Barrier RF Stacking

1. Barrier RF Stacking Weiren Chou and Dave Wildman Fermilab, U.S.A. October 20, 2004 Presentation at the Proton Driver Session ICFA-HB2004, Bensheim, Germany, Oct 18-22, 2004

2. Barrier RF Study Group • Fermilab-KEK-Caltech collaboration: • Fermilab - D. Wildman, J. Griffin, K.Y. Ng, J. MacLachlan, C. Bhat, W. Chou • KEK - A. Takagi, Y. Mori • Caltech - H. Zhang, D. Michael Acknowledgement: Helpful discussions with Takayama’s group ICFA-HB2004 Workshop, October 20, 2004

3. Outline • Motivation • Goals and methods • Simulations • Barrier rf system • Beam experiments • Summary http://www-bd.fnal.gov/pdriver/barrier/ ICFA-HB2004 Workshop, October 20, 2004

4. Collider Experiment Run2 Pbar target CDF D0 ICFA-HB2004 Workshop, October 20, 2004

5. Neutrino Experiment NuMI ICFA-HB2004 Workshop, October 20, 2004

6. Booster – the Bottleneck • The newMain Injectorcan accept25e12protons per Booster cycle. • However, the oldBoostercan only deliver5e12particles per cycle. Webber’s data in October 2000 Prebys/Lackey’s data in January 2004 ICFA-HB2004 Workshop, October 20, 2004

7. Solution - Stacking • A solution is to stack two Booster bunches into one Main Injector RF bucket • This is possible because the Main Injector longitudinal acceptance (0.72 eV-s) is larger than the Booster beam emittance (0.13 eV-s) ICFA-HB2004 Workshop, October 20, 2004

8. Goals • Run2 – To increase protons per second (pps) on the pbar target by 100% • Present: 5e12 every 2 sec • Goal: 2 x 5e12 every 2 sec • NuMI – To increase pps on the NuMI target by 70% • Baseline: 3e13 every 2 sec • Goal: 2 x 3e13 every 2.333 sec ICFA-HB2004 Workshop, October 20, 2004

9. Two Methods • Adiabatic stacking: • Beam injected on-axis • Adiabatically compress the beam by moving rf barrier • Fast stacking: • Beam injected off-axis • Using two barriers, one stationary, another moving • Continuous injection and stacking • First proposed by J. Griffin ICFA-HB2004 Workshop, October 20, 2004

10. Two Types of Barrier Stationary barrier +V -V Moving barrier +V -V ICFA-HB2004 Workshop, October 20, 2004

11. Adiabatic Stacking Simulation (K-Y. Ng) Measurement ICFA-HB2004 Workshop, October 20, 2004

12. Fast Stacking Simulation: 2-Batch (courtesy K.Y. Ng) ICFA-HB2004 Workshop, October 20, 2004

13. 2-Batch Stacking(cont…) ICFA-HB2004 Workshop, October 20, 2004

14. Fast Stacking Simulation: 12-Batch (courtesy K.Y. Ng) ICFA-HB2004 Workshop, October 20, 2004

15. 12-Batch Stacking(cont…) ICFA-HB2004 Workshop, October 20, 2004

16. 12-Batch Stacking(cont…) ICFA-HB2004 Workshop, October 20, 2004

17. 12-Batch Stacking(cont…) ICFA-HB2004 Workshop, October 20, 2004

18. 12-Batch Stacking(cont…) ICFA-HB2004 Workshop, October 20, 2004

19. 12-Batch Stacking(cont…) ICFA-HB2004 Workshop, October 20, 2004

20. 12-Batch Stacking(cont…) ICFA-HB2004 Workshop, October 20, 2004

22. Barrier RF System • Design goal:  6 kV wideband RF system • Two main components: • Cavity: made of Finemet cores (Hitachi, Japan) • Modulator: made of high voltage fast switches (Behlke, Germany) ICFA-HB2004 Workshop, October 20, 2004

23. Fast Switch (Behlke) HTS 161-06-GSM Peak voltage 2  16kV Peak current 60 A Pulse width 300 ns Pulse spacing 0.4-11s Repetition rate 100 kHz Burst length 400 ms Burst rep rate 0.5 Hz Finemet Core (Hitachi) FT3M OD 500 mm ID 139.8 mm thickness 25 mm Inductance 56 H (per core) Resistance 190  (per core) Specifications ICFA-HB2004 Workshop, October 20, 2004

24. Barrier RF System(cont…) Finemet core High voltage fast switch ICFA-HB2004 Workshop, October 20, 2004

25. Finemet vs. Ferrite (4M2) ICFA-HB2004 Workshop, October 20, 2004

26. Barrier RF System(cont…) Modulator Cavity ICFA-HB2004 Workshop, October 20, 2004

27. Full-Bridge Push-Pull Bipolar Circuit 9:1 1:9 upstairs in the tunnel ICFA-HB2004 Workshop, October 20, 2004

28. Bench Test Before tuning After tuning trigger current primary voltage gap voltage 6 kV ICFA-HB2004 Workshop, October 20, 2004

29. Beam Experiment in the Main Injector RF voltage Beam intensity acceleration capture rebunch debunch squeeze ICFA-HB2004 Workshop, October 20, 2004

30. Beam Experiment(cont…) Beam squeezing 6 kV Moving barrier Squeezing Squeezed ICFA-HB2004 Workshop, October 20, 2004

31. Mountain View 1.6 s t 3.2 s Stacking off Stacking on ICFA-HB2004 Workshop, October 20, 2004

32. More Mountain Views ICFA-HB2004 Workshop, October 20, 2004

33. High Beam Intensity after Stacking 8.3e12 @120 GeV squeezing ICFA-HB2004 Workshop, October 20, 2004

34. Try Even Higher Beam Intensity Beam intensity (10e12) 53 MHz RF voltage ICFA-HB2004 Workshop, October 20, 2004

35. Emittance Simulation  ESME(2 x 5e12, final bunch after recapture, courtesy J. MacLachlan) Bucket size = 0.30 eV-s Bucket size = 0.35 eV-s ICFA-HB2004 Workshop, October 20, 2004

36. Emittance Measurement – Injected Bunch Stationary bucket, beam intensity = 5.23e12, emittance = 0.13 eV-s ICFA-HB2004 Workshop, October 20, 2004

37. Emittance Measurement – Stacked Bunch Low intensity High intensity Medium intensity ICFA-HB2004 Workshop, October 20, 2004

38. Emittance Measurement – Accelerated Bunch Bunch width = 10 ns moving area factor = 0.45 Stationary bucket area = 1.6 eV-sbunch emittance = 0.72 eV-s ICFA-HB2004 Workshop, October 20, 2004

39. Summary • A barrier RF system has been built and installed in the Main Injector • It has successfully stacked two Booster batches into one and reached 8.3e12 at 120 GeV, ~ 60% increase in beam intensity • There is large emittance dilution during stacking • Causing losses at the beginning of acceleration • Making bunch too long for pbar production • But not a problem for NuMI • A second system is under construction and will be used for fast stacking experiment ICFA-HB2004 Workshop, October 20, 2004

40. Questions?