Introduction to Accelerator Beam Diagnostics Dr. Peter Forck Gesellschaft für Schwerionenforschnung (GSI) & University Frankfurt, Germany

Demands on Beam Diagnostics Diagnostics is the ’organ of sense’ for the beam. It deals with real beams in real technical installations including all imperfections. Four types of demands leads to different installations: Quick, non-destructive measurements leading to a single number or simple plots. Used as a check for online information. Reliable technologies have to be used. Example: Current measurement by transformers. Instruments for daily check, malfunction diagnosis and wanted parameter variation. Example: Profile measurement, in many cases ‘intercepting’ i.e destructive to the beam Complex instruments for severe malfunctions, accelerator commissioning & development. The instrumentation might be destructive and complex. Example: determination of lattice functions at a synchrotron, e.g. tune Instruments for automatic, active beam control. Example: Closed orbit feedback using position measurement by BPMs. Non-destructive (’non-intercepting’) methods are preferred: The beam is not influenced The instrument is not destroyed.

The Role of Beam Diagnostics The cost of diagnostics is about 3 to 10 % of the total facility cost:  3 % for large accelerators or accelerators with standard technologies  10 % for versatile accelerators or novel accelerators and technologies. Cost Examples: The amount of man-power is about 10 to 20 %: very different physics and technologies are applied technologies have to be up-graded, e.g. data acquisition and analysis accelerator improvement calls for new diagnostic concepts.

Relevant physical Processes for Beam Diagnostics Electro-magnetic influence by moving charges Physics: classical electro-dynamics Technology: voltage & current meas., low & high frequencies Examples: Faraday cups, beam transformers, pick-ups Emission of photon by accelerated charges: (only for high relativistic electrons and p) Physics: classical electro-dynamics; Technology: optical techniques (from visible to x-ray) Example: Synchrotron radiation monitors Interaction of particles with photons Physics: atomic physics optics, lasers; Technology: optical techniques, particle detectors Examples: laser scanners, short bunch length measurement, polarimeters Coulomb interaction of charged particles with matter Physics: atomic & solid state physics; Technology: current meas., optics, particle detectors Examples: scintillators, viewing screens, ionization chambers, residual gas monitors Nuclear- or elementary particle physics interactions Physics: nuclear physics; Technology: particle detectors Examples: beam loss monitors, polarimeters, luminosity monitors And of cause accelerator physics for proper instrumentation layout. Beam diagnostics deals with the full spectrum of physics and technology,  this calls for experts on all these fields and is a challenging task!

Beam Quantities and their Diagnostics I LINAC & transport lines: Single pass ↔ Synchrotron: multi pass Electrons: always relativistic ↔ Protons/Ions: non-relativistic for Ekin < 1 GeV/u Depending on application: Low current ↔ high current Overview of the most commonly used systems: Beam quantity LINAC & transfer line Synchrotron Current I General Special Transformer, dc & ac Faraday Cup Particle Detectors Pick-up Signal (relative) Profile xwidth Screens, SEM-Grids Wire Scanners, OTR Screen MWPC, Fluorescence Light Residual Gas Monitor Wire Scanner, Synchrotron Light Monitor Position xcm Pick-up (BPM) Using position measurement Transverse Emittance εtrans Slit-grid Quadrupole Variation Pepper-Pot Wire Scanner Transverse Schottky

Beam Quantities and their Diagnostics II Beam quantity LINAC & transfer line Synchrotron Bunch Length Δφ General Special Pick-up Secondary electrons Wall Current Monitor Streak Camera Electro-optical laser mod. Momentum p and Momentum Spread Δp/p Pick-ups (Time-of-Flight) Magnetic Spectrometer Pick-up (e.g. tomography) Schottky Noise Spectrum Longitudinal Emittance εlong Buncher variation Pick-up & tomography Tune and Chromaticity Q, ξ --- Exciter + Pick-up Transverse Schottky Spectrum Beam Loss rloss Particle Detectors Polarization P Laser Scattering (Compton scattering) Luminocity L Destructive and non-destructive devices depending on the beam parameter. Different techniques for the same quantity ↔ Same technique for the different quantities.

Example: Diagnostics Bench for the Commissioning of an RFQ

Typical Installation of a Diagnostics Device Modern trend: High performance ADC & digital signal processing → action of the beam to the detector → low noise pre-amplifier and first signal shaping accelerator tunnel: → analog treatment, partly combining other parameters → digitalization, data bus systems (GPIB, VME, cPCI...) local electronics room: → visualization and storage on PC → parameter setting of the beam and the instruments control room:

The ordering of the subjects is oriented by the beam quantities: Outline of the Lecture The ordering of the subjects is oriented by the beam quantities: Current measurement: Transformers, cups, particle detectors Profile measurement: Various methods depending on the beam properties Pick-ups for bunched beams: Principle and realization of rf pick-ups, closed orbit and tune measurements Measurement of longitudinal parameters: Beam energy with pick-ups, time structure of bunches for low and high beam energies, longitudinal emittance Beam loss detection: Secondary particle detection for optimization and protection It will be discussed: The action of the beam to the detector, the design of the devices, generated raw data, partly analog electronics, results of the measurements. It will not be discussed: Detailed signal-to-noise calculations, analog electronics, digital electronics, data acquisition and analysis, online and offline software.... General: Standard methods and equipment for stable beams with moderate intensities.

Understanding the signal generation of various device Goal of the Lecture Signal generation Valid interpretation The goal of the lecture should be: Understanding the signal generation of various device Showing examples for real beam behavior Enabling a correct interpretation of various measurements.

Literature on Beam Diagnostics Conferences (with proceedings at www.jacow.org): American: Beam Instrumentation Workshop BIW Europe: Diagnostics and Instrumentation at Part. Acc. Conf. DIPAC now joined as International Beam Instrumentation Conference IBIC Books: V. Smaluk, Particle Beam Diagnostics for Accelerators: Instruments and Methods, VDM Verlag Dr. Müller, Saarbrücken 2009. D. Brandt (Ed.), Beam Diagnostics for Accelerators, Proc. CERN Accelerator School CAS, Dourdan, CERN-2009-005 (2009) see http://cas.web.cern.ch/cas/France-2008/Dourdan-after.html. P. Strehl, Beam Instrumentation and Diagnostics, Springer-Verlag, Berlin 2006. H. Koziol, Beam Diagnostic for Accelerators, Proc. CERN Accelerator School CAS, University Jyväskylä, Finland, p. 565 CERN 94-01 (1994), see http://cas.web.cern.ch/cas/CAS. J. Bosser (Ed.), Beam Instrumentation, CERN-PE-ED 001-92, Rev. 1994. P. Forck, JUAS Lecture Notes on Beam Diagnostics, see www-bd.gsi.de/conf/juas/juas.html. 11 11

Appendix: Example of Beam Diagnostics Installations The beam diagnostics installations for two example are presented: Heavy ion LINAC, synchrotron and transport line at GSI Germany Electron LINAC, booster and synchrotron at light source ALBA, Barcelona, Spain 12 12

The German Heavy Ion Accelerator Facility at GSI German national heavy ion accelerator facility in Darmstadt Layout: Acceleration of all ions LINAC: up to 15 MeV/u Synchrotron: up to 2 GeV/u Research area: Nuclear physics Atomic physics Bio physics incl. therapy Material research Extension by international FAIR facility

The German Heavy Ion Accelerator Facility at GSI: Overview SIS FRS ESR Ion Sources: all elements UNILAC UNILAC: all ions p – U : 3 – 12 MeV/u, 50 Hz, max. 5 ms Up to 20 mA current Synchrotron, Bρ=18 Tm Emax p: 4.7 GeV U: 1 GeV/u Achieved e.g.: Ar18+: 1·1011 U28+: 3·1010 U73+: 1·1010 ESR: Storage Ring, Bρ=10 Tm Atomic & Plasma Physics Radiotherapy Nuclear Physics

The German Heavy Ion Accelerator Facility at GSI: Overview Synchrotron: Current: 2 DCCT, 1 ACCT, 1 FCT Profile: 1 SEM-Grid, 1 IPM, 1 Screen Position: 16 BPM Tune, mom. spread: 1 Exciter + BPM 1 Schottky Ion Sources: all elements UNILAC SIS UNILAC FRS Transport Lines: Current: 8 FCT 15 Part. Detec. Profile: 10 SEM-Grid 26 MWPC 18 Screens Position: 8 BPM ESR LINAC: Current: 52 transformers, 30 F-Cups Profile: 81 SEM-Grids, 6 BIF Position & phase: 25 BPM Trans. emittance: 9 Slit-Grid, 1 pepper-pot Long. emittance: 3 devices

All ions, high current, 5 ms@50 Hz, 36&108 MHz GSI Heavy Ion LINAC: Current Measurement Faraday Cup: for low current measurement and beam stop, total 30 MEVVA MUCIS PIG RFQ IH1 IH2 Alvarez DTL HLI: (ECR,RFQ,IH) Transfer to Synchrotron 2.2 keV/u β = 0.0022 120 keV/u β = 0.016 11.4 MeV/u β = 0.16 Gas Stripper U4+ U28+ All ions, high current, 5 ms@50 Hz, 36&108 MHz Foil Stripper To SIS ↑ Transformer ACCT: for current measurement and transmission control total 52 device Constructed in the 70th, Upgrade 1999, further upgrades in preparation 1.4 MeV/u ⇔β = 0.054

Dipole, quadrupole, rf cavity Dipole, quadrupole, transfer line GSI Heavy Ion Synchrotron: Overview Dipole, quadrupole, rf cavity acceleration acceleration Important parameters of SIS-18 Important parameters of SIS-18 Circumference 216 m Inj. type Multiturn Energy range 11 MeV → 2 GeV Acc. RF 0.8 → 5 MHz Harmonic 4 (= # bunches) Bunching factor 0.4 → 0.08 Ramp duration 0.06 → 1.5 s Ion range (Z) 1 → 92 (p to U) Circumference 216 m Inj. type Multiturn Energy range 11 MeV → 2 GeV Acc. RF 0.8 → 5 MHz Harmonic 4 (= # bunches) Bunching factor 0.4 → 0.08 Ramp duration 0.06 → 1.5 s Ion range (Z) 1 → 92 (p to U) injec- tion injec- tion extrac- tion extrac- tion Dipole, quadrupole, transfer line

Important parameters of SIS-18 GSI Heavy Ion Synchrotron: Current Measurement acceleration ACCT: injected current 0.01... 1 MHz Important parameters of SIS-18 DCCT: circulating current 0... 10 kHz Circumference 216 m Inj. type Multiturn Energy range 11 MeV → 2 GeV Acc. RF 0.8 → 5 MHz Harmonic 4 (= # bunches) Bunching factor 0.4 → 0.08 Ramp duration 0.06 → 1.5 s Ion range (Z) 1 → 92 (p to U) FCT: bunch structure 0.01... 500 MHz injec- tion Faraday Cup: beam dump extrac- tion

The Spanish Synchrotron Light Facility ALBA 3rd generation Spanish national synchrotron light facility in Barcelona Layout: Beam lines: up to 30 Electron energy: 3 GeV Top-up injection Storage ring length: 268 m Max. beam current: 0.4 A Commissioning in 2011 Talk by Ubaldo Iriso: at DIPAC 2011, adweb.desy.de/mpy/DIPAC2011/html/sessi0n.htm see also www.cells.es/Divisions/Accelerators/RF_Diagnostics/Diagnostics

The Spanish Synchrotron Light Facility ALBA: Overview 3rd generation Spanish national synchrotron light facility in Barcelona Layout: Beam lines: up to 30 Electron energy: 3 GeV Top-up injection Storage ring length: 268 m Max. beam current: 0.4 A Commissioning in 2011 LINAC 100 MeV Booster 100 MeV  3 GeV Storage Ring: 3 GeV From U. Iriso, ALBA

The Spanish Synchrotron Light Facility ALBA: Current Meas. FCT DCCT FCUP AE BCM LTB 1 FCT 1 FCUP 3 BCM BOOSTER 1 DCCT 1 AE BTS 2 FCT SR Beam current: Amount of electrons accelerated, transported and stored Several in transport lines One per ring Abbreviation: FCT: Fast Current Transformer DCCT: dc transformer FCUP: Faraday Cup AE: Annular Electrode BCM: Bunch Charge Monitor Remark: AE: Annular Electrode i.e. circular electrode acting like a high frequency pick-up From U. Iriso, ALBA