1

Luminosity of 1035 cm-2s-1

at KEKB

Preliminary planMachine parameters

RF systemVacuum system

Injector

Y. OhnishiKEKSnowmass2001

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Preliminary Plan

• Luminosity of 4.49x1033 cm-2s-1 was achieved at KEKB.• Major target of B physics is CP violation, especially sin21(or sin

2):– Belle/KEKB : 0.58±0.33 (10.5 fb-1), March 2001.– Int. luminosity from KEKB is 30 fb-1 now. Statistical error will be 0.19.– There is a chance to say 3 S.D. significance this summer(?).

• Integrated luminosity of100 fb-1 is needed to achieve the required accuracy of 0.1 for sin21.

• We expect to reach 100 fb-1 within 1.5 year even if the luminosity is still 4x1033 cm-2s-1. (very conservative)

• BTeV and LHC-B will become strong competitors in 5 years.

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Preliminary Plan (cont’d)

• KEKB will loose its competitiveness in 2005-2007.– Luminosity of BTeV or LHC-B corresponds to 1035 cm-2s-1 e+e- collider.

• SUSY related B physics at 1035 cm-2s-1 e+e- collider is a very attractive choice.

• We hope to upgrade KEKB to Super KEKB(1035 cm-2s-1 ) during 2004-2005 and begin physics run in 2006.

• We try to improve luminosity to 1034 cm-2s-1 up to 2004.

• KEKB is R&D machine for Super KEKB.• Super KEKB project consists of

theorists/experimentalists/accelerator staffs of universities and KEK. (18/5/30)

• We will submit LoI to HEP community and KEK in winter 2001

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Parameters for Super KEKB(1035 cm-2s-1)

• Luminosity formula:

• Beam-beam tune shift parameters:

• Assumed that the “transparency” conditions:

• Alternative expression for luminosity:

L=NeN e f4πσ x

*σ y* RL

L=γe

2ere

Ieξy

y*

⎛

⎝ ⎜ ⎞

⎠ ⎟ 1 +

σ y*

σ x*

⎛

⎝ ⎜ ⎞

⎠ ⎟ RL

Rξy

ξx,ye =re

2πγe

Ne βx,ye*

σ x,y* σ x

* +σ y*

( )Rξx,y

γeIe =γe Ie , εe =εe , etc.

L∝Ieξyβy

*

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Parameters for Super KEKB (cont’d)

Design luminosity of KEKB is 1034 cm-2s-1. To achieve 1035 cm-2s-1:

Squeeze beta at IP. : y* σz 3 mm (coherent radiation?)

Higher beam current : 10 A for LER and 3 A for HER

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Coherent Synchrotron Radiation

• Power of coherent synchrotron radiation (Kheifets,Zotter)

N: particles/bunch : bending radius h: height of chamber

Particles: Gaussian distribution

incoherentE √∝ N P ∝N

coherentE ∝N P ∝N2

z

z

coherent condition

z≦

Pcoherent≈πN2remec

2 f0ρ

ρσ z

⎛

⎝ ⎜ ⎞

⎠ ⎟

43

Γ 2/3,xth( )

xth=23πρh

⎛ ⎝

⎞ ⎠

3 σz

ρ

⎛

⎝ ⎜ ⎞

⎠ ⎟

2

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Coherent Synchrotron Radiation(cont’d)

• The ratio of coherent power to incoherent:

PcoherentPincoherent

=3N4γ4

ρσz

⎛

⎝ ⎜ ⎞

⎠ ⎟

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Γ 2/3,xth( ) Pincoherent=4πNremec

2 f0γ4

3ρ

⎛

⎝ ⎜ ⎞

⎠ ⎟

LER: 3.5 GeVBending radius: = 16.3 mChamber height: h=47mm

Coherent radiation can be ignore for 3mm bunch length (?)

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Questions• Beam current is 10x3 A.• Beta(y) at I.P = 3 mm• Bunch length = 3mm• Energy(or Particle) exchange:

– 3.5 GeV e+/8 GeV e- to 3.5 GeV e-/8 GeV e+

– Advantage: • Beam blow-up due to photoelectron cloud(?)

If fast ion instability for electron beam is ok. • Injection (injection rate: e- > e+ at KEKB).

• Once machine parameters are fixed, questions are:– RF system ?– Vacuum system ?– IR design ?– Injector ?

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Layout of KEKB (not Super KEKB)

Double ring,Asymmetric collider

Circumference:3km

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RF System

• Beam current at Super KEKB is 3 times larger than KEKB.

• Number of bunches is 15000 or 5120 ?• If we choose harmonic number of15000, we have to

develop completely new 1.5 GHz RF system. (Current RF frequency is 508 MHz.)

• We consider RF frequency is 508 MHz to minimize the cost, time, and man power.

• Normal conducting cavities (ARES) for LER and normal+superconducting cavities(SCC) for HER.

• The severe requirement on HOM damping.• Rf system for LER depends on whether wiggler exists

or not.

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RF System (cont’d)

• RF parameters (RF unit includes klystron, power supply, wave guide, circulator, dummy load, cooling, etc)

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RF System (cont’d)

• RF system needs small modifications if we keep 508 MHz RF frequency used at KEKB.

• However, we have to develop new HOM damper for higher beam current.

• We increase NC(ARES) cavities from 32 to 36 and SC cavities from 8 to 12.– We should have 36 NC(ARES) cavities for KEKB, we only add 4 SCC.

• Klystron for Two NC(ARES) cavities is modified to Klystron for one NC(ARES) cavity. Number of RF units becomes twice of KEKB.

• We consider RF system with wiggler for LER at this stage.

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Vacuum System

• Parameters of vacuum system

Max. cooling power is 〜 8 MW. New powerful cooling system has to be built.This issue is for institute not for accelerator division.

It is difficult forcopper chamber.

510 A/m130 A/m200 kV/m

These valuesare tested andconfirmed.

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Vacuum System (cont’d)

• Ante-chamber for positron ring:

We have no experience even if GlidCop is used.

R&D for material.Make incident angleslant?

practicable

In the case ofenergy exchange

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Vacuum System (cont’d)• Movable masks.• Photo shows the early version

of movable mask.• SiC blocks were equipped as a

HOM absorber, since trapped mode was very serious.

• However, beam current was limited by the absorbed power(estimated to be 500W).

• This kind of mask can not be used for huge beam current machine.

• The most serious problem is damage of mask head.

• R&D for the structure and material is needed.

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Vacuum System (cont’d)• Latest version of movable mas

k at KEKB(LER).• Movable chamber. The chamb

er works as a mask.• There is no trapped mode.• We have already observed ma

sk damage(looks like previous photo).

• To avoid mask damage, mask should be hybrid structure of Al and copper.(Just make energy loss point at mask)

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Positron Beam Blow-up

• Positron beam blow-up caused by photoelectrons is reduced by solenoid field.

Beam size measurement using SR interferometer.

Spec. Luminosity/bunch

All solenoid off

All solenoid on

Partialsolenoid off

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Positron Beam Blow-up (cont’d)

• Solenoid coils are also necessary for Super KEKB.• Chambers in positron ring are wrapped by solenoids:

– Straight section as well as bending section.– Bellows, inside of steering magnets, …

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Injector

• Short lifetime due to collision: 10A/100 min=1.7 mA/s.• Powerful injector is needed to keep the rings filled up.• Super KEKB will be very inefficient machine.

KEKB(current status:4.3x1033)3mA/s(e-)/1.5mA/s(e+)800mA(HER)/900mA(LER)High efficiency!

Super KEKB3mA/s(e-)/1.5mA/s(e+)3A(HER)/10A(LER)

Top-up

Super KEKB(upgrade injector)15mA/s(e-)/3mA/s(e+)3A(HER)/10A(LER)

Inj.+dead time=6.5min

Inj.+dead time=50min

Inj.+dead time=12.8min

Lum

inosi

ty e

ffici

ency

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Injector (cont’d)

• Improvement of Injection rate:– Charge intensity can be increased from 1nC to 5 nC for electron.– Positron charge becomes twice, if two-bunch acceleration is performed.

We have already tested.

• Energy exchange(3.5 GeV e-/8GeV e+) may help beam blow-up due to photoelectron cloud in positron ring.

• To accelerate positron up to 8 GeV, there are two possibilities:① Improvement of accelerating electric field(simple):

• C-band is a candidate instead of S-band.• One of techniques of Japan Linear Collider.

② Recirculation(S-band) with damping ring(similar to SLC):• In order to do recirculation, next RF pulse is used.• Damping ring is needed so that beams wait for next RF pulse.• Beam transport lines are very complicated.

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Injector (cont’d)

e+ Targete- 3.7 GeV

ECS

KEKB e+3.5 GeV

J-Arc1.7 GeV

S-Band

Gun C-BandB A

C 1 2 3 4

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40 MeV/m 1.1x2 + 2.2x3 = Max 8.8 GeV

Layout of injector for super KEKB

Layout of injector for KEKB

Super KEKB e- 3.5 GeV

Super KEKB e+ 8 GeV

ECS

J-Arc1.7 GeV

GunB A

C 1 2 3 4

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e+ Targete- 3.9 GeV

KEKB e-8 GeV

S-Band

Preliminary plan

10nC e- for e+ production1 nC e- for injection

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Summary

• Machine parameters of Super KEKB:– Beam current: 10A(3GeV e-)/3A(8GeV e+)– Beta at I.P: y*=3mm– Bunch length: σz=3mm– Number of bunches: 5120– Crossing angle at I.P: 15 mrad(?)

• RF system is not so difficult (practicable).– Development of HOM damper

• Vacuum system is very difficult.– R&D of materials and structure of vacuum chamber

• Injector will be widely modified to exchange energy and improve beam intensity.– C-band or recirculation– Two-bunch acceleration