Beam Commissioning
with Crab Cavities
12th KEKB Accelerator Review
March 19, 2007
Haruyo Koiso

Crab Crossing
bunch headbunch tailIPIPcrabcavity

crabcavity

2 cavities per ring

1 cavity per ring
beamcrabcavity

beamorbits of bunch head and tail

Operation History•
•••
••
•
•

Feb. 13 Beam operation started without crab kicks(Crab OFF).
Feb. 14- Tuning of SR monitors, streak cameras,etc. Aging of crab cavities without beams.
Feb. 19 First beam with crab kicks (Crab ON). Crabkicks were observed with BPMs and streak cameras.
Feb. 21 Crab crossing started.
Feb. 22- Collision tuning with crab kicks. 30 mA in
31 bunches.
Feb. 27-Mar. 1 Higher total currents 200 mA (LER) /174 mA (HER) in 1389 bunches. (no collision)
Mar. 2- More bunches. Max. currents : 75 mA (LER)/ 50 mA (HER) in 51 bunches.
Mar. 11 Luminosity 0.55/nb/s

2007.2.13 - 3.19

crab crossing

One Day History 3.11

Machine Parameters• Crab optics• Horizontal emittance : LER 18 nm, HER 24 nm• Tune : LER (45.508, 43.585), HER (45.509,43.585)• βx* : LER 0.59→0.84 m, HER 0.56→0.80 m• βxcrab : LER 40→ 74 m, HER 200→174 m• Vcrab : LER 0.9-1.0MV, HER 1.4 MV• Currents– 75mA(LER)/50mA(HER) in 51 bunches (collision mode)– 200mA(LER)/174mA(HER) in 1389 bunches (agingmode)• Luminosity : 0.55/nb/s (ξy~0.078 preliminary )Crab Optics since September 2005
Nikko Section

HERPhaseΔψx=(N+1/2)πcrab cavity

crab cavity
e+LER

IPe-PhaseΔψx=(N+1/2)πcrab cavity

crab cavity

Machine Parameters (preliminary)

K. OideSpecific Luminosity

Crab Crossing

22 mrad crossingTuning items for crab crossing• Observation of beam tilt with streak camera (H. Ikeda, etal.)• Adjustment of crab phase• Adjustment of crab angle (crab voltage)• Horizontal orbit feedback at crab cavities• Adjustment of horizontal offset to keep head-on collision
precisely• Adjustment of head-on condition in the vertical plane– Reduction of vertical crabbing• Adjustment of beam optics– βx*, βcrab, horizontal emittance• Luminosity tuning–tunes, orbits, couplings, vertical dispersions, waists,chromaticities

Crab Phase Scan (LER)
Horizontal orbit by crab
kickcrabcrab

Horizontal kick by crab cavity (rad)(Estimated from orbits)
72

108

36

144
360

0

180324
216
252

288

Phase 0：175 deg.
Vcrab set:1.0MV, estimated: 0.987MV
KCG Shift Report 2007_02_19_17

agree very well

Vcrab ScanLER

HER

design 1.0
2.2mraddesign 1.4
1.6mradVcrab Scan (HER)

Beam life

V sizeLuminosity Ratio
design
3.6 mradCrab crossing

Working Point ofTunes

22 mrad crossing

We are here.

Simulations give goodguidelines.

HERLER

K. Ohmi, et al.
Phys. Rev. ST Accel. Beams 7,104401(2004)

Horizontal Offset

K. Ohmi, 2007/3/5 report
・Luminosity is degraded by small errors in head-on condition,
optics, etc.
・H offset must be less than 40 µm.
・H offset is now adjusted by a feedback so as to keep thehorizontal beam-beam parameter constant.
・May need more intelligent feedback.

H Offset ScanHER σy*

LER σy*Head onHorizontal beam-beam kick

Luminosity (Blue ratio)

Horizontal offset
KCG Shift Report 2007_02_26_09
LER: ~0.75mA/bunch
HER: ~0.48mA/bunch

Horizontal bump height (µm)

Crab Angle Check (I)V sizeLER σy blowup

80

Luminosity

Reversed LER crab angle

120

Reversed LER & HER

Crab Angle Check (II)HER σy blowup

60

V sizeLuminosity

Reversed HER

200

Original directions

Vertical Crabbing ?

Lifetime

V sizeLuminosity

asymmetricsymmetric

V size dependence on the vertical crossing angle should
be symmetric at head-on collision.

IP Coupling
physicalnormal" X % "µ$ ' $$ PX ' = $ 0$ Y ' $ r1
$ ' $# PY & #r30µ(r4r3r2r4µ0r2 %" x % " ) x %'$ ' $ '(r1 '$ p x ' $) px '(*p$'$''y)
0y'$ p ' $) 'µ &# y & # py &µ 2 + det R = 1
LER
HER!(set by IP knob tuning)
R1
4.12
4.16
R2
2.01
-3.96
R3
63.90
0R4-64.69
128.52LER
HER(measured at the optics correction)
0.01
0.17
mrad
0.001
-0.07
mm
-98.5
72.3/km-150.
-23.7mradHow to keep
the vertical head-on condition
Adjust R1 of one ring at fixed R1 of another ring tofind the head-on condition.

symmetric

asymmetricDifferent sets of R1s
Vertical angle
scanFill Pattern

51 bunches：

98 sp → 49 sp, 8 trains

Plans• Step I : Continue machine tuning at low
currents (~ 75mA(LER)/50mA(HER), 51bunches) till advantage of crab crossing isclearly observed, or, our tuning ideas forhigher luminosity are run out.
– We have already achieved the vertical beam-beamtune shift parameter of 0.078 in HER, which ishigher than our record 0.062 with a correction of
the geometric gain.

• Step II : Try higher currents for physics run.