1. Simulation and Experimental Results of SSRF Top-up Operation Haohu Li, Manzhou Zhang SSRF Top-up Workshop, Melbourne 2009.10.08

2. Contents Brief introduction of SSRF Project Demands of top-up operation in SSRF Goal of top-up operation Requirements for top-up operation Some simulation and experimental results Summarize

3. Brief introduction of SSRF Project SSRF is a third generation light source, the main parameters are as follows –Energy 3.5GeV –Circumference 432m –Effective Emittance ~4nm·rad –Beam Current 5mA(single bunch)/300mA(multi bunch) –Lifetime >10hours –Orbit Stability <10% of beam size –Straight Section sixteen 6.5m / four 12m

5. Machines In SSRF 150Me V Linac Full Energy Booster C=180m 3.5GeV Storage Ring C=432m

6. Lattice Parameters 20 DBA cells, 4 superperiods Four 12m long straight section used for –One for injection system –One for RF system –Others for users Theoretical minimum emittance 1.5nm.rad Norminal working point 22.22/11.29

7. Twiss Functions for 1/8 ring

8. Main Milestones during SSRF Construction 2004.12.25Ground breaking 2007.05.15First beam from LINAC 2007.10.05First 3.5GeV beam in booster 2007.12.24First stored beam (3GeV) in storage ring 2008.01.03Reached 100mA@3GeV 2008.05.10Light reached the end of the first beamline 2008.09.30Reached 200mA@3.5GeV200mA@3.5GeV 2009.03.07Light reached the end of the last beamline 2009.05.06Open to user 2009.07.18Reached 300mA@3.5GeV

9. Running status for users 595 people did 122 experiments in about 2 and a half months

10. The longest non-stop running for users -137 hours

11. Hardware failure during user time (05.06-07.16)

12. Demands of Top-up Operation in SSRF To provide more stable beam for users –Electron orbit stability, which we have already taken a lot of methods to keep the beam stabilized within 2~5 microns –Heating stabililty of beamline monochromator, which must be solved by keeping beam current as stable as possible, i.e. top-up injection Beam current will oscillate within less than 1% level during top-up operation, that means the injection process will running frequently, mostly once per several minutes, and the users can still do experiment during this period.

13. Orbit vs. current

14. Goal of top-up operation Current stability –Single bunch <1% –Multibunch <0.1% Orbit disturbance –Stored beam oscillation <0.1mm

15. Requirements of Top-up Operation To achieve a good current stability, the system must have High injection efficiency >99%

16. High injection efficiency The injection efficiency of storage ring will be affected by the following conditions –Extraction beam property from booster –Injection system acceptance –Stored beam loss during injection For the booster, digital power supplies are used to get a stable extraction beam’s energy, slow bump magnets (100ms) and high performance septa are helpful to increase the stability of the extraction orbit. For the injection system of storage ring, we use collimators to limit the injection beam’s emittance, and this will also protect our insertion device with small gap. For the stored beam, there should have no loss during injection, if the injection elements’ performance is good enough, because of its very small beam size, just 0.3mm for 1σ x. SP1 QD SP2-1 QD BP2 QF BEND KICK BP1 BP3 SP2-2

17. Efficiency of the injector(15~20 minites)

18. Injection efficiency of Storage ring During injection, we measured the booster and storage ring’s dcct, injection efficiency >95% Booster DCCT 0.74mA ~0.444nC SR DCCT 0.3mA ~0.43nC

19. High injection efficiency The injection efficiency of storage ring will be affected by the following conditions –Extraction beam property from booster –Injection system acceptance –Stored beam loss during injection For the booster, digital power supplies are used to get a stable extraction beam’s energy, slow bump magnets (100ms) and high performance septa are helpful to increase the stability of the extraction orbit. For the injection system of storage ring, we use collimators to limit the injection beam’s emittance, and this will also protect our insertion device with small gap. For the stored beam, there should have no loss during injection, if the injection elements’ performance is good enough, because of its very small beam size, just 0.3mm for 1σ x.

20. Collimator System Collimator system is used to protect the elements, especially small-gap IDs. Two collimators: horizontal and vertical Location : inject straight section Material : Ta Thickness : 30mm(H)/60mm(V)

21. Horizontal Collimator 95% of total lost beam are lost on the collimator Gap : ±14mm

22. Vertical Collimator In-vacuum ID （ cell 15 ） In-vacuum ID （ cell 17 ） Without V Collimator 99.5% of total lost beam are lost on the collimator With V collimator, gap ±2.7mm

23. Experimental Results Vertical Lower Part Vertical Upper Part

24. Requirements of Top-up Operation To achieve a good current stability, the system must have High injection efficiency >99% Sufficient long life time, >5 hours for single bunch and >10 hours for multibunch

25. Sufficient life time For single bunch mode, the designed beam current is 5mA. Assume the lifetime is τ, the beam will lose 1% after τ*ln(1/0.99)=0.01 τ. When τ equal 5 hours, that means we must inject electron each 3 minutes. For multibunch mode, the designed beam current is 300mA. In the same way, when life time equal 10 hours, the injection should be running each minute to reach ±0.1%.

26. Requirements of Top-up Operation To achieve a good current stability, the system must have High injection efficiency >99% Sufficient long life time, >5 hours for single bunch and >10 hours for multibunch Good diagnostic system for beam current, especially single bunch mode, at least 50 μA resolution. The store beam orbit stability during injection is only depends on the injection elements’ performance, such as septum’s leakage field, kickers’ jitter, kickers’ field uniformity, and the difference between four kickers, etc.

27. Injection System of SSRF storage ring

28. Main Parameters of injection elements Name Magnetic Length (m) Strength (mrad) Field (Tesla) Waveform Up/Down (  s ) Stability of Amplitude Timing Jitters Vacuum Aperture H/V (mm) Repetitio n Rate (Hz) Kicker 1&4 0.604.830.09440.5%  10ns 64/242 Kicker 2&3 0.60-4.830.09440.5%  10ns 64/242 Septum 1 0.80550.80600.2%  100n s 28/122 Septum 2 0.80550.80600.2%  100n s 28/122

29. Effects of Injection elements’ error Errors –Timing jitter of kickers –Field reproducibility –Field uniformity –Installation misalignment –Injection beam mismatch –Leakage field of septa –…… The first four types of errors will not only affect the injection beam, but also the stored beam. The fifth error will only affect the injection efficiency. The last one’s effect can be negligible with magnetic shielding layer on septum.

30. Timing jitter and field reproducibility of kickers The horizontal emittance of the injection beam and the stored beam is about 110 nm·rad and 4~10 nm·rad, respectively, so the field instability will mostly affect the stored beam The effective emittance will grow due to the power supply instability If the amplitude of the kicker strength is θ 0, the phase is φ 0, and their errors are Δθ i and Δφ i, respectively, the subscript i represents different kicker, then we have

31. Timing jitter of kickers Timing Jitter ( σ=2ns ) Horizontal orbit disturbation RMS(μm )Maximum( μm ) 1σ70440 2σ110750 3σ130840 4σ130860 5σ130880 6σ130920 Right Figure: After injection process, store beam center position at the center of injection straight (timing jitter : 2ns, seed : 1000)

32. Timing jitter and field reproducibility of kickers 1000 seeds ， 3σ

33. Field uniformity of kickers This error mainly comes from the metallic coating in ceramic vacuum chamber, because the kicker’s waveform width is very short, only 4μs. From SLS kicker measuring result, when the average coating thickness is 3μm and waveform width is 6μs, the field uniformity will reduce to 2%, and this value is far less than 1%. In SSRF, the average coating thickness is about 1.5 μm, and the waveform width is 4μs, the field uniformity will better than 3%. This error is a system error, it will cause the stored beam disturbance, and can be reduced by adjusting their strength.

34. a = 2% a = 5% Simulation Results Eddy current effect Before correctionAfter correction KIK2 Strength KIK3 Strength 1%0.4mm11μm-4.925mrad-4.725mrad 2%0.8mm20μm-5.02mrad-4.62mrad 5%2.0mm47μm-5.305mrad-4.305mrad 10%4.0mm128μm-5.78mrad-3.78mrad

35. Installation Misalignment Only roll tolerance of kickers can effect on the stored beam, this is a system error, can not be reduced. Assume the roll tolerance is 0.2mrad, 3σ,1000 seeds

36. Commissioning Results TBT data at BPM(1,2), where beta function is about 12m in both plane

37. Injection Beam Mismatch Injection efficiency with injection beam twiss parameter Injection efficiency with injection beam orbit error

38. Requirements of Top-up Operation To achieve a good current stability, the system must have High injection efficiency >99% Sufficient long life time, >5 hours for single bunch and >10 hours for multibunch Good diagnostic system for beam current, especially single bunch mode, at least 50 μA resolution. The store beam orbit stability during injection is only depends on the injection elements’ performance, such as septum’s leakage field, kickers’ jitter, kickers’ field uniformity, and the difference between four kickers, etc. The control system must be able to estimate when start and stop the injection process, which bucket need to be refill, and how many electrons need to be filled, etc.

39. Other considerations of top-up injection and operation Control system –Running automatically –Reading beam current and comparing it with the current limit –Choosing buchet and setting timing system –Switching on/off the injection process –Send signal to users Safety problem: Because the users will still work during injection, the safety of the optical elements must be very carefully studied. Precise model of storage ring : the necessary condition for autocontrol during top-up operation

40. Problems BPM offset will change with –Beam current –Bunch current distribution –Some unknown reasons

41. Filling Pattern Initial pattern After 12 hours

42. COD Difference between different filling pattern 20 buckets vs. 40 buckets

43. COD Difference between different filling pattern 100 buckets vs. 200 buckets

44. SOFB results on 2008.06.04 VerticalHorizontal The last orbit difference with the initial value Total SOFB time: 5.5hours BPM number: 135 Eigen Values: 60/60 (H/V) Orbit drift in the last 5.5 hours H V

45. Beam Current and Lifetime in the 5.5 hours

46. SOFB results started from 2008.12.01 23:00, 14 hours 80 个 BPM Eigen values H : 40 V : 60

47. SOFB results started from 2008.12.01 23:00, 14 hours

48. Effects of septum’s leakage field Septum 1&2 BPM2 of Cell 01~04 100 times TBT data

49. Some Unknown reasons

50. Other BPMs

51. Summarize During injection period, the stored orbit disturbance should be less than 130μm(H)/10 μm(V) (rms value), now the best case is 80μm(H)/30 μm(V) (max. value) Beam current stability can achieve 1% ( single bunch ) / 0.1% ( multi bunch ). With collimator system, the injection efficiency can achieve 99%. (starting point behind collimator) There still have a lot of job need to do before the real top-up operation running.

52. Thank you !