MDI status
Belle II organization chart
MDI group(MDI= Machine-Detector Interface)

Belle II

SuperKEKB

Injector

Hiro Nakayama (KEK)

Since June 2023, two subgroups(Beam background, Loss monitor )are officially added under the “MDI” tree
In the Organization Charthiroyuki.nakayama@kek.jp

1

Our ultimate goal:

More integrated luminosity
Key Objectives

Major strategies

Challenges• Higherinstantaneousluminosity• Squeeze
beam size at IP• Increase
beam currents••••• Increase
effective beamtime• Reduce
downtime due totroubles• Minimize DAQdeadtime(injection veto)

••
•
••

Short beam life due to narrow dynamic/physicalaperture at small beta*y optics
Beam blowup at higher beam currents
Poor injection efficiency due to instability of injection
beam charge and quality (emittance blowup in BT)
Non-optimal collimator settings due to poor injection
quality, TMC instability (beam size blow up), and headsurface damage caused by severe beam loss
Beam background impact on sensor lifetime and data
quality for physics analysis
Beam current limit due to RF power
Sudden Beam Loss (SBL) events causing QCS
quenches and severe collimator/sensor damage
Long injection BG duration and large DAQ deadtime
and so on…

hiroyuki.nakayama@kek.jp

topics covered by MDI activities2

1-page summary of

MDI-related major improvements during LS1
Collimator/Injection• Installed a Non-Linear Collimator (NLC, or LER D5V1) to reduce impedance• Damaged collimator jaws were replaced. Copper coating were added on jaws for fireball suppression.

• Many improvements in injection chain (LINAC+BT)
Sudden beam loss
• Added more loss monitors and acoustic sensors to investigate Sudden Beam Loss (SBL) events• Also added Beam Orbit Recorders (BORs) to observe initial beam instability in SBL events
Beam background• Installed additional BG shields (bellows shield, QCS neutron shield)• Reinforced neutron measurements on top of Belle II (to understand PXD power supply trips)

Others• Developed real-time BG monitors (NN-based, ECL-based) to support machine/collimator tuning• Apply Machine-Learning technique for machine tuning
hiroyuki.nakayama@kek.jp

3

Beam background group activities• Neutron sensors installed around Belle II• Real-time BG composition monitors(NN-based, ECL-based)

ECL-based real-time BG composition monitor

More neutron sensors on top of Belle II
to understand PXD power supply trips

・Capable of segregating each BG component
based on neural-network training using hundredof EPICS PVs, or MC-template fitting using hit
distribution in ECL trigger cells
・Powerful tools for machine/collimator tuning
hiroyuki.nakayama@kek.jp

4Proposed machine studies for the Run 2• NLC commissioning study• Non-linear optics tuning (vary NLC K-value)• Collimator jaw position offset measurements• IP beam orbit angle optimization (BG, SR, luminosity)

Studies to be done inearly stage of beamcommissioning• Usual BG studies to separate each BG component• Single-beam measurements followed by the luminosity study• Comprehensive injection BG duration study• Varying injection beam size/amplitude, collimators, FB ON/OFF,tune resonance line, chromaticity, etc.

• Horizontal collimator scan for dynamic aperture check• New real-time BG monitor commissioning• Pressure bump study
hiroyuki.nakayama@kek.jp

Important studies tobe done once stablebeam operation isachieved

5More loss monitors installed during LS1

hiroyuki.nakayama@kek.jp•Beam loss monitors equipped with GPSsynchronized fast readout are installed
along the main ring•

We can track the chronologicalsequence of beam loss at loss monitors
and identify the ring location where initial
beam loss occurred during SBL events•

During LS1, we installed more loss
monitors at HER/LER collimators, which
provides more precise position analysis
and better understanding of SBL events•

We also installed loss monitors at
HER/LER injection points, which allows
injection loss timing analysis and usefulfor injection /collimator tuning tominimize injection BG.

•GUI panel is in preparation to provide
6
read-time feedback to machine operator

Acoustic sensors for “fireball” hypothesis

hiroyuki.nakayama@kek.jp•

Acoustic sensors can detect thesound produced by electric
discharge, which is expected in the“fireball” hypothesis proposed for
SBL events.

•During LS1, we installed many
acoustic sensors at LER collimators(D2V1/D5V1) and QCS beam pipes.

•

Ready for data taking, waiting for theSBL events in this run•

More details can be found here7

Faster beam abort delivery

hiroyuki.nakayama@kek.jp•

Shorter abort request path
• In the new path prepared during LS1,
abort requests can be directly
delivered to the abort kicker, notpassing the SKB control building• It can gain 1~2 us (20-40% chance for
5 us gain, depending on the timingfrom abort gaps)• Damage on Belle II sensor /collimator damage can be mitigated• Further improvement planned in thenext FY, by installing new racks andcables•

For longer-term R&D, we investigate thepossibility to utilize a new technology, suchas laser transmission in air• Feasibility tests in the main ringtunnel conducted during LS18Other loss monitor group activities•

CLAWS scintillators• CLAWS installed around QCS has been very
effective to issue fast beam aborts• We also installed similar setup around LER NLC,
aiming to issue earliest beam aborts upon beamloss on the new collimator•

Bunch Oscillation Recorder (BOR)• In addition to loss monitors, BORs can provide
important insights for SBL events.
• BORs can detect initial beam instability insidebeam pipe, which should happen before weobserve beam loss
• We installed more BORs during LS1. We also
developed a new module (called RFSoC) which
can be used for new BORs.
and so on..

•hiroyuki.nakayama@kek.jp

We offer distinctive opportunities forcollaboration with SKB members andparticipation in machine operations.
We welcome new students and postdocs,Come and join us!
9.

Machine-Learning assisted accelerator tuning

Since MR injection
septum/kicker magnets prefer
gradual change on its
parameters, we implemented“one-stroke function” in ouroptimization algorithm
hiroyuki.nakayama@kek.jp•

Currently, accelerator tuning depends ona limited number of experts, making it
unrealistic to maintain 24-hour coverage•

Therefore, we aim to develop a MLbased machine tuning algorithm which
can support non-expert operators•

In the past several months, machinestudies using LINAC e+ beam
demonstrated that our Bayesian
optimization approach seem promising•Now we plan to apply a similar method
for injection tuning to the MR. Machinestudies to be conducted during Run2

10

“hot from the oven”

Some initial observations from Run2
- Acoustic sensors- Beam orbit during SBL event
measured by “RFSoC”

hiroyuki.nakayama@kek.jp

11Okada, Abe, Uno

Can acoustic sensors distinguishbeam loss shower and vacuum arching event?
acousticsensors
collimator
collimator𝒆+𝒆+

In case of beam loss at the collimator, generated
showers first interact with the downstream
acoustic sensors and then the sound wave
propagates to the upstream acoustic sensors
AFTER O(~100us).

If vacuum arching occurs (as expected in the fireballhypothesis) at the collimator, it triggers the acoustic
sensors on the collimator but not the sensors on
downstream beam pipes, which are mechanicallydisconnected with the collimator. The upstream acoustic
sensors may be triggered AFTER ~10us (=1 turn), by theshowers generated further upstream.

Can acoustic sensors determine the timing precisely enough?

12Machine study to checktime resolution of acoustic sensor measurement
ac. sensor

ac. sensor

𝐭𝟎

Machine study:- Shoot the LER single bunch (0.5nC) to the collimator- Observed acoustic sensor signal waveforms are fitted with the modelfunction(*) to obtain the signal timing (t=t0)- Shoot five times and check the reproducibility of timing measurement
𝐞+ - Vary the hit position from the tip of collimator head (0~4mm)
0 (x ≤ 0)
U x =ቊ
1 (x > 0)

(*)

t=t0

13

Machine study to checktime resolution of acoustic sensor measurement (contd.)
How to interpret the plot:max
average of five measurements
min3mmd=4mm

2mm

1mm

d=0mm

→ Measurement based on acoustic sensors
is promising to distinguish beam loss
showers and vacuum arching events!!

Collimator hit position

𝐞+

d=4mm

The machine study demonstrate that we candetermine the timing of acoustic senor signal
at the resolution of < 10us (except d=0mm).
Similar result for other acoustic sensors.

𝐞+

d=0mm

14

Acoustic sensor signals at the event on
2024.02.14 at 9pm
CH2
CH3
collimator𝒆+CH32024/03/15

CH3

Downstream sensors triggered first& upstream sensors triggered O(~100us) later➔ Seems to be the beam loss event, not vacuum arching1515

Nomaru, Mitsuka

New BOR using “RFSoC” by AMD/Xilinx
Beam Orbit Recorder

RF System on Chip

• BOR could detect the initial beam instability inside thebeam pipe for SBL events (loss monitor can see beam
showers coming out of the beam pipe)• Need more BORs in the ring to pin down the location of theorigin of SBL• RFSoC is a good candidate for a new BOR, with larger ADC
resolution (8bit→12bit) and more portability (VME rack notneeded)
ZYNQFPGA(PL)CPU(PS)ADCDACRFSoC already sees recent LER SBL aborts
2024/3/8 03:58:25

vertical orbit measured by RFSoC~200nsintensity measured by RFSoC

cf. Bunch current measured by existing BOR

hiroyuki.nakayama@kek.jp

RFSoC is already installed toLER and provides interestingmeasurements for SBLs

17

Summary• Many improvements implemented during LS1• Newly installed loss monitors and acoustic sensors should provide moreinsights on SBL events• Several ongoing efforts to make beam abort even faster• Machine Learning looks promising for effective accelerator tuning• Interesting observations from Run2 are already coming out and detailed
analysis is ongoing.

• MDI efforts are crucial to cope with upcoming challenges in achieving
higher luminosity. Close collaboration between Belle II, SuperKEKB and
LINAC colleagues are required.
hiroyuki.nakayama@kek.jp

18

backuphiroyuki.nakayama@kek.jp

19Nov. 2023 BPAC recommendations
Full Report for BPAC Nov. 2023, Section 2 (Accelerator and MDI)
If equipment is not damaged, we can swiftly
restart the beam operation. However, ifcollimator is heavily damaged, it takes at least
several days for replacement work and following
vacuum baking. We use low-Z material for the“spoiler” collimator to avoid severe damage on it.

During LS1, we have implemented a series of improvements on beam injection:- New pulse magnets to improve e- injection beam (J-arc, sector-1,2)- New fast kickers to cure e- 2nd-bunch quality (J-arc, LINAC end, HER BT)- Renewal of LINAC accelerating structures- New HER chamber with larger aperture at injection point & improved septum magnet field- Install OTR (Optical Transition Radiation) monitors for more precise measurement of emittance & energy spread- etc..

Also, intensive injection studies has been conducted in the past few months, before resuming MR operation.
Analysis of those studies is currently ongoing and will be reported soon.

hiroyuki.nakayama@kek.jp20

Takuya Ishibashi

Collimators•

D05V1(NLC) installation work complete• 5m-long lead radiation shield downstream•All damaged jaws replaced with spare jaws
• Except HER D9V1, will finish before HER start• Coated with cupper to mitigate “fireball” phenomena•

Three spare jaws produced within this fiscal year
• Including “hybrid” type jaws (Carbon/Ta)•Additional displacement sensor will arrive next year
• Provides precise head-position measurement (<0.2um)

D05V1 (NLC)

Lead shielde+ beam

List of spare jaws
Tip Material(): longitudinal length in mm

Collimator to be installed(assumed)

HER vertical: Cu coated Ta (10)HER vertical: Cu coated Ta (10)HER vertical: Cu coated Ti (40)
HER vertical: Cu coated Ti (40)LER vertical: Cu coated Ta (10）LER vertical: Cu coated Ta (10）LER vertical: hybrid (3）LER vertical: hybrid (3）LER vertical: Cu coated Ta (10)LER vertical: Cu coated Ta (10)LER horizontal: Ta (10）

D01V1
D01V1
D09V1-V4, D12V1-V4
D09V1-V4, D12V1-V4
D02V1
D02V1
D05V1, D06V1-V2
D05V1, D06V1-V2
D02V1, D05V1, D06V1-V2
D02V1, D05V1, D06V1-V2
D06H4

Remarks
Plan to deliver in this fiscal year.
Plan to deliver in this fiscal year.

Delivered this Sep.
Delivered this Sep.
Plan to deliver in this fiscal year.
Plan to deliver in this fiscal year.

hiroyuki.nakayama@kek.jp

New displacement sensor
Support parts
Gap detector
Flat plate

21

V-shaped block

MDI structure in the Organization Chart
Two subgroups under the MDI tree
• Beam background group• Leader: Andrii Natochii• Moved from TB tree for close
communication with machine folks• Keep reporting at TB meeting to ensure
information flow to Belle II• Loss monitor group• Leader: Keta Uno• ~10 staff members from both Belle II andSuperKEKB, and 8 Msc/PhD students• Other important MDI-related activities
directly reported to MDI meetings
etc…
hiroyuki.nakayama@kek.jp • Collimator, Injection, Abort sensors, 22

Approved by EB at
June 2023 B2GM

hiroyuki.nakayama@kek.jp

23

Naoko Iida

LINAC/BT

Positron BT modification•••••

Positron horizontal emittance in BT significantly increases atlarge charge → caused by CSR effect?
If yes, the blowup should be reduced by moving the beam orbit
closer to the beam pipe inner wall
Bending magnets and chambers in positron BT 1st arc are shifted
upwards by 13mm(!)
LINAC operation already started on Oct. 16th
BT operation (with BT-dump mode) will start from Nov. 27th
• BT tuning could be challenging due to the 13mm offset(13mm)

hiroyuki.nakayama@kek.jp

25

Machine learning-assisted beam tuning• To achieve target luminosity,
improving the efficiency of beamtuning is essential• We conducted a machine study using
LINAC e- beam, to optimize beam
quality by parameter search based on
Bayesian optimization approach• The study demonstrated that charge
maximization and/or dispersion
minimization by adjusting LINAC pulse
magnet parameters was successful• We plan to conduct a similar study at
SuperKEKB MR in January
hiroyuki.nakayama@kek.jp

26

L. Vitale

Diamond aborthiroyuki.nakayama@kek.jp27