Summary of the SuperKEKB
beam monitors
Gaku Mitsuka (KEK Acc. Lab.)on behalf of the KEKB beam monitor groupOne-page summary
Pre-LS1

LS1

Post-LS1

Displacement sensors

No major trouble

Installation near NLC

Spare sensors production

BPM (narrowband)No major trouble

MaintenanceNo major trouble

BPM (turn-by-turn)Power supply failures

Power supply replacement

Some malfunctioning GTBTs

Feedback system

Concern on noise level

Detector upgrades

No major trouble

Bunch oscillation recorder

SBLs need more BORs

New BOR R&D

No major trouble

Beam profile monitors

No major trouble

Detector upgrades

No major trouble

Beam loss monitors

No major trouble

MaintenanceNo major trouble

Code development
Machine study at Linac

Machine study at SuperKEKB

ML-assisted beam tuning2

Displacement sensors• All displacement sensors are operating normally.
• In LS1, we newly installed the two displacement sensors near the non-linear collimator.
QN5OP

QN1OP

3

Beam position monitors (narrowband det.)• No major issue was found.
• In HER before LS1, we observed beam position jumping when the RF attenuator switched.
Then in LS1, we replaced the three 1 GHz narrowband detector boards.
• There are enough spare boards available.

Y pos.

Beamcurrent

X pos.

RF attenuator (0 down to -55 dB)
4Gated turn-by-turn BPMs
• In LS1, we have replaced an ATX power supply of all
GTBT boards to manage frequent power supply failures.
• First, the fan rotation slows down, the internal temperaturerises, and the entire power supply begins to fail.

• Multiple GTBTs malfunctioning after LS1• Case1: No signal is sent to the narrowband detector due to RF switching failure.
• Case2: Ch. C and D ADCs give too high or ~noise counts.
FPGA, DDR3

• Regulator voltage was abnormally low (3.3 V → 1.3 V).

SAW filters,Log Amp., ADCs

• We disconnected the cables from 5 of 140 GTBTs andbypassed them to the narrowband detectors.
• The manufacturer is investigating the cause.
• GTBTs help with beam injection tuning and measurementsfor physical/dynamic apertures using vertical or RF kickers.

RF gating switch

Button BPM

Narrowband detector
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BPMs at the injection regions• LS1 upgrade in HER; the vacuum chamber and injection septum magnet havebeen replaced for a wide aperture. We also installed a new-design injection BPM.
• The electrodes are symmetrically mounted on the top and bottom,
so X-Y coupling does not occur.

• The LER BPM is unchanged from the pre-LS1 system.
HER, April 2020

HER, March 2024

From BTHER

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Bunch-by-bunch feedback system• No major issue was found. The BxB FB system is working well.
LER injection region
FUJI straight section

Glass sealed (εr=4) SMA buttonelectrodes (diameter=6mm)
24 buttons×2 / Ring

7

Feedback detector upgrade in the LS1

Significant insertion loss (~22 dB)needs additional broadband amplifiers.

8

Amplitude (% of beam size)

Reduction of noise level
ADC counts with no beam

10
0.05V
0.1V
0.2V
0.3V
0.4V

864
2
0
0.5

0.55

0.65

0.7

0.75
0.55
0.56
0.58
0.60
0.62
0.65
0.68
0.72
0.75

233

13
12.5
120.8

Excited Veritical Tune

13.5

Luminosity(x10 /cm /s)

0.6

11.5
1110.5109.5

0510152025Amplitude(% of vertical size)

Lessons from KEKB:
Sinusoidal noise signal increases the beam sizeand degrades luminosity.
(Tobiyama & Ohmi, MOPD73, DIPAC2011)• RMS (noise level) was successfully
reduced from 13 (pre-LS1) to 3.
9

Investigation of detector performance

0.4 mA/bunch• Gain calibration with local beam bump assuresthe dynamic range of +/-1.5 mm.
• Their contribution to improving luminosity will be visible shortly.
10

Beam orbit feedback at the IP• IP-FB are working well.

Luminosity increases

Feedback turns on11Bunch Oscillation Recorder (BOR)• Since 2022, we have developed several types of BORs.
BORs measure the bunch position just before thebeam aborts over a few or more turns.
• We added BORs more densely in LER, where Sudden
Beam Loss (SBL) events were severe in before LS1,especially across the D06 collimators.
HERLocation

ADC bit

RF sync.

BOR

Fuji Upstream

8

Yes

iGp BOR

Fuji Up & Down

12

Yes

LER

Location

ADC bit

RF sync.

BOR

Fuji Upstream

8Yes

iGp BOR

Fuji Up & Down

12YesRFSoC BOR

Fuji Downstream

12

YesSimple BOR(Oscilloscope)D05

8No (5Gsps)

D06

8No (2.5Gsps)

• BOR
• iGp
• RFSoC• Simple
Beam dump
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RFSoC BOR• We started R&D in the fiscal year 2023 to apply a newarchitecture, Xilinx/AMD RFSoC, to BOR.
RFSoC: multi-ch. ADC, DAC, FPGA, and CPU on a chip

R. Nomaru (Master student)• The 1st prototype detector with the ZCU111 evaluation
board has been operating since February 2024.
• More details at IPAC2024 TUBD3 (cont. oral)
L. Ruckman

Bunch

8 March 2024 03:58:25~0.33mA/bunch

Vertical pos.

~200 ns

Bunch charge(arbitrary)13

X-ray beam size monitor• No significant issue is found in 2024.
The X-ray beam size monitors are working well.
• On the HER side, a new and large detector chamber(filled with He/N2 gas) was installed in LS1.
• On the LER side, there are no significant changes
from the pre-LS1 system. The YAG:Ce scintillator
screen was changed to a new one.
HERLER

Low speed CMOS
cam.

OKOK

Turn-by-turn CMOS
cam.

Parking atground floor

Parking atground floor

Si-sensor XRMInstalled without
Silicon sensor

Damagedby radiation

βy* = 3 mm

Meas.
Bestfit14

Visible-light beam profile monitors
HERLER

Visible-light interferometer

Horizontal beam size

OKNew in 2024

Gated camera

Bunch-by-bunch transverse

OKOK

Streak camera

Bunch-by-bunch longitudinal

OKOK

Intensity interferometer

LongitudinalNo

New in 2024

OKOK

Coronagraph (gated camera) Beam halo

• Since the optical line is healthy, we can measure
once the detectors are ready.
• For example, we checked the time axis
calibration of the streak camera in LER andfound no significant deviations.

• We added the visible-light interferometer andintensity interferometer in LER.
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Beam loss Monitors• The system is overall unchanged from pre-LS1 and is working well.
• We reinstalled the PINs that were once removed to install a non-linear collimatorand replace the collimator heads.
• After the operation started, we investigated some PINs with low signal output.
We found the (oldest) cable connectors badly damaged by radiation and replaced
them.

• More connectors and cables will need to be replaced in the future.
During long-term maintenance, the entire system will be inspected.
• Operating speed is fast enough as a source for an abort trigger.
• We are adjusting the threshold to avoid unnecessary aborts caused by small
beam losses.

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Machine-learning assisted beam tuning• We started developing a machine-learning tool tofacilitate beam injection in the fall of 2022, and a
graduate student joined the project in the spring of 2023.
• We conducted machine studies using Linac e+ beams
in LS1;
Bayesian optimization successfully optimized the beam
orbit, reduced dispersion, and maximized e+ yield.
[arXiv:2401.14739 and talk at IBIC2023 TH2C02]

S. Kato (Master student)

e+ injection efficiency to LER• After the resumption of SuperKEKB operation,a machine study is underway to maximize the beam
injection efficiency from BT to LER/HER.
• We are implementing the functions necessary for ring
operation, e.g., beam lifetime and care for the Belle IIdetector.
• The goal is to put the system into practical use by 2024.
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Summary• Beam monitors and feedback systems are generally working well.
• Upgraded performances have already been seen or will bevisible soon.
• Some monitors need continuous maintenance, especially• Gated turn-by-turn monitors• Beam loss monitor cables• New R&D projects started cooperating with grad. students andinternational collaborators.

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