SuperKEKB Design Overview
16th KEKB Accelerator Review
Feb. 7, 2011
Haruyo Koiso

http://kekb.jp

Mt. Tsukuba�

Nikko, Nasu�

Super KEKB Rings
3016 mBelle II�KEK Site

J-Linac�KEKB History
since Feb. 2007

designdesign1034 cm-2s-1=10 /nb/s

600 /pb/day

SuperKEKB
Nikko Straight Section
HER: RF, LER: wiggler(& RF)
e-Tsukuba Straight Section
Belle II�e+

Oho Straight Section
HER: RF & wiggler,
LER: wiggler �Fuji Straight Section
HER & LER: injection,
LER: RFInjector
J-Linac�Electron
Positron�Positron source�Circumference : 3016 m
Each ring consists of 4 arcs
and 4 straight sections.

HER (8->7GeV e-) ＋ LER (3.5->4GeV e+) ＋ J-Linac

e+e- Colliders
Next-generation
B-factories

Design Concept of SuperKEKB• Increase the luminosity by 40 times based on“Nano-Beam” scheme, which was first proposed for SuperB
by P. Raimondi.

Luminosity Gain•

Vertical β function at IP: 5.9 → 0.27/0.30 mm (× 20)•

Beam current: 1.7/1.4 → 3.6/2.6 A

(× 2)

•

Beam-beam parameter: .09 → .09(× 1)= 8 × 1035 cm-2s-1•Beam energy:

3.5/8.0 → 4.0/7.0 GeV

LER : Longer Touschek lifetime and mitigation of emittance
growth due to the intra-beam scattering
HER : Lower emittance and lower SR powerCollision Scheme
Nano-Beam SuperKEKB

KEKB head-on (crab crossing)" z 5-6 mm�

" *x 100-150 µm�

" *x 10-12 µm�
d2φ = 83mrad!

" z 6-7 mm�

!

!

" *x
d=#overlap region << bunch length

overlap region = bunch length!

Hourglass requirement*y" # $ z ~ 6 mm�

Half crossing angle: φ!

*x$" #~ 300 μm�
%*yVertical beta function at IP can be squeezed to ~300μm.
Need small horizontal beam size at IP.
→ low emittance, small horizontal beta function at IP.

!

Y. Ohnishi et al.

Design Concept of SuperKEKB• Use the KEKB tunnel.
• We have no option for polarization at present.
• Use the components of KEKB as much as possible.
• Preserve the present cells in HER.
••

Major change since the 15th KEKB Review.

Replace dipole magnets keeping other mainmagnets in LER arcs.

Comparison of Parameters
KEKB
DesignKEKB Achieved: with crab

SuperKEKB
Nano‐Beam

Energy (GeV) (LER/HER)

3.5/8.0

3.5/8.0

4.0/7.0

βy* (mm)10/10

5.9/5.9

0.27/0.30

βx* (mm)330/330

1200/1200

32/25

εx (nm)

18/18

18/24

3.2/5.3

εy /εx (%)

10.85/0.64

0.27/0.24σy(µm)

1.9

0.94

0.048/0.062

ξy0.052

0.129/0.090

0.09/0.081

σz (mm)46‐76/5

Ibeam (A)2.6/1.1

1.64/1.19

3.6/2.6

Nbunches

5000

1584

2500

1

2.1180Luminosity (1034 cm‐2 s‐1)

Y. Ohnishi et al.

Lattice• Low beta
LERHERβ x*3225mmβ y*0.270.30mm

LERHER

3.24.3*- 5.3• Low emittanceεxεy< 8.64 (0.27%) < 10.32 (0.24 %)nmpm* : with full wigglers• Ensure a sufficient dynamic aperture for••Touschek lifetime > 600 sec
Injection acceptance: Ax 707(LER) /377(HER) nm-> Morita, Iida

Colliding bunchese+ 4 GeV 3.6 A
Belle IINew IRe- 7 GeV 2.6 A
New beam pipe& bellows

New superconducVng /permanent ﬁnal focusingquads near the IP

SuperKEKB

Replace short dipoles
with longer ones (LER)

Add / modify RF systems
for higher beam current
Low emiTance positrons
to inject
Redesign the laRces of both rings
to reduce the emiTance

TiN‐coated beam pipewith antechambers

Positron source

Damping ring

New positron target /capture secVon

Low emittance gun

Low emiTance electrons
to inject" ± $ # *y ' I±*± y $ RL 'L=& )&1+ )2ere % # *x ( + *y % Ry (x 40 Gain in Luminosity!

Main Items to Upgrade•Rebuild the IR and Tsukuba straight section•

Improve optics in the arcs and wiggler sections•

Change the beam pipes•

Strengthen and reconfigure the RF system•

Upgrade Linac, including the construction of a positron
damping ring, strengthening the positron source, andinstallation of a low-emittance gun for electrons•

Implement speed and resolution improvements to the beamdiagnostics and control system•

Strengthen the cooling facilities

KEK’s Roadmap Revised April 30, 2010, http://www.kek.jp/Roadmap/pdf/100430roadmap-E.pdf

Interaction Region
New superconducting magnets
around IPQC2LP

QC2RE

QC1RE

QC1L
PIP
QC1RP
QC2LE

IRON IRON

QC1LE

QC2RP

IRON->N.N.
OhuchiOhuchiet al.

IR with local chromaticity correction

LCC sections needed forboth ringsIP

2.5 π cell structure
KEKB LER•Chromaticity correction with noninterleaved pairs of sextupoles which
are connected with a –I’ transformer.
•Major non linearity is cancelledwithin each pair.
•52-54 pairs / ring.
KEKB LER dynamic aperture
sextupoles-I’
2.5π-I’-I’•Large dynamic aperture.
•Large tuning range of the horizontalemittance and the momentum
compaction factor.

HER arc
HER emittance can be decreased to ~5 nmpreserving the KEKB cell structure

Present KEKB
24 nm @ 8 GeVSuperKEKB
5.2 nm @ 7 GeV-> Morita

HER Wiggler Section

Oho Straight SecVon

beam
Reuse LER wiggler

RF section

・Decrease the horizontal emittance with wigglers.
・Reuse LER wiggler magnets. (60%)
・Install more wigglers if possible. (+40%)-> MoritaTunability of the LER cell

Replace ~100 dipole magnets inthe arc sections to longer dipoles

εx (nm)LER arc

A. Morita, Y. Ohnishi, et al

L= 0.89 m → 4.2 m

αp-> Morita

KEKBLER wiggler section

SuperKEKB

Shorten wiggler period by ½ for lower emittance.

-> MoritaDynamic Aperture•

Dynamic apertures of both rings are limited by
nonlinear leakage fields of IR magnets for counterrotating beams. More serious in LER.

•

Physical apertures need sufficient clearances.
Leakage fields from QC1LP, QC1RP, & QC2RP

M. Iwasaki, N. Ohuchi

Example:LER->HER•

Optimization of magnetic fields and physical apertures isbeing in progress.
->Morita, Ohuchi

Dynamic ApertureLER

Max injection rate :LER: 4 nC/bunch, 2 bunches/pulse, 25 Hz
HER: 5 nC/bunch, 2 bunches/pulse, 25 Hz
Lower limit of lifetime:
LER >181 sec, HER > 105 sec-> Morita
K. Oide, Y. Ohnishi, A. Morita

Tunability of Parameters
SuperKEKB

Case ICase II

Energy (GeV) (LER/HER)

4.0/7.0

4.0/7.0

4.0/7.0

βy* (mm)

0.27/0.30

0.27/0.347

0.26/0.30

βx* (mm)

32/25

32/25

40/25

εx (nm)3.2/5.3

3.2/4.6

3.2/4.3

εy /εx (%)

0.27/0.24

0.28/0.25

0.48/0.41σy(µm)

0.048/0.062

0.049/0.063

0.063/0.073

ξy0.09/0.081

0.087/0.09

0.09/.078

σz (mm)6/5

6/5

6/5Ibeam (A)

3.6/2.6

3.6/2.6

3.6/2.6

Nbunches

2500

2500

2000

Luminosity (1034 cm‐2 s‐1)

80

80

80

Machine parameters are tunable to some extent.

Machine Parameters

Values in ()：without the eﬀect of intra‐beam scaTering

Y. Ohnishi

New Ante-chamber beam pipe
TiN-coated beam pipes with ante-chambers
to suppress - Heating of components : HOM and SR- Electron cloud instabilityNEG pump

SR channel

BeamAnte-chamber

Y.Suetsugu->
Suetsugu

Beam channelSR

Low SR power density
 Less photoelectrons
 Low beam impedanceAnte-chamber with clearing electrodes

Comb-type RF shield
For gate valve

Positron Damping Ring
The injected beam should have very low emittancebecause of poor dynamic aperture of the main rings

M. Kikuchi
Kikuchi->Beam energy (GeV)

1.1

Circumference (m)135# of train

2# of bunches/train

2

Maximum stored current (mA)

70.8

Horizontal damping time (ms)11

Injected-beam emittance (µm)

1.7Emittance @ extraction (H/V) (nm)42.5 / 2.07

Cavity voltage (Vc) (MV)

0.5

1.0

1.4

Bunch length (mm)

11.1

7.7

6.5

Momentum compaction (α)

0.0141

Energy spread (%)

0.055

Electron cloud will be mitigated by TiN coating and solenoid windings.
Founded for some components such as magnets.

SuperKEKB luminosity projection

Integrated luminosity(ab-1)We are here

Goal of Belle II/SuperKEKB
We will reach 50 ab-1
in 2021

Peak luminosity(cm-2s-1)

9 months/year
20 days/month

Commissioning starts
in late 2014.
Shutdownfor upgrade

YearY. Ohnishi

backupLER wiggler section
Oho Straight Section

wigglers

Straight Section

wigglers

Half pole wigglers (new) : 112
Single pole wigglers (new) : 56
KEKB two pole wigglers (reuse): 112

Total effective length: 120.8 m(Total pole length: 84 m)

Crab waist scheme
0% crab waist sextupoles OFF

after re-optimization

before50%

100%
after re-optimization

50%

beforeCrab waist sextupoles have decreased the dynamic
aperture in both transverse and momentum directions.

100%Crab waist scheme

Example of LER Crab waist

K2 5.95

NX 12.5
NY 12.25

NX 13.0
NY 12.25

K2 5.95

Dynamic aperture is not
sufficient with a crab waist.

Nano-beam Scheme (15-th KEKB Review)•The scheme proposed by P. Raimondi and SuperBGroup.

•

Squeeze βy* as small as possible: 0.27/0.41 mm.

•

Assume beam-beam parameter = 0.09 which has
been already achieved at KEKB.

•Change beam energies 3.5 / 8 -> 4 /7 GeV toachieve longer Touschek lifetime and mitigate theeffect of intra-beam scattering in LER.