Introduction to Beam Instrumentation - PowerPoint Presentation

1. Introduction toBeam InstrumentationCAS 2013Trondheim, Norway18th – 29th August, 2013Dr. Rhodri JonesHead of the CERN Beam Instrumentation Group

2. What 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 Introduction

3. More 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 dependent

4. 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 Tune and Chromaticityin diagnostics section of tomorrowLuminosityin diagnostics section of tomorrow

5. Measuring Beam Position – The Principle-----++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-+++--+-++--+--++-+-------+++++-+++--+-++--+--++-+-------++++-+++--+-++--+--++-

6. Wall Current Monitor – The Principle-----+++++-+++--+-++--+--++-+--+-------++++-+++--+-++--+--++-V+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++Ceramic Insert+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

7. Wall Current Monitor – Beam ResponseLIBVRCFrequencyResponse00IB

8. Electrostatic Monitor – The Principle-----++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-+++--+-++--+--++-+-------++++-+++--+-++--+-+-------++++-+++--+-++--+--++-+-V-------

9. Electrostatic Monitor – Beam ResponseVBVRCFrequency (Hz)Response (V)00+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

10. Electrostatic Monitor – The Principle-----+++++-+++--+-++--+--++-+-------++++-+++--+-++--+-+-------++++-+++--+-++--+--++-+-V--------+++++--+-+-+-+----+++-++-+--+-+-----+++-++--+-------+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

11. Electrostatic Pick-up – Button Low cost  most popular Non-linearrequires correction algorithm when beam is off-centreFor Button with Capacitance Ce & Characteristic Impedance R0Transfer Impedance:Lower Corner Frequency:Area Ar

12. Frequency (Hz)Response (V)00A Real Example – The LHC Button

13. Standard 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 modeImproving the Precision forNext Generation Acceleratorsf / GHzU / VFrequency DomainTM01TM11TM02U~QU~QrU~QCourtesy of D. Lipka,DESY, HamburgTM01TM11TM02

14. Obtain signal using waveguides that only couple to dipole modeFurther suppression of monopole modePrototype BPM for ILC Final FocusRequired resolution of 2nm (yes nano!) in a 6×12mm diameter beam pipeAchieved World Record (so far!) resolution of 8.7nm at ATF2 (KEK, Japan)Today’s State of the Art BPMsMonopole ModeDipole ModeCourtesy of D. Lipka,DESY, HamburgCourtesy of D. Lipka & Y. Honda

15. Accuracy mechanical and electromagnetic errors electronic componentsResolutionStability over timeSensitivity and Dynamic RangeAcquisition Time measurement time repetition timeLinearity aperture & intensityRadiation toleranceCriteria for Electronics Choice -so called “Processor Electronics”

16. Processing 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

17. Linearity Comparison

18. AB1.5nsB + 1.5nsABBeamAmplitude to Time NormalisationSplitterDelay linesCombinerPick-up

19. ABAmplitude to Time NormalisationA + (B + 1.5ns)ABB + (A + 1.5ns)Dt depends on position

20. BPM Acquisition ElectronicsAmplitude to Time NormaliserAdvantagesFast 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 usedLimitationsCurrently 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

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

22. 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

23. Current TransformersBeam currentMagnetic fieldriroFields are very lowCapture magnetic field lines with cores of highrelative permeability(CoFe based amorphous alloy Vitrovac: μr= 105)wN Turn windingTransformer Inductance

24. CSRBeam signalTransformer output signalWinding of N turns and Inductance LThe Active AC transformerRFRLAttIBUL

25. Fast Beam Current Transformer500MHz BandwidthLow droop (< 0.2%/ms)BEAMImageCurrentCeramic Gap80nm Ti Coating20W to improveimpedance1:40 PassiveTransformerCalibration winding

26. Acquisition ElectronicsFBCT Signal after 200m of CableIntegrator OutputData taken on LHC type beams at the CERN-SPS25ns

27. What one can do with such a SystemBad RF Capture of a single LHC Batch in the SPS (72 bunches)

28. The DC transformerBIAC transformers can be extended to very low frequency but not to DC ( no dI/dt ! )DC measurement is required in storage ringsTo do this: Take advantage of non-linear magnetisation curve Use 2 identical cores modulated with opposite polarities

29. DCCT Principle – Case 1: no beamIBModulation Current - Core 1Modulation Current - Core 2IMtHysteresis loopof modulator cores

30. DCCT Principle – Case 1: no beamIBVtdB/dt - Core 1 (V1)dB/dt - Core 2 (V2)Output voltage = V1 – V2

31. DCCT 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 – V2IB

32. Zero Flux DCCT SchematicBeamCompensation current Ifeedback = - IbeamModulatorV = R  IbeamPower supplyRSynchronousdetectorVa - VbVbVa

33. 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

34. Secondary Emission (SEM) GridsWhen the beam passes through secondary electrons are ejected from the wiresThe liberated electrons are removed using a polarisation voltageThe current flowing back onto the wires is measuredOne amplifier/ADC chain is used for each wire

35. Profiles from SEM gridsCharge density measured from each wire gives a projection of the beam profile in either horizontal or vertical planeResolution is given by distance between wiresUsed only in low energy linacs and transfer lines as heating is too great for circulating beams

36. Wire 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+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

37. OTR ScreenMirrorIntensifier -CCDBeamBeam Profile Monitoring using ScreensLensExit 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)

38. Beam 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

39. Beam 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 = 120’000 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

40. Luminescence Profile MonitorBeamN2 ground statee-N2 excited statePhotonemittedIon beamBlackened wallsVacuum gaugeValveViewport150mm flangeLens, Image-Intensifierand CCD CameraN2-fluorescent gasequally distributed

41. Luminescence Profile MonitorCERN-SPS MeasurementsProfile Collected every 20msLocal Pressure at ~510-7 Torr2DSide view3DImageBeam SizeTimeBeam SizeTimeInjectionBeam size shrinks asbeam is acceleratedFast extractionSlow extraction

42. The Synchrotron Light MonitorBeamSynchrotron Light fromBending Magnetor Undulator

43. The Synchrotron Light Monitor

44. Next Generation FELs & Linear CollidersUse ultra short bunches to increase brightness or improve luminosityHow do we measure such short bunches?Transverse deflecting cavityMeasuring Ultra Short Bunchesp+ @ LHC250psH- @ SNS100pse- @ ILC500fse- @ CLIC130fse- @ XFEL80fse- @ LCLS<75fsDestructive Measurement

45. Electro-Optic Sampling – Non DestructiveSpectral DecodingTemporal decodingLimited to >250fs by laser bandwidthLimited to >30fs by sampling laser pulse

46. 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

47. Beam 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 acceleratorCommon 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 effect

48. 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 Detectorsiin(t)iin(t) + IrefLHC

49. 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 109Beam Loss DetectorsHERA-pComparator

50. 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 conditionsCourtesy of E. Griesmayer

51. BLM Threshold Level Estimation

52. 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 acceleratorsSummary