< kazuro.furukawa @ kek.jp >Injector Linac

Kazuro Furukawa
for Injector Linac Groups
Many slides from M. Satoh and N. Iida
<http://www-linac.kek.jp/linac/>< kazuro.furukawa @ kek.jp >Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Contents
uInjector status
vOverview
vBeam sources
vAccelerator components³Structures, pulsed magnet, monitors, operation tools

vInjection management³Anomalous injection beam

vBeam controls³Especially positron beam emittance improvements

vBackground spikes³MysteryvSummary
Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Overview

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Fire Recovery
uFire at acc. structure assembly room on Apr.3
vSouthern part of the injector was much damaged as well as
the assembly roomuInterim injector recovery by Apr.26
uFull injector recovery during summer shutdown
uThe assembly roomcleaned up
vRestoration in AprilvS-band structure tests and
RF conditioning soon
Scaffold to clean up walls and ceilingat acc. structure assembly room
Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Injector Linac Mission

Mission of Electron/positron Injector in SuperKEKB
v Low emittance & low energy spread injection beams with 4 times higher beam current³ New high-current photo-cathode RF gun³ New positron capture section³ Positron damping ring injection/extraction³ Optimized beam optics and correction³ Precise beam orbit control with long-baseline alignment³ Simultaneous top-up injection to DR/HER/LER/PF/PFARv Balanced injection for the both photon science andelementary particle physics experiments
Low emittance
RF-gunDamping
Ringe–

Injector Linac

e+

600 m

High efficiency
e+ generator

2x beamcurrent

PF
2.5 GeV

e–

e+ BT

PF-AR
6.5 GeVe – BT

Beam from Injector and Storage Current
SuperKEKB:
7 GeV e2600 mA
4 GeV e+3600 mAPF:
2.5 GeV e450 mA
PF-AR:
6.5 GeV e60 mA

HER
7 GeV

SuperKEKB
3 km

LER
4 GeV

Belle II
40x
Luminosity

Injector Status

The single injector would behave as
multiple injectors to multiple storagerings by the concept of virtual
accelerator
K.Furukawa, 35th B2GM, Feb.2020

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Linac Beam Property Requirements

Linac Beam Parameters at KEKB/SuperKEKB
Stage

KEKB (final)

Beam

e+

e–

e+

e–

e+

e–

e+

e–

e+

e–

EnergyStoredcurrent
Life time(min.)

3.5 GeV

8.0 GeV

4.0 GeV

7.0 GeV

4.0 GeV

7.0 GeV

4.0 GeV

7.0 GeV

4.0 GeV

7.0 GeV

1.6 A

1.1 A

1.0 A

1.0 A

–

–

1.8 A

1.3 A

3.6 A

2.6 A

150

200

100

100

–

–

–

–

6

6

primary e- 10

Bunchcharge (nC)
Norm.
Emittance

Phase-II

1

0.5

1

310

2

2

→ 0.4

4
→4

200/401400

Phase-III (final)

primary e- 10

1000

130

(γβε) (mrad)
EnergyspreadBunch /
Pulse
Repetition
rate

Phase-III (interim)

primary e- 81→1

Phase-I

150/30100/40100/1540/20(Hor./Ver.)(Hor./Ver.)(Hor./Ver.)(Hor./Ver.)150(Hor./Ver.)

0.13%

0.13%

0.50%

0.50%

0.16%

0.10%

0.16%

0.10%

0.16%

0.07%

2

2

2

2

2

2

2

2

2

2

Simultaneous top-up
injection
(PPM)

50 Hz

25 Hz

25 Hz

3 rings(LER, HER, PF)

No top-up

Partially

50 Hz

50 Hz

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

u Limited improvements for operational electricity budget
Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Simultaneous Top-up Injections
uSuperKEKB integrated luminosity improvement
17.5 /pb in 5.15 hr(5 fills)
on May.6

41.6 /pb in 5.15 hr(top-up)on May.16

237%
improvement
Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Beam Sources

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Pulse to pulse switching:rf e- gun/thermionic e- gun

Thermionic DC e- gun (GU_AT)
w/ 2 subharmonic bunchers and 2 bunchers

・e+ production e-: 10 nC (for LER
injection)
・PF injection: 0.3 nC
・PF-AR injection: 0.3 nC

RF e- gun
（GR_A1 for HER injection）

Pulsed bend rep. up to 25 Hz (LER + PF + PF-AR)(magnet coil and chamber heating issue)
It will be replaced by new one in summer shutdown 2020
for full 50 Hz operation.
Injector Status

K.Furukawa, 35th B2GM, Feb.202010

One of Key Component: Photo Cathode RF Gun

Development of Photo-cathode RF Gun
M.Yoshida et al.

u Successfully deployed for injection into SuperKEKB HER
u Employs Yb-doped-fiber and Nd/Yb:YAG
laser, IrCe cathode, QTWSC or cut disk
cavitiesu Stability improving
u Beam instrumentation
improvements andcomparison withsimulation codes
Bunch length
Beam orbit measurementu Secondary RF gun was constructed
as a backup (under tuning)u Incorporate suggestions by review committee
for availability

Thermionic gun
Primary RF gun

Quasi traveling wave
side couple cavity

Secondary RF gun
Cut disk cavity

Injector Status

IrCe
CathodeElectron Guns

K.Furukawa, 35th B2GM, Feb.2020

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HER injection beam (RF e- gun) statusu HER injection has been done with only RF gun since thebeginning of Phase III (Mar. 11th, 2019)u Laser system has no significant fault
u In summer shutdown 2019, photocathode (Ir7Ce2) was
replaced by new one (Ir2Ce) aiming at better quantum
efficiency (Qe)v Discharge, frequent VSWR, gradual decrease of bunch chargeu In this winter shutdown,v After applying heat and laser cleaning of cathode, bunch charge was
not stable.
v Finally, photocathode was replaced by previous one (Ir7Ce2) toward
next run. Now, under rf conditioning.

Injector Status

K.Furukawa, 35th B2GM, Feb.202014

Qe of photocathode (Ir7Ce2, Ir2Ce)

M. Yoshida
Injector Statuse- source
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K.Furukawa, 35th B2GM, Feb.2020

e+ source setup 1
Positron target and capture section

DC solenoid
Large aperture S-band acc.
Structures (x10)e+ source
Injector Status

W target + flux concentrator (FC)

Y. Enomoto, SuperKEKB review, 2019
K.Furukawa, 35th B2GM, Feb.2020

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Positron Enhancement

21

Positron generation for SuperKEKB
top view
10 nC
primary e-bridge coils

DC quadspoiler

Y.Enomoto et al.

solenoid
LAS Accel.
structuretargetprimary
e- beam

e+

beam
hole

positronproduction
4 nC injection e-Target
Flux
Concentrator

pulsed ST
pulsed quad

Flux
Concentrator
BridgeCoils
e+ beam

New positron capture section after target with
Flux concentrator (FC) and large-aperture S-band structure (LAS)
Satellite bunch (beam loss) elimination with velocity bunching
Pinhole (2mm) for passing low-emittance electrons beside target (3.5mm)
Matching the beam optics for the damping ring injection
Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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12

Bunch charge (nC)6e+ beam history in 2019

Primary
e- beam

Summer shut down 20198

Fire accident

10

LIiBM:SP_AT_0_1:ISNGL:KBP:10S (e- gun)
LIiBM:SP_15_T_1:ISNGL:KBP:10S (W target)
LIiBM:SP_58_0_1:ISNGL:KBP:10S (Linac end)
BTpBPM:QMD13P_K_1:NC_1Hz (BT end)42

e+ beam0
2/1
20/02/03
e+ source

4/1

6/1

8/1
Date
22
22

10/1

12/1

2019

After large discharge…
After large discharge

Slit gap got narrow.
Not possible toapply high voltage
unless the gap will
be expanded.
Y. Enomoto, SuperKEKB review, 2019
Injector Statuse+ source
K.Furukawa, 35th B2GM, Feb.2020

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LER injection beam status
u Bunch charge
v Stable and enough bunch charge in this stage
v Primary e-: 11 nC (from gun), 9 nC (on W target), e+ : 1.2 nC (linac end), 0.8 nC (BT)u Flux concentrator (FC)v Previous FC was damaged by large discharge during PhaseII. It was removed
in Sept. 2018.
v Current FC was installed in Jan. 2019.
v 2 〜 3 kA operation current (design 12 kA) for stable operation. no significant
fault.

Requirements for material of the FC head are• Good brazing characteristic• High yield strength even after brazing• High electric and thermal conductivity

v New FC made of Cu-alloy (NC50: Cu-Si-Ni) has been tested w/o fault (〜 12 kA).
v New FC will be installed in summer shutdown of 2020 for aiming at design
operation current.
e+ source
Injector Status

24

K.Furukawa, 35th B2GM, Feb.2020 20/0

Accelerator Components

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Accelerator Structureu Approx. 230 accelerator structures employedu Many aged (40 years-old) structures are degraded
vRisk of 7 GeV / 4 GeV acceleration for Y(4S)
vCannot reach Y(6S)u As a 4-5 year plan, structures are being fabricated since
the last year
u First tests will be performed at the assembly roomu Possibly, a couple of structures would be installed
during summer

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Pulsed magnet systemu Pulsed quads (x 28) (w/ ceramic duct) and steering (x 36) were installed at
Sector3 to Sector5 in 2017 (on movable girder).
u Pulsed bend, additional quad and steering were installed in 2018 summer
and winter shutdown.
u PXIe based control system (Windows 8.1, LabVIEW, EPICS) have worked fine
w/o any serious trouble.
u Power supply stability: 0.01% (24 hours)
Pulsed magnet
BPM

27

Injector Status

Subsystems

Movable girder for pulsed magnet(remote controllable,
10 µm step)
K.Furukawa, 35th B2GM, Feb.2020

Monitors (1)u Beam position monitor (x 103)v Four strip line electrodes (x 97)³ Measurement precision ~ 10 µm

v Eight strip line electrodes (x 6) (J-ARC, LTR x2, PF BT, HER BT, LER BT)

u Profile monitor (x 104)v Al2O3/CrO3 (AF995R, Demarquest Co.). (t: 1 mm, 0.1 mm), YAG:Ce (t: 0.1 mm)

u Wire scanner (WS) (x 6)v SectorA, B, C, 2, 3, 5

u Streak camera (ST) (x 2)v SectorA, C, 3
u RF monitors for klystron, SLED, acc. structure
ST
WS
WS
ST
Injector Status

WS
WS

WS

WS

ST
K.Furukawa, 35th B2GM, Feb.2020

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Injection Management

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Injection BG tuning+ Stability
No drift
No jitter+ Injection beam
+ Injection tuning
Emittance
Septum angle
Orbit
Vertical angle
ChargeEnergyEnergyInjection phase
Energy spreadkicker heightNo
Bunching
…
BG
Laser
…
Optics correction(beta, X-Y coupling, dispersion)
Tune
iBumpFB target+ Ring condition
IP Knobs
Collimator
Luminosity
N. Iida…
Injector Status

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K.Furukawa, 35th B2GM, Feb.2020

Injection efficiency and backgroundu Injection tuning for squeezing βy*
1. Open collimators in the MR
2. Squeeze βy* -> Optics correction
3. Injection tuning using Turn-by-turn BPMs
4. Close collimators in the MR
LER

HER

Injection
efficiency

・The emittance and energy spread of theinjection beam are now good enough for
βy*=1.0mm.

Depends onthe vertical emittance andthe energy spreadof the injection beam

Background・Mainly comes from stored beam caused
by vacuum condition.
・Low enough from injection usually.
・”Spike” and “Duration of injection BG”
are most serious problems.

Mainly comes during
Injection.
Stability of e- beam should be
resolved.

33

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

Injection efficiency and background

Vertical emittance vs. HER Injection efficiency

Y. Ohnishi

36

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

・LER
γεx
[µm]

γεy
[µm]

DR

3

5

BT1 BT2DR

3

5

BT1 BT2

Y. Ohnishi

Reducing emittance is in time for βy*=1mm

Injector Status(6/Nov/2019)37(28/Jun/2019)
K.Furukawa, 35th B2GM, Feb.2020

Injection efficiency and background

LER

When the vertical emittance was improved
γεx
[µm]

γεy
[µm]
DR

3

5
BT2

BT1

6.Nov.2019 3:17

BGs from Vertex detectors

DR

3

5
BT2

BT1

6.Nov.2019 18:50

BG due to injection became smaller.

Signals from Loss monitors in the LER

38

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

Beam Controls

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

39

Feedback loops• Energy feedback (J-ARC, LTR, ECS, BT)
loops work fine.
• Orbit feedback at some locations.
– Large drift (～ 1 mm) can be corrected
within ~ 0.1 mm w/ feedback.

Beam energy deviation (%)– Energy stability at BT line < 0.025%

0.100

Energy @ BT

ee+

0.075

0.050

0.025

0.000
00:00

05:00

10:00

15:00

20:00

HH:mm

Energy FB

Orbit FB40

2. Improvements of emittance growthA) Residual dispersion
a. Dispersion correction
b. Residual dispersion at the acceleration forcompression systemB) Abnormal skew magnetic field from bends
C) Emittance growth caused by jittersD) Other sources
vWake field in the LINAC
vRadiation excitation in the e- BT line
41

Injector Status

K.Furukawa, 35th B2GM, Feb.2020 31.Ja

Residual Dispersion Function Correction
DesignMeasured

Y. Seimiya et al.
• Large residual dispersion function
was generated at the 180-degree J–ARC,
that caused beam instability.
• Dispersion correction by tuning the magnetic
field of quadrupole magnets made residual
dispersion function small enough.
Measured

BeforeAfter

Dispersion correction

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

42

Phase Space Jitter Reduction
After dispersion correction

Before dispersion correction

J-ARC e+ target

J-ARC e+ target

1nC

First figure
shows thestandard
deviation ofbeam position.
Second figure
shows emittance
growth induced
by beam jitter.

Linac end:

Linac end:

28 μm
7 μm

1.8 μm
0.9 μmBeam phase space jitter is reduced by dispersion correction.
••

Injector Status

Small emittance growth still occurred from after the target after the correction.
We should understand the source of the beam jitter to prepare for the high charged beamand for accidental jitter source which may occur at upstream.

K.Furukawa, 35th B2GM, Feb.2020

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Final targete-: εx/εy 40/20 µm
e+: εx/εy 100/15 µm

Beam emittance example(~1 nC) w/ multiple wire scanners

Interim targete-: εx/εy 100/40 µm
e+: εx/εy 180/30 µm

e- emittance growthBAe+: εx/εy ～100/2 µm
1.1 GeV

1.5 GeV eC

1e+: εx/εy ～100/6 µm

2

DR

3

4

5

BT
#1 straighte+: εx,y ～ 2500 µm (beforeDR)e-: εx,y ～20 µm
e-: εx,y ～ 50～80 µm
e-: εx,y ～ 50～80 µm
e-: εx,y ～10~20 µm

Emittance

Measured Emittancee+ beam (Phase3.2(6.Nov.2019))

DR

3

5

BT1 BT2e+e-γεx [µm]150100

γεy [µm]3040σδ [%]

0.16(1σ)0.1(1σ)DR → Sector 3、
BT1 → BT2、Emittances increase→Need study

γεy
[µm]

γεx
[µm]

Phase3.3

DR

3

5

BT1 BT2

e- beam (Phase3.2(4.Dec.2019))

γεy
[µm]

γεx
[µm]
B

Injector Status

C→Sector 3、
BT1→BT2、Emittances increase→Need studyC

３31.Jan.2020,
5 BT1 BT2
N. Iida

B

C

３

5

BT1 BT2

47

K.Furukawa, 35th B2GM, Feb.2020

Improvements of emittance growthA) Residual Dispersion in the BT line
Y. Seimiya
The dispersion functions have been corrected for each BT ARC one
by one.
Non-negligible residual dispersion is still observed

a. Dispersion function correction••

BT for e-

Straight line Straight line
(BT1)
(BT2)

BT for e+

Straight line
(BT1)

Straight line
(BT2)

49

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

Improvements of emittance growthb. Residual dispersion at the acceleration structure for acompression system (cont’d)• The bending magnets used in ECS/SY3 have quadrupole components.
• The beam feels B’ field passing through the design orbit in the bends,
which makes dispersion leakage.
• By moving the bends about 10mm, the beam pass the area of small B’.
This can explain the measured dispersion leak

T. Mori Magnetic field measurement

design orbit

T. Kamitani, H. Kakihara, T. Oogoe-10mm~10 mmBends were moved during sumer

BL along the horizontal direction
51

Injector Status

K.Furukawa, 35th B2GM, Feb.2020 31.Ja

Improvements of emittance growth

ECSηx = 0.50 m @Acc.

ECSηx = 0.15 m @Acc.

Y. Seimiya

DIfference fromdesign dispersion

The horizontal dispersion has been improved by moving ECS bends.
1nC

γεy
[µm]

γεx
[µm]
DR

Injector Status

3

5
BT2

BT1

LERの要求値

DR

3

5
BT2

BT1

Still a large vertical emittance remained
K.Furukawa, 35th B2GM, Feb.2020

52

Improvements of emittance growth

Simulation
Since the energy of the e+ beam increased to 4 GeVfrom 3.5GeV of the old KEKB, the gap of bend
narrowed asymmetry, which created an abnormal
skew component in the bend.
However, this can only explain about one third of
the measured skew quad component of the beam.
Anyway, try to correct.
It is considered that the vertical dispersion could be
M. Kikuchi corrected with the skew quads with permanent magnets.
e+ beam~1 kgauss

Measured vertical dispersion before SkewQ
Calculated vertical dispersion by
the skew quads which areinstalled.

Good agreement !
55

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

Improvements of emittance growth

11 of 16 Skew Quads with permanent
magnets were installed.

57

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

Improvements of emittance growth

Measured Dispersion

Y. Seimiya① Before installation of skew quads ② After installation of skew quads

γεy
[µm]

γεx
[µm]

DR

3

5
BT2

BT1

DR

3

5
BT2

BT1

Remaining SkewQuads will further improve the vertical emittance.
Injector Status

K.Furukawa, 35th B2GM, Feb.2020

58

Y. Seimiya

Wakefield in Acceleration Structure• Using a steering magnet, we searched an orbit so as to minimize
emittance.
• Emittance highly depends on beam charge and orbit.
• Wake free steering will be performed using RF gun in the nextrun.
Thermionic gun

1nC

4nC

65

Injector Status

K.Furukawa, 35th B2GM, Feb.2020 31.Ja

Beam abort caused by abnormal injection beamA) Abnormal energy beamB) Spike and injection beam

68

Injector Status

K.Furukawa, 35th B2GM, Feb.2020 31.Ja

Beam abort caused by abnormal injection beamA) Lower or Higher energy injection beam
Operation log for SuperKEKB

Energy jump

Additonal informationfrom LINAC
69
Injector Status

K.Furukawa, 35th B2GM, Feb.2020 31.Ja

Beam abort caused by abnormal injection beam

Injection beam just before abort can be monitored by,

Y. Seimiya, F. Miyahara

Fast beam position monitor(BPM) in LINAC
a.

b.

1.Jun.2019 19:56• LER D6V2 LM abort

v LER D6V2 LM abort
No energy deviation
Dispersive point

Beam energy was 50 MeV lower.
Orbit deviation

Straight line

One station for the power supplies(PS)was set to 0 [A] due to a trigger
missing of the PS.
Injector Status

1.Jun.2019 21:19

Dispersive point

Straight line

The klystron 51 was down at the time.
The estimation was -46.5 MeV which isconsistent with the beam position.70
K.Furukawa, 35th B2GM, Feb.2020 31.Ja

Beam abort caused by abnormal injection beam

Lower energy beam through the ECS

The longitudinal phase space
LINAC end

R56=0.9

Exit of the chicane

Exit of ECS acc. structure

ΔE=０

δ
dz
ΔE=-50MeV(δ=-1.25%)

BT

LER

Since the ECS restores the beam energy, the beam can inject while being shifted in the time
direction, which could cause a LER abort.
72
Injector Status

K.Furukawa, 35th B2GM, Feb.2020

4. Beam abort caused by abnormal injection beamB) Spike and Injection beamuStill mysteryuInjection beams sometimes have some correlation.
vmore detailed investigation is needed.

uTunes in LER are also related.
uIn smaller βy*, the spikes increased.

74

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

Beam abort caused by abnormal injection beam

2019-11-04 , βy*=1mm

Many spikes areobserved.
Only one seems to berelated to the LINAC orbit.
76

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

SummaryuFire recovery, simultaneous top-up injections,RF-gun deployment, went welluBeam sources and other subsystems aregradually upgradeduBeam controls are being improved based on
injection observations
uFurther beam studies are indispensablebalancing the resources and requirements inSuperKEKB complex

Injector Status

80

K.Furukawa, 35th B2GM, Feb.2020

Mt. Tsukuba

Thank you
SuperKEKB
dual rings
PF-AR
PF
Linac

Injector Status

K.Furukawa, 35th B2GM, Feb.2020

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Injector Status

K.Furukawa, 35th B2GM, Feb.202082