for Talk

Beam injection
in 2021ab(Feb.-Jul.)
SuperKEKB Review Committee
1st Sep. 2021
N. Iidafor Emittance preservation task force→ Beam Injection task force
Contributions by T. Abe, Y. Funakoshi, K. Furukawa, H. Ikeda, H. Kaji, T. Kamitani, T. Kawamoto, M. Kikuchi, T. Kobayashi, K. Kodama, K. Matsuoka,
T. Mimashi, T. Mitsuhashi, G. Mitsuka, T. Miura, F. Miyahara, T. Mori, H. Nakayama, T. Natsui, M. Nishiwaki, K. Oide, T. Oki, Y. Ohnishi, Y. Seimiya,S. Terui, Y. Suetsugu, R. Yang, M. Satoh, M. Yoshida, K. Yoshihara, S. Tanaka, M. Tawada, M. Tobiyama, K. Shibata, H. Sugimoto, H. Sugimura, T. Ueda,
Y. Yano, …, and all MELCO operators
Beam injection in 25th MAC, N. Iida

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Contents
1. Injection status of LER
2. Injection issues of HER① Poor “raw” injection efficiency (30-70%)② Unstable injection• Septum angle and position tunings were constantly necessary,
everyday, every shift, after every abort, …

3. Emittance blowup in the beam transport line (BT)• e• e+4. 2 bunch injection• HER (0% efficiency for 2nd bunch !!)• LER (~80% efficiency for 2nd bunch)

5. Others
6. Long term plan
7. Summary
Beam injection in 25th MAC, N. Iida

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1. Injection status of LER• The injection of 1st bunch(75~100%) is no problem,
but for 2nd bunch it is about
10% worse.
• The beam background toBelle II is larger than HER• Nakayama-sanʼs talkRaw injection efficiency
1st bunch
Average
2nd bunch2. Injection status of HER① Poor “raw” injection efficiency (30-70%)• Background at VXD is low.
• A recently simulation:•••

The injected beam mainly losses at the vertical collimators.
The main losses are due to the emittance growth or/and optics
mismatch rather than the injection oscillation.
The 70% injection efficiency can be explained.

• The magnetic field of the septum magnet
The field is getting lower as approaching the septum wall.
M. Kikuchi

einj=70.0%
・・・

dpy (rad)This may cause the transverse
tails of the injection beam.
Optics matching can suppress
it and it is expected that thecollimators can opened.

10,000 particles.
collimator setting on Jul. 1.
synchrotron radiation & strong
weak beam-beam are included.
No bunch-by-bunch FB.

px (rad)•Injected beam
20 turn4000 turn2. Injection status of HER (2)② Unstable injection• The injection tuning, septum angle and position must beset larger.
• After abort (a halt of injection), the septumangle(~40µrad) must be lowered temporally.
• The Raw injection efficiency does not depend on thebunch current.
• The residual radioactivity downstream the injection quad
has been one of the maximum level, 2.6mSv/h !
• The injection channel starts here.

• The output of the septum may depend on thetemperature of the capacitors in the power supply.

• Monitors are indispensable & urgent!
• Monitoring and logging of the septum
output current are extremely urgent.
• Injection-BPM is now progressing.
•3. Emittance blowup in BT• e• No obstacle has been found in thechamber of e- BT line.
• An SRM in the HER newly joined
the emittance measurements.

e+e-Horizontal• The reason why the horizontal emittance
growth between BTp1 and BTp2 is notresolved.
• The dispersion leak from ECS at SY3 will
be corrected by installation of a quad at
the center of chicane in the ECS in Aug.
2021.

• Synchrotron radiation causes the blowupof the horizontal emittance from 30 µm to76 µm.
• The emittance growth due to CSR effectis not confirmed yet.

Vertical• The vertical emittance growth can belower by installation of residual skew
quads for the correction of skew quadcomponents from the bends in Arc2-3.

• The vertical emittance growth should beresolved.
• Unexpected vertical dispersion has
been observed in Arc-1.

3. Emittance blowup in BT
Measured emittance and b-mismatch(BMAG) in e- BT：ge with WS●：gex measured with OTR●：gey measured with OTR● ：ge with SRM+gatedcamera●

•gex
(µm)

The emittances weremeasured larger by errors ofmeasuring systems of Q-scan.
• The HV sets were too high tomeasure the small beam size.
• Now the measured
emitttances are not explored
but still blowup.
●BMAGxBeam injection in 25th MAC, N. Iida

QMD4EBMAGy

QCD4Egey(µm)●8BTeY. Seimiya

M. Kikuchi, Y. Seimiya, N. Iida

① Changing dispersion patternand emittance measurements
for CSR study
BT2(0)(2)

Jul. 5gex [µm]BMAGx

gey [µm]

BMAGy

(0)

116.4±2.2

2.10

143.7±1.71.65(1)

108.3±2.1

3.13

113.9±2.42.77(2)99.6±1.3

2.34

149.5±1.91.56(3)97.7±1.1

2.14

113.6±1.4

2.27• The horizontal emittance of (3) issmallest.
• From these results, the CSR effects
are not clearly observed.

Some hints in the Arc-1
for the vertical emittance ?
(1)

The vertical dispersion is not
generated under thechanged dispersion in ARC1(3)Study with 2nC beam should be done.
• The vertical emittances of (1) and(3), in which the dispersion of Arc0changed, are small.
Beam injection in 25th MAC, N. Iida

② Seimiya-san is analyzing which quad with skew component
explains the leakage of this unexpected vertical dispersion function.

94. 2 bunch injection

e- BT
5/26

• HER

1st bunch: 65%• Injection efficiency of 2nd bunch is extremely low• 2-bunch injection had been successfully done for 6days in Jun. 2020 !
• Parameters below have been checked.

Average
2nd bunch: 40%••••

Orbits from LINAC to BT line
Beam energy at BT line
Kicker timing of HER
Emittance growth only for 2nd bunch between Sector Cand Sector 2• Timing mismatch in the RF phase in HER ?

The injection efficiency of 2ndbunch became a little bit higher.

5/28

• LER

1st bunch: 40%• 2-bunch injection is used for usual operation• 2-bunch injection was succeeded in Feb. 2021 bytuning an LLRF feedback loop in the DR.
• Injection efficiency and background of 2nd bunch areworse than those of 1st bunch.

Average
2nd bunch: 15%
Beam injection in 25th MAC, N.
Iida

Beam injection in 25th MAC, N. Iida10

But after 2 days 2nd bunch
can no longer be injected.

2 bunch injection and BG in 2020b e- injection
e+ injection

Injection
efficiency

VXD diamonds(BG monitors)

No problem !
At the beginning, the BG was low and no problem
with good injection efficiency, but it became
difficult to inject further for unknown reasons.

at this time without
any tuning…

This has been resolved !
Beam injection in 25th MAC, N. Iida

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5. Another improvement for operation• The “Fuji-mode” will be ready at 2021c operation.
• BT dump mode operation can be done, even if people enter the halfof the SuperKEKB tunnel, including Tsukuba area.
• The beam study in BT can be performed short works during theusual operation as well as in the long shutdown.
• Even in LINAC mode, there is an advantage that e- and e + can bestudied at the same time. (Currently, only one beam can bestudied. )6. Long term plan
• e- ECS in KEKB/BT lineuntil 2026
• Preparing by Mitsuhiro
Yoshida and H. Ego from2022.

• New e- BT line in the
AR/BT straight tunnel ?
• For smaller horizontal
emittance growth due to asynchrotron radiation• There may be no
mysterious emittance
growth.

KEKB

/ BTC
LINA

AR/BT

• e- Damping ring in theJarc ?
• Polarized e- beam ?

Beam injection in 25th MAC, N. Iida

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Summary1.

LER injection•••(same as P. 5)
2.

Poor injection efficiency for HER
•••
•

3.

The injection efficiency of 1st bunch is about 90%.
The injection efficiency and the BG of 2-bunch injection are much worse than 1-bunch.
LER 23 Hz operation is available.
The septum angles of the injection tuning panel are different from the design values. -> will be fixed.
The injected beam mainly losses at the vertical collimators.
The losses are not from injection oscillation but emittance growth or/and optics mismatch.
The 70% injection efficiency has been reproduced in simulation.

Septum position and angle drifting at the HER injection ?
•••
•

4.

The magnetic field of septum is changing ?
Beam losses right after the septum exit causes one of the highest residual activation in the main ring.
If the beam loss is decreased placing the orbit apart from the septum wall.
Monitors and logging for pulsed magnets are necessary.

Emittance blowup is still problem
•

HER
•
••

•

5.

Beam injection in 25th MAC, N. IidaLER•

A quad will install in the center of the chicane in SY3 for the correction of dispersion leakage.

•Residual skew quads in the ARC2-3 of e+ BT line

2-bunch injection•

6.

Synchrotron radiation increases the horizontal emittance.
Study for CSR effects is in progress.
The source of vertical blowup is still in question.

Injection efficiency of 2nd bunch is extremely low for HER.
•Emittance of 2nd bunch should be resolved.

•2 bunch injection of HER had been successful for 6 days in Jul. 2019.

Long-term plans are just begun to be considered.

14Questions from Catia-san•Slide 12: on the base of which considerations have you selected the collimator to open?
Belle II people opened.
Maybe, the collimators which are effective the injection from their experience.
Slide 16: i t seems that QCS aperture does not plays a main role in reducing injection efficiency
Yes, I think so, too. The injection beam with such emittances without mismatch are in the HER dynamic aperture.
Slide 30-31: did you observe any seasonal trend in the septum displacement in HER?
P. 26 shows more than one year. In 2020b, the septum angle and position were not changed higher, rather lower.
Have you to optimize septum position and angle in the LER too?
Yes, we did, but it was not so frequent as HER.
Slide 33: do you observe any drift of the stored beam orbit in the injection section as a function of the stored beam
current?
No, I have not yet. I will check it.
Slide 36: Monitoring pulsed power supply might be useful too.
Yes, the monitor setting is urgent !
SLIDE 65: vertical emittance reduction observed during the DR studies with 80 msec storing time suggests that aDR might improve the injection efficiency in HER, as you outline in your conclusions and future perspectives.
Yes, the smaller vertical emittanceis better.
The blowup in the vertical emittance in BT must be resolved as soon as possible.
SLIDE 66-67: have you already tested 2 pulse operation with the new optics?
No, we have not. The optics change has not succeeded yet. The next step is optics correction in the DR.