Approach to the more stable injector linac
for SuperKEKB

Hiroysu Ego

June 12, 2020

Contents• Linac status• Deterioration in accelerating structures• 5-year upgrade plan in progress• SummaryLinac status
Linac has many accelerating units with damaged structurese- 7.68 GeV (max)e+ 4.39 GeV (max)

1.1 GeV e+ damping ring

1.5 GeV arc

ZZZ

ZZZZZzzZZZZZZZZ: Damaged unit
: Markedly damaged unit
: Unit with the structure repaired temporally for water-leakZ

Deterioration in accelerating structure 1Many structures suffering from power reflection and/or
excessive field emission
108

Specified voltage

Units

6

Markedlypoor4

2090100110120130140

Unit voltage [MV]150160170180

Deterioration in accelerating structure 2
Severely damaged structure

Coupler irisBlackening

beam iris

Rough and matteiris surface

Rough and discoloredsurface

Deterioration in accelerating structure 3
Fatal case : water leakage
Water leakages occur to a few structures a year

Water flow
Leaking area

Fatal leakage inward

Leakage outward
temporary repair with sealants

Upgrade plan 1
5-year development plan for stable operation
New S-band structures
for wiping out the markedly damaged structures

Providing an additional RF source to a special unit

Development of a new pulse compressor for the special unit

$ 4,000,000 for R&D and manufacturing 16 structures,the pulse compressor and so on

Upgrade plan 2
5-year schedule
FY 2018

FY 2019

FY 2020

FY 2021

FY 2022

New S-band structure

Completed !
R&D

Completed !
Fabrication of four structures

High-power test&installation
Material procurementfor 12 structures

Fabrication of 12 structures
Conditioning
Installation

RF source addition
Device procurement

Installation

Pulse compressor
R&D
prototypehigh-power testFabrication

Installation

Upgrade plan 3
Complete cure : new designed S-band structures
Four structures completed and under high-power tests• Demonstrated high-power performance as designed• Stable operation at a rated power of 40 MW with extremely low breakdown• Ready for mass-production

Upgrade plan 4
Beam energy dependent on beam charge
Low charge caseHigh charge case of 4 nC

HER [GeV]

7.68

7.27

LER [GeV]

4.39

4.15

Injection condition• Long beam life
• Good injection rate

• Short beam life
• Bad injection rate

If we need a high charge of 4nC for injection,
the beam energy in linac reduces to 94.5% of the full energy.

Upgrade plan 5
The case of full energy acceleration but unstable

After the 5-year upgrade
ECM [GeV]LER [GeV]HER [GeV]

6S

Low charge injection

11.923

4.510

7.880

OK

Maximum charge injection

11.279

4.266

7.454

OKCurrent status
ECM [GeV]LER [GeV]HER [GeV]

6S

Low charge injection

11.613

4.390

7.680

OK

Maximum charge injection

10.986

4.153

7.265

NGUpgrade plan 6
The case giving priority to stable acceleration with two stand-by units

After the 5-year upgrade
ECM [GeV]LER [GeV]HER [GeV]

6S

Low charge injection

11.498

4.360

7.580

OKMaximum charge injection

10.877

4.125

7.171

NG

Current status
ECM [GeV]LER [GeV]HER [GeV]

6S

Low charge injection

11.203

4.240

7.400

OKMaximum charge injection

10.598

4.011

7.000

NG

5-year plan is necessary for the 6S operation
but insufficient for the stable operation.

Summary• Deterioration in S-band structures progress
hindering the operation of SuperKEKB• 5-year plan wiping out the markedly bad structures• First one of the new S-band structures tested andresulted in good performance• Continuous manufacture of the structuresindispensable for stable and sustainable operation ofSuperKEKB even after the 5-year plan, especially if weshould do 6S operation.

• Energy scan for the 6S operation dependent on not
only the Linac status but also the life time in thestorage ring and the beam injection rate.