1. Top-Up Injection Schemes
John Seeman,
SLAC
eeFACT, Daresbury
October 24-27, 2016

2. Abstract: Top Injection for PEP-II
The schemes for full-energy top-up injection into an e+e- collider will be discussed emphasizing technical issues to be accommodated. The issues include energy stability, energy spread control, transverse emittance reduction, transverse position and angle stability, collimation, background control in the detector, detector blanking of event triggers, and bunch filling strategies. Strategies and observations from PEP-II and KEKB will be included. Top-off injection was developed in PEP-II and KEKB from a linac injector to allow constant luminosity with the BaBar and Belle detectors, repectively, being fully operational during injection. The positron beam top-off in PEP-II was developed initially as its lifetime was the shortest and thus made the luminosity nearly constant. Second, the electron beam top-off was developed making the luminosity fully constant. For PEP-II either electrons or positron could be injection up to 30 Hz if needed, deciding pulse-by-pulse which beam (bunch) was desired. KEKB injector either electron or positrons as determined by the linac and transport line configuration. The implications for top-off into a circular Higgs factory will also be discussed. The injected beam emittances and septum parameters are presented.

3. Topics for Top-up Injection for Higgs Factory
Required injection parameters for a circular e+e- Factory Briefly: PEP-II /BaBar top-up injection Briefly: KEKB/Belle top-up injection Detector background masking Top-up injection commissioning

4. Acknowledgements
Many thanks to: PEP-II: S. Ecklund A. Fisher M. Sullivan J. Turner U. Wienands KEKB: Y. Funakoshi H. Koiso K. Oide S. Uno BaBar: S. Curry W. Kozanecki A. Perazzo C. O’Grady M. Weaver

5. Definitions (for this talk)
Trickle injection = Top-Off = Top-Up

6. Technical Items Needed for Top-Up injection
Measure each bunch charge in real time and determine when it needs refilling.
In the injector, initiate a bunch to deliver it to the needed particular bunch (bucket) in the ring.
Inject the bunch(es) into the collider with very low losses.
Determine the injected beam backgrounds in the particle physics detector and find cures using collimation and launch conditions.
Develop methods to monitor relevant backgrounds in real time for accelerator operators to tune on.
Develop trigger masking for the detector physics taking by turn and with azimuthal variation.

7. Future e+e- Collider Parameters
100 km
54 km
27 km

8. Electron and Positron Production
FCCee/CEPC stores about 6.2/1.9 x1013 e- and e+ per beam at the Higgs. FCCee/CEPC with 0.5 hr lifetime needs 4.5/1.4 x1013 e- and e+ per hour or about 1.5/0.5 x1010 e+ and e- per second at full energy (80% capture). Past production rate for positrons: CERN: LEP injection complex delivered ~1011 e+ per second. SLAC: SLC injection complex delivered ~6 x 1012 e+ per second.

9. Collider Injection Phase Space
Septum blade
Injection
orbit
Typical parameters:
bx at injection septum (stored) = ~200m
bx at injection septum (injection) = ~30m
exstored (stored) =9.4 nm
exinj (injected) =50 nm
sxstored at septum (stored) = 1.4 mm
sxinj at septum (injected) = 1.2 mm
Xs = Septum blade thickness =~ 5 mm
Xc = septum clearance distance = ~6sx
Xinj < Ax
Xinj = 4Xsinj+Xs+Xc = ~18 mm
Ax = machine aperture > ~20 mm
Stored
Beam
Orbit
Stored beam
Injection
bump on
Injection bump xc
Injected
beam
xinj Ax
Injection
bump off
(~one turn
later)
xinj

10. Top-up injection by full charge exchange
Dump
Kicker
Old bunch
Ring orbit
New bunch
Kicker
Injector

11. PEP-II / BaBar Top-Up (Trickle) Injection
Energy = 3.5 x 9 GeV
Circumference = 2200 m
One collision point (IR) at Lum = 1.2 x 1034
Full energy injection from Linac+Damping Rings
Number of bunches = 1732 / ring
Beam currents = 2.1 A x 3.2 A
Particles = 1.0 or 1.5 x 1014 / beam (HER/LER)
Lifetimes:
Vacuum = ~10 hours
Touschek = ~3 hours (LER)
Luminosity = ~1 hour
Lost particles per second = 4.2 x 1010 / second
Top-up injection = one bunch / pulse, either e+ or e-
Injection rate: ~3-15 Hz (30 Hz max)
Particles per injection: 3 to 9 x 109 / pulse, selectable
Bunch injection controller: pick the lowest bunch
Injection efficiency = 50 to 80%
Injection kicker pulse length = 0.4 msec
Ring path length = 7.3 msec
PEP-II
BaBar

12. Actual vertical injection phase space in PEP-II
(Decker et al)

13. PEP-II Interaction Region

14. PEP-II injected beams

15. PEP-II Injection Considerations for Top-up

16. PEP-II Top-up Injection Controls
Charge/pulse typically inject "small quanta only“ Maximum trickle (injection) rate about 3/sec average when setup & trickling "Pseudo lifetime" Normal, DCCT-based beam-lifetime for LER un-useable "Pseudo lifetime" calculated from bunch currents avoiding those just injected. Minimum beam current fraction Avoid "trickling from scratch"

17. PEP-II Bunch Trains

18. Bunch injection controller
Launches triggers
Master
pattern
generator

19. PEP-II LER Bunch Injection Requests
Different bunches have different beam-beam lifetimes and injection rates.

20. PEP-II top-up injection lengthened the average fill length
Both top-up
LER top-up
No top-up

21. Reduced injection jitter (by accelerator)
Ring orbit

22. PEP-II Integrated Luminosity Effect from Top-up Injection

23. Before PEP-II Top-up Injection

24. After PEP-II Top-up Injection

25. PEP-II/BaBar Top-Up Injection (Accelerator)
Improved peak and average luminosity.
Before Top-Up Injection
After Top-Up Injection

26. PEP-II Run Time Improvement with Top-up

27. KEKB and Belle Detector

28. KEKB/Linac injection controller and parameters

29. KEKB-Belle Top-up Injection

30. Belle Triggers and Masking

31. KEKB normal injection (<2005)

32. KEKB top-up injection (>2005)

33. Comparison of Top-up Injection Belle/BaBar

34. BaBar Injection Monitoring

35. BaBar setting of noise sampling gate

36. BaBar: details of setting noise windows

37. BaBar Endcap Calorimeter (EMC) signal analysis
Starting point before energy fix
Injection with energy fix
6.5 kHz = energy error

38. Top-up injection losses were higher with more stored current

39. BaBar trigger with LER top-up injection (1)

40. BaBar trigger with LER top-up injection (2)

41. PEP-II/BaBar Top-Up Injection (Detector)
One
turn
BaBar trigger masking:
Mask all of ring a few tens of turns.
Mask injected bunch area for 1250
turns or about 0.9 msec.

42. BaBar Vetoes versus bunch number and turn number.

43. BaBar/PEP-II top-up improvements needed during commissioning
What improvements did BaBar need (incomplete list) (~late 2004): Smooth out trickle-algorithm in BIC, avoid stoppage (including cleaning up BIC-MPG (bunch injection controller and master pattern generator) communication). Get EPICS bar-chart display showing rate of injection/bunch. Want display of total injection rate Get a hardware real-time injection indicator (pulsed LED or counter). Make sure injection (LESIT) feedbacks don’t stop if too many small quanta. Stabilize setup of quanta (intensity, energy). BaBar needed to update its interlocks (bypassed too many). Speed up refresh of injection-trigger histograms

44. FCC/CEPC Detector Masking
Detectors for FCCee/CEPC need to mask injection bunches. Ramped “Storage Ring” injector: Mask entire ring for ~10 msec every 5 minutes  large injected charge and many bunches (~50-100). Int. luminosity loss ~10%. Ramped “Main Injector” style: Mask entire ring for ~10 msec every 15 seconds  small injected charge and many bunches (~50-100). Int. luminosity loss ~1%. Rapid “synchrotron injector”: Mask ~1/80 of ring for ~10 msec at 0.1 Hz  small injected bunch charge but few bunches (~1-3). Int. luminosity loss << 1%.

45. Top-up Beam Commissioning Tuning Tools
Radiation detectors (diodes, xtals, SVTRAD) useable only when backgrounds are too high! Injection trigger counters count EMC triggers after injection pulse histogram of triggers vs time EPICS variables with integral counts FFT shows effect of beam-energy deviations. normalized to injection rate DCH current quite useful for monitoring of average background not fast, so not useful to assess injection spikes Trigger rate (L3) similar behaviour as DCH current

46. SPEAR top-up injected beam shape versus turn

47. Conclusions
Top-up injection will work for a circular e+e- factory. Top-up or full charge exchange works. A full energy injector is needed because of the short beam lifetime. The detectors will need to mask out the buckets during damping of injected bunches during data taking but not the whole circumference. Singe bunch injection controller needs to be worked out in detail for both the accelerator and the detector. Commissioning can be complicated as many issues both on the accelerator and detector arise: mainly detector backgrounds and masking.