Upgrade plan overview
Y. Ohnishi
The ninth KEKB Accelerator Review CommitteeFebruary 16-18, 2004
KEK1

Letter of Intent• LoI consists of physics, detector, accelerator
part.
• We submit accelerator part of LoI to KEKB
Review committee (complete LoI to LCPAC) :"Accelerator Design for a
Super B Factory at KEK"

• LoI is in draft stage, however, almost finished.
• This talk is overview of LoI, but all contents can
not be covered.

2Design strategy• Target luminosity is 2-5 x 1035 cm-2s-1.

– Original target luminosity is 1035 cm-2s-1 even if
crab-crossing is failed.

• Re-using components of KEKB as much as
possible• Maintaining acceptable detector backgrounds• Continuous injection and a powerful injection
system• Low beta function at IP• Finite-crossing and crab-crossing scheme• High beam currents3

Machine parameters!"#$"#%&'(1&8234435

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Beam-beam parameter is obtained from simulations : strong-strong (weak-strong)4Luminosity considerations• Fundamental formula for luminosity :*e±" e ± $ # y '$ Ie ±* y '$ RL ')L=&1+ * )&& * ))&&
2ere % # x (% + y (% R* y )(• Flat beam : 1 + σy*/σx* ~ 1!
• Reduction
factors : RL/Rξy• Beam-beam parameter : ξy
• Vertical beta function at IP : βy*• Beam current : I(part 1)
(part 2)(part 3)(part 4)
5

Part 1 Luminosity reductions
βx = 20 cm

θx = 30 mrad

εx = 24 nm
εy = 0.18 nm

εx = 30 nm
εy = 1.8 nm*• The ratio of RL/Rξy is larger as crossing angle increases.
• The ratio of RL/Rξy is larger as βx* decreases.
• The ratio is not big change. RL/Rξy~ 0.8. The change is~5% at most in a range of machine flexibility.
• Fundamental parameters : βy*(and σz), ξy, I
6Part 2 Beam-beam parameters• Beam-beam parameter is not a free parameter.
• Finite-crossing angle scheme achieves 0.05 from KEKB
experiences.
• Beam-beam limit is 0.05 ?
• Numerical simulations may help to understand orpredict the beam-beam limit .
• Colliding beam, more than 1011 particles, can not besimulated even though using Super-Computer.
• Models are needed and/or must be assumed.
• Weak-strong simulation– Gaussian model (beam shape fixed with Gaussian)• Strong-strong simulation– PIC model (beam given by macro-particles; arbitrary shape)
7

Head-on VS finite-crossing
W-SS-S

half crossing angle

bunch current

bunch current• Beam-beam limit is ~0.05 for finite-crossing collisionfrom the both simulations. (Not so difference between 11 and 15 mrad)• Head-on collision much improves beam-beam parameter.
• Discrepancy between W-S and S-S is a factor of 2 forhead-on collision.
8

Crab-crossing
Crab-crossing can achieve
the same performance ashead-on ?

head-oncrab-crossing

Non-linear term ?

• Finite-crossing angle can provide much benefits;– Simple IR design, avoiding parasitic collision etc.

• Crab-crossing restores full luminosity of head-oncollision.
• Crab cavity is needed to achieve higher luminosity.
• Beam-beam parameter of 0.14 is expected. (S-S)
9

Crab cavity future plans
New crab cavity•••••••

Superconducting crab cavity with squashed cell and coaxial beam pipe (Ib= 1~2 A)
We will start at KEKB-HER with a single crab cavity in the end of 2005.
Check hardware and modify if necessary.
Then we will install one crab cavity in LER in 2006 summer.
Beam will be crabbed in the whole ring. Is this OK ? HOM, RF cavity ?
If everything is OK, luminosity becomes twice higher than before ?
Simultaneously, we develop new crab cavity for 10 A.
10Part 3 Vertical beta function at IP• Move final focus quadrupoles closer to IP forlow beta.
βx* / βy*=20 cm / 3 mm.
• Physical aperture– Beam injection• Dynamic aperture– Beam injection / Lifetime

Magnet aperture

Good magnetic field quality
Small leakage field• Crossing angle– Beam separation / Magnet design• Synchrotron radiation from IR magnets– Heating of components / Detector background11

IR magnet layout for SuperKEKBx (m)30 mrad finite-crossing

QC2RE
QC2LP

QC1RE

Belle solenoid axis
8 mrad22 mrad

HER →

QC2LE

QC1LE

QCSL QCSR

IPQC2RP← LERs (m)12QCS for SuperKEKB and KEKB
θ=150°QCSL ESL-1ESL-2

EFC

SuperKEKB

θ=17°

ESR-2

QCSR ESR-1

KEKB
QCSR

QCSL
ESL

ESR

Move QCS closer to IP and compensation solenoid (ES) is divided intotwo parts; one is overlaid with QCS, the other is in front of QCS.
(Magnetic force on ES becomes weak.)13

IR aperture requirements• Required acceptance depends on linac
beam emittancex2+ " ring px2 = 2J x,ring" ringAcceptanceof ring

2Jx,ring

Px septum

2Jx,injx
Injectionbeam(x # x i ) 2+ " inj px2 = 2J x,inj" injx i = n r$ ring + w s + n s$ inj
2i inj2J x,inj = n %(ni,ns,nr)=(2,2,3)

nrσring wsnsσinj• Smaller beam emittance is preferable.
!
• Positron damping ring (DR) will be
constructed prior to IR upgrade.
14

Injector linac for SuperKEKB
1.

2.
~80 m

Two-bunch
operation

kicker

1. Positron dumping ring (1 GeV)
2. Positron energy upgrade with C-bandfor energy exchange (e- LER / e+ HER)

Electron cloud
Injection rate15

IR aperture requirements (cont'd)
LERHEREnergy

3.5

8Inj.
beame+ with DRe-εx/εy

1.4x10-8

2x10-8(GeV)(m)

HER transverse aperture :Ax=1.9x10-6 m(1.5x10-6 m due to inj. error)
Ay=8x10-8 m

Energy Exchangee+ Damping Ring ⇒ IR upgrade ⇒ Linac energy upgrade
LER

HER

Energy3.58Inj.
beame-e+ with DRεx/εy4.6x10-8

6.3x10-9(GeV)(m)

LER transverse aperture :Ax=2.6x10-6 m(1.8x10-6 m due to inj. error)
Ay=1.8x10-7 m

e- beam determines IR aperture.

16

IR magnet design• QCS (FFQ) and compensation solenoid (ES)– We consider that spatial constraints and electro-magnetic force
on ES for magnet design.

• Synchrotron lights from QCS– Effects of dynamic beta and dynamic emittance– Orbit displacement from design orbit (estimated from KEKBexperience)– PSR=65 kW from QCSL / 179 kW from QCSR

• QC1 (vertical focusing for e-)– Two options : superconducting or normal magnet– SR from QCS.

• QC2 (horizontal focusing for e- or e+)– normal magnet– SR from QCS.

17

QCS and QC1(superconducting magnet)
Crossing angle=30mrad, βx=20cm
beam envelope & synchrotron radiation(SR)pink: SR fans (design orbit)
green : SR fans (inc. dynamic effects and orbit displacement)
Synchrotron light passes through cryostat-bore

QC1LE

Left side

QCSL

QC1RE

QCSR

Right side18

IR optics

SuperKEKB HER

SuperKEKB LERLER IR optics with local
chromaticity correction
HER

LER
KEKB

SuperKEKB

βx* (cm)

56

20

3

βy* (mm)

7.0

3

225

729

βx max (m)

484

1600

625

400

βy max (m)

1225

2025

KEKB

SuperKEKB

βx* (cm)

59

20

βy* (mm)5.8

βx max (m)βy max (m)192.5π cell and non-interleaved
chromaticity correction
LER arc section

Two sextupole magnets in a pair are connected with -I' transformer.
Nonlinearities from sextupoles are cancelled. → Large dynamic aperture
Wide emittance range : 10~36 nm and negative momentum compaction is available.

20Part 4 Beam current• High beam currents

LER 9.4 A and HER 4.1 A– RF power
Increase number of cavities– SR– HOM heating Ante-chamber
Modify HOM damper– Cooling system– Beam instabilities
Feedback system
3.5 GeV e• Fast ion instability
OK ?
• Electron cloud instability• etc.

– Short bunch length (σz < βy*)Ante-chamber
Solenoid coils
Energy exchange ?

• HOM heating• Touschek lifetime
Increase(CSR)
number• Coherent synchrotron radiation– Injectionof bunches

Chamberheight ?

• Powerful injector, continuous injection
C-bande+ damping ring21

RF system• KEKB RF system will be used as much aspossible.
• ARES in LER• ARES + SCC in HER• Need improvements– Modified LER-ARES decreases CBI growth time (0.3ms to 1.6 ms). Increase energy ratio ofUstorage/Uaccelerating from 9 to 15.
– New HOM dampers– New RF couplers– Number of RF system will be doubled.
22

Vacuum system
Circular-chamber
Build-up ofelectron clouds• Ante-chamber and solenoid
coils in both rings.
• Absorb intense
synchrotron radiation.
• Reduce effects of electronclouds.

Ante-chamberAnte-chamberwith solenoid field23

Beam instrumentation• Beam position monitors• Bunch-by-bunch Feedback system– Transverse– longitudinal (Coupled-bunch instability due to RF cavities)• Gated tune meters• Synchrotron radiation monitors– HER/LER/DR– We monitor beam size to optimize luminosity.

Inevitable instruments
24

Coherent synchrotron radiation
Energy change as a function of z/σz

KEKB LER/ 2.6A (5120)

bunch length
dependence

chamber height
dependence• Numerical simulations with mesh (T.Agoh and K.Yokoya)– Analytic formula is not reliable due to strong shielding.

• Loss factor estimation :"c # h 3 $ % 2.5 mm– No synchrotron oscillation and no interference between bends.
!
– 1 V/pC for 6 mm bunch length (LER)– 10 V/pC for 3 mm bunch length (LER) ⇔ 30~40 V/pC in the ring25

Conclusion• ARES and SCC modified to store 9.1 A and 4.1 A.
• IR should be designed to satisfy requirements of low beta at IP,
physical and dynamic aperture, SR, detector backgrounds, etc.
• We need precise impedance estimations concerned with HOM.
• We need reliable simulations to estimate beam instabilities, FII,ECI, CSR, etc.
• To overcome electron clouds is the most important issue.
• Factor of 1035 cm-2s-1 depends on whether crab-crossing is successor not.
• The luminosity of 1035 cm-2s-1 is a new frontier of the next
generation of B factory.
• SuperKEKB is quite challenging.

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