First Collision of BEPCII

C.H. YuMay 10, 2007

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

Methods of collision tuning

Designed β function and beam size @IP ：β x* / β y*= 1.0m / 1.5cm x* / y*= 0.4mm / 5.5m

Designed backup scheme (without SCQ) β function and beam size @IP ：β x* / β y*= 2.0m / 5cm x* / y*= 0.5mm / 12.2m

Beam size from beam-beam scan fitting result @IP ：x* / y*= 0.5mm / 16m

e- e+

22mradHorizontal crossing angle

-0.002-0.001

00.001

0.002Horizontal Offsetm

-0.001

0

0.001Vertical Offsetm

-0.04

-0.02

0

0.02

0.04

V kick anglerad-0.04

-0.02

0

0.02

0.04

V kick anglerad

-0.002-0.001

00.001

0.002 HorizontalOffsetm

-0.001

0

0.001

VerticalOffsetm

-0.02

0

0.02

H kick anglerad-0.002

-0.0010

0.0010.002 HorizontalOffsetm

-0.001

0

0.001

VerticalOffsetm-3 -2 -1 0 1 2 3

-0.02

-0.01

0

0.01

0.02

-10 -5 0 5 10

-0.04

-0.02

0

0.02

0.04

Methods of collision tuningBeam-Beam kicker

Bassetti-Erskine formula

Before collision commissioningSoftware preparation According to the design of BEPCII IRBPM accuracy test Select BPM for the collision tuningIP 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 tuningCollision 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 （ ~5x ）。

Vertical beam separation at North Crossing Point (NCP)

Longitudinal position tuning The distance from the IP to R4CBPM00 is 0.6587m.

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

Procedures and data analysis

Transverse position tuningVertical 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 analysisTransverse position tuning

Horizontal offset and vertical offset

Scan: e- IP bump height Monitor: e+ IR BPMMax. H. kicker angle 0.049mrad & V. kicker angle 0.076mrad @ 3mA*3mA

Procedures and data analysisTransverse position tuning

Horizontal offset and vertical offset

Same results if we Scan: e+ IP bump height Monitor: e- IR BPMTransverse 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 44 one-turn transfer matrix in the physical system and normal system.

ICCI

MM

ICCI

Tv

u

0

0

1

43

21

rrrr

C

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 backgroundTune shift measurement

Tune shift can be observed clearly.

At May 8 day shift5mA*5mA collision horizontal tune shift is 0.014 and vertical tune shift is 0.012.

1-2-29*

34 scm105)(

)()()1(1017.2 cm

AIkGeVERLy

bby

Luminosity and backgroundBlowup phenomenon

Normal collision case Blowup caseSometimes blowup phenomenon appeared during collision scan.

Luminosity and backgroundLuminosity Detectors

Old BaBar detector used in BEPC

Zero degree photon detecore+ e- e+ e-

Luminosity and backgroundBLM data with horizontal offset scan

0

100

200

300

400

500

600

700

-2 -1. 5 -1 -0. 5 0 0. 5 1 1. 5 2 2. 5 3 3. 5e+ hori zontal bump hei ght @I P（mm）

Lumi

nosi

ty c

ount

0

100

200

300

400

500

600

700

-3 -2. 5 -2 -1. 5 -1 -0. 5 0 0. 5 1 1. 5 2 2. 5 3

e- hori zontal bump hei ght @I P（mm）

Lumi

nosi

ty c

ount

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 backgroundBLM data with vertical offset scan

0

10

20

30

40

50

60

70

80

-0. 1 -0. 075 -0. 05 -0. 025 0 0. 025 0. 05 0. 075 0. 1

e- vert i cal bump hei ght @I P（mm）

Spec

ific

lumi

nosi

ty

0

10

20

30

40

50

60

70

-0. 2 -0. 15 -0. 1 -0. 05 0 0. 05 0. 1 0. 15 0. 2

e+ vert i cal bump hei ght @I P（mm）

Spec

ific

lumi

nosi

ty

BLM works well. Both e+ and e- vertical orbit near the IP are not sensitive to the BLM background.

ebebb IIN

L

__

y LuminositSpecific

Luminosity and backgroundOld 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.