First synchronous measurement of single-bunchedelectron and positron beams with a wideband
feedthrough-BPM at the positron capture section of
the SuperKEKB injector linac
Muhammad Abdul Rehman#,, Tsuyoshi Suwada, Fusashi MiyaharaHigh Energy Accelerator Research Organization (KEK)
The 12th International Particle Accelerator Conference – IPACʼ21Contents
1. Introduction
2. Wideband feedthrough-BPM
3. Synchronous Measurement of e-/e+ bunch
5. Conclusion

ID 1090
MOPAB163#rehman@post.kek.jp2021 May 24

M. A. Rehman, KEK, IPAC2111. Introduction
 The SuperKEKB collider is currently in operation to study CP
violation in B mesons and also to search for new physics beyond
the Standard Model,
 Target luminosity 8 × 1035 cm-2s-1, 40 times higher than its
predecessor KEKB.
 High intensity e- / e+ beam required to achieve target luminosity.
 Electron beam is produced byphotocathode RF gun.
 Positron beam is generated bybombarding Tungsten target
with 3.5 GeV/ 10 nC electron
beam

2021 May 24

M. A. Rehman, KEK, IPAC21

SuperKEKB Collider2

2. Introduction

Rough Layout of Positron Capture Section The secondary e- produced during the positron creation process
and accelerated.
 Because of phase slipping in the capture section, the secondary
electron bunch is only ~180 ps away from the positron.
 Conventional stripline–type BPM cannot detect such closely
spaced and opposite polarity signals due to slow frequency
response and high cable losses.
 New Wideband BPM needed for efficient transmission of e+ beam
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M. A. Rehman, KEK, IPAC21

3

Wideband feedthrough-BPM
 A new feedthrough beam position monitor (BPM)
developed to detect closely spaced e-/e+ bunches The feedthrough-BPM consists of a vacuum pipeof length 431mm and inner diameter of 38mm
 Four SMA-type feedthroughs having innerconductor made of Kovar with π/2 rotational
symmetry The diameter of the feedthroughs is 1.8 mm andthey extend 1 mm to the center of the beam pipe.

(b)

(a)

LTFeedthrough

R

Beam

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M. A. Rehman, KEK, IPAC21

B4

1. Synchronous Measurement of e-/e+ bunch
Several kind of Coaxial cables have used totransmit signal from new feedthroughThe coaxial cables connected to real–time
BPM to Oscilloscope
Keysight oscilloscope of bandwidth 33 GHz 2m: long semirigid coaxial cableand a sampling rate of 128 GS/s.
 15m: long 10D
 2m: RG223
The typical bipolar waveform at the nominal
High-frequency losses of coaxial cables
rf-phase from feedthrough-BPM is shown
below
were measured by VNA in advance.

Cable Losses: Measured by VNA

e-/e+ signal: keysight UXR0334A
e+e-2021 May 24

M. A. Rehman, KEK, IPAC21

52. Synchronous Measurement of e-/e+ bunch Where beam position was determinedthe difference-over-sum method
 Intensity was determined by the sum offour electrode voltage
 Steering magnet currents have changed
to see the position response of BPM

2021 May 24

M. A. Rehman, KEK, IPAC21

G is conversion
factor.
𝑌𝑖𝑒𝑙𝑑 𝑟𝑎𝑡𝑖𝑜 =e+ Charge
Incident e− Charge

6Conclusions• The first synchronous measurement of e-/e+¸bunches have been performed with the wideband
feedthrough-BPM system at the positron capture
section of the SuperKEKB factory.
• The synchronous transverse position and intensityof the e-/e+ bunches were measured.
• The new wideband feedthrough-BPM proved as an
excellent monitor to optimize e+ transmission
through e+ capture section.

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M. A. Rehman, KEK, IPAC21

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backup

2021 May 24

M. A. Rehman, KEK, IPAC218

3. Synchronous Measurement of e-/e+ bunch Position

2021 May 24

M. A. Rehman, KEK, IPAC219