Parameters of SuperKEKB
Luminosity of 1035 cm-2 s-1

Y. Ohnishi (KEK)

KEKB Review Committee, Feb 25 2002

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Luminosity of SuperKEKB• Luminosity formula:
N N f
L = e *e * RL
4πσ xσ y• Beam-beam tune shift parameters:*Nβre x , yeRξ x , yξ x , ye = e***
2πγ e σ x , y σ x + σ y()• Assumed that “energy transparency” conditions:γ e Ie = γ e Ie , ε e = ε e , etc.

• Alternative expression for luminosity: Ieξ y  RLγe
L=(1 + r ) * 2ere β y  Rξ yY. Ohnishi (KEK)β y* ε y σ y*r= * == *βx ε x σ x“Optimal coupling”

KEKB Review Committee, Feb 25 2002

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Luminosity of SuperKEKB (cont’d)• Design of SuperKEKB is based on: Ieξ y  RLγe
L=
(1 + r ) * 2ere β y  Rξ yβ y* ε y σ y*r= * == *βx ε x σ x• Beam-beam tune shift: ξy = 0.05
– Expectation from our experience (0.04-0.07 @ KEKB)• Vertical beta at I.P: βy* = 3 mm

– Bunch length: σz = 3 mm to reduce hour-glass effect as possible.
Constraint of coherent synchrotron radiation
Y. Ohnishi (KEK)

KEKB Review Committee, Feb 25 2002

3Luminosity reductions• RL : Luminosity reduction due to geometrical• Rξ : Tune shift reduction• RL/Rξy is a function of crossing angle, beta, emittance, bunch length.

• Half crossing angle: θx = 15 mrad
• Horizontal beta at I.P: βx* = 15 cm• Emittance : 33 nm (6.4 % coupling)

RL/Rξy = 0.82

Half crossing angle (rad)βx*=15cm

2%RL/RξyRL/Rξy30cm

β*x (m)Y. Ohnishi (KEK)

KEKB Review Committee, Feb 25 2002

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Beam current• We choose flat-beam at present.
– Round beam ?
luminosity gain of factor 2.
– Lattice design is very difficult.
– Is it possible to squeeze beta with keeping higher
beam-beam tune shift ?

• To achieve 1035 cm-2s-1 :9.4 A (LER) x 4.1 A (HER)
 Idea of 1035 cm-2s-1 is higher beam current andsmaller β at I.P.
Y. Ohnishi (KEK)

KEKB Review Committee, Feb 25 2002

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List of parameters

1.1 / 0.67 mA@KEKB

Y. Ohnishi (KEK)

KEKB Review Committee, Feb 25 2002

6Coherent Synchrotron Radiation• Power of coherent synchrotron radiation
4(Kheifets,Zotter)πN 2 r m c 2 f  ρ  3Pcoherent ≈eρe0  Γ(2 / 3, xth )σz 2  πρ   σ z xth = 
3 h   ρ 3

N: particles/bunch
ρ: bending radius
h: height of chamber2

 incoherent

EσN PN coherent

Eσ
Y. Ohnishi (KEK)NP“Statisticalfluctuation”

N2σλ/2π

KEKB Review Committee, Feb 25 2002

7Coherent Synchrotron Radiation (cont’d)• The ratio of coherent power to incoherent:
43P(coherent)/P(incoherent)

Pcoherent
3N  ρ = Γ(2 / 3, xth )4 Pincoherent 4γ  σ z 10
4πNre me c 2 f0γ 4  Pincoherent =
3ρ


-2
11LER: 3.5 GeV
Bending radius:ρ = 16.3 m
Chamber height:
h=47mm

N=1.2x10 (Super KEKB; LER; 10 A)

10-7-1210

N=3x101010(KEKB; LER; 2.6 A)-17-2210

11.522.533.5

42 mm is OK but 1 mm is ?

Bunch Length σz (mm)Coherent radiation can be ignore for 3 mm bunch length.
Y. Ohnishi (KEK)

KEKB Review Committee, Feb 25 20028Lifetime• Luminosity lifetime– dN/dt = -σL– Cross section of radiative Bhabha: 2.14x10-25 cm2– Loss rate : 0.34 mA/s
– LER/HER : 460/200 min• Vacuum lifetime– ~10 hours (?)• Touschek lifetime– LER/HER : 330/1650 min• Overall lifetime of LER/HER : > ~150 min– Loss rate : 1 mA/s (LER)/ 0.46 mA/s (HER)• Continuous & Simultaneous injection– 5Hz (LER) / 10 Hz (HER) (70% injection efficiency)
Y. Ohnishi (KEK)

KEKB Review Committee, Feb 25 2002

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Energy exchange (HER:e+/LER:e-)• Advantage :– Effect of photoelectron cloud can be reduced.
– Injection time to full current can be reduced.
• Intensity of injector: e- > e+

• Unknown :– Multipactering is no problem for e+ in HER ?
• Height of vacuum chamber is smaller than LER.

– Is fast ion instability safe for e- in LER ?

• Major upgrade of injector is needed.
– Energy upgrade : C-band or re-circulation scheme– Good opportunity for changing linac frequency to:flinac/fring = integer if C-band is chosen.
Y. Ohnishi (KEK)

KEKB Review Committee, Feb 25 2002

10Summary• Machine parameters of SuperKEKB– Beam current: 9.4 A (LER) / 4.1 A (HER)– Beta at I.P: 15 cm (βx*) / 3 mm (βy*)– Bunch length: 3 mm
– Half crossing angle: 15 mrad

• RF system– Number of RF units becomes twice of KEKB.

• Vacuum system– Ante-chamber, masks, bellows• Injector will be widely modified to exchange
energy and improve beam intensity.
Y. Ohnishi (KEK)

KEKB Review Committee, Feb 25 2002

11Summary (cont’d)

HOM dampers in RF,
Photon stops and ante-chambers,
Injection schemes,
Final focusing schemes, …

Y. Ohnishi (KEK)

KEKB Review Committee, Feb 25 2002

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Cost estimation• Vacuum• RF• Facility• IR• Feedback & monitor• Injector• SuperBelle• Injector for PF,AR• TotalY. Ohnishi (KEK)

12.2
9.5
5.0
1.1
0.9
5.0
3.5
5.0
42.2 Billion yen

KEKB Review Committee, Feb 25 2002

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