12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - M O P 0 3 0

Si-Won Jang*, Garam Hahn, Jung Yun Huang, Changbum Kim, Dotae Kim, Gyujin Kim,
Bokkyun Shin, DongCheol Shin, Donghyun SongBeam Instrumentation Group, PAL, Pohang, South Korea
Woojin Song, POSTECH, Pohang, South Korea
Abstract
The emittance of the 4th-generation storage ring (4GSR)
to be constructed in Cheongju-Ochang, Korea, is expected
to be approximately 100 times smaller than the existing
3rd-generation storage ring. With the decrease in emittance, more precise beam stabilization is required. To meetthis requirement, the resolution of the beam position monitor (BPM) system also needs to be further improved. We
have conducted research and development on the electronics of the BPM system for the 4GSR storage ring. In orderto perform fast orbit feedback in the 4GSR storage ring, weneed to acquire turn-by-turn beam position data, with a desired beam position resolution of 1 µm. Additionally, prototypes of the bunch-by-bunch monitoring system are being developed for the transverse feedback system and longitudinal feedback system. The internally developed electronics are intended to be modified for future use as monitors for multi-bunch beam energy measurements at the endof the linear accelerator, by adjusting the logic accordingly.
In this presentation, we will describe more details of thecurrent status of the development of the beam position
monitor electronics for the 4GSR in Korea.

DEVELOPMENT STRATEGY OF 4GSR
BPM ELECTRONICS
The strategy for developing 4GSR BPM electronics is asfollows: First, we aim to develop BBB (Bunch by Bunch)
BPM electronics capable of providing the highest performance for bunch-by-bunch beam position measurements.
Subsequently, using this technology as a foundation, wewill proceed to develop TbT (Turn by Turn) BPM electronics specifically tailored for the 4GSR storage ring. By integrating the front-end and back-end electronics, we will create Transverse & Longitudinal feedback systems (TFS &LFS), referred to as TFS & LFS BPM electronics.
Following this, we plan to adapt the data processing
logic of the BBB electronics into a single-pass logic. This
adaptation will enable us to install these electronics along
the LTB (Linac. to Booster) beamline in the linear accelerator backend. They will serve as multi-bunch beam energy
measurement monitors. The diagram below illustrates thedevelopment strategy for 4GSR BPM electronics. Figure 2
shows that the development strategy of 4GSR BPM electronics systems.

INTRODUCTION
To achieve precise beam orbit stability in the 4th-generation storage ring with an emittance about 100 times
smaller than the existing 3rd-generation storage ring [1], amore precise beam position monitor system with higherresolution is required. Figure 1 shows the construction
view map of Korea 4GSR. In addition, the design of the4GSR BPM electronics should be measure and provides
Turn by Turn beam position data for Fast Orbit Feedback(FOFB) system with 375 kHz rate, which is a revolution
frequency of 4GSR storage ring.

Figure 2: Development strategy of 4GSR BPM electronics.

Development Status of BBB BPM Electronics

Figure 1: Construction view map of Korea 4GSR.
____________________________________________†siwon@postech.ac.kr

The BBB electronics are currently in the prototype development phase [2], and we are undergoing several beam
tests to ensure the system's stability. By configuring the desired storage ring parameters and turn counts, we have confirmed the capability of measuring the beam position for
all bunches.
Figure 3 shows signal processing logic of BBB electronics. The signal processing procedure of BBB electronics asfollows: To obtain a sufficient amount of bunch information, data is collected over several turns. Subsequently,
the ADC data from every bunch is rearranged to calculate
the beam position information for all bunches in the time
domain. However, as previously mentioned, BBB Electronics is also adaptable for use with TbT BPM Electronics.
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DEVELOPMENTS OF 4GSR BPM ELECTRONICS

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12th Int. Beam Instrum. Conf.
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In the case of TbT data, the design ensures that the average
beam positions of the bunches are calculated in the time
domain for each turn with 375 kHz rate.

Figure 3: Design and simulation of 4GSR BBB BPM electronics logic.
Figure 4 shows the circuit configuration of the developed
prototype BBB electronics. The prototype of BBB Electronics has been designed to synchronize two FMC ADC
boards (2 Channel) on a Xilinx evaluation board. It utilizes
1 GS/s ADCs for data acquisition and has successfullymeasured bunch-by-bunch beam positions with stability
during beam tests at the Pohang Accelerator Laboratory's
PLS-II (Pohang Light Source-II) storage ring. In the future,
to provide even more reliable performance, the entire board
is undergoing upgrades. It will also utilize embedded EVR
to receive the 500 MHz Master Oscillator RF signal, Machine Clock (MC), and 10 Hz Trigger signal, enabling theutilization of the 4GSR event system.

of additional Analog Front-End Electronics, for future application in TFS & LFS.

4GSR SR BPM ELECTRONICS& SYSTEM CONFIGURATION
For the 4GSR Storage Ring (SR), TbT BPM electronics
are currently in the process of being developed based on
the prototype of the BBB electronics. The timing system
for the storage ring utilizes the Event Network to provide
Trigger signals and the Machine Clock to the BPM electronics. Additionally, SR BPM electronics employ SFP(Small Form-factor Pluggable) modules to provide X, Y,and Sum information at a speed of 375 kHz for the FOFBcontroller, Fast Orbit Interlock (FOI) controller, and Fast
DAQ server. However, for Slow Acquisition (SA) data required to calculate the closed orbit of the storage ring, it issynchronized with a 10Hz Trigger and transmitted to theEPICS system for beam position information as shown inFig. 6. Figure 6 shows the I/O port configuration of SR
BPM electronics.

Figure 6: I/O configuration of 4GSR SR BPM electronics.
Figure 7 depict the data flow of SR BPM electronics for
TbT data and SA data case, while Fig. 8 illustrates the configuration of BPM cable connections for the storage ring.

Figure 4: The configuration of BBB BPM electronics.

Figure 5: The beam test results of BBB BPM electronics.
A signal reconstruction by using BBB signal with 51turndata at PLS-II storage ring.
Figure 5 shows the beam test results of BBB Electronics.
After acquiring ADC data for 51 turns at a speed of 1 GS/s,
the data was rearranged according to the bunch order, resulting in the acquisition of beam position information for
all bunches. While additional data was obtained for sufficient data acquisition and precise signal waveform reconstruction, it is our aim to acquire beam position information
for all bunches in a shorter time frame through the design

Figure 7: The data flow of 4GSR SR BPM electronics.
The feedback system for 4GSR is structured in twostages, with the first stage being the Slow Orbit Feedback
System (SOFB). This system calculates and corrects theclosed orbit at a rate of 2 Hz using a total of 288 BPMs andCorrectors across the entire storage ring. The correctedclosed orbit becomes the new Reference Orbit (Ref. Orbit).
Subsequently, the FOFB system operates at each cell, receiving TbT data from BPM electronics at 375 kHz intervals and providing new set point information to the kicker
MPS (Magnet Power Supply) every 15.6 khz.

MOP0308802 Beam Position Monitors

12th Int. Beam Instrum. Conf.
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Figure 8: The configuration of BPM RF & timing cable connections for the storage ring.
Ultimately, the FOFB system aims to perform fast orbit
feedback at a 10 kHz interval using fast BPMs and fast correctors to achieve a wide suppression bandwidth. While
there isn't a master feedback controller for the entire storage ring, the FOFB controller exchanges information between adjacent cells at every turn. As a result, this systemswiftly corrects distorted beam orbits in each cell and calculates kick angles for orbit correction based on the overall
storage ring's orbit changes. Table 1 describes that the target parameters of the 4GSR feedback system.
Table 1: Specification Goal of 4GSR Beam Stability
TypePosition
Resolution
[RMS]

Beam
Current
Dependence

DataSpec.

TbT[375 kHz]

1 µm

SA[10 Hz]30 nm

TbT[375 kHz]

100 µmConditions

400 mA
1065 Bunches

0.1 ~ 1 mA
(Commissioning)

1 µm

-

~1 µm

0.1 mA ~400 mA<500 µm

Before BBA< 5 µmMax.

After BBA

±0.2 µm

Day drift

1 µm

Week drift-Long-term
Stability[RMS]-

ACKNOWLEDGEMENTS
This research was supported by National Research Foundation of Korea (NRF-2021R1I1A1A01060401).

SA[10 Hz]

AbsoluteAccuracy

CONCLUSION
The Korean 4GSR project in Ochang is currently underconstruction with the goal of completion by 2027. Thebeam position monitor electronics system for 4GSR is in
the process of development, and initial beam tests havebeen conducted by using developed prototype of BBB
BPM electronics. Based on this, BPM electronics for thestorage ring and feedback systems for both TFS and LFS
are also under development. Additionally, preparations areunderway for BBB energy measurement BPM electronics,
which will be used for multi-batch beam energy measurements at the end of the linear accelerator. The aim is tocomplete the development of storage ring BPM electronics
by the end of 2024. Simultaneously, tests will be conductedat the PLS-II storage ring in collaboration with the ongoingdevelopment of the FOFB controller.

REFERENCES[1] G.S. Jang et al. “Low emittance lattice design for Korea4GSR”, Nucl. Instrum. Methods Phys. Res., Sect. A,
vol. 1034, 2022, p. 166779.
doi:10.1016/j.nima.2022.166779[2] S. W. Jang, “Development of Button BPM Electronics for the
Bunch by Bunch Feedback System of 4GSR”, in Proc.
IPAC'22, Bangkok, Thailand, Jun. 2022, pp. 332-334.
doi:10.18429/JACoW-IPAC2022-MOPOPT038

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IBIC2023, Saskatoon, Canada
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