Injector Linac Status
Takuya Natsui

Injector Linac
Injector DC gun
A sector

FCTargetC sector

RF gunDumping
Ring

RF gunR sector(J-arc)B sector

Pulse magnet

LAS

1 sector

2 sector

Flux Concentrator (FC)and Positron Target

3 sector

Thermionic DC Gun

4 sector

5 sector

Photo cathodeRF gunElectron beam
DC gunA sector

4 nC electron beam
FCTargetC sector

RF gunDumping
Ring

RF gunR sector(J-arc)B sector

Pulse magnet

LAS

1 sector

2 sector

3 sector

4 sector

5 sector

4 nC, 7.0 GeV

Quasi-traveling wave
side coupled cavities

Emittance is 6 mm-mradin simulation

Positron beam
10 nC electron beam
DC gunA sector

FCTargetC sector

10 nC, 3.3 GeV
Electron beam

RF gunDumping
Ring

RF gunR sector(J-arc)B sector

LAS

1 sector

2 sector

4 nC, Positron beam

Flux Concentrator(FC), Positron target

3 sector

4 sector

5 sector

4 nC, 4 GeV

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

Pulse Bend Magnet

Beam status
2021c

Final goal

Beame+e-e+e-Energy

4.0 GeV

7.0 GeV

4.0 GeV

7.0 GeV

Bunch charge
1st , 2nd [nC]

3.0 , 2.5

2.0 , -

4.0, 4.0

4.0, 4.0

Normalized
emmittance[mm-mrad]120, 5(Hor. , Ver. )50-20, 50-20(Hor. , Ver. )100, 15(Hor. , Ver. )40, 20(Hor. , Ver. )Simultaneous
top-upinjection

4+1 rings(LER, HER, DR, PF, PF-AR)

4+1 rings(LER, HER, DR, PF, PF-AR)Electron beam charge 2021c

RF Gun generation

Linac end

Positron beam charge 2021c
Electron

Gun generation
Primary electron at target

Positron after targetLinac end positron

PositronElectron beam emittance 2021c
In upstream of Linac
10 to 20 mm-mrad

In BT line

Under 20 mm-mrad in goodcondition.

Positron beam emittance 2021c
Primary electron beam

In BT line
After dumping positron beamHor. 120 mm-mrad

Ver. 5 mm-mrad

FC modulator improvement• In the past, FC was damaged by breakdown,
but the damage was avoided with improved
FC.
• However, the spike voltage that could induce
breakdown still remained.
• Spike voltage sometimes caused malfunctionof control equipment.
• In last summer, we modified the FC modulator
and succeeded in significantly reducing thespike voltage.

FC head improvement (2020c)
Spike high voltage had beendamaging to FC head

New FC is very robust.
No break down.
Before Base 7

Base 8・yoke shape optimization
・Insulator improvement

Y. EnomotoCircuit simulation of FC modulator for reduce spike voltage
We investigate a source of spike voltage and reduction method
1R1

1R1
66

D1
100k2

DC 20k AC 0 0

D1Rps

Lsy
0.5u/21511

1.4u C1

Lline1
0.25u/2

0.2/2
Rline1121010nCline

4Lline20.25u/20.2/2
Rline2100k9Rps
2L21u

80.1
Rfc

V1111

1.4u C1

Lline1
0.25u/2

4V1

70.1
Rsy

DC 20k AC 0 0

Lsy
0.5u/25121010nCline

Lline2
0.25u/2

0.2/2
Rline2

9L21u

80.1
Rfc
720.1
Rsy

Lfc
1.1u

0.2/2
Rline1

Lfc
1.1u

R7133

FC_basic.CIR

12.00K

18.00K
16.00K
14.00K

caused by parasitic
capacitance oftransmission cable

10.00K
8.00K
6.00K
4.00K

12.00K

6.00K
4.00K
2.00K
0.00K

0.00u-v(8) (V)

4.00u

8.00u

12.00u15.00K-2.00K
16.00u 0.00u-v(8) (V)15.00K

20.00u4.00u

8.00u

12.00u-2.00K
16.00u 0.00u
20.00u4.00ui(Lfc) (A) i(L2) (A)

8.00u

12.00u12.00K

12.00K

10.00K

10.00K

8.00K

8.00K

6.00K

6.00K

4.00K

4.00K

2.00K

2.00K
0.00K

0.00K
-2.00K

Reduce spike voltage

10.00K
8.00K

2.00K
0.00K
-2.00K

FC_basic_withCR.CIR

20.00K

Spike voltage

14.00K

100n

SW120.00K
18.00K
16.00K

C43SW10.00ui(Lfc) (A) i(L2) (A)

4.00u

8.00u
T (Secs)

12.00uT (Secs)

Set RC circuit to the FC modulator
RC circuit

Result of modified FC modulator

Measured reduction of spike voltage was almost same of simulation
result.
We have no trouble of FC noise in 2021c.

Issue of unstable positron primary beam
• Positron primary beam was often unstablebeam charge at target.
• It caused by energy unstable at injector line.
• Source of energy jitter is HV pulse shape andHV timing jitter.
• We adjust positron primary beam to stableoperation.

Energy jitter of AT line (Thermionic gun injector line) cussed beamloss at J-arc
R0_32 Charge

AT_J2 Energy

DC gunA sector

FCTargetC sector

RF gunDumpingRing

RF gunR sector(J-arc)B sector

LAS

1 sector

2 sector

3 sector

4 sector

5 sector

Thermionic gun modulator had been removed. Currently, one
modulator feed HV pulse to two devices which is klystron and gun.

We use klystron modulator withparallel connection.
It is abnormal usage.

Modulator feed pulse HV.

Flat pulse is necessary.
Vt

RF poewr-300 kV
5 usec4 usecNormalt usage

Modulator feed pulse HV.

Flat pulse is necessary.
Vt

RF poewr-300 kV
5 usec4 usecParallelconnectiont

At injector, gun wasconnected.

Sensitive to timing jitter

Modulator feed pulse HV.

Flat pulse is necessary.

Pulse shape was broken !!
Vt

Modulator pulse timing
jitter is 10 ns

RF poewr-300 kV
5 usec4 usecParallelconnectiont

At injector, gun wasconnected.

Operation delay timing is sensitive point for beam energy.
2022/01/17 study

HV delay

Energy(AT_J2 Y)

HV delay
1 step = 8.8 nsAT_22 Y

It was also experimentally confirmed that the timing of the voltage pulse greatly affects
the beam energy

Source of beam instability• Modulator has 10 nsec timing jitter• Normally, flat pulse is no problem.
• Exceptionally, A1_A klystron is greatly affected due tothe broken pulse shape.
10 nsec timing jitter

A1_A klystron pulse
Normal pulseWe found a delay timing that reduces the effect on beam energy.

We will adjust a positron primary beam to stable injection for 2022 SuperKEKB

Conclusion 2021c• Beam charge is still not achieved to final goal. But
it is enough charge in 2021c.
• Positron charge is almost achieved. We will
improve transmission ratio.
• We can increase electron beam with laser power
margin and 2nd bunch operation.
• Emittance is sometimes achieved final goal value.
But good condition is breaking easily. We must
make an effort to maintain stable conditions.
• We are making various improvements every day
to stabilize the beam. Hardware maintenance in
shutdown term and beam study in operationterm.