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Beam Instrumentation ChallengesDr. Rhodri JonesHead of the CERN Beam Instrumentation Group

1st oPAC Topical WorkshopGrand Challenges in Accelerator OptimisationCERN, Geneva, Switzerland - June 26th 27th 2013

Introduction to Beam Instrumentation2Beam instrumentation provides eyes for machine operatorsThe 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 innovate or improve existing techniques to fulfill new requirementsA combination of many disciplinesApplied & Accelerator Physics and a lot of Mechanical, Electronic & Software EngineeringA fascinating field of work!

What are the main beam parameters measured?Beam Position to control location of the beam in the acceleratorBeam Intensity to measure operational efficiencyBeam Loss to ensure safe operationTransverse Beam profilesLongitudinal Beam profilesto optimise operationBeam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Trends in Accelerators3Bigger, Faster, Better!High energy machines for particle physicsLHC, HL-LHC, HE-LHC (CERN) CLIC/ILC (R&D)High current machinesNeutron sources material scienceSNS (US), ESS (Sweden), CSNS (China), IFMIF (Japan), Neutrino ProductionT2K (JPARC, Japan), NuMI/Nova (FNAL, US), CNGS (CERN), Project-X (FNAL, US), High Brightness machinesX-ray Free Electron Lasers probing complex, ultra-small structuresLCLS (SLAC, US), European XFEL (DESY, DE),

Compact or Exotic!Rare radioactive isotope machinesFAIR (GSI, DE), HIE-ISOLDE (CERN)Anti-matter machinesELENA (CERN), FAIR (GSI, DE)Medical proton/ion therapy machinesBeam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Challenges for Beam Instrumentation4Unprecedented request for precisionPositioning down to well below the micron levelTreatment of increasingly more dataBunch by bunch measurements for all parametersDealing with high beam powersNon-invasive measurement techniquesRobust and reliable machine protection systemsDealing with the ultra-fastMeasurements on the femto-second timescaleDealing with the ultra-lowMeasurement of very small beam currents

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Challenges for Beam Instrumentation5The Quest for Unprecedented Precision

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Beam Position Monitoring The Challenges6Typically one of the largest BI systemsLHC has 1100 BPMs CLIC drive beam requires 40000! This implies:Precision engineering at low costSimple, robust, yet very highly performing electronicsDigitise as soon as possible (now doable with advances in ADCs & digital treatment systems)Radiation Tolerant (improves S/N, minimises expensive cabling BUT needs significant testing time)XFELs and Linear Colliders increasingly asking for very high resolutionWell below 1mm for single pass

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Improving the Precision for Next Generation AcceleratorsStandard BPMs give intensity signals - need to subtract them to obtain a difference which is proportional to positionDifficult to do electronically without some of the intensity information leaking throughWhen looking for small differences this leakage can dominate the measurementSolution cavity BPMs allowing sub micron resolutionDesign the detector in such a way as to only collect only the difference signalDipole Mode TM11 proportional to position & shifted in frequency with respect to monopole mode

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

Courtesy of D. Lipka,DESY, Hamburg

TM01TM11TM027Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)7Todays State of the Art BPMs

Monopole ModeDipole ModeCourtesy of D. Lipka,DESY, Hamburg

Courtesy of D. Lipka & Y. HondaObtain 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)

8Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)8Challenges for Beam Instrumentation9Maximising the Available Data

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Maximising the Available Data - Example10APDTDCsynchrotron lightLHC turn clockElectrical pulseArrival time

filterLongitudinal Bunch ShapeLHC Longitudinal Density MonitorAims:Profile of the whole LHC ring with 50ps resolutionHigh dynamic range for ghost charge measurementMethod:Single photon counting with Synchrotron lightAvalanche photodiode detector50ps resolution TDCBeam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Courtesy of A. JeffLDM On-line Correction11

Main bunchSatellitesAfterpulsingDeadtimeGhost bunchesCorrected for deadtimeCorrected for deadtime and afterpulsingBeam Instrumentation Challenges- Dr. Rhodri Jones (CERN)LDM Results12ResultsAble to profile the whole ring within a matter of minutesCritical input for accurate luminosity calibration of the experiments

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Challenges for Beam Instrumentation13Dealing with high beam powersNon-invasive measurement techniques

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Dealing with High Beam Power - The Issues14Traditional invasive diagnostics no longer suitableMaterials do not withstand energy depositionBurning of holes or breaking of wires Use of superconducting RF structures Risk of contamination on breakage or sputtering of the intercepted material

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Measuring the Size of High Power Beams15Synchrotron Light DiagnosticsOnly for electron & very high energy proton/ion machines (LHC)Difficult to separate the light from the beam for linear acceleratorsDifficult to get absolute calibrationImage correction factors typically bigger than the beam size!Additional challenges lie in fast cameras & signal treatment chains for bunch by bunch measurement

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)LHC Synchrotron Light DiagnosticsMeasuring the Size of Intense Bunches16Standard OTR not an option for short intense bunches (main issue for LCLS)Signal swamped by Coherent OTR from micro-bunching within the main bunchOne proposal is to go to luminescent ScreensThere will still be COTR at polished surfacesResolution might be a problemInvestigation of temporal suppression of COTRScintillation screen + fast gated cameraProof-of-principle at FLASH, DESYResolution of scintillation screens needs studySynergy with ion beam diagnosticsSimilar studies ongoing for FAIR

Al coated Si OTR screen, COTR light,Coherent SR

LuAG screen,COTR &scintillation light

LuAG screen+100ns delayOnly scintillation light

Courtesy of M. Yan

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Courtesy of K. WittenburgNon-Invasive Beam Size Measurement17Laser wire scannerGood candidate for H- & electronsCan measure down to micron levelNeeds conversion to turn-key instrumentReliable laser systemLaser distribution to multiple measurement stations

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Courtesy of A. Alexandrov

Non-Invasive Beam Size Measurement18Beam Induced Fluorescence

BeamN2 ground statee-N2 excited statePhotonemittedBeam Instrumentation Challenges- Dr. Rhodri Jones (CERN)

Non-Invasive Beam Size Measurement19Beam Induced FluorescenceIssuesSensitivity to radiationLow signal yield vacuum bumpDrift of excited gas molecules broadening of profile

Ion beamBlackened wallsVacuum gaugeValveViewport150mm flangeLens, Image-Intensifierand CCD FireWire-CameraN2-fluorescent gasequally distributedBeam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Courtesy of M. SchwickertNon-Invasive Beam Size Measurement20Residual Gas IonisationSome 10 times more sensitive than BIFMore complicated to buildHigh voltage networkGuiding magnetic fieldImage broadening due to space chargeAgeing of detectors an issue

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Courtesy of M. Schwickert

21Electron Beam ScannerDerive beam profile from deflection of low energy electron beam scanned across the high energy proton beam

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Non-Invasive Beam Size MeasurementCourtesy of W. Blokland22Electron Beam Scanner how it worksLook at the deflected projection of a tilted sheet of electrons

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Non-Invasive Beam Size Measurement

dydxQuadrupolesDeflectorElectrons

Multiple scanstake the derivative to get the profileCourtesy of W. Blokland23Electron Beam Scanner the challenges

Non-Invasive Beam Size MeasurementCourtesy of W. BloklandBeam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Challenges for Beam Instrumentation24 Dealing with high beam powersRobust and Reliable Machine Protection Systems

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Beam Loss Monitors New Materials25Diamond DetectorsFast & sensitiveUsed in LHC to distinguish bunch by bunch lossesInvestigations now ongoing to see if they can work in cryogenic conditions

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Courtesy of E. GriesmayerCryogenic Beam Loss Monitors26Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)SiliconSuccessfully used at 1 K at CERN in 1976DiamondSuccessfully in use as LHC BLM at room temperatureBetter resistance to radiation than Si at room temperatureLess leakage current than Si at room temperatureDoes it work in liquid helium?Liquid helium ionisation chamberAdvantage : no radiation hardness issueDisadvantage : slow (charge mobility of 0.02 cm2/V/s)Cryogenic Beam Loss Monitors27Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Diamond resultsSingle particle (response averaged from ~5000 pulses)

27Challenges for Beam Instrumentation28 Dealing with the ultra-fastMeasurements on the femto-second timescale

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Ultra-Short Bunch Length Diagnostics29Next Generation FELs & Linear CollidersUse ultra short bunches to increase brightness or improve luminosityHow do we currently measure such short bunches?Transverse deflecting cavityp+ @ LHC250psH- @ SNS100pse- @ ILC500fse- @ CLIC130fse- @ XFEL80fse- @ LCLS75fs

Destructive MeasurementBeam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Non Destructive Electro-Optic Sampling30

Spectral DecodingTemporal decodingLimited to >250fs by laser bandwidthLimited to >30fs by sampling laser pulse &response of electro-optic materials

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Non Destructive Electro-Optic Sampling31Shortest measured electron bunch profile79.3 7.5 fs at DESY FLASHUsing 65um thick GaP crystalBeam Instrumentation Challenges- Dr. Rhodri Jones (CERN)

Courtesy of A. GillespieChallenges for Beam Instrumentation32Dealing with the ultra-lowMeasurement of very small beam currents

Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Measuring very low Intensity Beams33Beam Instrumentation Challenges- Dr. Rhodri Jones (CERN)Measuring rare ions and antiprotonsCurrents well below 1mA resolution of traditional Direct Current Beam TransformersSuperconducting QUantum Interference DevicesCan overcome the limits of conventional systemsBoth low and high temperature versions have been developedChallengesShielding the detector from stray fieldsEarths magnetic field ~ 50TField produced by 100 nA beam at 10 cm ~ 0.2 pT !Making the system compact

Cryogenic Current Comparator (CCC)Charged particle beam induces screening currentsToroidal pick-up coil of niobium with ferromagnetic core is used to measure magnetic fieldSignal from coil is fed through a superconducting transformer for impedance matching to the input coil of the readout DC SQUID.

Conclusion34Particle Beam Diagnostic systems are continually evolving to meet the requirements ofever more powerful and sophisticated acceleratorsever more demanding specificationsMany synergies between the developments required for all types of new accelerator facilitiesIdeal subject for collaboration on an international levelWas already underway between the major accelerator laboratories worldwideNow strengthened and extended to universities and industry via European NetworksBeam Instrumentation Challenges- Dr. Rhodri Jones (CERN)