BEPCII Transverse Feedback System

Yue Junhui

Beam Instrumentation Group

IHEP， Beijing

Outline

Including three parts:

• The main parameters of BEPCII

• The coupled bunch instability

• The bunch by bunch feedback system

I : Some Parameters of BEPCII

Beam Energy, E GeV 1.89

Circumference, C m 237.53

Total beam current, A 0.91

Bunch current, mA 9.8

Revolution frequency, MHz 1.2621

RF frequency, MHz 499.8

Harmonic Number, h 396

Tunes, 6.57/7.61/0.034

Radiation damping times, ms 25/25/12.5

Number of Bunches, B 93

Bunch spacing, m 2.4

Bunch frequency, MHz 125

0I

bI

0f

RFf

zyx v/v/v

zyx //

bS

bf

The high beam current (0.9 A) and the large number of bunches (93 bunches) may cause the coupled bunch instabilities (CBI) in BEPCII

•

• Two source The higher order modes (HOMs) of RF cavities The resistive wall impedance

• Active feedback systems are required to suppress CBI

II :The Coupled Bunch Instability

Fastest growing time in the case of 99 bunches and 9.8mA per bunch HOMs Resistive wall ECI

Transverse (ms) 26.6 4.3 0.5

Longitudinal (ms) 12.8

• Bunch by bunch feedback system will be used on BEPCII

• The electronics bandwidth should be at least half of the bunch frequency

colliding mode 62.5MHz

synchronous radiation mode 250MHz

• The damping time of transverse feedback system is 0.5ms

III: Bunch by bunch Transverse Feedback System

The Transverse Feedback System

• Schematic diagram

• Front-end electronics

• Signal processing system

• Kicker and power amplifier

• Parameters of Transverse Feedback System

• The experiments of BEPCII TFB

The Schematic Diagram of TFB System

DBM

DBM

y1

y1

y2

A B

CD

H-1

83-4

M/A

CO

M

RG58/U

ZA

3PD

-2

ZA

3PD-2

ZA

3PD

-2

ZA

3PD-2

A B

CD

H-1

83-4

M/A

CO

M

RG58/U

ZA

3PD

-2

ZA

3PD-2

ZA

3PD

-2

ZA

3PD-2

y2Z

FRS

C-42

Mini

ZFR

SC

-42M

ini

BLP-300Mini

BLP-300Mini

ZFR

SC

-42M

ini

y

x

y-x

y+x

x-y

-x-y

M21CCR&K

ZHL－6AMini

DCPower

DCPower

ZHL－6AMini

weinschel3209-1

weinschel3209-1

75A250A

AR

HC

22-27T

el-Tech

HC22-27Tel-Tech

Digit Delay

ZFL-2500Mini

ZFL-2500Mini

HC22-2710K-250MHz

ZHL-6AMini

PADL3-10Gigabaudics

HJ5-50andrew

HJ5-50andrew

weinschel3201-1

ZFL-2500Mini

ZFL-2500Mini

GPS-1830台湾固维

LDF2-50andrew

33311BHP

ZFM-2000Mini

M21CCR&K

3428TARRA

3428TARRA

PDL-30Acol by

3428TARRA RG58/C

ZFR

SC

-42M

ini

Detct i on

ZFR

SC

-42M

ini

Detct i on

MultiFreq（*3）

RF频率

ZFR

SC

-42M

ini

Narda 3752ARRA

ZFM-2000Mini

The local station of the Transverse Feedback System

• Transfer the signal whose bandwidth is 500MHz at the center frequency of 1.5GHz to base band.

• Detection frequency is 1.5GHz， triple of RF.

Front-end electronics

y1A B

CD

BLP-750Mini

ZFM-2000Mini

H-1

83-4

M/A

CO

MH

-183

-4M

/A C

OM

H-1

83-4

M/A

CO

M

X

Y

H-1

83-4

M/A

CO

M

3× f

Signal processing system

• Full analog system simply using the cable line

• Three functions

Making the 90 phase shift

Rejection the closed orbit signal

One turn delay

• Realization

Two manual attenuators for 90 phase shift control

Notch filter rejection the revolution frequency

The time delay by cable

Signal processing system －

Phase shift and Notch Filter

Notch Filter

LDF4-50AAndrew

RG233HC22

27－

10K

-250

MH

z

HC22

27－

10K

-250

MH

z

BMA-3511

SRC-SMJ-205

RSA-3530D

RSA-3530D

combiner

attenuator

phase shift control

x1

x2

Kicker and Power Amplifier

• Four strip line electrode as kicker

(considering it is easy to realize, so the kicker length is 600mm just for every other bunches)

• One kicker per ring because the limited space

• Model 75A250A power amplifier is selected.

• Two 75A250A are connected in the differential style

Kicker and Power Amplifier

Specifications of the TFB system RF frequency MHz 499.8

Bunch spacing ns 8

Feedback damping time ms 0.5

Detection frequency GHz 1.5

Number of kickers per plane per ring 1

Kicker shunt impedance (at 125MHz) k 3.0

Total damping voltage per turn V 800

Kicker power for 800 V w 106

Number of power amplifiers per plane per ring 2

Bandwidth of power amplifier MHz 250

The experiments of BEPCII TFB(1)

With TFB system off, we can observe the vertical and the horizontal sidebands.

Only turn on the y direction TFB， the vertical sidebands disappear and the horizontal sidebands become strong.

The experiments of BEPCII TFB(2)

Turn on x direction TFB, the horizontal sidebands also disappear, the beam size become smaller.

The experiments of BEPCII TFB(3)

Conclusion

In a word ， This system can restrain coupled bunch instabilities. But stable and continued run need more efforts and more experiences。

Other parameters need to measure in the future study。

Thank you very much!