65th ICFA Advanced Beam Dynamics Workshop on High Luminosity Circular e+e- Colliders (eeFACT2022)
2022/09/15 WG6: Injection (parallel)

KEK e+/e- Injector Linac
Takuya Natsui
KEK1

Introduction of KEK LINAC

2

KEK Linac and 5-rings

PF-AR Ring

PF Ring

SuperKEKB HER, LER

InjectoDumping Ring

SuperKEKB injector is called J-Linac.
It is not only for SuperKEKB rings but
also for light-source rings.
We realized simultaneous top-up
injection to 4-ring.

rLi nac(J-Li nac)3

Injector Linac

A sector

FCTargetC sectorInjector DC gun
RF gunRF gunR sector(J- arc)

B sector

This is a brief introduction to an injector linac.
We use J-Linac. It consists of 8 sectors and Jarc. Two types of electron guns are used forelectron generation. A Photocathode RF gun isused for electron beam generation.
A thermionic DC gun is used for positron
primary electron generation. It is converted topositron with target and Flux Concentrator.

Dumping
Ring

Pulse magnet

LAS

1 sector

2 sector

Flux Concentrator (FC)and Positron Target

3 sector

4 sector

Thermionic DC Gun

5 sector

Photo cathode RF gun

4Electron beam
DC gunA sector

4 nC electronbeam
FCTargetC sector

RF gunRF gunR sector(J- arc)

B sector

Dumping
Ring

Pulse magnet

LAS

1 sector

RF gun and laser system generates low
emittance single bunch beam.
This RF gun has Quasi-traveling-wave side
coupled cavities. In the simulation,normalized emittance is under 6 mm-mradin 5 nC.
It is enough spec for SuperKEKB.

2 sector

3 sector

4 sector

5 sector

4 nC, 7.0 GeV

Quasi-traveling waveside coupled cavities

Emittance is 6 mm-mrad in simulation 5Positron beam

10 nC electron beam
DC gunA sector

FCTargetC sector

RF gunRF gunR sector(J- arc)

B sector

DumpingRing

The positron beam is converted from a 10nC electron beam. This 10 nC electron beam
is generated with a thermionic DC gun.
Accelerated 3.3 GeV 10 nC electron hit thetarget and focused with Flux Concentrator.
A converted 4 nC positron beam is injected
into the dumping ring. Finally, a low
emittance 4 GeV 4 nC positron is generated.

LAS

1 sector

10 nC, 3.3 GeV
Electron beam

2 sector

4 nC, Positron
beam

Flux Concentrator(FC), Positron target

3 sector

4 sector

5 sector

4 nC, 4 GeV

6Injector line
We have two lines in the injector sector for positron and electron beam.

10 nC primaryelectron

4We have two types of electronguns. The first one is aphotocathode RF gun for HER
electron beam. Another one is athermionic DC gun for a primaryelectron for the LER positron beam.
These two beam lines merged byusing a pulse bending magnet.

eambnort
nC elec

Pulse Bend Magnet
7

Several energy beam generation on the same beamline.
The KEK LINAC feeds beams to 4-rings, the beam parameters are totally different. Since the energy is split in
the downstream part of the beamline, we must use different optics for each beam.
To achieve the simultaneous top-up injection, We use a pulsed magnet.

After J-arc, the liner region

We use pulse magnets(quadrupole and steering magnet)
8

Pulse quadrupole magnet and steering magnet
Quadrupole magnet
Quadrupole

Steering

ParameterspecReputation

50 ppsMax. Pulse Current300 A

Max. Average Current

100 A

Max. Field Gradient

60 T/mBore diameter

20 mm

Steering magnet

Typical magnet set at 3-5 sector of LINAC

Parameter

specReputation

50 ppsMax. Pulse Current

10 A

Max. Field strength44.3 mT

Pole gap

20 mm

Pole length

80 mm

9Pulse Q magnet driver
Flat region(0.5 msec)
Set any current value
within 3 msec
Magnetcurrent

Magnet driver
We developed a pulse magnet driver.
The maximum current is 300 A at 50
pps. This is an energy recovery type.
We can change optics at 50 pps byusing the driver and magnets.

Current rising(< 2 msec)

Pulse Q magnet current

Energy recovery
10Current beam status and commissioning
1.Electron beam for HER
2.Positron beam for LER

11

Linac beam status for SuperKEKB
2022abBeamEnergyBunch charge
1st , 2nd [nC]
Normalized
emmittance[mm-mrad]Simultaneous
top-upinjection

Final goale+
4.0 GeV

e7.0 GeVe+
4.0 GeV

e7.0 GeV

3.0 , 2.5

2.0 , 1.5

4.0, 4.0

4.0, 4.0

120, 550-20, 50-20(Hor. , Ver. )(Hor. , Ver. )4+1 rings(LER, HER, DR, PF, PF-AR)

100, 1540, 20(Hor. , Ver. )(Hor. , Ver. )4+1 rings(LER, HER, DR, PF, PF-AR)

This is the beam status of the final goal and current status. The energy was set to require value.
The beam charge is still not achieved. But it was almost enough in 2022b. Emittance was improved
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step by step. Simultaneous injection to 4 rings and dumping ring is already achieved.

History of electron beam charge injection to HER
One-year history except for the summer shutdown.

Electron beam charge [nC]

RF Gun generation

Linac endStart charge feedback(Laser feedback)2022, stable 2 nC beam generation was achieved with a laser feedback system.
The amount of charge is almost enough current situation. But sometimes required to increase
the charge. We have to increase the beam charge for the next SuperKEKB operation.

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2 bunch operation of electron beam
Horizontal orbit

Vertical orbit

ChargeSometimes we try 2-bunch operation.
But the injection rate is not so good. We use 1 bunch operation as usual.
Beam orbit seems good. But emittance value or energy spread is not so good, maybe.
2-bunch operation is one of the problems to be solved in the next operation term.

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Long-term emittance value drifts due to emittance growth in Linac.

Emittance value of beam from RF gun
is always small
RF gun generation

Beamadjustment
Em

End of Linac

icenttawt
ogr

h5 months
15

The measured emittance is meet the required value just after a beam adjustment. But the value
increases gradually.

History of the positron beam generation
One-year history except for the summer shutdown.

Positron beam charge [nC]

Primary electron
GunPrimary at target
Beam reducing
by LER request.

Positron generation

End of LinacPositron

We achieved a 3.5 positron beam generation. It is almost the target value.
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Two bunches
operationhistory of KBP

Gun 1st bunch
Gun 2nd bunch

End of Linac 1st bunch
End of Linac 2nd bunch

We succeeded in the two bunches
operation for KBP.
2nd bunch charge is almost the same as
1st bunch charge.
We could maintain a stable two bunches
injection to LER.
17

Long-term (a few years) charge history of positron(KBP) beam
In 2020ab, the conversion efficiency is lower.
Improvement of FC was getting an increase inconversion efficiency.
Now primary beam is over 10 nC, conversion
efficiency is almost the same as thesimulation value.
The next matter is how to increase thetransmission ratio.

12charge (nC)

10
8
6
4
2
0
15_T

16_5

design2020ab-run

2021a

2021b

28_4
position
2020ab-study
2021c

DC_4

58_4

2020c
2022ab(暫定)18Flux concentrator (FC) improve for positron beam
1
R1
6D1

Spike high voltage had beendamaging to FC head

100kRps2

DC 20k AC 0 01Lsy
0.5u/2511

1.4u C1

Lline1
0.25u/2

4V1

0.1
Rsy

0.2/2
Rline1121010n
Cline

Lline2
0.25u/20.2/2
Rline2

9L21u

80.1
Rfc
72

Lfc
1.1u

R7
13C4

3100n

SW1

・yoke shape optimization
・Insulator improvement

Y. Enomoto
The new FC is very robust. It was installedin 2020. No breakdown from 2020c.

As a result of the circuit simulation, we found amodification of the modulator to reduce the spikevoltage. A noise reduction circuit to the modulator wasinstalled in 2021, enabling even more stable operation.
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Linac Upgrade Plan 2022-2026• Pulse magnet• Girder Mover• electron ECS• RF gun• Positron target and capture• Acceleration structure• High efficiency klystron… and so on
20

Pulse magnet upgrade
Fast kicker
InjectorDC gun
A sector

FCTargetC sector

New large pulse Q
magnet and fastkicker

RF gunRF gunR sector(J- arc)

B sector

Dumping
Ring

Pulse magnet(already used)LAS

1 sector

2 sector

3 sector

4 sector

5 sector

We already use a pulse magnet in 3-5
sector.
But we need an additional pulse magnet
at J-arc for matching with both beam ofKBP and KBE
21

Now we donʼt have pulse magnets at B andC sectors due to a big beam aperture.
A sector

FCTargetC sector

RF gunRF gunR sector(J- arc)

B sector

DC gunDumping
Ring

LAS

1 sector

2 sector

3 sector

4 sector

5 sector

Beam loss at J-arc, because of common optics

22

8 large pulse magnets will be installed at entrance and exit of J-arc✔

✔
✔

✔

✔

Fast pulse kicker✔

Pulse Qmagnet✔
✔

このパッケージは元の位置から 450 mm 上流へ

Diameter : 44 mm✔

The new pulse Q magnet
has a large aperture forpositron primary23

A new pulse magnet driver is also developing.
3-5 sector typeNew driver

Max Voltage [V]

230

400

Max Current [A]

330600Magnet inductance [mH] 11.5

Control method

PWM

ID-VGE analog control

24Fast kicker for 2nd bunch

Fast kicker affects only 2nd bunch.
Pulse raising time must be under
96 ns. The fast kicker will be tested
next operation term.
25

New acceleration structure
The old acceleration tube must be replaced.
New structures have higher accelerating gradientand lower surface electric field.
We will replace it with a new accelerating structure
to reach a collision at the higher energy resonanceof (6S).

New accelerating structure is high quality

A new pulse compression
system was also developed.

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Energy Compression System (ECS) for electron beam
Install accelerating structure in electron BT

We make R56 in Arc0 of BTe

In the LINAC, we have ECS for only the positronbeam. We will install accelerating structures in theelectron BT line as ECS. We are currently preparing
the acceleration unit.
27

New positron rotation target and FC
Rotation target is very nice system for
not only positron beam but also electronbeam.
That way, both beam orbits will be on theaxis and big aperture for electron beam.

28

High efficiency klystron
Example of multi-beam klystron
1.3 GHz 10 MW, TOSHIBA(Canon)

Klystron efficiency is related to perveance (A/V^1.5).
Efficiency [%] = 78-16*uPv (well known empirical formula)
Currently, we use the old type of the S-band 50 MW klystron, with an efficiency of 45 %.
One of the new high-power high-efficiency klystron candidates is the multi-beam klystron.

29

High efficiency klystron3D magnet design

gun parameter
250 kV

Total Current

440 Ain8

im# of beam

aryVoltage

55 APrel

We are starting the design of ahigh-efficiency klystron for KEK
LINAC.
It will be replaced with an old typeklystron. It is designed to use thesame modulator.

uPv

0.44

Expected efficiency

71 %Expected output power

80 MW

Current

2D,3D electron gun simulation

1D,2D klystron simulation30

SummaryElectron beam• Beam charge is stable at 2nC.
• Emittance is almost satisfied with a required value.
Next challenges• 2 bunches operation.
• How to maintain good emittance.
• Increase beam charge, over 2.0 nC.
• Avoid emittance brow up at BT.
Positron beam
• Beam charge is almost reached the target value.
• 2 bunch operation is succeeded.
• Emittance is almost satisfied with a required value.
Next challenges• Increase beam charge to 4.0 nC• Stable operation.
• Avoid emittance brow up at BT.

Linac upgrade is ongoing.

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