SuperKEKB Overview
Update10th KEKB Accelerator Review
Committee
22 February 2005
Toshihiro Mimashi, KEK(Many of the slides are borrowed from M.Masuzawa)Contents
 Goal of SuperKEKB
 Strategy to reach the goal of SuperKEKB
 Overview of each components
 What is the problem ? Where we stand.

 SummaryPeak Luminosity Goal
Super KEKB

from Samo Stanic and modified by T.Mimashi

8GeV
Positron beam
4.1 A

3.5GeVElectron beam
9.6 A

Construction Scenario“Minor” upgrade

Belle“Major” upgrade

Crab cavity

KEKB
KEKB

1000fb-1

construction

J-PARC 1 construction

Budget
2004

05

06

07

shutdown

08

09

10

S-KEKBILC construction

11

12

Calendar year

Most of the components (magnets, klystrons, etc) will be re-used.

Installation of
Crab Cavity

Shutdown

We are here.

Shutdown for 18-26 months in 2009-2010 for upgrade.
0.6 /ab/month in 2020.

SuperKEKB Budget profile

Strategy
Lorentz
factorBeam-beam parameter

Beam current*e±" e ± $ # y '$ Ie ±* y '$ RL ')L=
&1+ * )&& * ))&&
2ere % # x (% + y (% R* y )(Classical electron
radius!

Beam size ratio@IP
1 ~ 2 % (flat beam)

Ratio of luminosity &tune shift reduction
factors: 0.8 ~ 1(short bunch)

Vertical beta function@IP

Increase beam currents•1.6 A (LER) / 1.2 A (HER) → 9.6 A (LER) / 4.1 A (HER)

Smaller βy*•6 mm→3 mm

Increase ξy•0.05→0.14

For Peak Luminosity
improvement
 Increase Beam current
Vacuum Upgrade (Y.Suetsugu)
ARES & SCC Upgrade (T.Abe,T.Furuya) Smaller βy*Lattice (Y.Ohnishi)
QCS (N. Ohuchi)IR design (Y.Funakoshi,K.Kanazawa) Increase ξyCrab crossing increase Luminosity ?

For Integrated Luminosity
improvement and others
 Injector UpgradeContinuous injection @ 50Hz ?
Minimize Belle dead time caused by the injectedbeam (Dumping Ring) 3.5msec dead time x 50Hz => 17.5% dead time

Charge exchange : 8Gev e+ beam (T.Kamitani)
Positron source (T.Suwada) OthersIssues
 Charge exchange ? (LER:e- and HER:e+) LER/HER Current ratio is 9.1/4.5 ?
 Can we fill 5000 buckets ?
 Bunch-by-bunch Feedback System

 Beam-BeamParasitic collision ? (M.Tawada) Single Beam
Photoelectron (Ante-chamber+Energy switch+Low SEY surface chamber +Solenoid)(S.Katoh, Y.Suetsugu)
 Can we get enough budget ?

Summary SuperKEKB aims at a peak luminosity of

1-5×1035 cm-2 s-1, a new luminosity frontier forcolliders.
 The basic design work has been finished and a
Letter of Intent was published this year (Edited by
J.W.Flanagan and Y.Ohnishi,KEK Report 2004-4 June
2004).
 More simulation and intensive hardware R&D

work towards SuperKEKB are on-going.

Impedance and Collective Effects(K.Shibata) Resistive Wall Instability
 Growth rates (800-1000 s-1) <damping rate of feedback system (5000s-1).
 Closed Orbit Instability due to long-range resistive wake (Danilov)
 Thresholds (12.3/12.2 A for LER/HER) > design currents
 Electron Cloud Instability (Positron Ring) With ante-chambers and positrons in the HER, simulations show that
60G solenoid field should clear the electrons.
 Uncertainties:
 Distribution on walls and amounts of electrons.
 Behavior of electrons inside lattice magnets.

 Ion Instability (Electron Ring) Currently suppressed by feedback.
 With electrons in LER, simulated initial growth rate faster thanfeedback damping rate, leading to dipole oscillation with amplitude oforder of vertical beam size →possible loss of luminosity.
 Coherent Synchrotron Radiation (T.Agoh)Lattice Design
Beam Optical Parameters
LER

HER

Unit

24

24

nm

βx/ βy

200/3

200/3

mm

Momentum compaction

αp

2.7×10-4

1.8×10-4

Momentum spreadσδ

7.2×10-4

6.8×10-4

RF voltage

Vc

15

20

MV

Bunch length

σz

3

3

mm

Synchrotron tune

νs

0.031

0.019

Horizontal emittance
Beta function at IP

εxLattice Parameters and Beam-Beam Effect(from Ohnishi)bare latticewith beam-beam

unit

Beam current (LER/HER)

I

9.4/4.1

9.4/4.1

A

Beam energy (LER/HER)

E

3.5/8.0

3.5/8.0

GeV

Emittance

εx

24

77

nm

Horizontal beta at IP

βx*

20

4.5

cm

Vertical beta at IP

βy*

3

2.3

mm

Horizontal beam size

σx*

69

59

µm

Vertical beam size

σy*

0.7

1.4

µm

Beam size ratior = σy */σx*

1

2.4

%

Crossing angle

θx

0

0

mrad

Luminosity reduction

RL

0.86

0.81

ξx reduction

Rξx

0.99

0.97

ξy reduction

Rξy

1.11

1.17

Reduction ratio

RL/Rξy0.78

0.70

Horizontal beam-beam(estimated with S-S simulation)

ξx

0.08

0.05

Vertical beam-beam(estimated with S-S simulation)

ξy

0.14

0.12

LuminosityL

2.5 x 1035

2.5 x 1035

cm-2s-1

Lattice Design: the arc section
The beam-optical parameters
can be adjusted toSuperKEKB withoutchanging the lattice in thearc section.

KEKB lattice: 2.5π cell and non-interleaved chromaticity correction scheme.
→Wide tunability of horizontal emittance, momentum compaction factor.
→Principle nonlinearities in sextupole pairs cancelled out to givelarge dynamic apertureLattice Design: the IR section

KEKB (& S-KEKB HER)

Issues:
8 mrador superconducting?
•QC1 normal
KEKB LER•Strong synchrotron
light
from
QCS.
22 mrad•Aperture→need damping ring for positrons, at least.

Move final focus quadrupoles closer to IP for lower beta functions at IP.
QCS and solenoid compensation magnets overlap in SuperKEKB.
Rotate LER 8 mrad (total crossing angle of 30 mrad).

Vacuum parameters (SR related) for SuperKEKB
LER

HER

Unit

Beam energy

3.5

8.0

GeV

Beam current

9.4

4.1

A

Bunch length

3

3

mm

# of bunches

5018 (with 2% abort gap)

Bending radius

16.31

104.46m

Bending angle

56.1

mrad

Half aperture

112

mm

Total SR power

7.65 (without wiggler)

14.21

MW

Max.line power density fromSR

27.8 (~2 times higher)

21.6 (~4 times higher)

kW/mMax.power density from SR

38.7(almost same as KEKB,
ante-chamber)

35.0 (2.4 times higher)

W/mm2

Critical SR energy

5.84

10.88

keV

Ave. photon density

1.21×1019(4 times higher)

1.20×1019(4 times
higher)/m/s

Ave. gas load

4.56×10-8

4.54×10-8

Pa m3/s/m

Vacuum parameters (HOM related)for SuperKEKB
Loss factor k(V/C)

Length or# of components

Total k(V/C)

HOM
power(kW)Resistive wall

4.1×109

2200 m

8.9×1012

1780

Pumping holes

8.8×105

2200 m

1.9×109

0.38

Flanges

1×108

800

8×101016

Bellows

4×109

800

3.2×1012

640

Photon mask

1×104

800

8×106

0.0016Gate Valve

3×109

16

4.8×1010

9.6

Movable mask

1×101216

1.6×1013

3200

Taper

3×109

72

2.2×1011

44

HOM dampers needed.

Vaccum components R&D
 Proposed basic designs for arc are:
 Beam Duct: Copper beam duct with an ante-chamber
 Distributed pumping by NEG strips
Beam Inner surface with low SEY [e+] or/and solenoid Bellows and gate valves: With comb-type RF shield Connection flange: MO-type flange or conventionalRF bridge + vacuum seal

 Movable mask (collimator)

 New design with low impedance

From Suetsugu

NEG Strip

RF parameters for SuperKEKB
Parameters

LER

HER

Unit

Beam current

Ib

9.4

4.1

A

Energy loss/turn

U0

1.2

3.5

MeV

Loss factor

ktotal

40

50

V/pc

Bunch length

σz

3

3

mm

Radiation loss power

Pb,rad

11.3

14.3

MW

Parasitic loss power

Pb,para

7.1

1.7

MW

Total beam power

Pb,total

18.4

16.0

MW

Total RF voltage

Vc, total

14.0

23.0

MV

RF frequency

fRF

508.887

MHz

Revolution
frequency

frev

99.4

kHz

Type of cavities

ARES

ARES/SCC# of cavities

28

16/12

Voltage/cavity

Vc

0.5

0.5/1.3

MV

Beam power/cavity

Pb

650

650/460

kW

Wall loss/cavity

Pc

233

150/-

kW

Detuning frequency

Δfa

45

31/74

kHz

28

16/12

930

850/480

kW

40

23/10

MW

# of klystrons
Klystron power
Total AC power

Pkly

Required RF power
provided to beam is fourtimes as high as those of
KEKB. But the required
RF voltage is relatively
low.
Adopt the same RF
frequency as KEKB anduse the existing RF
system as much as
possible.
ARES Upgradefor Super-KEKB
HER: 4.1 A (Nb = ~5000, σ z = 3mm) by 16 ARESs + 12 SCCs
ARES cavities of the current version. (KEKB 12ARESs+8SCCs)LER: 9.4 A (Nb = ~5000, σ z = 3mm) by 28 ARESs (KEKB 20 ARESs)
Remodel the A-cav part together with upgrading the HOM loads
The S-cav will be reused.
8 or more sets of ARES cavities are needed to increase the beam
current up to 9.4 A.
Super KEKB one ARES/klystron configuration（KEKB: two ARES/one klystron）
The input power to each cavity will be nearly doubled.
The number of klystrons will be more than doubled. From Kageyama

Remodeling ARES Cavity (A-cav Part)
Increase ka (the coupling factor
between A-cav and C-cav)by enlarging the coupling aperture
between A-cav and C-cav

Increase the stored energy ratio:

Upgrade HOM Waveguide Load!

Upgrade GBP Load

KAGEYAMA, T.
HL6, KEK,
Nov. 16, 2004

U s ka2= 2
U a ksSuperconducting
Cavity Cavity Field 1.4-2.0MV OK
 Input Coupler 380kw  460kW OK (test) Coupler already tested more than 500kW(800kW in shorttime),beam test will be done.

 HOM Power 10 kW  60kW to be solved
 HOM damper is most important issue for Super-KEKB SCC.
Max Power of 40kW have been tested in air condition. Highpower test under high vacuum will be done.

 Add 4 Cavities
 If possible 4mm bunch length is help full reducing HOM
problems and saving cost.
From Mitsunobu

Item

Coupled-Bunch Instabilities due to RF Cavities
Freq.
LER
HER
Cure
(MHz)
# of
cav.

Growthrate (ms)# of cav.

Growthrate (ms)Longitudinal modes
ARES-HOM

1850

26

SCC-HOM

1020

Crab-HOM at LFM

655

2

ARES 0/p modes

504

Fundamental -1 mode
Fundamental -2 mode

5

16

47

Bunch by bunch FB

1249

No need

41

2

214

No need

28

4

16

29

Bunch by bunch FB

508.79

28

1.6

16+12

1

FB in RF control system

508.69

28

20

16+12

21

FB in RF control system

16

33

Bunch by bunch FB

12

12Bunch by bunch FB

2

12Bunch by bunch FB

Transverse modes
ARES-HOM

633

SCC-HOM

688/705

Crab-HOM

773

28

2

4

4

Crab crossing scheme!"#$%&'%()*+,#-+./#-.01)2#3

4@!
@'%()+*78

B@!

;?CC#DE
4%.56*7-*''181*7

A*81)+*78-+*88179#:79'%####,;;#<#=#>#+.5?3;?C;#DE;?C;#DE;?CC#DE

Palmer for LC (1988)
Oide and Yokoya for storage rings :Phys,Rev.A40,315(1989)
Recent simulations by Ohmi showed significant increase of luminosity withcrab crossing. It effectively creates a head-on collision.

Crab crossing in KEKB andSuper-KEKB
KEKBSuper-KEKB

Ring

LER

HER

LER

HER

Beam energy (GeV)

3.5

8.0

3.5

8.0

Beam current (A)

2.6

1.1

9.4

4.1

Bunch length (mm)

7

7

3

3

RF frequency (MHz)508.887508.887

Crossing angle (mrad)

±11

±15

βx* (m)

0.6

0.6

0.2

0.2

βx, crab (m)

40

200

100~200

300~400

Required kick (MV)

1.47

1.51

1.10 ~ 0.78

1.45 ~ 1.26

Restore kick?

No (single kick)Yes (both sides of IP)

Crab cavity in Super-KEKB


Possible problems for 10A with σz=3mm
Large HOM power (300kW) to dampers.
Growth rate can be higher than the radiation
damping rate.

 Improvements needed → New design
Reduce the loss factor for σz= 3mm.
Much heavier damping of parasitic modes.

Two different types based on different methods to damp theaccelerating mode (Lower Frequency Mode).
Coaxial coupler
Notch filter

Additional
waveguide damper
Notch filter

Waveguide damper
for the LFM

Additional waveguide damper(1) Coaxial couplers Type

(2) Waveguide damper Type

From Akai

Other Components
Beam Position Monitors
Use same front-end electronics
New button electrodes
12 mm →6 mm diameter-> Signal power matches dynamic range of existing front-end
electronics.

Main Ring Magnets
Outside of the IR, will largely reuse present KEKB
magnets & power supplies.

Bunch-by-bunch Feedback
systemTransverse feedback similar to present design→Target damping time 0.2ms-Detection frequency 2.0→2.5 GHz.
-Transverse kicker needs work to handle higher currents-Improved cooling, supports for kicker plates.
Longitudinal feedback to handle ARES HOM & 0/p

mode instability →Target damping time 1ms-Use DAφNE-type (low-Q cavity) kicker.
New general-purpose feedback signal processor underdevelopment at/with SLAC will be used.
-Low noise, high speed (1.5 GHz), with custom filtering functions
possible.
-Extensive beam diagnostics.

Linac Upgrade Requirements
KEKB
SuperKEKB(1) Beam Energy (e–)
8.0 GeV----->
3.5 GeV(e+)
3.5 GeV----->
8.0 GeV !
(2) Beam Intensity (e–) 1.0 nC x 1 bunches ----->
2.5nC x 2 bunches !
(e+) 0.6nC x 2 bunches ----->
1.2nC x 2 bunches !
-> with 7-10 Tesla flux concentrator in e+ capture section(3) Smaller e+ emittance to fit for IR & C-band module apertures-> e+ damping ring(4) Faster e+/e– mode-switching for Continuous e+/e– Injection-> separated e+/e– beam lines-> non-destructive beam monitoring

From Michizono

Linac Upgrade
Intensity Upgrades◆Electron: increase bunch
current from pre-injector◆Positron: stronger focusing
field in capture section aftertargetEnergy Upgrade (Positrons)
KEKB:21 MV/m (S-band) x 231 m = 4.8Gev

max

e+ energy is boosted byC-band accelerator modules

SuperKEKB:
21 MV/m (S-band) x 46 m
+ 42 MV/m (C-band) x 185 m=8GeV

The kicker magnet will be
installed before positron target
for quick switching between
beams (50 Hz).

Damping Ring
Positron emittance needs to be damped, to pass reduced aperture of C-Bandsection and to meet IR dynamic aperture restrictions.(e+ Injection)

Electron DR may beconsidered later toreduce injection
backgrounds in physics
detector.

Summary SuperKEKB aims at a peak luminosity of

1-5×1035 cm-2 s-1, a new luminosity frontier
for colliders.
 The basic design work has been finishedand a Letter of Intent was published thisyear (Edited by J.W.Flanagan and
Y.Ohnishi,KEK Report 2004-4 June 2004).
 More simulation and intensive hardware
R&D work towards SuperKEKB are ongoing.