LINAC Status and Plans
Monday, 21th October 2019
B2GM
Accelerator Laboratory (5th)Y. Seimiya

Contains
1. Introduction
2. New Findings of Injection BeamA) Emittance GrowthB) Belle II Background by Injection BeamC) Beam Abort by Injection BeamD) Yield of Positron Beam

3. Recent Activity of LINAC
4. Plans

2

Contains
1. Introduction
2. New Findings of Injection BeamA) Emittance GrowthB) Belle II Background by Injection BeamC) Beam Abort by Injection BeamD) Yield of Positron Beam

3. Recent Activity of LINAC
4. Plans3

1. Introduction

SuperKEKB comparison with KEKB
• Small emittance and high-intensity beam are required for injection beam.
• “Emittance charge squared”, 100 times higher performance is desired.
ChargeHor./Ver. EmittanceElectron Beam

KEKB

3 times

1/8

4

310

Energy Spread

SuperKEKB
1/16

1.3 times

310

0.07
0.05

1.28

20

40

Charge'[nC]Positron Beam
5 times

40.82
Charge'[nC]Normalized'Hor.
!"x [µm]
Emittance'[µm]Normalized'Ver.
!"y [µm]
Emittance'[µm]Energy'spread'
Energy'Spread'[%]

1/14

1/93

1.1 times

1400

0.15 0.16

1400

100
!"x [µm]
Normalized'Hor.
Emittance'[µm][%]15!"y [µm]
Normalized'Ver.
Emittance'[µm]Energy'spread'
Energy'Spread'[%][%]4

1. Introduction

Footprint of LINAC and Beam Transport Line (BT)J-ARC

SectorA

S

RTL

LTR

Sector2

Sector3e+

Jarc

SectorB

Electron Gun

DR (Damping Ring for e+)

SectorC

Sector1

Positron Generation Target& FC (Flux Concentrator)

Sector4

Sector5

LINAC end

Su

R
V LE
e
G B
4 EK
WS:
K
r
BT1
pe

V HER
e
G
7 EKB 1
e
K
r
e
up
WS:

BT2-e

WS:
BT2-p

BT (Beam Transport line)5

Contains
1. Introduction
2. New Findings of Injection BeamA) Emittance GrowthB) Belle II Background by Injection BeamC) Beam Abort by Injection BeamD) Yield of Positron Beam

3. Recent Activity of LINAC
4. Plans

6A) Emittance Growth

Main Reasons of Emittance Growth blue line: design particle!Residual Dispersion of Momentum

red line: high energy particle

Design ARC• If there is magnetic error in a ARC, it
can causes beam size blowup depended
on energy spread after the ARC.
• Beam size blowup= energy spread x residual dispersion
beam

bend
quadrupole

With error

beam

1. Residual dispersion increases emittance through energy spread.
2. If there is residual dispersion “in acceleration cavity”, it causes further serious
emittance growth.
(bunch length increases emittance through the residual dispersion -> z-dispersion)

In each case, emittance growth is reduced bysuppression tuning of the residual dispersion.

7A) Emittance Growth

Residual Dispersion in ECS cavity.
ECS(Energy Compression System)

Design Optics

Blue: Horizontal dispersion
Red: Vertical dispersion

Dispersion Measurement
Y. Seimiya

ECS
Discrepancy between
design dispersion andmeasured one.

acceleration cavity•

In the design, dispersion in the cavity is zero.

• However, non-zero dispersion wasmeasured in the cavity.

acceleration cavity

8A) Emittance Growth

Emittance Measurement• Horizontal emittance became 5 times larger by
ECS cavity with residual dispersion.

June 2019

N. IidaM. Kikuchi
T. Mori

Y

X

Requirement

DR(Sector)3$$

5$$ BT1$ BT2

ECS

1 nC

DR 3$$(Sector)

5$$ BT1$ BT2ECS9A) Emittance Growth

Reason of the Residual Dispersion
and the Countermeasure• It was found that beam passed through non-flat magnetic field.
• There is not quadrupole magnet in this ARC, we could not suppress theresidual dispersion.
• We moved bending magnets so as beam passes through the flat field region.
Measured integrated magnetic fieldof bending magnet in ECS@SY3ECSMany people

T. MoriBM̲61̲5
BM̲61̲2
BC2P-LBC2P-R
6.40mm BM̲61̲3 BM̲61̲4 12.86mm
BC3P-R
BC3P-L
-10.77mm -13.05mm

10A) Emittance Growth

Improvement of Residual Dispersion
Before Correction

After Correction

N. IidaM. Kikuchi
Y. Seimiya

Blue: Horizontal dispersion
Red: Vertical dispersion
Difference between design
dispersion and measured one.

acceleration cavity

ηx = 0.50 m @cavity

acceleration cavity

ηx = 0.15 m @cavity
11A) Emittance Growth

Improvement of emittance (for LER beam)• After the dispersion correction by bending magnet
alignment, emittance growth by ECS cavity almost
disappeared!

• Vertical emittance increases between BT1 and BT2. One of themain reasons is vertical residual dispersion in BT.

X

N. IidaM. Kikuchi
T. MoriY

Jun.-2019
Oct.-2019
Requirement

DR(Sector)3$$

5$$ BT1$ BT2

ECS

1 nC

DR 3$$(Sector)

5$$ BT1$ BT2

ECS

12

A) Emittance Growth

Residual Dispersion in BT• Non-negligible residual dispersion was observed.
• We should minimize the residual dispersion at the BT end.
• Additional skew quadrupole magnets will be installed toreduce vertical residual dispersion.

BT(for(e+Blue: Horizontal dispersion
Red: Vertical dispersion

N. IidaM. Kikuchi
Y. Seimiya

Straight(line(WS@BT1)
Straight(line(WS@BT2)

13

Contains
1. Introduction
2. New Findings of Injection BeamA) Emittance GrowthB) Belle II Background by Injection BeamC) Beam Abort by Injection BeamD) Yield of Positron Beam

3. Recent Activity of LINAC
4. Plans

14B) Background by Injection Beam

Background

Stability
Injection Beam
Orbit
Emittance
Energy0spread
ChargeEnergyBunching
Laser…

High quality andstable beamtransportation isnecessary for LINAC.

No0drift
No0jitter

Injection Tuning

No
BG

Septum0angle
Vertical0angle
EnergyInjection0phasekicker0height…

Optics0correction
Tune
iBump0FB0target
IP0Knobs
Collimator
Luminosity…

Ring Tuning15B) Background by Injection Beam

Background reduction by tuning of injection beam
• Orbit, energy spread, and emittance tuning were performed.
• By injection beam tuning, background was reduced.
• Next step is stabilization.
beam tuning

M. Yoshida
N. IidaHER injection
After
TuningBeforeTuningEnergy1spread!"x=147µm!"y=262µm

Energy1spread!"x=99µm!"y=68µm
16B) Background by Injection Beam

For injection beam stabilization

TBI:%To%be%introduced

Tool

Place

EnergyEnergy feedback

Jarc, DR, BT

Energy spread

Sub Harmonic Buncher 1(SHB1) for LER beam

Thermionic Gun

SHB2Achievement

Feedback

◯

◯

◯

ー

TBI

ー

RF Phase monitor

LINAC

◯

TBI

RF Induced wave monitor

LINAC

△

ー

OctoPos BPM monitor

Jarc

△

TBI

BT

TBI

TBI

Temperature control

LINAC

△

Orbit feedback

LINAC + BTー◯Offset injection

LINAC

TBI

TBI

Orbit jitter

Pulsed magnet PS

Sector 3-5○

ーEnergy jitter

Energy knob phase

Sector B, 2, 5△ーRF phase

LINAC

△

ー

Injection phase

FB of Master oscillator

LINAC and MR◯◯

Emittancee- RF gunRF Gun△(stability)

TBI

e+ DR

DR

◯

ー

Wire scanner

LINAC, BT◯ーEnd of BT

△

ー

Orbit

Many people17B) Background by Injection Beam

Orbit Feedback• An example of orbit FB (Shown BPM place in the LINAC end)
• Orbit FB is operated correctly.
BeforeAfter
Y. Seimiya

18

Contains
1. Introduction
2. New Findings of Injection BeamA) Emittance GrowthB) Belle II Background by Injection BeamC) Beam Abort by Injection BeamD) Yield of Positron Beam

3. Recent Activity of LINAC
4. Plans

19C) Beam Abort by Injection Beam• Sometimes abnormal injection beam induces beam abort.

Trigger Missing of Pulsed Magnet
Measurement

EnergyOrbit

Klystron Down

Measurement

Y. Seimiya
F. Miyahara

Orbit

Energy~50 MeV reduction

Simulation

Simulation

BT lineCollimators in the BT could cut thebeam of the abnormal orbit.

BT lineNew collimator installation isplanned.

20

Contains
1. Introduction
2. New Findings of Injection BeamA) Emittance GrowthB) Belle II Background by Injection BeamC) Beam Abort by Injection BeamD) Yield of Positron Beam

3. Recent Activity of LINAC
4. Plans

21D) Yield of Positron Beam

• Measured positron yield is 30% less than simulated one.
• Non-axisymmetric field component were observed byelectron beam deflection.
• This could cause e+ beam loss.
Yield

Beam

Measurement

0.26

Simulation

0.34

Solenoid

Beam Orbit

Measured BPM

Solenoid magnetic
field is tilt!
T. Kamitani

Solenoid Current

22D) Yield of Positron Beam

Countermeasure of the Positron Yield Problem• For understanding the phenomena and controlling beam orbit, we areplanning to install orbit correction coils and BPMs.
• Detailed field distribution is being evaluated, including return yokes
and structures (Fe) around solenoid.
Solenoid

BPM

Steering coils



Bx
By

Y. Enomoto















23







Next Tasks
A) Emittance Growth! Tuning to reduce the residual dispersion.
! At BT for e+, additional skew quadrupole magnets will be installed toreduce vertical residual dispersion.
B) Background by Injection Beam! Emittance and energy spread tuning.
! RF phase FB is being introduced for stable energy spread.
C) Ring Abort by Injection Beam! To stop abnormal beams, installation of collimators is planned in thiswinter for HER and in the next summer for LER, respectively.
D) Yield of Positron Beam
! We are planning to install orbit correction coils and BPMs in the next
summer.

24

Contains
1. Introduction
2. New Findings of Injection BeamA) Emittance GrowthB) Belle II Background by Injection BeamC) Beam Abort by Injection BeamD) Yield of Positron Beam

3. Recent Activity of LINAC
4. Plans

25

3. Recent Activity of LINAC• 4 ring simultaneous top-up injection• Long-term continuous operation of RF gun• Completion of recovery from fire accident• Main works in this summer shutdown.
• RF gun• Vacuum exhaust of laser waveguide.
• New air conditioning and insulation in laser hut.
• Laser line preparation of RF gun for backup.

• Beam line

• Alignment• Mover installation for acceleration unit girder.（4 units)• Monitor• Installation of additional high resolution profile monitors.
(OTR, YAG)26

3. Recent Update of LINAC

4 Ring Simultaneous Top-Up Injectionσ=

6.25%Hzσ=

6.25%Hzσ=

4.16%Hzσ=

4.16%Hz

Many people27

Contains
1. Introduction
2. New Findings of Injection BeamA) Emittance GrowthB) Belle II Background by Injection BeamC) Beam Abort by Injection BeamD) Yield of Positron Beam

3. Recent Activity of LINAC
4. Plans

28

PlansThis Winter• HER/LER 2 bunch injection• Additional skew quadrupole magnets installation in e+ BT• Collimator installation for HER

Next Summer• Collimator installation for LER• Installation of orbit correction coils and BPMs at e+ capture
section• New FC installation→ e+ charge increase• New pulsed bending magnet in merger line installation andnew laser for RF gun installation→ 50 Hz single beam operation

29

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

Thermionic DC e- gun(GU̲AT)・e+ production e-: 10 nC(for LER injection)・e- study/HER injection: 1 nC

RF e- gun（GR̲A1 for HER injection）

New pulsed bends for 50 Hz
operation will be installed.
( 2020 summer)
30

Thank you for your attention!

31

back%up

32A) Emittance Growth

Main Reasons of Emittance Growth!Residual Dispersion

1. If there is Residual Dispersion after ARC, energy spreadincreases beam size through residual dispersion.
2. If there is Residual Dispersion in compression acceleration
cavity, bunch length increases beam size through residual
dispersion.
������������ �������

Usual Acceleration
Compression Acceleration(Make energy gradient)�Anyway, emittance growth reduce
if dispersion is suppressed.

33

CountermeasuresA) Emittance Growth! Tuning to reduce the residual dispersion.
! At BT for e+, additional skew quadrupole magnets will be
installed to reduce vertical residual dispersion.
B) Background by Injection Beam! Emittance and energy spread tuning.
! Orbit FB and RF phase FB.
C) Ring Abort by Injection Beam! To stop abnormal beams, installation of collimators is planned.
D) Yield of Positron Beam!

We are planning to install orbit correction coils and BPMs.

! 2 bunch operation, primary e- increase, beam loss
reduction, field of flux concentrator increase.

34D) Yield of Positron Beam
• Measured positron yield is 30% less than simulated one.
• Non-axisymmetric field component were observed byelectron beam deflection.
Beam
Solenoid

Beam Orbit

Measured BPM

Solenoid magnetic
field is tilt!

•

T. Kamitani

Solenoid Current•

First we checked beam pass through beamline straightly by turning off all magnet
between BPMs.
If solenoid tilt physically, there is 20 mmmisalignment. This is unreal.
35D) Yield of Positron Beam

Countermeasure of the Positron Yield Problem
For understanding the phenomena and controlling beam orbit,
we are planning to install ST coils and BPMs in next summer.
Detail simulation, which includes return yoke and structure (Fe)around solenoid, is performing now. (Y. Enomoto)••Steering coils


Bx
By

Y. Enomoto









BPM














Possible causes:• In DC solenoid, return yoke and supports of
the acceleration cavity brake symmetry
against of the solenoid axis.
• Though wires of DC solenoid is thick,current do not flow symmetry against of
the solenoid axis.
• Bridge coilʼs shape has asymmetry andmaterial of the return yoke has problem
36(magnetic field is saturated).

A) Emittance Growth

Emittance Measurement（for HER）
• Emittance was worse than Phase 2, because tuning time waslimited by fire accident.
• It seems that wakefield by beam cause emittance growth fromsector C to sector 5.
• To reduce tuning time, we are preparing automatic emittanceminimized program.

X

N. IidaM. Kikuchi
T. MoriY

Requirement

B""""C"""3""""5""BT1"BT2

1$nC

B""""C""""3"""5""BT1"BT2
37

Ununiform)magnetic)field)of)bending)magnet)• There are two type of bending magnet.
• One is C-type, the other is H-type.
• C-typeʼs magnetic gap is easier to shrunkby own magnetic field than that of H-type.
• By the shrunk gap, ununiform magnetic
filed is generated.

C$typeH$type38

Typical Charge in Phase 3
Beam for HER
1 nC @Linac end
0.7 nC @BT end

Beam for LER
1 nC @Linac end
0.7 nC @BT end

39

Positron Charge at some point
primary'
e)
(nC)

FC
(kA)

Yield
(simulation)

Yield
(measured/simulated)

2019/6

7.5

3

0.34

Ideal5case
except5charge5loss

10

12

0.58

e+ (nC)e+ (nC)e+ (nC)before'LTR@Linac'end@BT'end0.7

1.5
measured1
measured0.7
measured1

4.9(extrapolation)

3.2(extrapolation)

2.3(extrapolation)

It is necessary to reducebeam loss.

DesignF. Miyahara
Y. Enomoto

2019/640

Other Sources of Emittance Growth
Candidates of emittance growth in LINAC or BT.
1. Beam Phase Space Jitter• The emittance that includes beam phase space jitter, called as effective
emittance, must be satisfy the SuperKEKB requirement.

2. Wakefield in Acceleration Structure• Wakefield, generated by a head of bunch, kicks its own tail.
• Thus if the beam is off-centered in the structure, the transverse wakefield
increases beam emittance.

3. Radiation Excitation• Radiation excitation effect on emittance is proportional to both Lorenz gamma to
the fifth power and inverse of curvature radius to the third power.
• Especially, electron beam (7 GeV) is strongly affected by the radiation excitation
effect.

41A);Residual;Dispersion

A) Residual Dispersion in LINAC• Large residual dispersion had been observed at the J-ARC before
dispersion correction.
• By tuning the strength of quadrupole magnets, residual dispersion
became small.
J-ARC

J6ARC

Designx=⌘<latexit sha1_base64="/j+sXJ8fXHgB3mLaSsIyeYHmdjs=">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</latexit>

p
p

=⌘

m

Measured

BeforeRMS !"x =#0.43#m#$%x =#187# 27#µm

Thermionic gunm

Measured

After

Dispersion
correction

Δ#$%x =#-47#µm

m
RMS !"x =#0.02#m#$%x =#140# 33#µm

42A)&Residual&DispersionA) Other sources of Residual Dispersion• Both orbit and angle of a beam which pass through bending magnets.

• Orbit&displacement&at&quadrupole&magnets&that&have&a&large&strength&creates&a&
sizable&dispersion.
• Orbit of a beam which pass through sextupole magnets.
To keep residual dispersion minimized, orbit feedback is necessary.
Dependence between orbit+angle and dispersion

Effect of sextupole magnets••

Orbit & angle
correction
before J-ARC
Orbit & angle
correction
before chicane

J;ARC

Chicane

LINAC&end

There are 6 sextupole in J-ARC.
Orbit displacement cause
quadratic force.

ON

OFF

LINAC&end
43A)$Residual$DispersionA) Orbit Feedback• An example of orbit FB (Shown BPM place in the LINAC end)
• Orbit FB at the end of LINAC was operated correctly.
• Orbit FB of J-ARC upstream will be performed next run.

BeforeAfter

44A)(Residual(DispersionA)#Magnet#used#in#the#orbit#FB#at#the#end#of#BT
LINAC(FB(start

LINAC(FB(start

The(orbit(FB(in(LINAC(helps(thr orbit(FB(in(the(BT.

45A)%Residual%Dispersion

A) Residual Dispersion at BT line••••

We had corrected dispersion of each BT ARC one by one.
After that dispersion of the BT overall was measured changing thebeam energy.
Non-negligible residual dispersion was still observed.
We will minimize Δη and Δηʼ at the end of BT in the autumn run.
Straight%line Straight%line
Straight%line% Straight%line%(WS@BT)(WS@BT2)(WS@BT1)(WS@BT2)

BT%for%e+BT%for%e+46B) Beam Phase Space Jitter
B)4Beam4Phase4Space4Jitter• In 2018, large orbit jitter was measured (1000 shots).
• Emittance estimated from beam jitter, called jitter emittance, was
not negligible.

1nC

J0ARC

e+4target
Bunch4charge4(nC)
Emit.4@BT4end(!"#)4(µm)

Orbit jitter (RMS)

Emittance growth
converted from beam jitter

Phase&3
final

4
40/20
(Hor./Ver.)

Linac end:

28/7 μm(Hor./Ver.)q✏ef f = ✏20 + ✏2j + 2✏0 ✏j Bjmag

Design beta function<latexit sha1_base64="upxAsRlptP+Rek8PX09m+E6HLjc=">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</latexit>m✏0 + ✏j

B jmag ( 1) express amount of
mismatching between beam optics
and the jitter optics.

LINAC4end

47B)%Beam%Phase%Space%JitterB) Wakefield effect and Beam Phase Space Jitter• Electron beam straightly pass through the positron generation
target hole, whose diameter is 2 mm.
• We suspected wakefield effect as a orbit jitter source.

e:wake potential induced bytarget hole (simulation)
Color%differences%show%differences%of%distance%between%center%of%hole%and%beam%position.

14%mm

e+
e:

From the beam position before
and after target, amplification
factor are derived.

φ2%mm

Comparison of orbit jitter
Target%IN

Growth%factor20

Target%OUT

Growth factor of beam phase space jitter:

LINAC%end< 0.1@1nC << Measured growth factor

Wakefield effect of target hole is negligibly small.

48B) Dispersion and Beam Phase Space Jitter
B)2Beam2Phase2Space2Jitter• We focus on dispersion which convert to orbit jitter through energy jitter.
• By dispersion correction, jitter emittance become less than 1 µm.
J-ARC e+ target

J-ARC e+ target

BeforeAfter

Dispersion
Correction

Linac end:!"#j < 1 μm

49B)%Beam%Phase%Space%JitterB) ! Function and Orbit Jitter• Remain orbit jitter can be explained by ! function.
• Using Twiss parameters measured by WS at C sector, ! function
near target is derived.
• ! function is highly correlated with orbit jitter.
• We conclude that large orbit jitter sources are mainly bothresidual dispersion and ! function.

50B)%Beam%Phase%Space%Jitter

B) Other Sources of Beam Phase Space Jitter

Binarization of Pulse Magnet

Three valued RF phase
Large RF phase jitter cause orbit jitter.

[mrad]•

By further investigation, we found that following items were sometimes sources ofjitter. Pulse magnet and RF phase jitter was almost resolved by person in charge.
To identify the jitter source, monitoring beam jitter is important.

x’%•

x%[mm]
Slope of RF phaseΔp/p=0.042%

Δp/p=0.027%

Near%zero%cross%phase

Near%crest%phase

If RF phase is near zero cross, energy jitter is enlarged
by the slope of phase.

Degree@KL_B3

Degree@KL_C8

51B)2Beam2Phase2Space2JitterB) Beam Phase Space Jitter at BT line•••

In the RTL and BT, orbit jitter is much larger than that in LINAC, partly because BPM resolution is poor.
Orbit jitter of first straight line in BT is about ~150 μm@1σ. This value is probably BPM resolution.
Assumed that calculated jitter emittance at the first straight line came from BPM resolution, jitter emittance atsecond straight line is estimated as following:• e- beam: !"#jx/!"#jy @BT end ~ 40/50 μm• e+ beam: !"#jx/!"#jy @BT end ~ 30/30 μm• High resolution BPM is strongly desirable at BT. An upgrade of some BPMs for higher resolution isplanned.

e6

Straight2line

e+

BT

RTL

LINAC

WS@B
WS@C

WS@3

WS@5

WS@BT1

WS@BT2

Straight2line

LINAC

WS@3

BT

WS@5

WS@BT152

WS@BT2

C)(Wakefield(in(Acceleration(StructureC)#Wakefield in Acceleration Structure• Using a steering magnet, we searched an orbit so as tominimize 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

53

E)'Radiation'ExcitationE) Emittance growth induced by radiation excitation in BT
Theoretical emittance growth induced by radiation
excitation:

BT2∝ !5,'1/$3
BT2

Particle tracking simulation was performed from the endof LINAC to the end of BT.

Simulation

InitialWith
Phase2III3final
particles Radiation requirementBT1

e$ (7'GeV) !"#x [µm]206540 $>'The'maximum'emittance'can'be'relaxed.

e+'(4'GeV)'!"#x [µm]

64

74

100

• Radiation excitation has little dependence
on initial emittance.
• By the radiation excitation, emittance
growth of e-/e+ beam is about 48/10 µm.

M.'Kikuchi Simulation Result!#x ='65'µm!#x ='20'µm

Now'in're$considering

e- beam• The'beam'size'at'the'injection'septum'is'0.31'
mm,'assuming'βx'='20'm.'The'required'injection'aperture'is'still'dominated'by'the'septum'width'of'2.5'mm.'Although'the'emittance growth'due'to'synchrotron'
radiation'is'very'big,'it'plays'only'a'minor'role'
on'the'injection'aperture'itself.'

54