Top-Up Experience at SPEAR3

Transcription

1 Top-Up Experience at SPEAR3

2 Contents SPEAR 3 and the injector Top-up requirements Hardware systems and modifications Safety systems & injected beam tracking Interlocks & Diagnostics

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

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

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

6 current (ma) 100mA and 500mA Operation SPEAR vs. 500 ma Fill Scenarios lifetime = ma = ma ~6.5 Amp-hr ma =180ma 100ma =12ma time (hrs)

7 current (ma) current (ma) 500mA Injection Scenarios delivery time = 8 hr t fill = ~6-7 min delivery time = 2 hr t fill = ~1.5-2 min SPEAR ma Fill Scenario lifetime = ma SPEAR ma Fill Scenario lifetime = ma delivery time = 0.5 hr t fill = ~17 sec delivery time = 1 min t fill = ~0.5 sec (or 10ms single shot) time (hrs) time (hrs)

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

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 Plan view Stored beam Elevation view

10 Septum wall Septum wall Hardware Upgrade: BTS Windows With windows: ~20% beam loss No windows: ~no loss 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: Before correction After correction 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 Huang, Safranek & Sebek

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

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

15 Hardware Upgrade: Thermionic Cathode as a Photo-Emitter Nominal configuration Tungsten dispenser-cathode (1000 C) 1.5 cell RF gun e- beam GHz (2 s) 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 cold-cathode e- beam (~500ps) GHz (~2 s) UV or green laser 1.5W heating Cu S.Gierman high singe-bunch charge for top-off - reduce beam loading in linac - eliminate cathode back bombardment - eliminate chopper UV Green 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 o AP studies to demonstrate injected beam can not escape shielding o Many clever scenarios (dreams and zebras) o BL shielding sufficient? (higher average current, more bremsstrahlung) o PPS/BCS interlock modifications o Do users wear badges? Efficient injection into main ring o Injection time, charge/shot, repetition rate Safety is complicated!

18 Synchrotron Radiation Exit Ports SPEAR3 DBA cell 18

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

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

21 A Closer Look

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

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

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

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

26 Horizontal Angle (rad) X' [rad] Trajectories in Phase Space vacuum chamber acceptance fixed mask Phase Space at Z = Fixed Mask Phase Space at Z = Ratchet Wall Ratchet Wall Opening Fixed Mask Opening spread in angles o 10 bend (far fringe field) X [m] Horizontal Position (m) 26

27 X' [rad] X' [rad] X' [rad] X' [rad] Evolution of allowed phase space A1 A2 Fixed Mask I Ratchet Wall BPM 7 BPM 1 Insertion Device QF QD BEND SD HCOR X-Rays to Beamline Stored Beam on design orbit Initial: A1 and BPM7 After BPM BPM1 After QF A2 Dipole Entrance X [m] Dipole Entrance Dipole Exit SD Exit X [m] Allowed Phase Space in BL coordinates Z = SD exit Z = Fixed Mask Z = Ratchet Wall X [m] X [m] 27

28 X' [rad] The Metric: Separation in Phase Space to Apertures Phase Space at Z = Fixed Mask Phase Space at Z = Ratchet Wall Fixed Mask Opening Ratchet Wall Opening X [m] 28

29 Offset [m] BL apertures and Extreme Ray position [m] The Extreme Ray A1 BPM 7 ID BPM 1 A2 QF QD BEND SD beam pipe w/apertures 0 Beamline apertures and the most severely mis-steered beam Beamline Axis Extreme Ray Stored Beam on design orbit Extreme Ray Separation at Fixed Mask rise/run ~ -0.1 rad BL4 BL5 BL6 BL7 BL9 BL10 BL11 mis-steered beam ratchet wall -1.2 All other Trajectories Z [m] Position along beam line [m] 29

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

31 BL aperture and Extreme Ray position [m] Parameter Sensitivity BL5 BL6 BL7 BL9 BL10 BL11 Nominal B/B = -10% B/B = -50% B/B = -60% Z[m] from ID center Parameter To Pass Beyond Fixed Mask To Pass Beyond Ratchet Wall E INJ /E SPEAR +59% +100% +10% B/B -48% -60% -1% (-10%) QF -100% Only with polarity reversed -25% Target Value for Interlock Limit QD +300% 55% (PS Limit) HCOR 22 mrad 30 mrad 3mrad (2 x PS Limit)

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

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

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 35

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

37 A Rastafarian Logic Table Corbett & Schmerge

38 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

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