Observation of Wakefield Effects with Wideband feedthrough-BPM at thePositron Capture Section of the SuperKEKB Injector LINAC*M.
A.
RehmanandT.
SuwadaMOPP10*rehman@post.kek.jp

High Energy Accelerator Research Organization (KEK)

Abstract
At the SuperKEKB injector linac, e+ are generated by striking electron beam at tungsten target. The secondary e- are also
produced during positron creation and accelerated in the positron capture section. A new wideband feedthrough beam+position monitor (BPM) system was developed for synchronous detection of secondary produced e and e beams with+temporal separation of about 180 ps. When e /e bunches pass through the accelerating structure or vacuum duct of different
radius, they generate wakefields. These wakefields can be directly observed with the feedthrough-BPM. A simulation study has
also been carried to validate the observed wakefield effects with the feedthrough-BPM. The effects of wakefields on beam
parameters will be reported in this poster.

Introduction
 The e+ beam is produced by striking the e- beam of energy 3.5 GeV and bunch charge of 10 nC at a tungsten target.
 The secondary e- produced during the positron creation process and accelerated.
 Because of phase slipping in the capture section, the secondary e- bunch is only 135-243 ps away from the e+ bunch.
 Conventional beam monitors cannot detect such closely spaced and opposite polarity signals due tolow frequency response and high cable losses.
 New Wideband BPM is needed for synchronous detection e+/e- and efficient transmission of e+ beam

Wideband Feedthrough Beam Position Monitor𝝅 The feedthrough-BPM consists of four SMA-type feedthroughs made of Kovar with rotational symmetry.
𝟐

 The SMA connectors of the feedthroughs are first connected toserval kind of coaxial cables.
 The cable losses have been measured in advance by a VNA andhave been de-embedded from the feedthrough-BPM signals.

Wakefield simulation of Wideband feedthrough-BPM
 When a charged particle travels through any obstacle
electromagnetic fields generates, know as wakefield.
 In order to understand the wakefield field effect on thefeedthrough-BPM signal, a time-domain simulation in CSTwakefield solver has been done.

Experimental Results
Summary

To estimate the effect of the wakefield on the experimental signal of thedouble bunch, it is assumed that the wakefields induced voltage oscillates
The short-range wakefield has been observed as
and decays as follows:a ringing signal after a double bipolar signal inComparison between Experiment and Simulation

The model described in above is used to fit theexperimental data and then extrapolated it on thebipolar signal to estimate the effect of thewakefields on the beam parameters.

synchronous measurements of the e- and e+bunches with the wideband feedthrough-BPM
system at the e+ capture section of theSuperKEKB factory.
A simulation study and analytical function fitting
on experimental data have been successfully
carried out to estimate the effect of thewakefield on the beam parameters measured by
the new beam monitor.
The estimated wakefield errors for the beam
parameters are consistent in experiment andsimulation.

References

Tsuyoshi Suwada, Muhammad Abdul Rehman, Fusashi
Miyahara, “First Simultaneous Detection of Electron andPositron Bunches at the Positron Capture Section of theSuperKEKB Factory”, Sci Rep 11, 12751 (2021),
https://doi.org/10.1038/s41598-021-91707-0.