1. Commissioning Issues of BEPCII
Sheng Wang
AP group, Accelerator Centre,IHEP, CAS
Oct. 5th, 2010

2. Outlines Brief introduction to BEPC and BEPCII
Overview of the BEPCII performance
Luminosity commissioning
Problems in the luminosity enhancement

3. A Bird View of BEPCII 1988, first beam obtained from BEPC
2006,first beam from BEPCII

4. 1. Overview of the BEPCII performance
2006 Oct. Installation completed
2006 Nov First beam stored
2007 Mar First collision
2007 May Luminosity reached that of BEPC
2007 Oct. Installation completed without detector
2007 Oct First beam stored
2007 Nov First collision
2008 Jan Luminosity >11032cm-2s-1
2008 June. Installation completed with BESIII in the IR
July 19, First event detected with BESIII
April 8, Luminosity reached 2.3 1032cm-2s-1
May19, Luminosity reached 3.3 1032cm-2s-1
Phase 1
Phase 2
Phase 3

5. Luminosity evolution in Phase 3
3.31032cm-2s-1
@523mA×529mA
After screen
monitor
removed
Tunes move to
half integers

6. Main parameters achieved in beam collision
design
Achieved
BER
BPR
Energy (GeV)
1.89
Beam curr. (mA)
910
~630
Bunch curr. (mA)
9.8
~8.0
Bunch number 93
93(86)
RF voltage
1.5
1.5 (1.35)*
1.5 (1.35)
ns @1.5MV
0.033
0.032
y* (m)
0.015
~0.013
Lifetime (hrs)
Lum. (1033cm-2s-1) 1
0.33
* Calculated with the measured synchrotron tune

7. 3. Problems in the luminosity enhancement
High dark current of the detector
--- bottleneck of the high current collision
--- source of the dark current (Touscheck effect,
beam-gas scattering, etc.)
--- way to lower the dark current

8. --- Reasons? Instability? Feedback tuning? Others?
Luminosity with multi-bunch collision is not linearly proportional to the single bunch collision at the same bunch current.
e.g. Ls.b. = * 8.5mA
Lm.b.= * 580mA (70 bunches)
--- Reasons? Instability? Feedback tuning?
Others?

9. Beam-beam issue
Low beam-beam parameter : peak y ~ 0.02
@ Ibunch=0.82Ibunch0

10. Beam blow-up after collision
Single bunch
collision
BPR BER
Multi-bunch
collision

11. --- How to reduce blow-up
--- How to reduce blow-up? --- Curing blow-up by changing tunes, IP offsets, etc., but not repeatable after every collision --- The stronger the beam current, the more serious the blow-up

12. Beam lifetime --- The real lifetime is much shorter than expected
--- Lifetime of e is shorter than e+ (smaller coupling?)
--- Possible reasons for short beam lifetime:
vacuum pressure?
physical aperture?
dynamic aperture?
other reasons?

13. More bunches A reasonable way to enhance luminosity But
Serious instability observed if bunch number > 90
How about 120 bunches or more with big bunch current?
Can feedback systems work well under more bunches?

14. Thanks for your attentions !