1

Luminosity limiting factors
and the countermeasuresand strategy after LS1.
B2GM 2023/10/23

H.IKEDA

2

Luminosity Limiting factors
 For Luminosity↑ Beam Current↑ Beam Size↓

1.

Beam size blowup

 Collision Tuning

2.

Optics & Orbit problem

3.

Beam Lifetime

4.

Injection

5.

Sudden beam loss：

１．Beam size blowup

𝜀𝑦 (pm)vertical emittancevertical beam size𝜎𝑦∗ (𝜇m)

Beam size is measured by X-ray Monitor

LER

HER

𝐼𝑏+ 𝐼𝑏− (mA )𝐼𝑏+ , 𝐼𝑏− (mA)2

data: physics run

Beam size blowup is significant in LER.
3

Y.OnishiBeam size blowup：Specific Luminosity

The CW improved luminosity.
Data without CW was not the same period as CW
data.
We will confirm the luminosity gain in the next
operation.
Also the CW ratio will be optimized by lifetime andluminosity gain.

Crab Waist ratio is 0 %data from 2019.

Lsp = 8.935 x1031 cm-2s-1/mA2
𝛽𝑦 = 1 mm, 𝜀𝑦+ = 35 pm, 𝜀𝑦− = 25 pm, 𝜎𝑧+ = 4.6 mm, 𝜎𝑧− = 5.1 mm
4

Y.OnishiBeam size blowup：Beam-Beam Simulations
Simulation was done for LER with current parameters (𝛽𝑦∗ =1mm）.
Small energy and large vertical impedance.
X-Z instability is well suppressed at the current working point (tune).
In the presence of the impedance, vertical beam blowup occurs at certain working points when beam-beam interactions
are factored in.
This is 𝜎-mode instability (in-phase oscillation) and is an exponential growth of the vertical dipole and quadrupole moments.
It is called TMCI-like instability.
In order to reduce this effect,

Increasing chromaticity, different tuning in the two rings.
Non-linear collimators are also useful for impedance reduction.

K.Ohmi
Y.Onishi5

Beam size blowup：Beam-Beam Simulations (cont'd)
LER

Y. Zhang et al., Phys. Rev. Accel. Beam. 26, 064401 (2023)

0.8 mA/bunch

1.0 mA/bunch

45.532 / 43.573

44.525 / 46.589

Measure the beam size with changing the verticaltune after LS1.
6

Y.Onishi7

2. Beam Optics & Orbit

Reproducibility and stability of the machine are important because small orbit changes can cause large optics
disturbances.



The measured orbit may not be completely corrected to the Gold orbit.
 Cooling water effect Beam current dependence The beam pipe is thermally deformed where the synchrotron radiation hits it and the BPM pushes thequadrupole magnet. Reproducibility may be poor at the same current. Large discrepancies at the local
chromatic aberration correction, wiggler, and injection areas.

 Repeated aborts at high currents result in poor reproducibility.


Slow fluctuation of orbit over several days.



Effects of orbit changes due to earthquakes↓

Luminosity deterioration due to orbit change may be recovered by daily knob tuning.

Beam Optics & Orbit : Cooling Water Temperature (MAG)
There is a correlation between magnet cooling water and orbit variation, but the reason is still unknown.
Under consideration of task force of Cooling Water.

AOH572: マグネットTN内純水冷却水往温度（大穂3M機械棟）
AOH573: マグネットTN内純水冷却水環温度（大穂3M機械棟）
AOH522: マグネットTN内純水冷却水往温度（大穂6M機械棟）
AOH523: マグネットTN内純水冷却水環温度（大穂6M機械棟）
7分周期

ATU147: 筑波冷却マグネット往温度
ATU154: 筑波冷却マグネット環温度
AOH149: 大穂冷却マグネット往温度
AOH150: 大穂冷却マグネット環温度
ANK147: 日光冷却マグネット往温度
ANK148: 日光冷却マグネット環温度

AFJ129: 富士冷却マグネット往温度
AFJ136: 富士冷却マグネット環温度

AOH572: マグネットTN内純水冷却水往温度（大穂3M機械棟）
AOH573: マグネットTN内純水冷却水環温度（大穂3M機械棟）
ANK147: 日光冷却マグネット往温度
AOH149: 大穂冷却マグネット往温度

8Y.OnishiBeam Optics & Orbit : Cooling Water Temperature (MAG)

冷却環
冷却往

Vacuum system

Temperature of vacuum cooling system is very stable.

Magnet system

Y.Onishi9

Beam Optics & Orbit : Current Dependence at Strong Sextupole Region in
HER• The orbit at the SLY (sextupole for local aberration
correction) near the IP has the largest impact on OPTICS.
• A change in orbit of about 20 microns can change
the beta function of the colliding point by as much as
20%.
• The horizontal orbit at SLY depends on the beam current.

strongsextupolestrongsextupole

BPM readings (Horizontal)

Beam current
inne
r

oute
r

1
0

Y.OnishiBeam Optics & Orbit :Hypothesis of why orbit
depend on beam current

BPM
Quad. moves like yaw
and horizontal shift
if BPM pushes quad.

Radiation from the bending magnet
thermally deforms the beam pipe.
▸ BPM and quadrupole magnet (Q) areconnected by supports.BPM▸ When the beam pipe moves due to heatgeneration, BPM and Q move.
▹ Beam receives a dipole kick.
The fact that BPM is connected to Q
complicates matters.
▸ If BPM and Q are disconnected, theproblem becomes simpler.
▸ If the connection is severed, Q will not
move even if the beam pipe is deformed
and no orbit will be generated.
▸ Beam test scheduled for next operation

Crab Sextupole in the HER
BPM and Quadrupole Magnet

The beam pipe (BPM) is fixed to the1quadrupole
magnet.
1(Δ𝑥, Δ𝑦)

Gap sensor measures
between BPM andsextupole.
Relation between BPM and quad. does not change. (seeleft fig.)Yao, Mu-Lee

水平方向にチェンバーが変形する。強い6極の場所では、ビーム光学系（β関数）が大きく歪む。

Y.Onishi13

Beam Optics & Orbit :Beam optics degradation of unknown cause

Optics correction was performed
every two weeks.


HER beam performance
deteriorates in a few days underhigh current operation.

Frequent beam adjustments reduce
operating efficiency.

Residuals (measured orbit - gold orbit)• Residual does not appear to deteriorate in one
direction in about 3 days. However, there is acorrelation between residual and consistency,
and daily differences are visible.
• Temperature dependence?
→Measure the temperature dependence of thecoaxial cable characteristics of BPM using theexisting cable and SG.

Tsukuba city

*consistency=RMS of x and y positions obtained with
3 electrodes of BPM

Y.Onishi15

4. Injection
The beam created at the linac injected to the MR via the DR(e+) and BT.

The amount of beam current that can be accumulated is limited by the
injection beam and the beam lifetime.

The injection system consists of special equipment such as kickers andseptum magnet, and ceramic beam pipes.



A low emittance beam is required for the nanobeam scheme (focusing
the beam into a small size), and stable injection efficiency is essential tocompensate for the short beam life of the main ring.

Injection beam
Septum Magnet
Bump Orbit
Storage beam
Injection kicker
（K1）

QD

QF

QD

Injection kicker（K2）

50% less than required !!

Injection : Possible causes of low injection
efficiency




16

HER


Emittance blowup in the beam transport line (BT)Drift of the emittance of injection beam

The orbit and emittance drift of 2nd bunch of the injection beam

We could not put the injection beam close to the septum plate because of the magnetic field drop →The horizonal oscillation becomes larger.



Misalignment in the injection regionShorter lifetime than the design

LEREmittance blowup in the beam transport line (BT)

We could not put the injection beam close to the septum plate because of the magnetic field drop →The horizonal oscillation becomes larger.



Misalignment in the injection regionShort lifetime
MDI, 19.Oct.2023, Injection, N. Iida

17

Injection : LINAC and BT Upgrades done in LS1
Many pulsed magnets and fast kickers(for the 2nd bunch) were installed in LINAC

Tuning for each beam (HER, LER, PF, and PF/AR) becomes better.

New accelerator structure installation

Decreased down frequency, and high-energy beam can be supplied.

Auto-tuning gives LINAC fast beam rise and beam stabilization.
 Improved the septum magnetic field for HER and enlarging the aperture near the
injection pointThis contributes to injection recovery that is degraded by canceling coil errors.

DR kicker modification will speed up the DR injection/extraction tuning.
 OTR (Optical Transition Radiation) conversions of the screen monitor
make the investigation of the cause of the emittance blowup in BT more sophisticated.

The chambers at bending magnets in the e+ BT 1st arc was vertically shifted.
 A CSR monitor is installed in the e+ BT 1st arc.


MDI, 19.Oct.2023, Injection, N. Iida

Studies regarding the offset of the first arc in e+ BT 18

Vertical emittance

Horizontal emittance

Measured emittance1.

Since the horizontal emittance blowup seems to depend on theamount of charge, we suspected the influence of CSR and
decided to move the e+ beam closer to the chamber innerwall of the first arc bend (BH1P) to see if the blowup would be
reduced.

2.

However, there was no large gap between the chamber andbend, so it was decided to offset the chamber and bend
upwards.

3.

In normal operation, the beam is designed to pass near thevertical center of the bend, but if the offset is set to 14 mm,there is a concern that the unexpected vertical dispersion
generates due to the influence of the fringe magnetic field of
the bend. We confirmed it using tracking simulation to find thatthe beam tuning will take a longer time than before.

BT2
BT1

BT2

BT1

MDI, 19.Oct.2023, Injection, N. Iida

Bending magnet chamber

The bellows were replaced with ones with a 13mm offset on the left and right sides.

19

K. Shibata
MDI, 19.Oct.2023, Injection, N. Iida20



The cause of injection emittance blowup in BTs are still mystery.



In the next BT dump mode operation in DecemberIn the e+ BT, we will study if the horizontal emittance blowup in the e+ BT is suppressed or not.


If YES, we know that CSR is the cause, or if NO, we need to consider other causes.

We also plan to conduct a study to improve the accuracy of emittance measurement forinvestigating the emittance blowup.

MDI, 19.Oct.2023, Injection, N. Iida

21

5. SBL : What is “Sudden Beam Loss”
Beam loss that occurs suddenly within 1 turn
(10µs) without precursory phenomena. ＝Sudden Beam Loss （SBL）


The cause of SBL is unknown.



A significant percentage of the beam is lost
before the abort trigger is applied.

Beam signal measured by
Beam Oscillation Recorder(BOR) & Bunch Current Monitor(BCM)→ Harmful effects of SBL;

Damage to collimators and other accelerator
components,

Quench of the final focusing superconducting
magnets (QCS),

Large backgrounds to the Belle-II detector,

Inability to store high current due to beam abort.

22

23

Sudden Beam Loss (SBL) : Observation
The beam suddenly disappears just before the abort.

Beam loss occurs in both HER and LER, but the damage to the hardware isparticularly large when loss occurs in LER.



We don't know if it will happen even with a single beam or low current
beam because we haven't operated for a long time.

The starting point of beam loss depends on the tuning of the collimatorand is not limited to a specific location.



Just before the beam loss begins, the orbit appears to move, but its value
is small～O(0.1 mm).

The orbit is changing < O(1mm) after the beam loss.

No oscillations that could be precursors to beam loss are observed.

Pressure bursts have been observed all over the place and rarely occur inthe same place except at the collimator section.

Regarding the pressure of D06H3 and H1 collimators there are rapid or
nonlinear increase of pressure depending on the beam current.

24

SBL : Candidate Reasons for SBL
 Damage of vacuum component (RF Finger) @KEKB & PEP-II Beam phase changes (beam energy losses) observed ms to several hundred μs before aborts. → The time scale differs from that of SBL.
 Abnormal temperature rise at bellows chambers had been observed and the catastrophic damages in the RF-finger had been
confirmed. → We could not find that damage.
 Dust : Early stage @ SuperKEKB Vacuum chambers were cleaned or tapped to remove as much dust as possible.
 Electron Cloud SBL should be measured only in LER.→ SBL is also measured in the HER beam.
 Curious behavior of the pressure in D06H3 collimator may suggest the formation of a discharge or electron cloud.
 Simulations show that the electron density distribution changes with time and a maximum electron density is on the order of
1E13/m3 to 1E14/m3 → How this relates to SBL?
 Fireball : Measured @ RF cavity
 The vacuum chamber is made of copper with low sublimation point and collimator head is made of tungsten or tantalum with highsublimation point.
→ The situation has the potential for a fireball to be formed.
 This fireball hypothesis could explain SBL (~μs) due to the fast plasma evolution (~100 ns at the fastest).

25

SBL : Fireball

Fireball : Measured @ RF cavity



The vacuum chamber is made ofcopper with low sublimation point andcollimator head is made of tungsten or
tantalum with high sublimation point.

→ The situation has the potential for afireball to be formed.
This fireball hypothesis could explain
SBL (~μs) due to the fast plasma
evolution (~100 ns at the fastest).

26

SBL : Work during LS1
For preventing SBL
Replacing damaged collimator head.



Copper coating of collimator heads (D6H3, D6V1, D5V1, D2V1). （Cover material with a high sublimation point,
which could be the seed of a fireball, with material with a low sublimation point.)

Installation of permanent magnets in all SuperKEKB-type horizontal collimators. （In order to reduce the electron
cloud effect…）


LER D02H4, D02H3, D02H2, D02H1, D03H1, D06H3, D06H4



HER D01H3, D01H4, D01H5

For investigation the cause of SBL

Add BOR to investigate beam orbit change in locations that may be the cause of SBL.


Measure the orbit at two different locations with phase differences.



Add a simplified version to measure in phase with the collimator, although with less accuracy.

Install acoustic sensors to observe the sound when the Fire-ball occurs.(D2V1:minimum physical aperture, D5V1:newcollimator)

Add loss monitor for timing measurement

2023-09-15 v1 Tetsuo ABE: Acoustic sensor

1

2

5

4
3
X
Acoustic loss monitor?

On the undersidein the same manner

28

Summary

There are many factors of limiting luminosity.
Beam size blowup



Optics & Orbit

Beam Lifetime

InjectionSudden beam lossHardware that could be addressed in LS1 was addressed.

In addition, monitors were prepared for a better understanding of eachproblem and to prepare for future operations.

29International Task Forcecollective effects



injectionbeam tuning



SBL



IR Upgrade

30

backupBeam-Beam Parameter
Vertical beam-beam parameter

𝜀𝑦− = 25𝑝𝑚

𝜀𝑦+ = 35𝑝𝑚

Vertical beam-beam parameter (incoherent)

Bunch lengthening is an important parameter.
Here, the nominal bunch length is used.

physics run and HBC - High Bunch Current Study (393 bunches)

Beam-Beam parameter in the LER is alreadylarge at 0.8 mA.
31
Especially, incoherent tune-shift is 𝜉 ~ 0.065. (-15% due to bunch lengthening)

Y.OnishiProgress and outlook for emittance blowups of the injection beam
e- beam

Issue

Solution

LS1

Sometime after LS1

Horizontal emittance gex
growth (Charge dependent)

Cancellation of
CSR

Exchanging to thenarrower chambers

Nobalance with budget

Low dispersion optics if goodunder consideration

New straight BT line

Nobalance with budget

Horizontal emittance gex
growth (Charge independent)

ISR

Vertical emittance gey growth

Still mystery

Longitudinal acceptance

Just barely in HER
acceptance

ECS installation(already decided)No

to be completed in
BT1 by 2024

e+ beam

Issue

Solution

LS1

Sometime after LS1

Horizontal emittance gex
growth (Charge dependent)

CSR

V. Offset of bendingin e+BT Arc1

Yes

will be studied in
DecemberLow dispersion optics

If goodunder consideration

Horizontal emittance gex
growth (Charge independent)

Blowup somewherefrom DR to BT1

Vertical emittance gey growth

Still mystery

Longitudinal acceptanceno problem

Low emittance
optics in the DR

under consideration

32

MDI, 19.Oct.2023, Injection, N. Iida

1. Pulsing quadrupole magnets
Y. Okayasu

33

J-ARC
Matching
sections •••Current optics at J-ARC

Replace 3 DC quads with 4 pulse
quads at both of entrance andexit.
Optics matching can be done forboth HER and LER beams.
By making beta functions in J-ARC
become small, the beam loss
there will be suppressed.
New optics at J-ARC
with pulsed quads

Sector 1-2•Δγε𝑥 ~ 100 um, 𝛽𝑥 = 45.2 m••

MDI, 19.Oct.2023, Injection, N. Iida

Y. SeimiyaΔγε𝑥 ~ 40 um, 𝛽𝑥 = 16.3 m

Y. Seimiya

End of LAS
cavityStart of Sband cavity
Bunch tail is kicked backby quad, and temporally
emittance is reduced.

e- beam

Emittance growth due tothe transverse wake fieldof e- beam will be
suppressed by the smaller
beta functions with the newpulsed quads.

Sector2 end
e+ target
Before optimizationachieved smaller
betatron function

e+ target

Sector2 end
After optimization

34

2. New accelerator structure

Mitigation of accelerating structure failures

Originally designed for 8 MeV/m (PF injector), but used at 20 MeV/m(KEKB upgrade)

Degradation that lead to high field emission rate and discharges



Water leaks, field emission , discharge in waveguide, and so on



Not only future Y(6S) but even Y(4S) could be suffered(29 of 60 units have some problems)

New S-band 2-m-long TW acc. structure

5-year upgrade plan to fabricate and install new accelerator structures (FY2018 –FY2022)

4 units (16 acc. structures) will be replaced by new one. (Unit44 in sector 4 was alreadyNew acc. structure: acc. gain ↑7%, surface field ↓20% (reduce breakdown)

New pulse compressor (SCPC) was also developed and installed in Unit44.

replaced in the summer of 2022)

H. Ego
MDI, 19.Oct.2023, Injection, N. Iida

35

3. Fast kicker for 2nd bunch orbit correction• Ceramics Chamber with integrated Pulsed Magnet• Magnetic field type kicker with four parallel coil wires• The current configuration described above• Parallel and anti-parallel currents generate horizontal dipole magnetic field (vertical beam kick)• Two fast kickers will be installed at the LINAC end and the electron BT line in this summer.
• Prototype one was already installed at J-ARC in summer 2022.

T. Kamitani, T. Natsui
MDI, 19.Oct.2023, Injection, N. Iida

1. BT ARC4 alignment
HER

LER

36

M. Tawada, M. Kikuchi
The surveyed electromagnet position (2018)
was analyzed.
- The HER was tilted 46 μrad relative to the BT
coordinate system- The QI4E position was offset by (2.9mm,2.73mm) from the BT coordinate system.
- The position of the electromagnets in the
4th arc was different from the "Official
Design" Optics.
Using the straight part of the ramp as areference, align the last four Q magnets andthe BPM (about 1 mm). All four Septum
magnets need adjustment.

Analysis of measured electromagnet positions (2018)- Both BT and LER electromagnet positions are misaligned by about ΔGy~2.5mm relative to design- Relative relationship between BT and LER electromagnets is almost
correct.
Using the straight section of the ramp as a reference, change the bend
angle of the 4th arc Bend design Align the B and Q magnets with the BPM
for the changed Bend. Septum needs to be readjusted.
MDI, 19.Oct.2023, Injection, N. Iida

Dynamic
aperture
(DA)
of
HER
for
injection
Simulation
Designed vertical emittance of injected beam(b) gex=100mm(a) gex=40~100mm
Recently, a wrong fabricationin canceling coil has been
noticed.
Reflecting this effect, allinjected particles no longer
entered in the DA as shown in(d).
However, by widening theaperture near the injection
point and by an improvementof the magnetic field of the
septum magnet in LS1,
it was found that the situation
recovers to some extent asshown in (c).

In the future
Tracking simulation of
HER injection under theconditions below to
obtain the injection
efficiency.
MDI, 19.Oct.2023, Injection, N. Iida

gey=20mm
2000 turns

37

Measured best emittance of injected beam

gey=50mm
2000 turns±5s~6.3s

2JX=0.76mm±4s(c) gex=100mm
gey=50mm
2000 turns

2JX=0.76mm

Injectedbeam

After LS1w cancel coil error
and large injection oscillation(d) gex=100mm
gey=50mm
2000 turns
2J =1.1mm Injected
X

beam

38

5. Convert screen monitor to OTR
e- for HER

e+ for LER

Beam size can be quantified by converting the screen to OTR, which enables
more precise emittance and energy spread measurement.
T. Mori
MDI, 19.Oct.2023, Injection, N. Iida

39

Beam Abort SystemIn order to protect the hardware components against the high beam currents, we installed thecontrolled abort system.

The beam is kicked by an abort kicker, taken out of the vacuum chamber through an abort window
made of Ti, and throwed into a beam dump.

Dumped beam length : one revolution time (10 μs).



Build-up time of the abort kicker magnet : 200 ns (empty bucket space).

Synchronization of the kicker timing and the abort gap is required for the protection of hardware.



We minimized abort trigger time to protect the hardware damage.

Abort Trigger Delays
Beam Abort
requesta failure is detected…

Devicerequests
Abort> ~2μsHardware dependent

40

Beam Interlock system
Process

2 ~10 μs

earliest abort
request arrival to
CCR

Kicker fired

Beam Dumping
System waiting
for beam abort gap
3μs～8μs

All bunches
are aborted
max 10μs

t3t2t4
Synchronization of the abort request signal withrevolution/2 in FPGA.：Max delay=5μs
Delay to synchronize to the abort gap(fixed delay) :～0μs
Depends on the optical cable Delay from CCR to kicker (400m) : 2μs
length from the local control
Thyratron ON :1μs
room to CCR.
Rise time for the kicker : 200ns
Minimum Abort Delay = 17～30μs

t1
To summarize the abort
request on the beam abortsystem.

41

Observation : Beam Loss Monitor


Checked the loss monitor at
the time of abort occurrence
which was probably due tobeam loss.
↓

There were many instances ofsudden beam loss occurring
simultaneously in the entire
ring collimator section and in
the Belle-II detector.

42
Observation :Bunch Current monitor & Bunch Oscillation Recorder••

The beam suddenly
disappears just before
the abort.
Beam loss occurs inboth HER and LER, but
the damage to thehardware isparticularly large whenloss occurs in LER.

Abort

10µs=1turnObservation :Loss Monitor Specialized for Timing
Measurements

We checked the starting point of
SBL in the ring by using loss monitors
specialized for position identification

The beam loss mainly started at the
D06V1 collimator (a narrow aperture
to suppress background to Belle-IIdetector).

When the D6 collimator wasdamaged and the aperture waswidened, beam loss began in theD2 collimator section near the IR.

43→The starting point of beam loss
depends on the tuning of the collimatorand is not limited to a specific location.

(Y.Liu)44

Observation : Beam/Bunch Current Dependence

It is likely to occur
when a certain
bunch current isexceeded.

We don't know if itwill happen evenwith a single beam
or low current beam
because we haven't
operated for a longtime.

(K.Matsuoka)

45

Observation : Beam Orbit

Just before the beam loss begins,
the orbit appears to move, but its
value is small～O(0.1 mm).

The orbit is changing < O(1mm)after the beam loss.

No oscillations that could be
precursors to beam loss areobserved.

46

Observation : Beam Size

We checked for beam size fluctuations byinstalling an ultra-high speed CMOS
camera in the X-ray monitor to take 1µs
data at 100kHz when the abort is triggered.



There was no sign of a significant change
in beam size before the SBL.

Status of LER collimator

47

Name

Type

Tip Material(): longitudinal length in mm

Tip Condition

Remarks

D06H3
D06H4
D03H1
D02H1
D02H2
D02H3
D02H4

SuperKEKBSuperKEKBSuperKEKBSuperKEKBSuperKEKBSuperKEKBSuperKEKB

Cu coated C (160)
Ta (10)W (10)W (10)W (10)W (10)W (10)

healthyhealthyhealthyhealthyhealthyhealthyhealthyspoiler against inj. kickers’ accidental firings
absorber against inj. kickers’ accidental firings

D06V1
D06V2
D05V1
D02V1

SuperKEKBSuperKEKBSuperKEKBSuperKEKB

Cu coated Ti (10)hybrid (3)Cu coated Ta (4)Cu coated Ta (10)healthyhealthyhealthyhealthy(T. Ishibashi)Status of HER collimator
Name

Type

D09H1
D09H2
D09H3
D09H4
D12H1
D12H2
D12H3
D12H4
D01H3
D01H4
D01H5

KEKB
KEKB
KEKB
KEKB
KEKB
KEKB
KEKB
KEKB
SuperKEKBSuperKEKBSuperKEKB

Tip Material(): longitudinal length inmm
Cu coated Ti (40)
Cu coated Ti (40)
Cu coated Ti (40)
Cu coated Ti (40)Ti (40)Cu coated Ti (40)Ti (40)Cu coated Ti (40)W (10)W (10)W (10)

D09V1

KEKB

D09V2
D09V3
D09V4
D12V1
D12V2
D12V3
D12V4
D01V1

KEKB
KEKB
KEKB
KEKB
KEKB
KEKB
KEKB
SuperKEKBTip Condition

Drive
Mechanismdamageddamageddamageddamagedhealthydamagedhealthyhealthyhealthyhealthyhealthy-

Cu coated Ti (40)damagedupgradedCu coated Ti (40)
Cu coated Ti (40)
Cu coated Ti (40)
Cu coated Ti (40)
Cu coated Ti (40)
Cu coated Ti (40)
Cu coated Ti (40)
Cu coated Ta (10)healthyhealthyhealthydamageddamagedhealthyhealthyhealthy

Remarks

Plan to replace with new jaw (Cu coatedTi (40))upgraded
upgraded
upgraded-(T.
48Ishibashi)Layout of LINAC, BT, Injection to MRe+ beam is injected into the LER via DR:
The injection BG is not almost affected by thebeam condition at upstream of the DR.

49

e- beam directly injects into HER:
The injeciton BG is directly affected by thecondition of RF-gun, LINAC, and BT.
Injection Points

LINAC
1.1GeV Damping Ring (DR)for positron

Jarc

primary e- for e+: Thermionic Gun
e- : RF Gun
Sector B Sector A
Sector C

Sector1

BCS
Sector2

Beam Transport line (BT)
Arc4
BT2

LTR

ECS

BT1

Sector3

Sector4

ECS
for e+

Slope2Arc2-3

Sector5e+ target

BT1 and BT2: Wire scanners(WSs), MSE.10:OTR
BCS: Bunch Compression System (for e+)
MDI, 19.Oct.2023, Injection, N. Iida
ECS: Energy Compression System (for e+)

Arc0

BT1

Arc1

MSE.10(OTR)(=BT1.5)

50

RF SystemRF system is operating stable.



For more stable and long-term operation, we will continue to conduct regular inspections
and update equipment of RF system.

Beam current limit by the present RF system is evaluated.
 RF power delivered to beam

: LER 3.6 A (design), HER 2.2 A

 HOM power absorbed by dampers: LER 2.6 A, HER 2.0 A

 For HER, the adding two RF stations and the reinforcement of the cooling capacity for

HOM damper cooling are necessary.

Stability analysis of RF accelerating mode (zero mode) was performed in SuperKEKB
operation conditions.
 The results showed effective measures without requiring big budget to improve thestability. And the results could be used as guidelines for future beam operation by
M.Nishiwaki KEKB ARC2022, RF systemincreasing the beam current step by step.