June 3, 2024

SuperKEKB during2024a/b
Y. Ohnishi

48th B2GM
June 3 - 7, 2024 at KEK

2024ab Operation
Achievements until May 31
LER Current: 1450 mA
HER Current: 1160 mA
Number of Bunches: 2346
Peak Luminosity: 4.08 x 1034 cm-2s-1
Integrated Luminosity: 71.4 fb-1 / 77.4 fb-1
IssuesSudden Beam Loss (SBL)
Short Lifetime in LER
Beam Pipe Deformation due to SR Heating
Poor Injection Efficiency in HER2

Measure Against Seven Major Issues
1. Sudden Beam Loss➡ Copper Coating of Collimator Head, Additional Monitors (Acoustic Sensors, Loss Monitors, Specific TBT BPM)
2. Beam-Size Blowup due to Beam-Beam Interactions➡ Chromatic X-Y Coupling Correction, Reduction of Machine Error in IR
3. Beam-Related Background➡ More IR Radiation Shields
4. Injection Efficiency and Emittance Blowup in the Beam Transport Line

➡ Wider Aperture at Injection Point, Suppression of CSR by using Beam Pipe Offset (Shielding Effect) in BTp
5. Difficulties to Keep Beam Orbit Stable➡ Beam Pipe Deformation due to SR Heating, BPMs Push Quadrupole Magnets. Isolation of BPM Is Tested.
6. Short Lifetime and Narrow Dynamic Aperture with β*y Squeezing➡ Sextupole and Octupole Optimization
7. Beam-Size Blowup due to -1 Mode Instability in LER → Reduce Impedance and BxB FB Optimization
3

SBL → the Next Talk

4

Candidates of SBL Source

Knocker Study in 2016

Knockerat the Dipole Magnet

Y. Suetsugu, MAC 2011, 20165

Clearing Electrode
Wiggler Section

Photons Emitted from Beam Create Electrons.

Discharge due toBeam Current

Cupper
Al2O3 Insulator (0.2 mm)
Tungsten (0.1 mm)

e+ Beam →(A) Dust Drops
Photonse-(B) Dust (Al2O3) due to Dischargeee- (Photoelectrons)

Clearing Electrode (Prototype)

Dust Can Take an Electrical Charge by Photoelectrons.

(A) Drop due to Gravity
Low Beam Impedance

Dust(B) Discharge
6Turn Over the Top and Bottom

Dust

Cupper Coating ?

Dust in the Vacuum"Dust in the Wind" is a song recorded by American progressive rock band Kansas and written by band member
Kerry Livgren, first released on their 1977 album "Point of Know Return".

Beam-Beam Performance8

Crab Waist ON and OFF
Try HER → 60 %LER: CW 80 % / HER: CW 40 %Crab Waist Is Effective.
νy+ = .567
νy+ = .59

9

* HBC = High Bunch Current (393 Bunches)

Nonlinear Collimator

10Reduction of Impedance: Nonlinear Collimator
Nonlinear Collimator (D05V1) to Reduce Impedance (vertical)
About 60 % Improvement for BG Reduction
20 % Reduction of Impedance
Before LS1

Drop Beam Halo with Larger Aperture. → Low Impedance
K2 2Δpy =Δy2

OHO Section

After LS1

D05V1(Collimator)

Positronwiggler Section

Positron

Skew Sextupole
Pair (SNAP)

M = -I'
Damping time (msec):
X : 45.67757
Y : 45.68328

Z :22.84954

11Damping time (msec):
X : 52.99557
Y : 53.00312

Δψy = 2π to QC1RP

Z :26.50934

Nonlinear Collimator
Beam Halo Can Be Scraped by Larger Collimator Aperture.
This Can Reduce Impedance.

Vertical Angle (rad)2Jy = 46 μm
Skew Sextupole OFF: 0 (1/m2)

Skew Sextupole ON: -6 (1/m2)
pyy (m)Vertical Position
Collimator Head12

Beam Loss and Radiation Dose at OHO Experimental Area
D05V1 Works to Reduce Stored Beam Background.
Nonlinear Collimator (D05V1) Can Not Be Closed Very much due to High Radiation Dose at OHO Experimental Area.
We have to Use D06V1 to Reduce Radiation Dose. We Consider More Radiation Shield.

20 μSv/hLarger than What We Expected !

GammaNeutron
20 μSv/hRadiation Dose Rate < 20 μSv/h

13

LER

Pressure Burst at Wiggler Section and near D05V1 Collimator in LER
Vacuum Sensors (CCG)

Beam Current

SBL
Abort

Skew
Sextupole

D05

Skew
Sextupole

Nonlinear Collimator

D04/D07

D10/D11

D07 L09: s= 1614 m (Injection Kicker K1)
L20

D10 L06: s = 811 m (QW2NLP, Wiggler Section)
D10 L07: s = 820 m (QW3NLP, Wiggler Section)

L24 L25

Higher Order Mode Effect due to Pipe Structure ?
Positron Beam

Clearing Electrodes

L23

Positron Beam
L26

14

D05 L23: s= 2213 m
D05 L23: s= 2234 m
D05 L24: s= 2246 m
D05 L25: s= 2252 m
D05 L26: s= 2259 m

Beam Pipe Deformation
due to SR Heating

15

Isolation Between BPM Block and Quadrupole Magnet

HER

BPM Block (Beam Pipe) Moves in the Horizontal Direction due to SR Heating.
BPM Block (Beam Pipe) Pushes Quad.

BPM Block (Beam Pipe) Doesn't Touch Quad.

BPM Block is
supportedby Quadrupole
Magnet.
New Support

16

Quad. Displacement

BPM Block Displacement

Sudden Shifts
Sometimes Beam Aborts
10 μm

100 μmBPM Support Was Separated
from Quadrupole Magnet.

HERIsolation Works Very Well.

After Modification

1 V = 100 μm

No Displacement at I > 1 A

In addition,Optics Feedback Systems Are Working.
Orbit Offset Induces Optics Degradation.
LER also Has Similar Problem.

Beam Current

Beam Current

Lifetime18Lifetime in LER

LER

Lifetime VS Bunch Current

Vertical Emittance VS Bunch Current
Collision(2346)

Single Beam
(2346, Decay)
Collision(2346)

Collision(393)
SuddenLifetime
Drop

Vacuum Effect1⌧V /nb Ib+<latexit sha1_base64="lE/R+ldSktslW+Dvy3TIcBIm7uo=">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</latexit>

Touschek Effect<latexit sha1_base64="j+E9DAf80cjdpw5n4SSojdlR0ww=">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</latexit>⌧T /p"yIb+

Beam-Beam Blowup ?
orDipole Oscillation ?

Collision(393)Single Beam(2346, Decay)

I = 1.8 A
I = 1.4 A(2346 Bunches)

Lifetime at 1.4 A for Collision (2346) is about 300 s(Sudden Lifetime Drop) even though Beam Blowup. Beam-Beam ?

Lifetime: 300 s = Loss Rate: -4.7 mA/s at 1.4 A.
6.9 mA/s Can Be Provided by Linac > 4.7 mA/s
2-Bunch Injection: 2.7 nC (80% eff.) and 1.8 nC (60% eff.) with 23 Hz Repetition (BCE: -5 %)But It is Difficult to Increase Beam Current Larger than 1.4 A. The Reason is Unclear.
19

Lifetime in HER

HER

Lifetime VS Bunch CurrentSingle Beam(393)

Vertical Emittance VS Bunch Current

Collision(393)
Beam-Beam Blowup ?

Collision(2346)

I = 1.2 A
I = 0.8 A with 2346 Bunches
Vacuum Effect1⌧V /nb Ib+

Lifetime at 1.2 A is about 1000 s.
Loss Rate is -1.2 mA/s.

Touschek Effect<latexit sha1_base64="j+E9DAf80cjdpw5n4SSojdlR0ww=">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</latexit><latexit sha1_base64="lE/R+ldSktslW+Dvy3TIcBIm7uo=">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</latexit>⌧T /p1.8 nC, 2-Bunch Injection with 23 Hz Repetition→ 15 % Injection Efficiency"yIb+

Linac: 1st Bunch 1.9 nC, 35 % eff. 2nd Bunch 1.4 nC 20 % eff.
23 Hz Repetition → 2 mA/s20

Plan21

Plan and Achieved Beam Currents
A) High Current Plan
LER: 1.8 - 2.0 A / HER: 1.2 - 1.4 AB) Beta Squeezing Plan → 2nd Week until Endβ*y = 0.8 mm (includes Adiabatic Squeezing)
First Week in JuneWe Need to Investigate the Reason
that We Can't Increase Currents
Larger than 1.4 A in LER.
Dynamic Aperture, Physical Aperture, Beam-Beam,Vacuum, Instabilities, etc.
Poor Injection Efficiency in HER
Dynamic Aperture, Physical Aperture
Improve Luminosity Performance
Vertical Angle Scan in LER, CW 60 % in HER+ SBL Study22

Strategy Toward 2.4 x 1035 cm-2s-1
LLsp =Ib+ Ib nb<latexit sha1_base64="+SRgfvdhxFx/L1SC48DiIHoQ3b4=">AAAChXichVHLSsNAFD2N7/po1Y3gplgUQVqm4gtBFN0odKHW2oKVkMSpBtMkJGlBQ7Yu/AEXrhRERLf6A278ARd+gris4MaFN2lAVNQ7zMyZM/fcOTMjm5pqO4w9RYSm5pbWtvaOaGdXd08s3tu3aRtVS+F5xdAMqyhLNtdUnecd1dF40bS4VJE1XpD3l/z9Qo1btmroG86Bybcr0q6ullVFcogS44ms6NqmN1cqW5LiZj13RXTlMc8fU54uyp4YT7I0CyLxE2RCkEQYq0b8EiXswICCKirg0OEQ1iDBpraFDBhM4rbhEmcRUoN9Dg9R0lYpi1OGROw+jbu02gpZndZ+TTtQK3SKRt0iZQLD7JFdsTp7YNfsmb3/WssNavheDmiWG1puirHjgdzbv6oKzQ72PlV/enZQxkzgVSXvZsD4t1Aa+trhST03uz7sjrBz9kL+z9gTu6cb6LVX5WKNr58iSh+Q+f7cP8HmeDozlZ5cm0guLIZf0Y5BDGGU3nsaC1jGKvJ07hFucIs7oU1ICRPCVCNViISafnwJYf4DvgmWdA==</latexit>

Target Beam Currents of 2024abwith β*y = 1 mm
2.75 A / 2.2 A

2.08 A / 1.48 A
Increasing Bunch
Currents
We are Here.

Strategy for 1035
Increase Bunch Current. Max. Number of Bunches is 2346 (Design Value).
Sudden Beam Loss Problem Has to Be Fixed. Clearing Electrode Is SBL Source ? How to ?
Sudden Lifetime Drop in LER (Found in 2024b Run)
Larger Dynamic Aperture and Physical Aperture Should Be Realized by Sextupole Setting andBetter Detector Background Controls. (Trial and Error)
Beam Injection
Emittance Blowup in the Beam Transport Line (BT) Has to Be Fixed. No Concrete Solution so far.
Luminosity Performance at High Beam Currents

Nonlinear Magnetic Field in BTp

Single Beam Blowup Has to Be Suppressed Enough.
Reduce Machine Error (SR Heating Problem, also LER)
How to Squeeze Beta Function at IP ?
First Target is 0.8 mm. Then, Try 0.6 mm.
Machine Study Is Needed to Make Larger Dynamic Aperture (Longer Lifetime).

24

Appendix

25

We Consider Lower βx at Skew Sextupoles to Reduce Injection Beam Background as well as Stored Beam Background.

Vertical Kick at Skew Sextupoleβx at skew sextupole for D05V1 (nonlinear collimator)

Measured injection error:
2Jx = 2 x 10-6 mLER:εy = 20 pm

35σy<latexit sha1_base64="IntU9KiTOwHhdsKv/3gntOSLr2E=">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</latexit>

ny =yyLower βx at the skew sextupole is preferable for the vertical size larger than 35σy.

Y. Ohnishi

Injection

27