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Top-Up Experience at SPEAR3 Jeff Corbett Stanford Linear Accelerator Center (SLAC)

Top-Up Experience at SPEAR3 Jeff Corbett Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory Presented at University of Melbourne 9 October, 2009. Contents. • SPEAR 3 and the injector • Top-up requirements • Hardware systems and modifications

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Top-Up Experience at SPEAR3 Jeff Corbett Stanford Linear Accelerator Center (SLAC)

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  1. Top-Up Experience at SPEAR3Jeff Corbett Stanford Linear Accelerator Center (SLAC) National Accelerator LaboratoryPresented at University of Melbourne 9 October, 2009

  2. Contents • SPEAR 3 and the injector • Top-up requirements • Hardware systems and modifications • Safety systems & injected beam tracking • Interlocks & Diagnostics --------------------------------------- • Beam lifetime rate equation • PEP-X

  3. E S N W SPEAR3 Accelerator Complex NEXAFS PX XAFS PX PX PD/XAS SAXS/PX XAS/TXM 3GeV 10nm-rad 500 mA BTS 5W, 1.6nA ARPES 10Hz Single bunch/pulse Coherent Environment XAS Booster (White Circuit) LINAC/RF Gun 3GeV Injector

  4. Top ‘off’ at SPEAR3 • Rebuild SPEAR into SPEAR3 (1999-2003) • Operated at 100mA for ~6 years (beam line optics) • Recently increased to 200mA • Chamber components get hot at 500ma (450kW SR, impedance) • 500mA program suspended because of • power load transient on beam line optics • Instead worked to top-off mode (beam decay mode, fill-on-fill) RF system and vacuum chamber rated for 500ma

  5. Present Status • 13 exit ports taking SR (9 Insertion Device, 4 Dipole) • 7 ID ports presently in ‘fill-on-fill’ open shutter mode • 4 dipole beam lines open shutter injection by end of October 2009 • Last two ID shutters fill-on-fill by June 2010 • Trickle charge 2011

  6. 100mA and 500mA Operation ~6.5 Amp-hr 500ma D=180ma 100ma D=12ma

  7. delivery time = 8 hr tfill = ~6-7 min delivery time = 2 hr tfill = ~1.5-2 min delivery time = 0.5 hr tfill = ~17 sec delivery time = 1 min tfill = ~0.5 sec (or 10ms single shot) 500mA Injection Scenarios

  8. B120 B116-101 RF HVPS B117 control room B131 B118 power supplies SLM room B132-101 B132-102 RF BTS B130 LTB 120 MeV linac 3 GeV Booster B140 • Gun • higher current • stablize emission rate • “laser-assisted” emission • Linac • restore 2nd klystron • (higher energy, feedback) • phase-lock linac and booster rf • Booster • improve capture with modified lattice • improve orbit and tune monitors • develop fast turn-on mode • BTS • eliminate vacuum windows (done) • diagnostics • SPEAR • add shielding, interlocks • improve kicker response • transverse feedback • Beamlines • add shielding, interlocks • timing Hardware Upgrades

  9. SPEAR3 Injection Notes • Vertical Lambertson septum (booster outside ring) • - operates DC, skew quadrupole added • Three magnet bump • ~15 mm amplitude, ~12mm separation • Injection across three cells (sextupoles) • Slotted stripline kickers (DELTA, low impedance) • Transverse field dependence in K2 Injected beam Stored beam Elevation view Plan view

  10. Hardware Upgrade: BTS Windows With windows: ~20% beam loss No windows: ~no loss Septum wall Septum wall Huang & Safranek

  11. Injected beam profile measurements Turn number Visible diagnostic beam line Movies…

  12. Hardware upgrade: Injection Timing and Energy • Synchrotron oscillations measured with turn-by-turn BPMs: • Kickers set to dump injected beam each cycle • Injection energy stable • Injection time varies over hours • RF cable temperature • Develop method to measure timing with stored beam Before correction After correction Huang, Safranek & Sebek

  13. Single shot injection kicker transient = ~10 ms (~0.1 ms with feedback) Hardware upgrade: Injection Bump Closure • Kickers can interrupt data acquisition • What is interruption sequence? • depends on current ripple, beam lifetime and charge/shot • bunch train filling needs new booster RF system • Gated data acquisition • Tests with beam lines  no complaints • Lots of work to match kicker waveforms Huang & Safranek

  14. Hardware Upgrade: PEP-II Bunch Current Monitor downconverter chassis downconverter schematic bunch-by-bunch processor chassis - visible APD (ASP) - x-ray APD (CLS) A.S.Fisher

  15. Hardware Upgrade: Thermionic Cathode as a Photo-Emitter Nominal configuration 1.5 cell RF gun Tungsten dispenser-cathode (1000 C) e- beam 2.856 GHz (2ms) ► S-band RF gun with thermionic cathode, alpha magnet, and chopper ► Most charge during the 2 μs RF pulse stopped at the chopper ► 5-6 S-band buckets pass into the linac, single booster bucket ► SPEAR3 single bunch injection, 10Hz presently ~50pC/shot

  16. Photo-emission cathode (cont’d) Laser-driven configuration 1.5 cell RF gun e- beam (~500ps) cold-cathode UV or green laser 2.856 GHz (~2ms) 1.5W heating Cu S.Gierman UV Green ► high singe-bunch charge for top-off - reduce beam loading in linac - eliminate cathode back bombardment - eliminate chopper Sara Thorin/MAXLab, EPAC'08 'Turning the thermionic gun into a photo injector has been very successful '

  17. The Injected Beam Safety Dilemma • Radiation Safety: the first hurdle • AP studies to demonstrate injected beam can not escape shielding • Many clever scenarios (dreams and zebras) • BL shielding sufficient? (higher average current, more bremsstrahlung) • PPS/BCS interlock modifications • Do users wear badges? • Efficient injection into main ring • Injection time, charge/shot, repetition rate Safety is complicated!

  18. Synchrotron Radiation Exit Ports SPEAR3 DBA cell

  19. BPMs V3 MASK V4 MASK 220 L/S ION PUMP H2 ABSORBER ID BPM V1, V2 MASKS TSP BM-1 H1 ABSORBER H3 ABSORBER QFC BPM TSP BPM 220 L/S ION PUMP BELLOWS BPM 150 L/S ION PUMP TSPs BELLOWS BM-2 BPM ADDITIONAL BPM SET 24 mm 18.8 mm 13 mm EDDY CURRENT BREAK ID BPM 34 mm 44.2 mm 84 mm Vacuum Chamber Construction

  20. Photon Beam Exit Channel outside absorber inside absorber photon beam e- beam

  21. A Closer Look…

  22. Stored Beam Injected Beam ACCIDENT X-Rays X-Rays Injected Beam Top-Up with Safety Shutters Open Ratchet Wall Fixed Mask Stored Beam NORMAL Injected Beam X-Rays X-Rays Stored Beam Injected Beam Stored Beam Injected Beam SAFE X-Rays X-Rays Injected Beam

  23. Is this a real possibility? Stored Beam Experimental Floor Injected Beam ACCIDENT Injected Beam X-Rays X-Rays Stored Beam Shield Wall • Bad steering, energy • Bad magnet fields Simulation is necessary!

  24. SSRL Approach to Calculations Beamline Incoming Beam SPEAR3 Magnets Ratchet Wall Fixed Mask II Comb Mask 9.1 Fixed Mask I A2 A1 CM INSERTION DEVICE QD BEND SD QF Stored Beam on design orbit • No assumptions about initial steering • All physical positions and angles possible • Energy errors! • No magnetic field • Straight trajectories • Beamline Apertures • Vacuum Chamber • Radiation Masks Field simulation region Start Point Safe Endpoint • Wide fringe fields A.Terebilo

  25. Forward Propagation Only Photon Beam Line Fixed Mask Ratchet Wall (2-ft Concrete) A2 Aperture Injected Beam A1 Aperture Stored Beam Chamber boundary

  26. Trajectories in Phase Space fixed mask vacuum chamber acceptance spread in angles o 10 bend Horizontal Angle (rad) (far fringe field) Horizontal Position (m)

  27. A2 Ratchet Wall Fixed Mask I A1 X-Rays to Beamline BPM 1 BPM 7 QD Insertion Device BEND SD HCOR QF Stored Beam on design orbit Evolution of allowed phase space

  28. The Metric: Separation in Phase Space to Apertures

  29. A1 BPM 7 ID BPM 1 A2 BEND SD QF QD The Extreme Ray Beamline Axis Extreme Ray Stored Beam on design orbit beam pipe w/apertures Separation at Fixed Mask ratchet wall Offset [m] rise/run ~ -0.1 rad Extreme Ray All other Trajectories Position along beam line [m]

  30. Condition for ‘Abnormal’ Scenario special SLAC interpretation Large SPEAR3 magnet field error - and/or - Large injected beam energy error - AND - “extensive intentional steering”

  31. Parameter Sensitivity

  32. Ratchet Wall A2 A1 A3 X-Rays to Beamline PM Insertion Device BEND SD HCOR QF QD Stored Beam on design orbit Beamline-Specific Aperture SPEAR Apertures BL9: +112 / -101 mm +60 / -43 mm +50 / -43 mm Alignment of Apertures is Critical

  33. Fixed Mask • ID source Mechanical Drawings & Tolerances Experimental Floor x x x Ring Aperture Documentation Periodic checks More documentation

  34. Dose Calculations & Testing mis-steer and measure… Bauer & Liu

  35. ‘Hazard Mitigation’ • Passive Systems • Limiting apertures in transport line (BTS) • Limiting apertures in SPEAR3 and beam lines • - Permanent magnets for dipole beam lines • Active Systems (Redundant Interlocks) • Injection energy interlock • - BTS dipole supply • SPEAR3 magnet supplies • Stored beam interlock • - Radiation detectors at each beam line

  36. Interlock Hierarchy Hardware Interlock Envelope (reportable incident) Software Alarm Envelope Software Monitor Envelope path 1 A B * * path 2

  37. A Rastafarian Logic Table Corbett & Schmerge

  38. Accident Event Probability Analysis – Dipole Short Config Control Orbit Intl’k Volt Intl’k Rad Mon Dipole Short SCI r=100mm grain of sand: V=10-12 m3 How much sand? 1027 * 10-12 = 1015 m3 = 106 km3

  39. SPEAR3 Operating Sequence • 1. Load operational lattice • - software check of PS readbacks • 2. Inject to <20 mA (orbit interlock) • 3. Start orbit feedback (few microns) • 4. Inject to 50 mA – top-off permit • 5. Open beam line injection stoppers • 6. Fill 500 mA maximum (FOFB runs continuous) • 7. Fill-on-fill or trickle charge

  40. Thank you for hosting the Australian Synchrotron TopUp Workshop…

  41. Electron Beam Lifetime - Analytic Calculations Classically, for short times t, where ~ More technically, use a rate equation (units) Coulomb Touschek bremsstrahlung

  42. Big rate equation from before… Touschek Coulomb bremsstrahlung The gas pressure has two terms: static and dynamic Then Collecting terms or first-order, non-linear rate equation where a=a(Mbunch,VRF, yscraper) b=b(VRF, yscraper) NOTE: keep it simple – no coupling, dynamic aperture or bunch lengthening

  43. Finally integrating the rate equation yields ~ What's the point of all this? a. want to know the relative Toushek, bremsstrahlung & Coulomb contributions b. plan for top-off shot/charge, fill pattern, duty cycle c. plan for future coupling (high brightness operation) d. ID collimators e. shielding, etc Excellent, tractable student project Delves deep into particle beam and accelerator physics, NN application

  44. Very low emittance with on-axis injection: bunch replacement • Assume ~30-40 pm natural emittance (15-20 pm/plane, fully coupled), very small dynamic aperture • Lifetime (not yet calculated) < 1 h • Injection options: • Accumulator ring used to replace all bunches in ring • Bunch train replacement (~20 bunches per train, trains separated by gaps (~10-20 ns, 5-10 buckets) to accommodate rise- and fall-times of injection kicker • ~0.5 nC/bunch (68 mA/bunch x 20) • 116-140 trains (~160-190 mA total) • inject every 1-10 sec, depending on desired current stability R. Hettel

  45. multi-bunch injection limit single-bunch injection limit PEP-X: h = 3492 nb = 3400 Trev = 7.336 ms t(0) = 1800 sec itot = 1.5 A qtot = 11010 nC ibavg = 0.441 mA qbavg = 3.235 nC R. Hettel

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