1. The 4th EIC workshop May 19-23, 2008 Experience with Crab cavities The 4th Electron Ion Collider Workshop 19-23 May, 2008 Hampton University Mika Masuzawa, KEK

2. The 4th EIC workshop May 19-23, 2008 Contents 1.Introduction Where/What is KEKB? Characteristics of KEKB 2.Machine performance before Crab cavities Luminosity history Machine parameters 3.Machine performance with Crab cavities Crab crossing scheme Cavity production & installation Beam commissioning with crab cavities Can we confirm the prediction? 4.Summary

3. The 4th EIC workshop May 19-23, 2008 1. Introduction Where/What is KEKB? Characteristics of KEKB

4. Mt. Tsukuba Nikko KEKB tunnel ~11 m below Ground Level Belle @IP Linac Aerial view of KEK Tokyo Mt.Fuji About KEKB Where

5. The 4th EIC workshop May 19-23, 2008 Superconducting cavities (HER ) e- e+e+ ARES cavities (LER) 8 GeV e- 3.5 GeV e+ Linac e+ target ARES cavities (HER) IR Belle detector KEKB B-Factory Beam energy – 8GeV (electron, “HER”) – 3.5GeV (positron, “ LER”) Circumference – 3016 m – Uses TRISTAN tunnel RF system – f RF ~ 509MHz – ARES (LER) – ARES+SCC (HER) The construction of KEKB began in 1994, and was completed in November 1998. Commissioning started in Dec.1998. What is KEKB About KEKB

6. The 4th EIC workshop May 19-23, 2008 Characteristics of KEKB

7. The 4th EIC workshop May 19-23, 2008 Superconducting Cavities Storage of high current >1.4 A ARES normal conducting cavities: Large storage cavity for stable acceleration Finite crossing angle Superconducting Q magnet for final focus. Small beam size achieved at IP 2.5  Cell Lattice: Low non-linearity high flexibility J-LINAC: Efficient acceleration in a limited space Two bunch positron injection Bunch-by-bunch feedback system Solenoids to reduce electron cloud effects IR SCC Arc section magnets ARES Solenoids on vacuum pipe Characteristics of KEKB

8. The 4th EIC workshop May 19-23, 2008 Interaction Region Vertical focusing by a pair of superconducting Q-magnets （ QCSL/QCSR ）. Extra vertical focusing by QC1L/R for the electron beam. One beam must go off axis due to the finite crossing angle at the IP. To minimize the flux of SR through the IP, the incoming positron (electron) beam orbit is set on the axis of QCSL (QCSR). Superconducting solenoid magnets SL/R used for compensating the detector solenoid field. Characteristics of KEKB

9. PEP-II KEKB KEKB has 22 mrad horizontal crossing angle at the IP: Easier beam separation Simpler design around the IP. Fewer components. Less synchrotron radiation. Less luminosity-dependent background. Space for compensation solenoid, etc. More on Interaction Region Characteristics of KEKB

10. The 4th EIC workshop May 19-23, 2008 2.Machine performance before Crab cavities Luminosity history Peak luminosity Integrated luminosity Machine parameters (Design & Best)

11. The 4th EIC workshop May 19-23, 2008 Luminosity history Peak Daily design

12. Peak luminosity The 4th EIC workshop May 19-23, 2008

13. The 4th EIC workshop May 19-23, 2008 Highest luminosity ever achieved by a collider

14. The 4th EIC workshop May 19-23, 2008 10 34 10 33 10 32 10 31 10 30 10 29 Peak luminosity (cm -2 s -1 ) 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year

15. Integrated luminosity The 4th EIC workshop May 19-23, 2008

16. The 4th EIC workshop May 19-23, 2008 The best day (1.23 /fb/day) before Crab cavity installation Design luminosity

17. The 4th EIC workshop May 19-23, 2008 Continuous injection scheme since 2004

18. The 4th EIC workshop May 19-23, 2008 Integrated luminosity

19. The 4th EIC workshop May 19-23, 2008 Machine parameters

20. The 4th EIC workshop May 19-23, 2008 11/15/2006DesignUnit LERHERLERHER Beam Current1.651.332.61.1A # of bunches13895000 Bunch current1.190.960.520.22mA Emittance  x 182418 nm *x*x 595633 cm *y*y 0.650.591.0 cm *x*x 10311677 mm *y*y 1.9 mm xx 0.1150.0750.039 yy 0.1010.0560.052 Bunch length7644mm Luminosity17.1210/nb/s  Luminosity/day 1232~600/fb Machine parameters (Best & Design)

21. The 4th EIC workshop May 19-23, 2008 More on the machine parameters of Nov.15, 2006 LERHERUnit Circumference3016m RF frequency508.88MHz Horizontal Emittance1824nm Beam current16621340mA # of bunches1388 Bunch current1.200.97mA Bunch spacing2.1m # of bunch trains1 Total RF voltage Vc8.015.0MV Synchrotron tune s -0.0246-0.0226 Betatron tune x/ y 45.505/43.53444.509/41.565 Beta’s at IP  x*/  y* 59/0.6556/0.59cm Momentum compaction a3.31 x 10 -4 3.38 x 10 -4  *y (estimated) 1.9 mm Beam-beam  x/  y 0.115/0.1010.075/0.056 Beam lifetime110 @ 1600180 @ 1340min. @ mA Luminosity17.1210 33/cm 2 /sec / day / 7days / 30days1.232 / 7.809 / 30.21/fb

22. The 4th EIC workshop May 19-23, 2008 Machine performance Summary before Feb. 2007 (without crab cavities) Recorded highest luminosity of 17 /nb/sec (1.7x10 34 /cm 2 /s), with a crossing angle at the IP.

23. The 4th EIC workshop May 19-23, 2008 For even higher luminosity Achieve a head-on collision while keeping the crossing angle at the IP.  Crab Crossing Scheme

24. The 4th EIC workshop May 19-23, 2008 3.Machine performance with Crab cavities What is Crab crossing scheme? Cavity production and installation Beam commissioning

25. What is Crab crossing scheme? The 4th EIC workshop May 19-23, 2008

26. Input Coupler Liq. Helium Vessel Stub Support Coaxial Coupler Copper Bellows 80 K Liq. Nitrogen Shield Notch Filter RF Absorber Aluminum End Plate Aluminum End Plate SUS Support Pipe Crab Crossing Scheme Crossing angle 22 mrad Head-on (crab) (Strong-strong simulation) Simulation by K. Ohmi K. Hosoyama, et al. First proposed by R. B. Palmer in 1988 for linear colliders. Need two RF deflectors for each ring

27. The 4th EIC workshop May 19-23, 2008 Crab crossing scheme (our choice) Install one crab cavity per ring, at Nikko straight section where superconducting acceleration cavities (SCC)are located. Saves on cost of cavities and cryogenic systems. Avoids synchrotron radiation hitting the cavity.

28. The 4th EIC workshop May 19-23, 2008 Crab crossing scheme Comparison between two cavities/ring and one cavity/ring IP beam crab cavity crab cavity bunch tail bunch head crab cavity 1 cavity per ring 2 cavities per ring orbits of bunch head and tail Different COD between head and tail Same COD

29. The 4th EIC workshop May 19-23, 2008 Crab Crossing Scheme (KEKB) Beam tilts all around the ring. z-dependent horizontal closed orbit. tilt at the IP (head on): Crab cavities Streak cameras to observe the tilt LERHER xx 22mrad *x*x 80 cm cxcx 73162m  x /2  0.5050.511  c x /2  ~0.25 VcVc 0.951.45MV  rf /2  509MHz Typical parameters for Crab crossing Tilt angle depends on crab voltage,  x *and  x(Crab).

30. The 4th EIC workshop May 19-23, 2008 What crab cavity looks like

31. Concept of the KEKB Crab Cavity E EB The squashed cell shape cavity scheme was studied extensively by K. Akai at Cornell in 1991 and 1992 for CESR-B under KEK-Cornell collaboration. We adopted this design as a base design. Crab Kick TM110 B-field Coaxial Coupler TM010, TE111 Squashed Cell Shape Cavity TM110* Top View Squashed Cell Shape Cavity

32. Crab Cavity & Coaxial Coupler in Cryomodule Support rod Jacket type main He vessel(SUS316L) Jacket type sub He vessel Coaxial beam pipe (Nb) Stub support Crab cavity cell Notch filter Support pipe tuning rod RF absorber (Ferrite) Extract TM 010, TE 111 mode frequency tuning Input coupler Bellows RF absorber (Ferrite) K. Hosoyama et al

33. The 4th EIC workshop May 19-23, 2008 Schematic Drawing of Cryostat

34. The 4th EIC workshop May 19-23, 2008 Cavity production and installation

35. Crab Cavity Fabrication Procedure Nb Sheet Half Cell Hydro-forming Mechanical Polishing & Trimming Electron Beam Welding Crab Cavity Cell Grinding of Welding Part Barrel Polishing Electro-Polishing High Pressure Water Rinsing Annealing Electro-Polishing Beam Pipe & Flange Nb Sheet Rolle High Pressure Water Rinsing Assembling for Cold Test Cold Test in Vertical Cryo. MHI Kobe KEK Tsukuba Nomura Plating Kanuma Kinzoku Giken Mito Tokyo Denkai 5 mm t RRR = 180 Cell Equator ~ 100 mm EP 1 ~ 100 mm EP 2 ~ 5 mm 700 o C x 3 hr 80 bar. 60 min.

36. Forming and barrel polishing Forming of 4 Half-Cells for Crab Cavity for LER and HER Feb. 14, 2005 at Mitsubishi Heavy Industries, LTD. Kobe Barrel Polishing Nov. 11, 2005 at KEK Polishing Time 312 hours

37. High Pressure Rinsing and Assembling for RF Cold Test Nozzle High pressure water rinsing by 80 bar Ultra-Pure water Rotation & up-down motion Set flanges of beam pipes and ports in Class 100 clean room

38. Electro Polishing & Annealing Cathode: Aluminum Straight Pipe Crab Cavity: Rotating ~ 1 rpm Annealing at 700 o C for 3 hours at Kinzoku Giken Ltd. Titanium Box EP 1 ~ 100  m EP 2 ~ 5  m Electro Polishing at Nomura Plating Ltd.

39. Alignment of coaxial coupler Determine the axis of the coaxial coupler set in the cryostat by using transit. Align the axis of the coaxial coupler which will be connected to the coaxial coupler on cryostat side.

40. Move to Test Stand for Cool-down & High Power Test Mt. Tsukuba Crab cavity for HER April 26, 2006 1st Oct. 16, 2006 2nd Crab cavity for LER Dec. 6, 2006

41. Q 0 vs. E sp Curve LER Crab CavityHER Crab Cavity shows the target value in the operation. These figures show the comparison of Q 0 vs. E sp curve between Vertical and Horizontal Test for the both Crab Cavities.

50. The 4th EIC workshop May 19-23, 2008 Two crab cavities were installed in KEKB in January 2007. HER (e-, 8 GeV)LER (e+, 3.5 GeV)

51. The 4th EIC workshop May 19-23, 2008 Beam commissioning with crab cavities Be very careful as we have no spare cavities Will the beam receive the kick that we want? Can we collide the crabbed beams? No extra heating due to crabbing in the entire ring?

52. The 4th EIC workshop May 19-23, 2008 2007.2.13 - 3.19 (first beam operation with Crab cavities) Collision tuning with crab on Tuning (SR monitors, streak cameras and so on). Crab cavitiy aging without beams. Feb. 19 First beam with crab kicks (No collision when Crab on). Feb. 21 First collision with Crab crossing.

53. The 4th EIC workshop May 19-23, 2008 Is the beam really crabbed (tilted)?

54. The 4th EIC workshop May 19-23, 2008 Tilt confirmed! LER HER inside of the rings outside of the rings Observation with Streak Cameras (H. Ikeda et al, FRPMN035) The streak camera longitudinal horizontal

55. Crab Phase Scan (LER) 0 36 72 108 144 180 216 252 288 324 360 Crab voltage V crab set was 1.0MV Obtained from the data was 0.987MV Agrees very well. crab Horizontal orbit by crab kick crab Horizontal kick by crab cavity (rad) (Estimated by orbit fit)

56. The 4th EIC workshop May 19-23, 2008 One Day History of collision tuning with Crab On March.11 Luminosity 0.55/nb/s  y~0.078 preliminary

57. The 4th EIC workshop May 19-23, 2008 Specific Luminosity Crab Crossing 22 mrad crossing  y 0.078 in HER was achieved. This is higher than our record in Nov. But not as high as we expected (a factor of 2 was predicted by simulation). 12th KEKB Accelerator Review March 19, 2007 Haruyo Koiso

58. The 4th EIC workshop May 19-23, 2008 For higher luminosity! luminosity specific luminosity beam-beam tune shift Can we confirm the prediction?

59. The 4th EIC workshop May 19-23, 2008 Crab detuned Feb.2007-Apr.2008 Summer shutdown Winter shutdown Lpeak~15/nb/s I HER = 0.7 A, I LER = 1.3 A, L > 10 34 with crab crossing. Warm up 300K

60. The 4th EIC workshop May 19-23, 2008 Oct.-Dec. 2007 3.53.06 buckets Peak: 14.7 /nb/s  x  cm We tried different optics different fill pattern Higher HER/LER currents

61. The 4th EIC workshop May 19-23, 2008

62. The 4th EIC workshop May 19-23, 2008 Specific luminosity with crab crossing Simulation (no Crab) Simulation (Crab) Higher than without Crab, but not as high as prediction.

63. 22 mrad crossing 3.06 bucket spacing Specific Luminosity ★ A number of measurements indicate effective head-on collision. ★ The vertical tune shift became higher than 0.088. Before crab, it was 0.055. ★ The specific luminosity / bunch was improved more than the geometrical gain. ★ Need more time to achieve the goal (X2 specific luminosity). the highest vertical beam-beam tune shift was about 0.088. before crab, tune shift was 0.055 Simulation 22 mrad  x*=90 cm  x*=68 cm  x*=80 cm  x*=100 cm Simulation head-on Crab Crossing 49 sp.  x*=80, 84cm

64. The 4th EIC workshop May 19-23, 2008 Specific Luminosity Crab crossing 49-sp  x*=80, 84cm  x=18, 24 nm 3.5-sp  x*=80cm 3.06-sp  x*=80cm 3.06-sp  x*=90cm 22 mrad crossing y=-16.35x+26.54 Green Ratio=100% Green line  y ~0.093 (HER) (4/3)

65. The 4th EIC workshop May 19-23, 2008 Beam-beam parameter [mA] :experiments Crab crossing Crossing angle 22mrad

66. The 4th EIC workshop May 19-23, 2008 Why specific luminosity not doubled? Possibilities We can not find a parameter set which gives a higher specific luminosity, even if such a parameter set exists? –Too large a parameter space? Faster parameter search, more efficient method of parameter search –Short beam lifetime prevents us from reaching a better parameter set? Identify the mechanism to determine the beam lifetime Implement e- and e+ simultaneous injection （ autumn 2008 ） Some unknown effects are responsible for the low specific luminosity? –Synchro-betatron resonance? –Vertical crab? –Fast noise? –Bunch-by-bunch orbit difference? –Lattice non-linearity? –Global x-y coupling? –Others?

67. The 4th EIC workshop May 19-23, 2008 Tuning parameters 2 - 2 4 1 - 1 2 16 106 4 2 Many knobs are determined by scans only on the luminosity, beam sizes, and the lifetime. Scan is slow, each takes about 30 minutes. Problem in multi-dimensional nonlinear optimization.

68. IP Coupling LER HER LER HER (set by IP knob tuning) (measured at the optics correction) R1 4.12 4.16 0.01 0.17 mrad R2 2.01 -3.96 0.001 -0.07 mm R3 63.90 0 -98.5 72.3 /km R4 -64.69 128.52 -150. -23.7 mrad normal physical

69. Example of parameter scan

70. K. Ohmi sharply-peaked-optimum-on-a-broad- shoulder (SPOOABS) An example: the Horizontal Offset and the crossing angle at the IP Luminosity degrades by a small error in any one of the collision parameters. The horizontal offset of two beams and the crossing angle at the IP are such an example. Horizontal offset must be much less than 25 μm, and the crossing angle less than 1.5 mrad to see the effect of crab crossing. There are more than 20 of such parameters. If one of them is largely off, the optima of other parameters cannot be found.

71. The 4th EIC workshop May 19-23, 2008 Downhill simplex method Reflect Expand Contract+ Contract- Shrink 1 2 3 Method of Minimization {1, 2, 3} 1(best)<2(next-to-the worst)<3(worst) Evaluate 3 R If 3 R <1, If 3 E <3 R, {1, 2, 3 E } : Expand, if not, {1, 2, 3 R } : Reflect If 1<3 R <2, {1, 2, 3 R } : Reflect If 2<3 R <3, Reflect 2 proposed by A. Hutton If 3 C+ <3 R, {1, 2, 3 C+ } : Contract+, if not, {1, 2, 3 R } : Reflect If 3<3 R, Reflect 2 If 3 C- <3, {1, 2, 3 C- } : Contract-, if not, {1, 2 S, 3 S } : Shrink/Reflect2 39 Simplex makes an N+1 vertex shape for N parameters. So for a 2-parameter plane, you make a triangle in parameter space, and measure the luminosity at each of the three vertices. Then you try to "walk" uphill, by reflecting the lowest point to the opposite side of the other two. After a while, when there is no improvement, you shrink the scale of the simplex down and continue trying to move up the smaller-scale peak.

72. Simplex scan (example)

73. Synchrotron-betatron resonance The horizontal tune is set near the half integer resonacne and its synchrotron sidebands. At the resonance, the single beam sizes blowup(left). This effect can be calculated by “anomalous emittance” effect. The blowup depends on the sextupole setting (below). LER tune

74. 54 sextupole families Sextupoles A B C D E F Jumped from  x=0.516 to 0.506.  x=.512 is the resonace 2  x+  z=integer Beam Current Difference between “A” and “D” We tested 5 different sextupole configurations. We checked beam loss by changing tune across the resonance. Finding better sextupole setting: “bungee jump” No beam loss with “D” sexts 19

75. Synchro-betatron resonance In many cases, the synchro-betatron resonance (2 x + s = integer) limits the KEKB performance. –Beam size blowup, short lifetime, beam loss etc. The resonance is stronger in HER where no local chromaticity correction is installed. Strength of the resonance is strongly dependent a choice of sextupole setting. The resonance has something to do with the low specific luminosity at high bunch currents?

76. LER  x,  y tune dependence  x - x =integer  x + s =integer

77. Negative-  Optics Motivation –To weaken the synchro-betatron resonance particularly in HER –To shorten the bunch length Results –We have succeeded to weaken the synchro-betatron resonance line in HER. We could operate the machine with x below the resonance line. –We have successfully shorten the bunch length of both beam. ~6mm -> ~4.5mm –However, we found unexpectedly large synchrotron oscillation in LER and gave up the trial of the negative-  optics. 2ν x + ν s = integer 2ν x + 2ν s = integer 2ν x - ν s = integer 2ν x - 2ν s = integer ν x :.5112,.5224 with given ν s ~ -.0224

78. Synchro-betatron resonance in HER Positive-  –We could NOT operate under the resonance (2 x + s =integer) Negative-  –We could operate under the resonance (2 x - s =integer)

79. 4.Summary The 4th EIC workshop May 19-23, 2008

80. Crab Crossing Started at KEKB Two crab cavities were installed. Beam commissioning with crab crossing started in Feb. 2007. The effective head-on collision was confirmed by streak camera crab-phase scan horizontal beam-beam kick, etc. The highest vertical beam-beam tune-shift parameter is about 0.088 so far, which is higher than the geometrical gain due to head-on colliison by 15%. 16.1/nb/s was obtained yesterday. There are a few speculated reasons for why the luminosity is lower than the prediction, but not yet confirmed. We will do more study & machine tuning. Crab crossing is a must for SuperKEKB. The 4th EIC workshop May 19-23, 2008 First in the world

81. spare

82. The 4th EIC workshop May 19-23, 2008 Phase stability (histogram of phase detector signal) HERLER 0.007° 0.046° Distribution of cavity phase (cavity feedback loops on) Linear scale Log scale The tuner phase unstability was suppressed by low level RF control system.

83. Luminosity (estimated) 1350/700 1400/725 1500/775 1600/825 Beam currents 1700/875 mA 3.5 buckets 3x7 4x7 3.27 3x11 4x4 3.06 3x15 4x1 2.88 3x15 2x2 The specific luminosity is assumed to be on the line Green Ratio=1.

84. Crab Voltage Scan 4.6 mrad  y* design Oct. 13 100 bunchesNov. 19 1585 bunches Lifetime Luminosity Lifetime  y* Luminosity The ratio of crab voltages was adjusted to give the same kick in both rings. The scan was done, keeping the voltage ratio.

85. The 4th EIC workshop May 19-23, 2008 LERHER RF Phase Stability Phase stability of the crab mode was better than the requirement with the rf feedback. Slow stability below 1 Hz is shown above. Independent measurement by a spectrum analyzer shows better than 0.01 deg for f > 2 kHz, 0.1 deg for 2 Hz < f < 2 kHz. Backlash or friction exists in the coaxial tuner for the LER.

86. 86 Phase stability Span 200 kHz Sideband peaks at 32kHz and 64kHz. Span 10 kHz Span 500 Hz Sideband peaks at 32, 37, 46, 50, 100 Hz. Spectrum of pick up signal is consistent with phase detector data. Phase fluctuation faster than 1 kHz is less than ±0.01°, and slow fluctuation from ten to several hundreds of hertz is about ±0.1°. They are much less than the allowed phase error obtained from the beam- beam simulations for the crabbing beams in KEKB. According to b-b simulation by Ohmi-san, allowed phase error for N-turn correlation is 0.1×√N (degree). Spectrum around the crabbing mode measured at a pick up port of the LER crab cavity. Beam current was between 450 and 600 mA. LER crab phase HER crab phase ± 1 deg Phase detector signal. Beam current was 385mA (HER) and 600 mA (LER). K. Akai

87. Sign Change in the Crab Angle Luminosity Vert. size LER σ y blowup 12080 Reversed LER crab angle Reversed LER & HER Reversed HER HER σ y blowup Both correct 20060 H. Koiso

88. The 4th EIC workshop May 19-23, 2008 Crossing angle Transformation from lab. Frame to head-on frame. (  : half crossing angle) Linear part Oide and Yokoya for storage rings (1989)

89. The 4th EIC workshop May 19-23, 2008 Transverse kick by Crab Cavity Crab cavity makes z dependent dispersion z x = -  at the IP, which cancels the crossing angle effect (  << 1).. Crossing-angle termCrab-cavity term

90. The 4th EIC workshop May 19-23, 2008 Crab-crossing simulation 0-mrad vs. 11-mrad crossing angle (K.Ohmi) Beam-beam limit is ~0.06 for 11 mrad half-crossing angle (both models agree well). 0-mrad (head-on) collision gives a higher  y. Beam-beam limit for 0-mrad crossing depends on the model. Weak-Strong model Strong-Strong model Bunch current