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Status & Some Issues of BEPCII
ZHANG, Yuan
for BEPCII team
2014.3.6, @KEK
Outline
• History & Status • ParasiEc Beam-‐Beam Effect • Nonlinear Arc “ContribuEon” • CollecEve Effect & Instability
Peak Luminosity at different energy
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)
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
If the horizontal separation help
We did not see any posi&ve contribu&on from the horizontal separa&on.
Specific lum versus the vertical separation
The main contribu&on comes from the ver&cal blowup
Question
• Why the modificaEon of NCP does not help to increase luminsoEy?
Now the beam is separated 30σx in horizontal direcEon.
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?
Optimization of lattice, Aperture
Optimization of lattice, Chromatic
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.
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
Luminosiy Loss
Old lattice
Lum Spec. lum
FMA of solenoid contribution
Sol. Off Sol. On The difference is not very clear, Maybe the area is important for luminosity
Tune spread2νx-‐νs=N
Optimized BPR (e+)
Lum Spec. lum
FMA of Optimized BPR2νx-‐νs=N
Solenoid effect in Optimized BPR
Sol. Off Sol. On The difference is clear, (Maybe) the area is importan for luminosity
Optimized BER (e-)
Lum Spec. lum
Solenoid effect in Optimized BER
Sol. Off Sol. On Which one is more important for luminosity?
Knob the tune of old lattice: (6.508,5.570) -> (6.505, 5.575)
Tune Spread
8mA
9mA
10mA
2νx-‐νs=N
Amplitude Dependent
8mA
10mA
9mA
Bunch Length Fitting with Physics Data
Bunch Length from Physics Data Run
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
Abnormal Instability in BER
• Only 10 bunches，1 bunch every 32 buckets • Beam Current 70mA • The horizontal sideband very clear when the feedback off
Bunch luminsotiy degradation along the train
E+: 360mA E- : 390mA
Bunch luminsotiy degradation along the train (2)
E+: 330mA E- : 220mA
Bunch luminsotiy degradation along the train (3)
E+: 265mA E- : 340mA
Longitudinal feedback kicker
• PEP-II feedback kicker -> DAFNE Type Cavity Kicker?
Loss Factor: 0.25V/pC
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.
Thanks for your auenEon!
