Upgrade status of the injector LINAC

Hiroyasu EGO
KEK Injector Linac division

BPAC Feb. 05, 2024

1

Contents• Issues: difficulties in stabilizing beam condition• Upgrade works and countermeasures against the issues• Summary

BPAC Feb. 05, 20242

Issue : Difficulties in stabilizing beam acceleration
Issue : Water leaks, field emission, discharge in the structures limit the operation of the rated acceleration
Countermeasures : New high-gradient accelerating structures

Water-leakage

Discharged damages

BPAC Feb. 5, 2024

Discharged damages of waveguide circuits

3Linac upgrades : Accelerating structures
UPGRADE : Successful completion of 5-year upgrade plan against deterioration of accelerating structures• 12 water-leaked structures were replaced with the new structures in the summer of 2023
• One unit (#44) reinforces beam-acceleration from 20 MV/m to 28 MV/m
SLED

SLED

New-type pulse compressor

KL_44B
KL_44

KL_44A

44Bに実装した新型パルスコンプレッサー• 10 deteriorated structures are still to be replaced
Remaining issues• Water leakage may occur in the future (Two structures suffered from the leak in 2023)• Production of 12 new structures start from this fiscal year (3-year plan)
BPAC Feb. 05, 2024

H. Ego4Issue : Difficulties in stabilizing beam condition

Best tuning condition is destroyed gradually in a day

2022.5.29 8:42:42

2022.5.29 13:18:53

x-position

y-position

chargeBeam orbit and emittance of electron beam
tuned fine in the morning

BPAC Feb. 05, 2024

Beam orbit unstable and emittance worse
charge lost in the afternoon

5Issue : Beam-degrading areas
J-ARC
BT

Inflexible optics
for matching of ebeams

Unstable beam in BT
by bare longitudinalemittance, selfinduced SR and so one+ capture

Suitable focus for e+ beam but weak focus for e- beam

Horizontal orbit

Vertical orbit

ChargeBeam position in LINAC and BT to HER
BPAC Feb. 05, 2024

6

LINAC upgrades : Beam optics 1Issue : Beam loss, emittance deterioration in the J-ARC
Countermeasure : Large-aperture pulsed Q magnets

e- beam orbit
Bmag YY. Seimiya

Large-aperture pulse Q-magnets

cit
poenFi

Bmag Y

Bmag Xamsgnihct

Matching simulation• At the entrance and exit of 180 deg. J-ARC region, a good optics
matching is indispensable to mitigate beam loss and emittance
growth.
• Simultaneous matching for both of HER and LER injection beams
requires the pulsed Q magnets.
• From the simulation results, four pulsed Q magnets at the entrance
and exit of J-ARC are required for the matching.

Large-aperture pulse Q-magnets

BPAC Feb. 05, 2024

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LINAC upgrades : Beam optics 1
UPGADE : Installation of the new pulsed Q magnets in J-ARC• Large-aperture pulsed Q magnets installed in the summer of 2023
• New high-power pulsed power supply of energy-recovery type driving the pulsed Q magnet up to 600 A - 400 V600
500

Large-aperture pulse Q-magnets
I [A]

400
300
200
1000234567Time [ms]pulse interval 20 ms

Bore diameter : 44 mmInductance : 1 mH
Magnetic gradient : 20 T/m @ 600 A

・Energy recovery low-loss, compact, high power supply

・Drives the large-aperture pulsed quadrupole magnet up to 600 A

・Rise and fall speed 2.5 ms supporting pulse-to-pulse current change
K. Yokoyama, T. Natsui

・Energy recovery efficiency > 83%BPAC Feb. 05, 2024

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LINAC upgrades : Beam optics 1
Wire Scanner data history

2024/02/02 15:31

UPGADE : Installation of the new pulsed Q magnets
Beam Mode inKBE J-ARC
Bunch 1stSector Selection

Bsec• Large-aperture pulsed Q magnets installed in the summer of 2023
Wire Selection

Start date 2024-02-02

3-wire:ABCCsec

2sec

3-wire:ABDTime Span

LTR

3sec

3-wire:ACD-1year5sec

BT

3-wire:BCD

4-wire:ABCD• New high-power pulsed power supply of energy-recovery type driving
the pulsed Q magnet up to 600 A - 400 VShow plot Emittance Bmag Charge Auto-cutoff-data disable
UpdateOld opticsoptics√βx,√βy (√m)

12√βx√βy10810844200ηxp, ηyp (mm)12662

Large-aperture pulse Q-magnets

export: CSVNew low-beta low-dispersion

ηxp
ηyp

500

500

00-500-500

010203040506070 m

0Y. Seimiya
10203040506070 m

Z [m]

Z [m]

Optics matching results of HER beamMarkedly improved
BPAC Feb. 05, 2024

9Linac upgrades : Beam optics 2Upgrade during LS1
Upgrade during LS1
Pulsed Quads atIssue
J-ARC
for elowbeta(cont’d)PulsedQuads
atoptics
J-ARC
fore- low
beta
optics(cont’d): Weakfocusfor
HER
electronbeam
in 1-2
sector(positron-capturesection)ly these four pulsed
quadsonly
are optimized
forthe ebeam,thebetatron• Afterthese fourCountermeasure
pulsedquads
areoptimized
fortheebeam,thebetatron: Large-aperture pulsed Q magnets
can be decreased. function can be decreased.
on result shows thatit can help result
to decrease
lesshalf. the emittance less than half.
• Simulationshowsthethatemittanceit can help
tothandecrease
Old optics

New optics

Δγε𝑥 ~ 100 um, 𝛽𝑥 = 45.2 m••

End of LAS cavity
Start of S-bandcavity••

Bunch tail is kicked back byquad, and temporally
emittance is reduced.

e+ targetΔγε𝑥~ 40𝛽𝑥 m= 16.3 mΔγε𝑥 ~ 100um,𝛽𝑥 um,= 45.2Δγε𝑥 ~ 40 um, 𝛽𝑥 = 16.3 m• Large emittance e+• The four pulsed Q magnets

End of LAS cavity
Start of S-bandcavity

beam is accelerated from0.1 GeV to 1.1 GeV for
DR injection.
Bunch tail is kicked back bytemporally
O p andera
tion of DC Q
• quad,emittance is reduced.
achieved
smaller for-magnets
is optimized
e+ betatronbeam. function• For e- beam (3 to 4GeV), the focusing force
is so weak as to cause
its emittance growth.

Sector2 end e+ target
e+ targetachieved smaller
betatron function

Sector2
end end e+ target
Sector2

Sector2 end

Before optimization
After
optimization
BeforeDec.
optimization
KEKB Accelerator Review Committee,
13-14, 2022
optimization
Y.2022
Seimiya 30
KEKB Accelerator Review Committee, Dec.After
13-14,BPAC Feb. 05, 2024•

can optimize both the eand e+ beams, thebetatron functions can bedecreased.
Simulations shows thatthey can help to decrease
the emittance growth toless than half.

Y. Seimiya 30

10Linac upgrades : Beam optics 2
UPGRADE : Installation of four large-aperture pulsed Q magnets

BPAC Feb. 05, 2024

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Linac upgrades : Beam Control - Machine learning
Issue : Loss of positron charge
UPGRADE countermeasure : Machine-learning control + Large-aperture pulsed Q magnets

x-position

y-position

Charge~100% beam passing
through J-ARC
Electron gun
10 nC

TargetMarkedly reduction in beam loss

Beam dump

Bunch charge : 3 → 5 nC

Electron gun

TargetBeam dump

BPAC Feb. 05, 2024

12LINAC upgrades : Beam optics 3Issue : Low injection efficiency of 2nd bunch in double-bunch operation
Countermeasure : High-speed pulsed kicker

Bunch 1

Bunch 2

• Double-bunch acceleration (spacing: 96 ns) is employed forboth e- and e+ beam deliveries at an injection frequency (< 25Hz).

HER injection efficiencies• Injection efficiency of the 2nd bunch is usually lower than that of
Vertical beam positions in LINAC

Bunch 1Bunch 2

the 1st bunch in both e- and e+ beam operations.

• One of the reasons is the beam orbit difference between 1st and2nd bunches.

N. IidaBPAC Feb. 05, 2024

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LINAC upgrades : Beam optics 3
UPGADE : High-speed pulsed kickers• Fast kickers kicking only 2nd bunch transversely to correct
the orbit difference between 1st and 2nd bunches• Sufficient current response time (< 96 ns)

C. Mitsuda, T. Natsui,
Y. Okayasu

HSPK at the entrance of J-ARC

HSPK at the exit of LINAC

BPAC Feb. 05, 2024

HSPK at SY3 in HER-BT
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LINAC upgrades : Beam optics 3
UPGADE : High-speed pulsed kickers
Success in independent beam-orbit control of 2nd bunch only
Only the 2nd bunch is controlled by using the high-speed kicker

2nd bunch

1st bunch

Operating region: 2nd bunch kicked independently
Without using the high-speed kicker, the two bunches are on the same position.

T. Kamitani
Kicker positon
BPAC Feb. 05, 2024

15

Linac upgrades : Injection efficiency
ECS reduces the longitudinal emittance of electron beams for HER

We are exploring what causes the degradation of beam quality in BT

UPGRADE : Installation of BTe in 2024

UPGRADE : To be shown in the next BPAC

N. Iida, Y. Seimiya, T.
Yoshimoto

M. Yoshida

Findings:• No bunch-charge dependence of beam emittance in BTparcs 2 and 3 was observed.
=> No wakes, No CSR wakes.
S-band 3m-long TW structures• There would be magnetic errors to explain the horizontalemittance growth.

• High-power RF sources prepared• Successful operation of 3 m-long TW accelerating structures
up to a rated power of 55 MW in the test bench• Waveguide system under fabrication
BPAC Feb. 05, 2024

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Summary• Upgrades in this year carried out as planned• New accelerating structures against deterioration smoothly installed and operated• Beam optics improvements by installing new large-aperture pulsed Quads at J-ARC andpositron capture section• Demonstrated high-speed kickers for 2nd bunch orbit correction• Arrangements of RF sources and accelerating structures for ECS in the electron BT
Waveguide system under fabrication and ECS installation to be carried out in this FY• Beam degradation in the BT lines to the MR rings under exploration

BPAC Feb. 05, 2024

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Summary2018

2019

2020

2021

2022

New S-band structure
４prototypes

tests & installation✔

Installation

12 structures

Design✔

New pulse compressor
Designprototype2023

real #1 & installation

2024

✔

real #2✔
✔

Large-aperture pulsed Q magnet
DesignFabrication

Installation

High-speed pulsed kicker
DesignPrototypeInstallation

2025

More fabrication
BTe-ECS

Design✔

RF Source
Accelerating structures

Waveguides
Installation
Other instrumentsAir conditioners renewal✔

Automatic beam tuning
Beam diagnostic line

LS1
BPAC Feb. 05, 2024

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Thank you

BPAC Feb. 5, 2024

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