Replacement of the Single-Pass BPM System withMicroTCA.4-based Versatile Electronics at SPring-8,1,22222,1MOP0222,1H. Maesaka* , H. Dewa , T. Fujita , M. Masaki , N. Hosoda , S. Takano
1: RIKEN SPring-8 Center, 2: Japan Synchrotron Radiation Research Institute (JASRI)

Introduction

SP Data for Injected Beam

• Low-emittance upgrade of the SPring-8 storage ring, SPring-8-II [1].

• Requirements for the BPM system.

- Single-pass (SP) BPM resolution: 100 μm std. (for a 0.1nC injected bunch)- Electrical center error: ±100 μm (before the beam-based calibration)- Stability: 5 μm peak-to-peak for 1 month- Remaining eleven units are now being installed in this summer shutdown period.

MTCA.4-based Electronics [3]• Both SP BPM and COD BPM are processed at the same time.
• The COD BPM logic generates Turn-by-Turn (209 kHz), 10 kHz, and 10 Hz data.
16-bit, 370 MSPS ADC x 10x4x4+

Ext. RF

BALUN

SplitterStep Att.

x4Ext.
CLK

ADC

Clock

FPGAADC

Digital I/O

ADC
ADC

AMC Connector
AMC Backplane

Pilot Tone
PLL

ADC

BALUN

RF BackplaneClockRF

SPDT++ADC

Digital I/O

SDRAM
Ext. Clock

Clock
Distribution[mm][mm]- Due to finite horizontal dispersion at the BPM.
- Errors on energy and timing of the injected bunch.

• Vertical position data has small but finite betatronand synchrotron oscillations.
- Vertical offset of the beam orbit of the injected bunch.
- Dispersion leakage to vertical direction.

Digital I/O

00.015• Sum phase also shows synchrotron oscillation.

- Since the sum signal is calculated by the vector sum ofcomplex amplitudes of the four electrodes, the beam arrival
phase with respect to the reference RF signal can be obtained.
- Synchrotron oscillation phase of the sum signal is π/2 shiftedfrom that of position data.
- This behaviour is consistent with the time evolution ofelectrons in the longitudinal phase space.

- ADC: 10-channel, 16-bit, 370 MSPS max.
- Under-sampling scheme.
- Digital down conversion and beam position calculation in FPGA.

0200

1000

400600Turns

800

10000.10.0

Sum Phase

80706050400200• SP resolution was evaluated by kicking a stored
beam with dipole kickers to make an orbit bumpfor beam injection.
- Stored current: 0.1 mA (bunch charge: 0.5 nC)- Orbit oscillation amplitude: ~0.4 mm• SP data from 7 BPMs were taken.
• The beam position of one BPM was compared withthe prediction from the the other 6 BPMs.
• Horizontal position resolution: ~17 μm

0.1
0.2
0.3
0.4
0.4

0.3
0.2Prediction [mm]SPBPM Resolution

2015105012• Beam injection trigger etc. are distributed by MTCA.4 trigger modules [5, 6].

345BPM ID

67Injection Orbit Bump Adjustment by SP BPM

Software• BPM system is controlled by an MQTT messaging system and MDAQ framework [7].
- All the 10 Hz COD BPM data are stored to the event-synchronized database.
- The other COD BPM data (TbT and 10 kHz) and SP BPM data are dumped to data files on request.

• Graphical User Interface (GUI) for SP BPM• A pulsed orbit bump is generated by four dipole kickers for beam injection at SPring-8.
- The four kicker magnets need to be matched to avoid the disturbance on the stored beam by closing theorbit bump.
- Tuning of the kicker magnets is necessary at the beginning of each operation cycle [8].

• Injection orbit bump adjustment.

- SP BPM data are taken by shifting the kicker pulse timing every 50 RF buckets (98ns).
- Orbit oscillation amplitude outside the orbit bump due to the unmatched kickers for each bunch address
is evaluated.
- Amplitude and timing of each dipole kicker power supply are adjusted to minimize the error kick.

Horizontal Position
Raw amplitude waveformfrom each electrode for thetiming adjustment to therevolution trigger.

• Matching of the kickers used to be adjusted by using the old SP BPM system• The same adjustment procedure should work well with the new MTCA.4 SP BPM.
• We checked the performance of theRMS oscillation amplitude
0.4
residual kick measurement of the dipole
Old SPBPM
kickers.
New SPBPM
0.3• The obtained orbit oscillation amplitude
was consistent with that of the old SP BPM.
0.2
- The difference between the old and new SP BPM
was sufficiently small (less than 0.1 mm).

Amplitude Sum

Control widgets

References[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, TUPG18.
[3] H. Maesaka et al., “Development of MTCA.4-based BPM Electronics for SPring-8 Upgrade”, in Proc. IBIC’19, WEBO03.
[4] M. Masaki et al., J. Synchrotron Rad., vol. 28, pp. 1758–1768, 2021.
[5] H. Maesaka et al., “Development of a Trigger Distribution System Based on MicroTCA.4”, in Proc. IPAC’22, TUPOPT067.
[6] H. Maesaka et al., “Full Energy On-Demand Beam Injection from SACLA to SPring-8 Storage Ring”, in Proc. IPAC’21, FRXA01.
[7] T. Sugimoto et al., “Status of the control system for fully integrated SACLA/SPring-8 accelerator complex and new 3 GeV lightsource being constructed at Tohoku, Japan”, in Proc. ICALEPCS’19, WECPL01.
[8] T. Ohshima et al., “Suppression of Stored Beam Oscillation Excited by Beam Injection”, in Proc. EPAC’04, MOPKF047.

• Consequently, the new MTCA.4 SP BPM
system is ready for the tuning of thecurrent SPring-8 storage ring.

Amplitude [mm]Control widgets

Vertical Position

8000.0050.0- Since the size of the SPring-8-II vacuum chamber will besmaller than that of the current SPring-8 storage ring,
the SP BPM resolution is expected to be better than thismeasurement.

• High-speed Digitizer AMC (Advanced Mezzanine Card)

400
600
Turns

0.010

0.000

• SP BPM resolution satisfies the requirement for
SPring-8-II.

- Band-pass filter (BPF) at 508.58 MHz (acceleration RF).
- Level adjustment by step attenuators and amplifiers.
- Four pilot tone generators for gain correction.

1000Sum Amp- For an electron bunch with 0.5nC.
- It corresponds to 85 µm for a 0.1 nC bunch.

• BPM Frontend RTM (Rear Transition Module)

200d.

BALUNADC

8000.0st

Step Att.

Zone 3

Step Att.

ADC

400600Turns

Y5.0SP Resolution

ADC

10002.5

Data [mm]ADC

8002.5Resolution [ m]BALUN

400600Turnsµm

BPM 2

Step Att.

200

17BPM 1BPF

Digitizer AMC

05.0[deg.]- 24 BPM readout units in total (1 unit per 2 cells and, in total 48 cells in the SPring-8 storage ring)- One BPM in every 2 cells is used for SP BPM.
- Three MTCA.4 units were first installed for the adaptive feed-forward correction of the error kick fromthe fast helicity switching beamline [4] in 2019.
- Ten units of the SP BPMs were upgraded to the new electronics in 2021.

Step Att.

5.0arb. unit

• Old SP BPM electronics have been replaced with the new MTCA.4-based electronics.

0.0
2.5

• Horizontal position also shows synchrotron
oscillation (period: ~100 turns)- Button BPM electrode made of molybdenum [2].
- Investigation of radiation tolerant coaxial cables.
- Readout electronics based on MicroTCA.4 (MTCA.4) [3]BPF2.5- The injected beam is horizontally offset from the beam orbit.

• Developed BPM components

BPM RTM

5.0• A single bunch of approximately 0.2 nC wasinjected.
• Sum amplitude is suddenly increased at the firstturn and almost constant after injection.
• Horizontal position shows large betatron oscillationin first a few 100 turns.

- Natural emittance: 2.4 nm rad → 100 pm rad- Beam energy: 8 GeV → 6GeV
- Lattice: Double-bend Achromat (DBA) → 5-bend achromat (5BA).

X0.1
0.0

01234Turns

56Summary• We developed a MTCA.4-based versatile BPM readout electronics for SPring-8-II.
• A half of the old SP BPM electronics were already replaced with new ones, and theremaining half are now being upgraded in this summer maintenance period.
• 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.
- Sufficient for SPring-8-II.

• The residual kick of the dipole kickers for injection orbit bump were compared
between the old and new electronics, and confirmed to be consistent each other.
• Thus, the MTCA.4-based BPM electronics is ready for SPring-8-II.

78