Commissioning of the BEPC-II
Storage Rings
Qing Qin

For the BEPC-II commissioning group
IHEP, Beijing 100049, P.R. China
2010-04-12

WAO'10Contents• Brief introduction on the BEPC-II• Commissioning of the SR and collision modes• Problems during luminosity commissioning• Operation for users• Possible upgrades in the near future• Summary
2010-04-12

WAO'101. Brief introduction on the BEPC-II• BEPC-II — An upgrade project of the BEPC
— A double-ring factory-like machine— Deliver beams to both HEP & SR
RF

SR

II

RF

I
North

e

III

2010-04-12

WAO'10IV

IP

Milestones of BEPC-II• July 1997, Proposal on BEPC upgrades (single-ring)• July 2000, Official approval from government• Jan. 2001, Double-ring scheme proposed• Jan. 2004, Construction started• Nov. 2004, Linac finished upgrade and delivered beam
• July, 2005, BEPC stopped, ring disassembly started• Nov. 2006, Ring commissioning started• July 2008, First hadron event collected in BES-III• May 2009, Luminosity reached 3.31032cm-2s-1
2010-04-12

WAO'10Layout of the Double-ring scheme
RF

SR

II

RF

I
North

e

e

III

IV

IP
2010-04-12

WAO'10Goals of the BEPC-II Collision Mode
 Beam energy range

1-2.1 GeV Optimized beam energy

1.89 GeV Luminosity

3-101032 cm-2s-1 @1.89 GeV

 Full energy injection

1-1.89 GeV

 SR Mode Beam energy

2.5 GeV Beam current

250 mA Keep the present beam lines useable

2010-04-12

WAO'10• Geometry of the IR and RF regions
1.5
R4IMB1R3

region

R4
1

e-

Q1b
0.5

-10

Q3

Q2

Q1a

SCQ

-5

5

-0.5

e+

Q4

e+

IP

ISP B

-15

region

10

SCB
SCQ

15

e-

Q1a
Q1b

Q2

Q3
Q4

R4OBL1 R4O-1Geometry of Interaction Region
67.5
R2 region

Wall

Wall

R1

region

67

RFC

66.5

SR

R1OMB0
R1OQ2
R1OBL1

R1OQ3

R1OQ4

R1OMB1
R1OBL2

RFC

66

65.5

65
e-

e+
64.5

R1IQ1

R1IBL1
AMB

2010-04-12
-15

-10

WAO'10
Geometryof RF region
-5

5

R1IQ2

R1IQ3

10

R1IQ4

R1IMB1

15

ISPB

SCQ

IP

Interaction region for the collision mode

SCB

2010-04-12

SCB

WAO'10Interaction region for the dedicated SR mode

Lattice design of the storage rings• Design philosophy
 Use the existing BEPC tunnel
 Keep the BEPC SR ports for beam lines
 Use as more BEPC magnets as possible
 Keep the BEPC injection scheme Fit 500MHz RF system, and the two-bunch
injection scheme in the future Luminosity and other requirements from
hardware2010-04-12

WAO'102010-04-12

WAO'10Design Parameters of Ring (Col. Mode)
EnergyGeV

1.89

Circumferencem

237.53

Beam current

A

0.91

Bunch number

93

Bunch current

mA

9.8

Bunch spacingm

2.4

Bunch length

cm

1.5

RF frequency

MHz499.80Harmonic number
Emittance (x/y)

396nmrad144/2.2m

1.0/0.015

Crossing angle

mrad

± 11

Design luminosity

cm-2s-1

1 x 1033

 function at IP (x/y)

2010-04-12

WAO'10Design Parameters of Ring (SR Mode)
EnergyGeV

2.5

Circumferencem241.13

Beam Current

mA

250

Natural emittancenmrad120

RF frequency

MHz499.80Harmonic number

402

RF Voltage

MV

3.0

Energy loss per turn

keV

335

SR PowerkW

84

Natural bunch length

cm

1.2

Momentum compact factor

0.016

Tune (x/y/z)

7.28/5.18/0.036

SR Damping time (x/y/z)
2010-04-12

ms
WAO'1012/12/6

Parameters of on-line lattice (collision mode)
Circumference（m）

237.53

Beam energy（GeV）

1.89

RF voltage（MV）

1.5

Tune（x/y/s）

6.54/5.59/0.035

Momentum compaction factor

0.0237Nature chromaticity（x/y）

10.8/20.8

Nature horizontal emittance（nmrad）

132

Nature energy spread

5.16104

Nature bunch length（cm）

1.36

x,y @ IP（m）(x/y)

1/0.015

x,y, max @ IR（m）(x/y)

70.2/91.4

x,y, max @ arc（m）(x/y)

24.2/23.5

Dx,max（m）

2.28

2010-04-12

WAO'10Detector solenoid compensation

AS1 – 3 are connected in series, but AS2 and AS3 have trims

2010-04-12

WAO'103. Commissioning of the SR and collision modes
2006 Oct. Installation completed with NIM-IR
2006 Nov 18
2007 Mar 26
2007 May 14

First beam stored
Phase 1First collision
Luminosity reached that of BEPC

2007 Oct. Installation completed with SIM-IR
2007 Oct. 24
2007 Nov. 18
2008 Jan. 29

First beam stored
First collision
Luminosity >11032cm-2s-1

Phase 2

2008 June. Installation completed with BESIII in the IR
July 19, 2008 First event detected with BESIII
April 8, 2009 Luminosity reached 2.3 1032cm-2s-1
May19, 2009 Luminosity reached 3.3 1032cm-2s-1

2010-04-12

WAO'10Phase 3

Time of beam BSR: 4.5 days, 11/13/2006 – 11/18/2006
accumulation BER: 2 days, 02/06/2007 – 02/07/2007
BPR: 1 day, 03/04/2007

2010-04-12

WAO'10Beam optics realization
With LOCO (Linear Optics from Closed Orbits), the parameters of acomputing model can be adjusted until the model response matrix
fits the measured response matrix well enough.

 2( M mod,ij  M meas,ij ) 2



i, j

2
i

  Vij2
i, jDetermine the errors by,Vij  






Vij
K q

K q VijGi

Gi  Vij
 j j  

Vij
 j

 j  ......

ΔK q — error of quadrupole strength
ΔGi — error of BPM gainΔθj — error of corrector strengthΔδj — energy shift when horizontal corrector strength change

2010-04-12

WAO'10Beam optics analysis
 The change of quadrupole strengths to restore the optics is
described by using the amplitude fudge factor.

K  K 0 * AF
K0 : design strength

K : optimized strength Most of the quad’s fudge factors are within 1%
 Some quads, such as Q15 and Q02, △AF ~ 6%.
Reason: same polarity with the neighbour quads.

 Problems found from the abnormal AF s:shortcut of magnet poles: R1OQ16 and R2OS7

grounding problem of R3OQ04
fitting method for the SCQs @ IP.
2010-04-12

WAO'10-0.02

-0.06

-0.08

2010-04-12-0.04

WAO'100
R4OQ1A

0.02

R3OQ1A

0.04
R4OQ02BPR

R3OQ020.1
R4OQ04-0.08

R3OQ04-0.06
R4OQ06-0.04

R3OQ060.04

R4OQ08R4OQ10

R4OQ12

R4OQ14R4OQ16R1OQ17

R1OQ15

R1OQ13

R1OQ11R1OQ09R1OQ07

R1OQ05

R1OQ03

R2IQ01R2IQ03

R2IQ05R2IQ07R2IQ09R2IQ11

R2IQ13

R2IQ15R2IQ17R3IQ16R3IQ14R3IQ12

R3IQ10

R3IQ08R3IQ06R3IQ04R3IQ020.06

R3OQ08R3OQ100.06

R3OQ120.08

R3OQ14R3OQ16R2OQ17

R2OQ15

R2OQ13

R2OQ11R2OQ09R2OQ07R2OQ05

R2OQ03

R1IQ01

R1IQ03

R1IQ05

R1IQ07

R1IQ09R1IQ11

R1IQ13

R1IQ15R1IQ17

R4IQ16

R4IQ14R4IQ12

R4IQ10

R4IQ08R4IQ06

R4IQ04R4IQ02

R3IQ1A-0.02

R4IQ1A

0.08

BER

0.02

0

2010-04-12
R3IQ05R3IQ02R3IQ02

R2IQ12R2IQ09R2IQ06R3IQ050

R3IQ0810

R3IQ0820

R3IQ1130

R3IQ1140

R3IQ14

BetaY_design

R3IQ1450

R3IQ17

BetaY_measured

R3IQ1760

R2IQ15m

R2IQ15R2IQ12R2IQ09R2IQ0650

R2IQ03

R1OQ02

R1OQ05

R1OQ08R1OQ11

R1OQ14

R1OQ17

R4OQ15

R4OQ12

R4OQ09R4OQ0660

R2IQ03

R1OQ02

R1OQ05

R1OQ08R1OQ11

R1OQ14

R1OQ17

R4OQ15

R4OQ12

R4OQ09R4OQ0670

R4OQ03

R4OQ1A80

R4OQ03

R4OQ1A

Resultsm

70

BetaX_measured

40
BetaX_design

30

20

10

0

The comparison of measured and design Beta function
afterWAO'10
optics correction• After the optics corrections with response matrix,
measured tunes are close to the nominal values.

Nominal2010-04-12

Measured Measured
(BER)
(BPR)

x

6.54

6.544

6.540

y

5.59

5.559

5.596

WAO'10Understanding the fudge factors• Large fudge factors --- hardware problems: magnet,
PS, database, model of special magnet, etc.
• Small fudge factors --- interaction between quad andsext in arcs, fringe field effect of dipoles and quads.
• Aim --- get fudge factors as small as possible, K  K0
• Experiment performed at BSR, no wiggler and no optics correction,
nominal tunes (7.28,5.38)
Design lattice

Increase the strength of
Q5~Q13 by 0.6%

Include fringe filed effectof Q and B in modelBothconsidered

Measured tunes
x/y0.1685/0.2834

0.1917/0.3174

0.2005/0.3413

0.225/0.379

x/y0/0

0.023/0.034

0.0315/0.058

0.054/0.096

2010-04-12

WAO'10Beam injection

Time delay scan
Fixed

4

X osc. after opt
Y osc. after opt
X osc. before opt

3.5
Residue Osc. (mm)Set the right timing and amplitude of thetwo kickers => reduce the residual orbit
oscillation of stored beams during
injection

3
2.5
2
1.5
1
0.5

Amplitude scan

0
0

100

200

300

400

Bunch No.

=>For timing: fix k1, scank2 ; do in turn for k2=>For amp: fix k1 or k2
amp, scan the other2010-04-12

 After optimization with on bunch,
the residual orbit oscillation of
all the other bunches during
injection reduced to around
0.1mm/0.1x.
Injection on collision possible.
WAO'1023

Result of multi-bunch injection

2010-04-12

WAO'10Impedance and instability issues
Bunch lengthening• Measured with streak camera.
• Single bunch case, in the bunch length measurement.
• Keep Vrf fixed, measure the bunch length vs. bunch
current.
3400
3200

 1

( z  z )2
 ( z )   0  1 exp  
2
2 
2
(
1

sgn(
z

z
)
A
)

z 


3000
2800
2600
2400

2010-04-12

2200

WAO'10
250

500

750

1000

1250

1500

1750

Sigmaz/Sigma0

1.5
y = 0.0173x + 1

1.3
1.1

BPR

0.9
0.7
0.5
0

5

10

15

20
Ib(mA)

Sigmaz/Sigma0

1.5
1.3
1.1

BER

0.9

y = 0.007x + 1

0.7
0.5

2010-04-120

10

20
WAO'1030

Ib(mA)

40

• Tune variation vs bunch current• Betatron tunes vary with single bunch current• Effective impedance can be got from the tune variation

d 
R

  Z ,effdI
4  ( E / e) lb2
Z ,0 
Z ,eff
2R• Estimated impedance Bunch lengthening 
BPR: |Z/n|0 =0.94, BER: |Z/n|0 =0.25
 Tune variation 
BPR & BER: |Z/n|0 ~ 1.0 
2010-04-12

WAO'10Luminosity optimization
Optics compensation (*, _IR, *, tune) and Golden orbit
Set vertical bump at NCP（4～5x）
Longitudinal position tuning（bunch spacing ~ 3.6ns）
Scan e+/e- orbit to get collision offset
Scan e+/e- offset at IP, optimize luminosity according to backgroundSingle bunch luminosity tuning (tune, coupling, -waist, etc.)
Scan orbit again to optimize luminosityMulti-bunch injection and collision (BCM to watch the uniform injection)
Multi-bunch optimization (instability, filling pattern, background)Luminosity with multi-bunch
2010-04-12

WAO'10Orbit scan for the transverse offset at IP

Scan e+ orbit

Scan e- orbit
Step for tuning orbit < 1m
2010-04-12

WAO'10Tuning vertical crossing angle of two orbits at IP

Scan RF phase to get the vertical crossing angle,
and reduce it with 4-bump
2010-04-12

WAO'10Transverse coupling tuning

0.035

(Coupling coefficient)

0.030

Model

Polynomi

Adj. R-Squ

0.99967

Model

Value

Standard Er

EIntercept 0.0047

9.0235E-5E

B1-0.005 4.18525E-5E

B20.0015 9.07241E-6

0.035

0.025
0.020

BPR
0.015
0.010
0.005

Polynomia

Adj. R-Squar

0.030

 (Coupling coefficient)

0.040

0.99948
Value

Standard Erro

E

Intercept

0.00466

1.19698E-4

E

B1-0.0025

3.94765E-5E

B2

0.00237

1.80248E-5

0.025
0.020

BER

0.015
0.010
0.005

0.000

0.000

-0.005
-4

-2

0

2

4

6

-4

8

-3

-2

-1

0

1

2

y (R1OBPM09) (mm)y (R2OBPM09) (mm)Vertical orbit at one sextupole vs. transverse coupling

2010-04-12

WAO'103

45

  **

*-waist tuning

Angle tuning at IP
2010-04-12

s2

WAO'10Detector solenoid compensation
1

AS2L

0. 5

AS2R
AS1L

AS3L

AS1R
IP

SCQ

AS3R
SCQ

0

Skew Q

Bz T

Skew Q

AS3L

AS2L

± 65A

± 65A

AS1L

AS1R

1300A

AS2R

AS3R

± 65A

± 65A

0. 5

1

1. 5

1300A

2

1

0
Position m

1

2

100
BETY (Blue: No solenoid; Red: with solenoid; Yellow: after SCQ compensation

90)

Vertical beta function along the ring before and after
setting SCQ fudge

80
70
60
50
40
30
20
10
0
0

2010-04-12

50

100

150

WAO'10200

250

Instability observation
BPR – ECI or other inst.?

BER -- resistive wall, ion

Sidebands of the electron beam with 99
bunch, uniform filling, spacing 4 buckets,
beam current 40mA.
2010-04-12

Sidebands of the positron beam with 99
bunch, uniform filling, spacing 4 buckets,
beam current 40mA.

WAO'1034

Observation on e+ bunch transverse sizes

Sigma_y of head bunch= 90.1Sigma_y of tail bunch= 95.6e+ bunch train

2010-4-13
2010-04-12

SeminarWAO'10at LNF35

A bunch-by-bunch lengthening in e+ ring observed

Bunch length

Bunch length

BER: 420mA/70 bunches

2010-04-12

BPR: 386mA/70 bunches

WAO'10Longitudinal dipolar oscillation observed

Single e- bunch, I = 6mA
Sigma = 9.99 ps

Single e+ bunch, I = 6mA
Sigma = 9.44 ps

Similar in both rings!
2010-04-12

WAO'10Longitudinal quadrupolar oscillation observed

Head of e- bunch train
420mA/70 bunches
Sigma = 14.8 ps
2010-04-12

Tail of e- bunch train
420mA/70 bunches
Sigma = 24.2 ps
WAO'10Head of e+ bunch train
420mA/70 bunches
Sigma = 28.3 ps

Tail of e+ bunch train
420mA/70 bunches
Sigma = 51.3 ps

Much stronger than BER!
2010-04-12

WAO'10Luminosity reduction due to long. quad. oscillation
25000

20000

15000

Bunch-by-bunch
luminosity

10000

5000

0
1

14

27

40

53

66

79

92 105 118 131 144 157 170 183 196

Single bunch: 5.0mA*5.0mA，Lum_bunch=2.5× 1030cm-2s-1
Multi-bunch: 93 bunches, 450mA*450mA，Lum_total~1.1× 1032cm-2s-1

Lum_total~93*lum_bunch/2
2010-04-12

WAO'10Luminosity of head and tail bunches from different beams

10 e- bunches vs 70 e+ bunches
2010-04-12

70 e- bunches vs 10 e+ bunches
WAO'10Source of the instability —— ECI? Impedance?

• No strong evidence of ECI effect• Longitudinal oscillation along bunch train
affects luminosity• Difference of impedance for two rings
cause the different oscillation

2010-04-12

WAO'10Impedance from the annular slot of profile

Model

Frequency
(GHz)

Q

R

R/Q

Field decay time(ns)

Small cavity

1.81712256.986160

38.1774

198

Vacuum pump2.34328335.64579

0.54933

556

Difference from the BER and BPR!
2010-04-12

WAO'10Simulation on the longitudinal instabilities• Map in longitudinal• Beam – cavity interaction
Vm and im : conjugate variables

2010-04-12

WAO'10Results on impedance of Q=1028, R=40000, f=1817MHz

2010-04-12

WAO'10Evolution of bunch length

2010-04-12

WAO'10• Remove the PR in e+ ring in Feb. 2009
• Start the new run of luminosity commissioning
from March 20092010-04-12

WAO'10Luminosity recovery after removing the PR
Peak Lum trend
3.00E+32

Removing PR of BPR

lum

2.50E+32
2.00E+32
1.50E+32
1.00E+32
5.00E+31
0.00E+00

12-7-09
11-7-09
10-8-09
9-8-098-9-097-10-09
6-10-09
5-11-09
4-11-09
3-12-09
2-10-09
1-11-09
12-12-08
11-12-08
10-13-08
9-13-088-14-08
7-15-08

2010-04-12

WAO'10Luminosity recovery after removing the PR

Luminosity (cm-2s-1)

3.00E+32
2.50E+32
2.00E+32
1.50E+32

Lum2009
Lum2008

1.00E+32
5.00E+31
0.00E+00
0

2010-04-12

200

400
600
Current (mA)

WAO'10800

Scan BPR

On-line tune scan for two rings

Scan BER

2010-04-12

WAO'10Moving tunes close to half integers
x  6.51，6.508

BPR: y* ~1.38 cm (measured)y  5.58，5.587

BER: y* ~1.33 cm (measured)2010-04-12

WAO'1002010-04-12
WAO'102009年5月26日

2009年5月19日

2009年5月12日

2009年5月5日

2009年4月28日

1

2009年4月21日

2009年4月14日

2009年4月7日

2009年3月31日

2009年3月24日

2009年3月17日

2009年3月10日

2009年3月3日

2009年2月24日

2009年2月17日

2009年2月10日

L(×1032cm-2s-1)

Lpeak = 3.31032cm-2s-1 !
4
After removing PR

3

2

Tunes close tohalf integers

Luminosity and beam current trends
Beam current in BER  650mA
June 22, 2008 – Dec. 13, 2008
Peak Lum history
3.50E+32
3.00E+32
lum

2.50E+32
2.00E+32
1.50E+32
1.00E+32
5.00E+31
0.00E+00 7
1
5
0
8

8
1
4
0
8

9
1
3
0
8

1
0
1
3
0
8

1
1
1
2
0
8

1
2
1
2
0
8

1
1
1
0
9

2
1
0
0
9

3
1
2
0
9

4
1
1
0
9

Beam current in BPR  700mA
June 26, 2008 – Dec. 13, 2008

5
1
1
0
9

Got peak luminosity@ ~550*550mA
2010-04-12

WAO'102010-04-12

WAO'10Luminosity with 80 bunches collision

Luminosity
reduction
due to dipole
oscillation

2010-04-12

WAO'10• Longitudinal feedback system was installed in bothrings in last summer to cure the longitudinal dipolar
oscillation.

Result of longitudinal feedback

Luminosity trend in this run

Luminosity（E32/cm2/s）
3.5
3
2.5
2
1.5
1
0.5
1-2

1-22

2-11

3-3

3-23

4-12

Achieved beam-beam limit

2010-04-12

WAO'10Blow-up due to beam-beam interaction

Single bunch
collision
BPR

BER

Multi-bunch
collision

2010-04-12

WAO'103. Problems met during luminosity commissioning

Background of detector• 2 horizontal moveable masks installed, each for one ring,~8m upstream from the IP.
• They reduced ~50% of the beam-related background.

2010-04-12

WAO'10Dark current variation in MDC layer 1(e+, 6mA/bunch)

2010-04-12

WAO'10Dark current variation in MDC layer 2 (e+, 6mA/bunch)Dark current variation in MDC layer 1(e-, 6mA/bunch)

2010-04-12

WAO'10Dark current variation in MDC layer 2 (e-, 6mA/bunch)New masks installed last summer to reduce background2010-04-12

WAO'10• Data taking @ E=1.84GeV, (s)• High dark current for higher beam current @ x~0.51

2010-04-12

WAO'10HOMs heating problem
1) More than 1000 thermal couplers used
2) Display in colour according dangerousness: green, yellow
and red.
3) In most case, the temperature rise (SR) => flux of cooling water
adjusted

2010-04-12

WAO'10Bad contact of the RF finger in the shielding of bellows
caused HOM heating, vacuum leakage in April 2009.

2010-04-12

WAO'10••••

Replace the new bellows
Re-design the RF fingers of the shielding
Cooling water and wind for the new bellows
Restrain the bunch current and beam current(Ib<6mA, I < 550mA)

2010-04-12

WAO'10Kicker problem (ceramic board broken in Mar. 2010)
Normal case

Bad vacuum in BPR-K2

2010-04-12

WAO'10Beam lifetime• Real beam lifetime much lower than estimated• Single bunch: both BER and BPR < calculated value• BER> BPR at single bunch case.
Dynamic aperture? Longitudinal acceptance?
Lifetime (hr)
11
10
9

8
7
EE+

6
5
4
3
2

1
0

mA
0

2010-04-12

1

2

3

4

5

6

WAO'10

7

8

9

10

11

• Multi-bunch: BER>BPR• Possible cause: vacuum, PBPR >PBER• BPR is getting better with vacuum improving.

2010-04-12

WAO'10Experiment on beam lifetime and long. acceptance

Effective longitudinal acceptance ~0.0046,
smaller than theoretical value 0.007
2010-04-12

WAO'104. Operation for users• Deliver beam to SR users for ~5 months every
year• Run for HEP data taking @ J/ energy, getting
200 M events in 2009
• HEP data taking @ (s) for 40 days, getting 100
M events in 2009
• Running at (2s) now, expecting 1.2 fb1 before
this July.

2010-04-12

WAO'10Luminosity vs beam current during (s) run

2.16
1.5*1032

2*500mA

2010-04-12

WAO'102.29

Luminosity vs beam current during (2s) run thisyear

2010-04-12

WAO'10Synchrotron radiation operation

2010-04-12

WAO'105. Possible upgrades for luminosity• Normal measures:
 Longitudinal feedback, installed this summer, to cure thelongitudinal dipolar oscillation
 Increase bunch current, beam current
 Shorten bunch spacing, to get more bunches Squeeze y* Tunes closer to half integers
Possible peak luminosity: L ~ 4 – 51032cm-2s-1

2010-04-12

WAO'10Problems on the way of further upgrades• Heating of bellows, vacuum chamber, etc.
• Background when bunch current increases• Possible ECI after bunch current increases orbunch spacing shortening• Longitudinal instabilities after bunch spacing
shortening• Etc, etc.

2010-04-12

WAO'10Long term upgrade of the BEPC-II• Crab-waist for higher luminosity• Collision with polarized beam
 Physics requirement
 Possibility of realization (e- beam? Location for
rotators?) Budget limitation
 Other problems…
2010-04-12

WAO'106. Summary• The three rings of the BEPC-II reached their design
parameters after 2.5 years’ commissioning and operation.
• Luminosity reached the lowest design value after curing
the instability due to impedance and moving tunes close
to half integers.
• Some problems, low beam-beam parameter, short beam
lifetime, high background under strong bunch current,
etc, still exist and need to be studied further.
• Further luminosity upgrade is needed.
• Possibilities of crab waist and beam polarization needmore studies.
2010-04-12

WAO'10Acknowledgement• Commissioning team of the BEPC-II• People from KEKB, PEP-II and DAFNE• All others from labs around world…

Thanks for your attentions!

2010-04-12

WAO'10