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Status & Some Issues of BEPCII
ZHANG, Yuan
for BEPCII team
2014.3.6, @KEK
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Outline
• History & Status • ParasiEc Beam-‐Beam Effect • Nonlinear Arc “ContribuEon” • CollecEve Effect & Instability
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Peak Luminosity at different energy
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Crosscheck using SAD
• The closed orbit excited by the parasiEc effect is compensated very carefully
• The tune shiS excited by the parasiEc effect is compensated very carefully (NEW)
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Luminosity loss versus vertical separation
Even for 10mm, The loss is about 15% near 7~8mA.
It is s&ll concluded that we should try to suppress the parasi&c effect
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If the horizontal separation help
We did not see any posi&ve contribu&on from the horizontal separa&on.
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Specific lum versus the vertical separation
The main contribu&on comes from the ver&cal blowup
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Question
• Why the modificaEon of NCP does not help to increase luminsoEy?
Now the beam is separated 30σx in horizontal direcEon.
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Another working point (0.508,0.570) -> (0.505, 0.575) Same verEcal separaEon (10mm) The relaEve lum loss reduces from 15% -‐> 5%
Two reasons maybe explain the failure of the modificaEon: ① The separaEon is larger than expected ② The real working point is opEmized and not sensiEve
to the parasiEc effect Now, we go back to the start point, how to explain the saturaEon of beam-‐beam parameter? Maybe bunch lengthing is more serious than expected? Or maybe the lagce is not so good?
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Optimization of lattice, Aperture
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Optimization of lattice, Chromatic
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Optimization of lattice, non-chromatic resonance• Try to limit the amplitude of GNFU (DEFINITION IN MADX) (1,0,2,0) (1,0,1,1) (2,0,2,0) (2,0,1,1) (1,1,2,0) Since they couple the horizontal oscillaEon to verEcal direcEon.
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Crosstalk between nonlinear arc & beam-beamThree lagces • Old: (6.508, 5.570), sol off/on, εx~150nmrad • New BPR (7.505, 5.580), sol off/on, εx~110nmrad
• New BER (7.505, 5.580), sol off/on, εx~110nmrad
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Luminosiy Loss
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Old lattice
Lum Spec. lum
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FMA of solenoid contribution
Sol. Off Sol. On The difference is not very clear, Maybe the area is important for luminosity
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Tune spread2νx-‐νs=N
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Optimized BPR (e+)
Lum Spec. lum
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FMA of Optimized BPR2νx-‐νs=N
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Solenoid effect in Optimized BPR
Sol. Off Sol. On The difference is clear, (Maybe) the area is importan for luminosity
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Optimized BER (e-)
Lum Spec. lum
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Solenoid effect in Optimized BER
Sol. Off Sol. On Which one is more important for luminosity?
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Knob the tune of old lattice: (6.508,5.570) -> (6.505, 5.575)
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Tune Spread
8mA
9mA
10mA
2νx-‐νs=N
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Amplitude Dependent
8mA
10mA
9mA
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Bunch Length Fitting with Physics Data
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Bunch Length from Physics Data Run
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Tune shift of Mutibunch Bunch• dQx/dI ~ +0.004 A-‐1, dQy/dI ~ -‐0.005 A-‐1
• It is esEmated dQx/dI ~ 0.005 A-‐1, dQy/dI ~ -‐0.006 A-‐1 ref:
A. Chao, PRST-‐AB, 5, 111001
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Abnormal Instability in BER
• Only 10 bunches,1 bunch every 32 buckets • Beam Current 70mA • The horizontal sideband very clear when the feedback off
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Bunch luminsotiy degradation along the train
E+: 360mA E- : 390mA
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Bunch luminsotiy degradation along the train (2)
E+: 330mA E- : 220mA
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Bunch luminsotiy degradation along the train (3)
E+: 265mA E- : 340mA
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Longitudinal feedback kicker
• PEP-II feedback kicker -> DAFNE Type Cavity Kicker?
Loss Factor: 0.25V/pC
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Discussion
• The OpEmized lagce seems good enough. But in the real machine, we should make sure the 2*nux-‐nus resonance do not bring side effect.
• Could we find more profit from the lagce opEmizaEon? (Twiss parameters choice?, Emiuance choice?)
• The mysterious instability source should be found. And the bunch luminosity drop should be cured.
• High beam current is a must for high luminsoEy As a mauer of fact, we sEll could not run with the design beam current normally Ell now.
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Thanks for your auenEon!