#! $$"$&$$
 "%!"  $ " 
MOPMF074' $   $  #%% !

• Beam#phase#space#jitter#and#effective#emittance#are#reduced#by#dispersion#suppression#
after#JJARC#section.#• While,#enhanced#factor,#which#is#ratio#of#before#to#after#jitter#emittance,#is#not#significantly#changed.
• Dependence#on#flux concentrator,# solenoid,#bridge#coil,#pulsed#magnet,#and#chicane#is#small.
• Though#the#target#hole#is#being#suspected#as#a#beam#jitter#source,#both#measured#and#simulated#data#(assumed#design#β)#suggest#that#the#wake#field#effect#is#small.#We#mustcheck#beta#function#after#the#target.

• In#SuperKEKB#linac,#stable#high#charged#low#emittance#beam#is#necessary.
• Transported#beam#to#MR#must#be#stable#to#the#extent#that#the#beam#can#be injected#
inside#MR#acceptance.
• SuperKEKB#requirement#must#be#satisfied#for#emittance#including#beam#phase#space#jitter,#called#as#effective#emittance.
• Large#amplitude#beam#position#jitter#has#been#measured#at#LINAC#end.#• We#evaluated#that#the#effect#of#the#beam#position#jitter#to#effective#emittance#and#
investigated#the#cause#of#the#beam#position#jitter.

SuperKEKB injector$linac

Dispersion$suppression$effectThermionic$gun,$1nC
Before$correction

There#are#two#type#of#electron#gun#in#the#LINAC;#
thermionic#gun#and#RF#gun.
• RF#gun:#SuperKEKB#eJ for#low#emittance#beam.
• Thermionic#gun:#eJ for#SuperKEKB#e+#generation#or#
for#PF#and#PFJAR.

After$correction

Dispersion#correction

Jitter$emit. Before Afterεxj
1.8#μm 1.3#μm
εyj
1.8#μm 0.9#μm

No$noticeable
differencesRF$gun,$1nC
Dispersion#correction

Jitter$emit. Before Afterεxj
28#μm 1.8#μm
εyj
7#μm 0.9#μm• Electron#beam#straightly#pass#through#the#positron#generation#target hole,#which#diameter#is#2#mm.
• Electron#come#from#upstream#and#pass#through#FC,#target,#bridge#coil,#and#DC#solenoid.
• After#the#DC#solenoid,#chicane#for#dump#electron#beam,#that#is#generated#together#with#positron#beam.

Requirement$to$LINAC$for$SuperKEKB

Beam$jitter$source$investigation$around$positron$generation$target• Low#emittance#&#high#charged#beam#transportation#is#required#for#SuperKEKB.
• Transported#beam#to#MR#must#be#stable#to#the#extent#that#the#beam#can#be
injected#inside#MR#acceptance.
• SuperKEKB#requirement#must#be#satisfied#for#emittance#including#beam#phase#space#jitter,#called#as#effective#emittance.

Dependence$on$flux concentrator,$ solenoid,$bridge$coil,$
Positron$beam,$that$does$not$pass$though$the$target$hole
pulsed$magnet,$and$chicane• Difference#of#positron#beam#(hits#the#target)#and#electron#• We#check#whether#these#components#are#sources#of#jitter#beam#(through#the#target#hole).
or#not#by#turn#off#these#components#between#BPMs#before# • It#seems#that#target#hole#enhance#beam#position#jitter#
and#after#target.
remarkably.#Wake#field#effect#is#suspected.
Thermionic#gun

H/V$nor.$emittance Charge Energy$spread
(μm)
(nC)
(σ)

150/150

10.1%

40/20

40.07%• Assuming#that#beam#position#and#transfer#matrix#between#two#BPMs#are#
identified,#we#can#derive#beam#angle.#Using#the#beam#position#and#angle,
effective#emittance#is#derived#by#p< (x +x)2 >< (x0 +x0 ) 2 >x)(x0 +< (x +x0 ) > 2 .

• If#beam#jitter#is#independent#of#particle#motion,✏ef f ==q
✏20 + ✏2j + ✏0 ( 0 <rq= ✏20 + ✏2j + 2✏0 ✏j Bmag
✏0 =✏j =pp2↵0 ↵ +2< xx0 >2 ,x2 ><<x2 >0x2 >)<)<< x2 >< x2 ><x x0 > + 0 <x2 > +2↵0 <0✏20 + ✏2j + 2✏0 ✏j (x0 ><latexit sha1_base64="zusRRg6N46MR7XSa/lDQCJ//O2I=">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</latexit>

0

Amplification$factor$and$correlation$coefficients• To#find#the#wake#field#effect,#beam#position#pass#through#the#target#hole#was#changed#by#steering#magnet.
• From#the#beam#position#before#and#after#target,#amplification#
factor#and#correlation#coefficients#are#derived.
• It#seems#that#beam jitter dependence on beam#position#pass#through#the#target#is#small.
• Wake effect is not found from this result.#

After#target

After#target

PositronElectron

Big$differences.
Wake$potential$induced$by$the$target$hole.
• Simulation#analysis#is#also#performing#(CST studio).
• Though#target#hole#size#is#small#(φ2#mm),#higher#
order#wake#field#affect#beam.
• Longitudinal#wake#has#little#position#dependence.#
While,#transverse#wake#increase#nonlinearly.
• Enlargement#factor#is#about#2#(assumed#design#β)#
even#beam#pass#through#the#hole#at#0.9mm#from#the#center.#This#is#smaller#than#the#measured#factor,~20.#We#must#check#beta#function#after#the#target.
Longitudinal#wake#potential

Nominal#emittance
Jitter#emittancex x0 >.

212↵0 ↵ + 0 ) = 4 +20OFFx>• Bmag shows#mismatch#between#measured#Twiss#parameters#and#that#of#design.#
The#Bmag is#larger#than#or#equal#to#1.#If#there#is#not#mismatch,#Bmag =1#and#effective#emittance#is#just#ε0 +#εj.
1
Bmag = ( 02

After#target

No$noticeable$differences

Effective$emittance$and$jitter$emittance✏ef f =

After#target

ON

SuperKEKB#requirement#for#electron

Phase#2#
Phase#3(goal)• Position#jitter#and#effective#emittance##are#reduced#by#dispersion#suppression#after#JJARC.
• While,#enhanced#factors,#which#is#ratio#of#before#to#after#jitter#emittance,#are#not#so#changed.#
After#the#target,#position#jitter#is#still#remained.

+

↵0s

↵
0s

0!2 35

1

Transverse#wake#potential

Amplification#factor

Correlation#coefficients

No$noticeable$differences

X#=#Beam#
position#from#the#center#of#
target#hole.