Development of cavity-type beam position monitor with a resolution of a few nano-meter

Si-Won Jang, Ae-young Heo, Ji-Gwang Hwang, Eun-San Kim*, Hyoung-Suk Kim, Hyangkyu Park Kyungpook National University, Daegu, Korea

INTRODUCTION OF LOW-Q IP-BPM ATF2 in KEK

-Accelerator Test Facility 2 for the International Linear Collider (ILC)

-The second goal: Achievement of nano-meter level beam position resolution for

beam stabilization.

The characteristics of Low-Q IP-BPM

- Achievement of higher beam position resolution (~nm)

- Short decay time (15ns for Y-port)

- Beam position measurement possibility of the bunch train

THE SCHEME OF BEAM POSITION

RESOLUTION TEST FOR LOW-Q IP-BPM

Measurement Scheme:

-A one Low-Q IP-BPM (KNU)

-Two High-Q IP-BPMs (KEK)

-Two sets of horizontal and

vertical movers

-Electronics for each IP-BPMs

-11bit oscilloscope

BEAM POSITION RESOLUTION

MEASUREMENT OF LOW-Q IP-BPM

I-Q tuning

X-port Y-port Reference

f0 (GHz) 5.712 6.426 6.426

β 8 9 0.0117

Q0 5900 6020 1170

Qext 730 670 100250

QL 656 602 1156

τ (ns) 18 15 29

We developed a low-Q cavity-type BPM system that includes electronics and data analysis. We have performed the beam

tests on the beam position resolution for the low-Q cavity-type BPM. Resolution tests for the low-Q BPM were

performed at KEK ATF2 in Jan. 2011. We got the results of beam position resolution of 70 nm and present the detailed

experimental procedures and test results, and upgrade plans that aims at a resolution of 2 nm.

Electronics (Right figure)

- Produce I-Q signal (90 degree difference)

- I-Q tuning by using phase shifter

- I-Q tuning by using phase shifter

- Signal process time = 20 ns

Installed appearance of Low-Q IP-BPM

and High-Q IP-BPMs in the ATF2

Electronics block diagram of

Low-Q IP-BPM

Calibration run

Resolution run

UPGRADE PLAN FOR 2nm RESOLUTION

Al LOW-Q IP-BPM

NEW ELECTRONICS

CONCLUSION We got the results of beam position resolution 70nm for the Low-Q IP-BPM in Jan. 2011. Three IP-BPMs will be fabricated to install at the IP region. The electronics of Low-Q IP-BPM was upgraded to get the high beam position resolution. The ultimate goal is to obtain a resolution of 2nm and orbit stabilization through beam feedback at the IP region.

Calibration run was performed to calibrate the

sensor cavity response to actual beam position. To

monitor the response of sensor cavities due to

vertical beam position, the electron beam was

swept against sensor cavities by vertical movers.

Calibration factor

(mV/nm)

Stat. Error

(mV/nm)

Low-Q IP-BPM

(40dB Amp.) 0.674 0.0264

High-Q IP-BPM 1 0.922 0.0451

High-Q IP-BPM 2 0.720 0.0260

Calibration factor = 0.674 mV/ nm

beam

)R/Q(Q

ZqV

ext

0 out2

2

2

0

228

ybab

LT)y(

Q

R

IF

Base plate

post

mover

IP-BPM

Beam signal calibration

X X X

Beam position prediction

X X X

Beam position measurement

Convert to residual

nm 70factorn Calibratio

ResidualFactor_lGeometricaResolution

Residual Gaussian fitting

Residual value = measured position – predicted position

Sampling number

I-Q tuning was performed by using oscilloscope.

When I signal shows the maximum position, Q signal

is set to zero position by using phase shifter. For this,

I & Q signal means the beam position signal and

angle signal, respectively. If we do not performed I-Q

tuning, the electronics will be easily saturated by large

beam angle signal. Thus we also can’t expect good

beam position resolution.

Port f0 (GHz) β Q0 Qext QL τ (ns)

X-port 5.7059 5.6 4955.64 884.83 750.78 20.94

Y-port 6.4228 7.5 4884.67 649.74 573.46 14.21

Port f0 (GHz) β Q0 Qext QL τ (ns)

X-port 5.7050 4.48 4005.53 894.80 731.41 20.40

Y-port 6.4217 6.17 3903.95 632.36 544.21 13.49

Copper ver.

Aluminum ver.

The aluminum Low-Q IP-BPM was designed to reduce weight and was simulated to compare with copper version IP-BPM. The performance of the designed Al Low-Q IP-BPM shows the similar result to copper version Low-Q IP-BPM. Nevertheless, the weight of Al Low-Q IP-BPM was reduced 1/3 of copper version Low-Q IPBPM.

BPFPA

Phase

shifter

Power

divider

Hybrid

CouplerBPFRing

CouplerMixer

LNA

LNA

LO

RF

RF

Detection

Power

divider

LNA

DA

IF1(I)

IF1(Q)

OPAMP

Phase

Control

LPF

BW : 40MHz

Atten. Atten.

LNA

Feature of new electronics 1. High conversion gain (70dB) 2. High isolation in the mixer 3. Remotable phase shifter 4. Short latency time