Nano-Beam Scheme forSuperKEKB
15th KEKB Accelerator ReviewFeb. 15, 2010
Haruyo Koiso

14th KEKB Accelerator Review Committee•

In order to significantly increase the luminosity ofKEKB, there are two possible approaches: increase
the current (more intense beams), or decrease theemittance (brighter beams). ….. It is recommended
that the KEKB team evaluate the low emittance
option to see whether it would provide a suitablebasis for SuperKEKB.

•A great deal of component R&D has been carriedout over the last few years and great strides havebeen made. Most of this R&D would be applicable
to both design solutions, so this work should carryon.

14th KEKB Accelerator Review Committee•

However, it is suggested that the machine design
work concentrate on the low emittance option for
the next few months, with a focus on identifying
any possible showstoppers. The design should bebrought to a point where an informed decision
between the two options can be made.

•We have started intensive design works on theNano-Beam scheme, and have decided to selectthat scheme for SuperKEKB.

Issues on High-Current Scheme•

Although a new luminosity record has beenachieved with skew sextupole magnets, the verticalbeam-beam parameter still remains ~0.09 at crab
crossing after two years of intensive tuning.

•The bunch length σz* = 3mm is difficult in LER due
to CSR. The minimum bunch length has been
estimated as 5 mm. (K. Oide, 14th KEKB ARC)

•Realistic IR design for βx* =20 and ξy = ~0.3 has
not yet been found.

•The construction and operation costs should bedecreased.

HOW much is the IMPACT ON
the LUMINOSITY?

* All luminosities assume that Crab Crossing works perfectly.
No technical solution has been found yet.
K. Oide, 21 May 2009 @ HEPAP �Nano-beam Scheme•

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.

Parameter Optimization

Main parameters can be quickly optimized with this panel.

Beam Parameters
KEKB
DesignKEKB Achieved: with crab

SuperKEKB
High‐Current

SuperKEKB
Nano‐Beam

Energy (GeV) (LER/HER)

3.5/8.0

3.5/8.0

3.5/8.0

4.0/7.0

βy* (mm)10/10

5.9/5.9

3/6

0.27/0.42

εx (nm)

18/18

18/24

24/18

3.2/2.4σy(µm)

1.9

0.94

0.85/0.73

0.059

ξy

0.052

0.129/0.090

0.3/0.51

0.09/0.09

σz (mm)4~65/3

6/5

Ibeam (A)2.6/1.1

1.64/1.19

9.4/4.1

3.6/2.6

Nbunches

5000

1584

5000

2503

1

2.115380Luminosity(1034 cm‐2 s‐1)Colliding bunches
Belle IINew IRe- 2.6 A!
New beam pipe
& bellows

SuperKEKB

New superconducWng /permanent ﬁnal focusing
quads near the IP
e+ 3.6 A!

Replace long TRISTAN dipoles
with shorter ones (HER)

Add / modify RF systems forhigher beam current
Low emiTance positrons
to inject
Redesign the HER arcs tosqueeze the emiTance

TiN‐coated beam pipe withantechambers

Positron source

Damping ring

New positron target /capture secWon

Low emittance gun

Low emiTance electrons
to injectx 40 Gain in Luminosity

Nonlinear Terms around IP*2yβ
Jy 0 =A(µy ) 2 *2  *1− KL  L
 3


K

L*Phys. Rev. E47, 2010 (1993)

KEKB
LLER

€

KEKB
R

SuperKEKB
L

SuperKEKB
R

βy*�

(mm)�

K

(1/m2)-1.777�

-1.778�

-4.425�

-6.003�

L*(m)1.332�

1.762�

0.7269�

0.7680�

Jy0 / A(µm)

8.425�

4.221�

0.03919�

0.02825�

5.9�

0.27�

Summary•

We have made great progress in the Nano-beamscheme:– Lattice: solutions exist, preserving the present tunnel. Optimization of
dynamic aperture is going on.
– IR: large crossing angle, independent quadrupoles for both beams.
– Electron cloud mitigation has been studied at KEKB.
– RF system will be added and modified to store beam currents twice as thoseof present KEKB.
– Design of e+ damping ring has been done.
– Low-emittance electron gun will be installed in linac.

•So far we have not found showstoppers. We still
have issues to be solved, but have been making
steady progress in all of them.

BackupBeam Parameters �