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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 2 2

REPLACEMENT OF THE SINGLE-PASS BPM SYSTEM WITHMicroTCA.4-BASED VERSATILE ELECTRONICS AT SPring-8
H. Maesaka∗ , 1 , RIKEN SPring-8 Center, Sayo, Hyogo, Japan
H. Dewa, T. Fujita, M. Masaki, N. Hosoda2 , S. Takano2 , JASRI, Sayo, Hyogo, Japan1
also at JASRI, Sayo, Hyogo, Japan
2also at RIKEN SPring-8 Center, Sayo, Hyogo, Japan
Abstract
We have developed a versatile BPM readout electronics based on the MicroTCA.4 (MTCA.4) platform for theSPring-8 upgrade project, SPring-8-II. The new electronics are comprised of an RF frontend rear transition module(RTM) and a high-speed digitizer advance mezzanine card(AMC) having 10-channel, 16-bit, and 370 MSPS ADC. The
field-programmable gate array (FPGA) on the AMC calculates both single-pass (SP) and closed-orbit distortion (COD)beam positions. The current BPM system at SPring-8 consists of approximately twenty SP-dedicated BPMs and morethan 250 COD-dedicated ones. In advance of SPring-8-II,
so far, we replaced half of the old SP BPM electronics with
the new MTCA.4 ones and the rest of the old SP BPM electronics are being renewed this summer. The SP resolutionof the new BPM electronics was confirmed to be better than
100 µm for a 0.1 nC single bunch, sufficient for SPring-8-II.
The new BPM electronics were applied to regular tuning
items, such as the adjustment of kicker magnets for pulsed
orbit bumps in the beam injection, and the functionalities
were confirmed to be compatible with the old SP BPM system. Thus, the MTCA.4-based BPM electronics are readyfor SPring-8-II.

INTRODUCTION
The low-emittance upgrade of the SPring-8 storage ring,
SPring-8-II [1] was proposed, and many new accelerator
components have been developed. The natural emittancewill be squeezed from 2.4 nm rad to 100 pm rad by reducing
the beam energy from 8 GeV to 6 GeV and by using a 5-bend
achromat lattice (5BA).
A new BPM system for SPring-8-II was also developed.
The single-pass (SP) BPM resolution is required to be
100 µm std. for a 0.1 nC injected bunch. The error on theelectrical center should be within ±100 µm before the beambased calibration. The closed-orbit distortion (COD) BPM
is demanded to be sufficiently stable within 5 µm peak-topeak for 1 month. To fulfill these requirements, we studied
the following BPM components:
1. Button BPM electrodes made of molybdenum [2].
2. Radiation-tolerant coaxial cables.
3. BPM readout electronics based on MicroTCA.4(MTCA.4) [3].
∗ maesaka@spring8.or.jp

Since the new electronics will benefit the operation of thecurrent SPring-8 storage ring, replacement of the BPM electronics was scheduled in advance of the actual upgrade work.
The SPring-8 storage ring has 48 cells (44 double-bend cells
and 4 long straight ones). There are typically 6 BPMs ineach cell and approximately 280 BPMs in total. Before
the development of the new MTCA.4-based electronics, theexisting BPM system has two types of readout electronics,
COD BPM and SP BPM, and typically one BPM out of 12(6 BPMs × 2 cells) is processed by SP BPM and the other 11
are precessed by COD BPM. Contrary to the old electronics, the new MTCA.4-based electronics have both SP BPM
and COD BPM functions. Therefore, both SP BPM andCOD BPM can be replaced with the MTCA.4 electronics.
Since the SP BPM system is more than 25 years old andhard to maintain, we decided to replace the SP BPM electronics with the MTCA.4 ones in advance of the COD BPM.
The COD BPM system will be upgraded to MTCA.4 in theactual SPring-8 upgrade work.
The new electronics were first installed into the current
SPring-8 ring to implement the adaptive feed-forward correction (AFC) of the error kick from the fast helicity switching
beamline [4] in 2019. Old SP BPMs connected to the four
BPM heads connected to the four BPM heads selected forthe AFC were replaced with the MTCA.4 at that time. Another ten units of SP BPMs were then upgraded to MTCA.4
in 2021 and the rest of the SP BPM units are being replacedin this summer shutdown period (2023).
We describe the design of the MTCA.4-based BPM electronics and introduce the software for data taking. The basic
performance of the SP BPM function is presented and compared with the old SP BPMs.

MTCA.4-BASED ELECTRONICS
A block diagram of the MTCA.4-based electronics is illustrated in Fig. 1. The signal from each BPM electrode isfed into the BPM rear transition module (RTM). The signal
is filtered by a band-pass filter at the accelerator frequencyof 508.58 MHz and the signal level is adjusted by step attenuators and low-noise RF amplifiers. The signal is thenconverted to a balanced differential signal by a BALUN since
the ADC on the digitizer advanced mezzanine card (AMC)
receives a differential balanced signal. The digitizer AMC
has 10 ADC channels and hence one board can process signals from two BPMs. The ADC has a 16-bit resolution anda maximum sampling rate of 370 MHz. Since the signal
frequency is higher than the Nyquist frequency of the ADC,

MOP02274

02 Beam Position Monitors

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 2 2

BPM 1BPF

BPM 2BPF

Step Att.

Digitizer AMC

16-bit, 370 MSPS ADC x 10

Step Att.

BALUN

ADC

x4
Step Att.

BALUNx4+Ext. RF

BALUN

SplitterStep Att.

x4Ext.
CLKClock
AMC ConnectorAMC Backplane

Pilot Tone
PLL

ADC
ADC
ADC

ADC
ADC

FPGA

ADC

Digital I/O

ADC
ADC

BALUN

RF Backplane
ClockRFSPDT++Zone 3

Step Att.

ADC

Digital I/O

Clock
Distribution

SDRAM
Ext. Clock

Digital I/O

Figure 1: Block diagram of the readout electronics.
the signal is detected by an under-sampling scheme. The
actual sampling frequency was set to 363.27 MHz, corresponding to 5/7 of the acceleration frequency. In this case,the waveform taken by the ADC looks like an intermediate
frequency (IF) signal having 145.31 MHz. This IF signal
is digitally converted to an IQ (In-phase and Quadrature)
baseband signal and the amplitude and phase are calculated.
The differential over summation (Δ/Σ) of the amplitudes ofthe four electrodes is calculated, and the beam position is
obtained from a polynomial function.
To correct gain drifts etc. of the electronics, the RTM isequipped with a 4-channel pilot tone generator. Each pilot
tone generator is connected to each electrode of a BPM.
In the FPGA, both SP BPM and COD BPM are processedin parallel. The SP BPM logic masks the period withoutany beam signal and integrates input signal power for eachturn. The COD-BPM logic decimates the IQ signal to thethree data rates, the revolution frequency of 209 kHz (Turnby-Turn), 10 kHz (Fast Acquisition, FA), and 10 Hz (SlowAcquisition, SA). The Δ/Σ for each signal stream is calculated, and the beam position is computed by a 7th-orderpolynomial. These data are stored in the RAM on the digitizer AMC and then transferred to the CPU via a PCI-expressbus.
The injection timing signal for the SP BPM trigger etc. is
distributed by MTCA.4 trigger modules [5] from the SACLA
linear accelerator [6]. The trigger module in the BPM system
receives the trigger signal from SACLA and transmits thedata acquisition trigger to the digitizer AMC via the AMC
backplane.

SOFTWARE
The digitizer AMC is controlled by an MTCA.4 CPU module, where the operating system of Ubuntu 16.04 is running.
The BPM system is controlled from an operating console byan MQTT messaging system, and the BPM data are takenby the MDAQ framework [7]. All the SA COD BPM dataare stored in the event-synchronized database with a data
rate of 10 Hz. The other COD BPM data (TbT and FA) andSP BPM data are dumped into data files on request.
Since the SP BPM data needs some timing adjustments
before data taking, we developed a graphical user interface(GUI) of SP BPM for convenient data acquisition. A screenshot of the SP BPM GUI is shown in Fig. 2. By using this,we can adjust the revolution trigger timing to the bunch timing from the raw signal amplitude waveforms and then set
the injection trigger timing to the first turn of the plot. Afterthe timing adjustment, SP BPM data at an injection triggercan be easily obtained and plotted.

Figure 2: Screenshot of the SP BPM GUI. Horizontal andvertical positions and sum value for each turn are plotted inthe left figures, along with some control widgets. The raw
signal amplitude waveform for each electrode is shown inthe right figures.
MOP02202 Beam Position Monitors

75

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BPM RTM

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 2 2

Injected BeamAn example of SP BPM data from one BPM is plottedin Fig. 3, where a single bunch of approximately 0.2 nC
was injected. The sum amplitude is promptly increased at
the first turn and almost constant after injection. Since theinjected beam is horizontally offset from the beam orbit, alarge betatron oscillation was excited in the first few hundred
turns. A synchrotron oscillation with a period of about 100
turns is also observed due to a finite horizontal dispersion
and errors in energy and timing of the injected bunch. The

vertical position data shows small but finite betatron andsynchrotron oscillations due to an offset of the beam orbitof the injected bunch and dispersion leakage to the verticaldirection. Since the sum signal is calculated by a vector
sum of complex amplitude of the four electrodes, the beamarrival phase with respect to the reference RF signal can bealso obtained, as shown in the bottom plot of Fig. 3. The
synchrotron oscillation is observed in the phase of the sum
signal as well, but the oscillation phase is 𝜋/2 shifted fromthat of the position data. This phase shift is consistent withthe time evolution of electrons in the longitudinal phasespace.

Position Resolution
X

5.0[mm]2.50.02.5
5.00200

400
600
Turns

800

1000

400600
Turns

800

1000

Y5.0[mm]

2.50.02.5
5.00200

0.00.010
0.10.005
0.0000200400600Turns

8001000

Sum Phase

8070Data [mm]arb. unit

The position resolution was evaluated by kicking a stored
single bunch with kicker magnets to make a pulsed orbit
bump for beam injection. The stored current was approximately 0.1 mA, corresponding to 0.5 nC, and the amplitude of the betatron oscillation was approximately 0.4 mm.
SP BPM data from 7 BPMs were taken in this measurement.
We compared the beam position of one BPM with the prediction from the other 6 BPMs. Figure 4 shows a scatter plotof the horizontal beam position at a specified BPM vs. theprediction from the other BPMs. The standard deviation of
the difference between data and prediction for each BPM isthought to be the position resolution. The horizontal position resolution was evaluated to be approximately 17 µm foran electron bunch with 0.5 nC, as plotted in Fig. 5. Whenthe bunch charge is reduced to 1/5 (0.1 nC), the position
resolution will be 5 times larger than this value. Even in thissituation, the resolution is still below 100 µm and enough forsingle-pass measurements in SPring-8-II. Since the size of
the SPring-8-II vacuum chamber will be smaller than that ofSum Amp0.015[deg.]

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SP BPM DATA

0.2

0.3

600.4

50400200

400600Turns

8001000

Figure 3: Example of SP BPM data from one BPM at beam
injection. Horizontal and vertical beam positions, sum amplitude, and sum phase are shown from top to bottom.

0.40.30.2
Prediction [mm]0.10.0Figure 4: Comparison between the horizontal beam position
at a BPM and the prediction from other BPMs.

MOP0227602 Beam Position Monitors

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

cillation amplitude data between the old and new SP BPMs
was small enough (less than 0.1 mm). Consequently, thenew MTCA.4 SP BPM system is ready for the tuning of thecurrent SPring-8 storage ring.

15SUMMARY10501234BPM ID

567Figure 5: Horizontal SP BPM resolution of 7 BPMs.
the current SPring-8 ring, the SP BPM resolution is expected
to be better than this measurement.

Injection Orbit Bump Adjustment
The current SPring-8 storage ring makes a pulsed orbit
bump with four dipole kicker magnets for the off-axis beam
injection. Since it is important to close the orbit bump as
perfectly as possible with matched kicker waveforms so as
not to affect the stored beam, adjustment of the dipole kickers
is necessary at the beginning of each operation cycle [8].
The kicker magnets used to be adjusted by using the datafrom the old SP BPM system so that the oscillation of thestored beam is minimized. The same adjustment procedure
should work well with the new MTCA.4-based BPM system.
Therefore, we measured the orbit oscillation caused by
the kicker magnets with both old and new SP BPM systems to confirm that both data were consistent with eachother. The SP BPM data were taken by shifting the kicker
magnet timing every 50 RF buckets (98 ns), and the orbit
oscillation amplitude due to the residual kick of the kicker
magnets for each bunch address was evaluated. Figure 6
shows the RMS of the beam positions at the used SP BPMs
as a function of the bunch address. The difference in the os-

RMS oscillation amplitude

Amplitude [mm]0.40.2[1] SPring-8-II Conceptual Design Report, Nov. 2014.
http://rsc.riken.jp/pdf/SPring-8-II.pdf[2] M. Masaki et al., “Design Optimization of Button-type
BPM Electrode for the SPring-8 Upgrade”, in Proc. IBIC’16,
Barcelona, Spain, Sep. 2016, pp. 360–363.
doi:10.18429/JACoW-IBIC2016-TUPG18[3] H. Maesaka et al., “Development of MTCA.4-based BPM
Electronics for SPring-8 Upgrade”, in Proc. IBIC’19, Malmö,
Sweden, Sep. 2019, pp. 471–474.
doi:10.18429/JACoW-IBIC2019-WEBO03[4] M. Masaki et al., “Adaptive feedforward control of closed
orbit distortion caused by fast helicity-switching undulators”,
J. Synchrotron Rad., vol. 28, pp. 1758–1768, 2021.
doi:10.1107/S160057752101047X[6] H. Maesaka et al., “Full Energy On-Demand Beam Injection
from SACLA to SPring-8 Storage Ring”, in Proc. IPAC’21,
Campinas, Brazil, May 2021 pp. 4508–4513.
doi:10.18429/JACoW-IPAC2021-FRXA01

0.1
0.0

REFERENCES[5] H. Maesaka et al., “Development of a Trigger Distribution
System Based on MicroTCA.4”, in Proc. IPAC’22, Bangkok,Thailand, Jun. 2022, pp. 1171–1173.
doi:10.18429/JACoW-IPAC2022-TUPOPT067

Old SPBPM
New SPBPM

0.3

For the next-generation hard X-ray light source project,
SPring-8-II, we developed MTCA.4-based versatile BPM
readout electronics. Since the new electronics are applicableto the current SPring-8, we decided to first replace the old
SP BPM electronics with the new ones. After finishing thereplacement of half of the SP BPM by 2021, we are now
upgrading the remaining half this summer. The SP BPM
performance of the MTCA.4 electronics were evaluated, andconfirmed to be sufficient for both SPring-8 and SPring-8-II.
The trajectory of an injected electron beam was appropriately
observed. The SP BPM resolution was obtained to be 17 µm
for a 0.5 nC single-bunch. The beam oscillation caused by
the residual kick of the injection orbit bump was compared
between the old and new electronics, and confirmed to beconsistent with each other. Thus, the MTCA.4-based BPM
electronics are ready for SPring-8-II, and the upgrade workof the BPM system is expected to be smoothly carried out
by replacing the readout electronics in advance.

01234Turns

5678Figure 6: RMS amplitude of the orbit oscillation by theresidual kick of the kicker magnets. The blue (orange) line
shows the data from the old (new) SP BPM. The horizontal
axis shows the bunch timing with respect to the bump pulsetiming.

[7] T. Sugimoto et al., “Status of the control system for fully integrated SACLA/SPring-8 accelerator complex and new 3
GeV light source being constructed at Tohoku, Japan”, inProc. ICALEPCS’19, New York, USA, Oct. 2019, pp. 904–908.
doi:10.18429/JACoW-ICALEPCS2019-WECPL01[8] T. Ohshima et al., “Suppression of Stored Beam Oscillation Excited by Beam Injection”, in Proc. EPAC’04, Lucerne, Switzerland, Jul. 2004, MOPKF047, pp. 414–416.

MOP02202 Beam Position Monitors

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JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0
d 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 2 2