First Collision of BEPCII C.H. Yu May 10, 2007

Methods of collision tuning Procedures and data analysis Luminosity and background Summary

Methods of collision tuning Designed β function and beam ： β x * / β y *= 1.0m / 1.5cm  x * /  y *= 0.4mm / 5.5  m Designed backup scheme (without SCQ) β function and beam ： β x * / β y *= 2.0m / 5cm  x * /  y *= 0.5mm / 12.2  m Beam size from beam-beam scan fitting ：  x * /  y *= 0.5mm / 16  m 22mrad Horizontal crossing angle

Methods of collision tuning Beam-Beam kicker Bassetti-Erskine formula

Before collision commissioning Software preparation  According to the design of BEPCII IR BPM accuracy test  Select BPM for the collision tuning IP 4-bump program and strength correction  IP orbit resolution and stability  Reduce 4-Bump orbit leak less than 3% Discuss luminosity issues with detector people Methods of collision tuning

IP 4-Bump for collision tuning （ orbit leak < 3% ） Methods of collision tuning

BESIII detector is located in south of storage ring. Methods of collision tuning Collision tuning items Beam separation at NCP Longitudinal position tuning Crossing angle tuning Transverse position tuning Luminosity optimization NCP

Procedures and data analysis For the consideration of injection rate, vertical local bump was set mainly by BER. The vertical separation between e+ e- beams at NCP is about 5mm （ ~5  x ）。 Vertical beam separation at North Crossing Point (NCP)

Longitudinal position tuning The distance from the IP to R4CBPM00 is m. According to the signal of the R4CBPM00, relative timing of two beams was adjusted by shifting RF phase so that two beams collide at the nominal IP. R4CBPM00 Accuracy 3mm R3CBPM00 Procedures and data analysis

Transverse position tuning Vertical crossing angle The vertical crossing angle was measured through RF phase scan. If the vertical crossing angle exists, the vertical offset of two beams will be changed in the horizontal scan. Therefore, the crossing angle can be detected by observing the vertical beam-beam deflection RF phase scan.

Procedures and data analysis Transverse position tuning Horizontal offset and vertical offset Scan: e- IP bump height Monitor: e+ IR BPM Max. H. kicker angle 0.049mrad & V. kicker angle 3mA*3mA

Procedures and data analysis Transverse position tuning Horizontal offset and vertical offset Same results if we Scan: e+ IP bump height Monitor: e- IR BPM Transverse offset and vertical crossing angle were removed by local 4-bump.

Horizontal offset scan Vertical offset scan First collision of BEPCII Mar. 25, 2007 The scan step of Horizontal IP bump and vertical IP bump are 10um and 2um respectively 。

Procedures and data analysis IP coupling tuning r1, r2, r3 and r4 at the IP can be adjusted independently. Coupling parameters tuning is a effective and important Luminosity optimization. T and M is 4  4 one-turn transfer matrix in the physical system and normal system.

Procedures and data analysis  y * waist tuning The  y * waist scan is realized by fitting the strength of a set of quadrupoles(Q2, Q3, Q4, Q5, Q6, Q7, Q8 and Q9) which are all located beside the IP.  function waist tuning is a effective and important method for Luminosity optimization.

Luminosity and background Tune shift measurement Tune shift can be observed clearly. At May 8 day shift 5mA*5mA collision horizontal tune shift is and vertical tune shift is

Luminosity and background Blowup phenomenon Normal collision case Blowup case Sometimes blowup phenomenon appeared during collision scan.

Luminosity and background Luminosity Detectors Old BaBar detector used in BEPC Zero degree photon detecor e+ e-  e+ e- 

Luminosity and background BLM data with horizontal offset scan BLM is a sensitive detector to monitor the situation of beam collision. The e+ horizontal orbit near the IP affect BLM background obviously. Usually we scan e- orbit for collision orbit optimization while keep e+ orbit unchanged.

Luminosity and background BLM data with vertical offset scan BLM works well. Both e+ and e- vertical orbit near the IP are not sensitive to the BLM background.

Luminosity and background Old BEPC BaBar luminosity detector Some device tuning works have been done. The background of the BEPC detector is very sensitive to both e+ and e- orbit in the IR. Luminosity value is still under study.

Summary Collision tuning methods have been tested successfully in BEPCII 。 Beam instrument system 、 IP bump magnets 、 power supply system 、 control system can satisfy precision collision orbit scan 。 However, there are still a long way for us to reach the designed luminosity goal.