000 pixels for a standard CCD more economicalSimpler mechanics & readout electronicstime resolution depends on choice of image capture deviceFrom CCD in video mode at 50Hz to Streak camera in the GHz range


39Luminescence Profile MonitorBeamN2 ground statee-N2 excited statePhotonemitted

Ion beamBlackened wallsVacuum gaugeValveViewport150mm flangeLens, Image-Intensifierand CCD CameraN2-fluorescent gasequally distributed


40Luminescence Profile MonitorCERN-SPS MeasurementsProfile Collected every 20msLocal Pressure at ~510-7 Torr

2DSide view

3DImageBeam SizeTimeBeam SizeTimeInjectionBeam size shrinks asbeam is acceleratedFast extractionSlow extractionDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

41The Synchrotron Light Monitor

BeamSynchrotron Light fromBending Magnetor UndulatorDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

42The Synchrotron Light Monitor


43Next Generation FELs & Linear CollidersUse ultra short bunches to increase brightness or improve luminosityHow do we measure such short bunches?Transverse deflecting cavity

Measuring Ultra Short Bunchesp+ @ LHC250psH- @ SNS100pse- @ ILC500fse- @ CLIC130fse- @ XFEL80fse- @ LCLS250fs by laser bandwidthLimited to >30fs by sampling laser pulseDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

The Typical InstrumentsBeam Positionelectrostatic or electromagnetic pick-ups and related electronicsBeam Intensitybeam current transformersBeam Profilesecondary emission grids and screenswire scannerssynchrotron light monitorsionisation and luminescence monitorsfemtosecond diagnostics for ultra short bunchesBeam Lossionisation chambers or pin diodesMachine Tunes and Chromacititiesin diagnostics section of tomorrowLuminosityin diagnostics section of tomorrow Dr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

46Beam Loss DetectorsRole of a BLM system:Protect the machine from damageDump the beam to avoid magnet quenches (for SC magnets)Diagnostic tool to improve the performance of the accelerator

Common types of monitorLong ionisation chamber (charge detection)Up to several km of gas filled hollow coaxial cablesPosition sensitivity achieved by comparing direct & reflected pulsee.g. SLAC 8m position resolution (30ns) over 3.5km cable lengthDynamic range of up to 104Fibre optic monitorsSimilar layout with electrical signals replaced by light produced through Cerenkov effectDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

Common types of monitor (cont)Short ionisation chamber (charge detection)Typically gas filled with many metallic electrodes and kV biasSpeed limited by ion collection time - tens of microsecondsDynamic range of up to 108Beam Loss Detectors

iin(t)iin(t) + IrefLHCDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

Common types of monitor (cont)PIN photodiode (count detection)Detect MIP crossing photodiodesCount rate proportional to beam lossSpeed limited by integration timeDynamic range of up to 109

Beam Loss Detectors

HERA-pComparatorDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

Beam Loss Detectors New MaterialsDiamond DetectorsFast & sensitiveUsed in LHC to distinguish bunch by bunch lossesInvestigations now ongoing to see if they can work in cryogenic conditions

Courtesy of E. GriesmayerDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

BLM Threshold Level Estimation


This was an overview of the common types of instruments that can be found in most acceleratorsOnly a small subset of those currently in use or being developed with many exotic instruments tailored for specific accelerator needs existingTomorrow you will see how to use these instruments to run and optimise acceleratorsIntroduction to Accelerator Beam Diagnostics (H. Schmickler)

Join the afternoon course:Beam Instrumentation & DiagnosticsFor an in-depth analysis of all these instruments and on their application in various acceleratorsSummaryDr. Rhodri Jones CERN Beam Instrumentation Group Introduction to Beam Instrumentation - CAS 2013

52Chart10.9980.99872081252.99956548820.80.85910250270.95424250940.60.6880795310.60205999130.40.4844722950.36797678530.20.25132890660.17609125910-0.00000233840-0.2-0.2513335835-0.1760912591-0.4-0.4844769719-0.3679767853-0.6-0.6880842079-0.6020599913-0.8-0.8591071796-0.9542425094-0.998-0.9987254893-2.9995654882

D/SAtn(a/b)loga-logbNormalized Position (U)Computed Position (U)Transfer Function

Transfer FunctionN.P.abD/Sloga-logbAtn(a/b)10.9990.0010.9983.000.9990.80.90.10.80.950.8590.60.80.20.60.600.6880.40.70.30.40.370.4840.20.60.40.20.180.25100.50.500.00-0.000-0.20.40.6-0.2-0.18-0.251-0.40.30.7-0.4-0.37-0.484-0.60.20.8-0.6-0.60-0.688-0.80.10.9-0.8-0.95-0.859-10.0010.999-0.998-3.00-0.9991.2

Transfer Function000000000000000000000000000000000

D/SAtn(a/b)loga-logbNormalized Position (U)Computed Position (U)Transfer Function

introduction to beam instrumentation cas 2013 trondheim , norway 18 th – 29 th august , 2013

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