KEKB / SuperKEKB
The Luminosity Frontier(number of events/unit time)= (cross section) X (luminosity)

Katsunobu Oide (KEK)Jan. 19, 2005 @ Kyoto Univ.
http://kekb.jp

KEKB = Asymmetric Double-Ring Collider for B-Physics
8 GeV Electron + 3.5 GeV Positron
Superconducting
cavities (HER)
Belle detectore-

KEKB B-Factorye+

ARES copper
cavities (HER)

ARES copper
cavities (LER)
TRISTANtunnel

8 GeV e3.5 GeV e+
Linace+ target

1989:

Design work started.

1994:

Approval of the budget, construction
started.

June 1995:

KEKB Design Report

Sep. 1997:

Commissioning of the injector Linac
started.

Dec. 1998:

First beam at HER.

Jan. 1999:

First beam at LER.

May 1999:

Belle roll-in.

June 1999:

First event at Belle.

Apr. 2001:

World record of the luminosity, 3.4/nb/s.

Oct. 2002:

World record of the integrated
luminosity, 100 /fb.

May 2003:

Exceeded the design luminosity, 10/nb/s.

Feb. 2004:

Exceeded 12 /nb/s & 200 /fb.

June 2004:

13.9 /nb/s & 288 /fb.

Dec. 2004:

338 /fb.

… continues rewriting own records …

Mt. Tsukuba

Nikko

Belle

KEKB Rings

KEK SiteLinac

Continuous Injection™

1034 cm-2s-1

600 /pb/day

The best day 5/23/2004>1000 /pb/day delivered
944 /pb/day recorded

The Competition

KEKB

Up to now, KEKB is taking the lead over
PEP-II by about 50% margin.

PEP-II

But cannot relax. They have a very
ambitious plan to 2.4x1034 cm-2s-1 by
2007.

Continuous Injection Mode (CIM)

before•••after

Belle takes data continuously, except for veto for 3.5 msec after
each injection pulse.
30% higher average luminosity.
More stable operation & higher operating currents.

The machine must be tuned up as ideal, toobtain the predicted luminosity….
• Four betatron tunes• Emittances• Grobal orbit/optics correction– Measure orbit responses at BPMs (450/ring)– Δβ/β ≤ 7 %– Δηy ≤ 7 mm
– X-y coupling• Tuning of local parameters at the IP– relative orbit offsets (5) - better than 0.1σ, looking at beam-beam
deflections, beam sizes, and Belle vertex– Vertical waists (2) ±0.5 mm– vertical dispersions (4)– x-y coupling parameters (8)Collision with a finite crossing angle
zEasier beam separation.
zNo bend for the incoming beam (less radiation).
zNo separation bends (less background).
zSimplified IR.
zRoom for solenoid compensation, smaller β∗.

So, the merits were obvious, but was that safe enough?
zWhat about the synchrotron-betatron coupling?

⎛x ′zy ′z ⎞H ≈ f ⎜x ++ θ x z, y +⎟δ (s − nC )⎝22⎠
z: longitudinal position in a bunch, θx: horizontal half corssing angle

Collision with a finite crossing angle
Synchrotron-betatron couplings are inevitable for a beam-beam interactionanyway, even with a head-on collision.
2⎞2⎛4 πξ y ⎛y ′z ⎞ ⎜ (x + θ x z) ⎟fy ≈ * ⎜y +δ s − nC ) + higher orders⎟ ⎜1−*2 ⎟ (⎠⎝2βy2σ x⎝⎠The relative magnitude of the crossing angle term isabout same as the original term.
Strong-weak simulations, KEKB Design Report, 1996

Crossing

Head-onCrossing angle is manageable, if we choose the tunes.

Crab crossing in the near futurezCrab crossing will boost the beam-beam parameter up to 0.14!
(Strong-weak simulation)

ξyK. Ohmi

Head-on(crab)◊◊◊◊(Strong-strong simulation)◊crossing angle 22 mrad
zSuperconducting crab cavities areunder development, will be installedin KEKB in early 2006.
Input Coupler
I.D. 240

I.R. 90

I.D. 120

I.D. 188

I.R.241.5

Coaxial Coupler

866

I.R. 20
I.D. 30
Monitor Port

0100

50150483

scale (cm)K. Hosoyama, et alFabrication& Processing 1

Nb
Half Cell

Hydro-forming

Grinding ofWelding Part

BarrelPolishingFabrication & Processing 2

Electro-PolishingHigh Pressure Water Rinsing
by 80 bar Ultra-Pure water

Annealing at 7000C for 3 hours

1 /ab comes on the horizon!
44 /fb/mo

24 /fb/mo.

Crab Cavity
Beam Test

Initial goal

18 /fb/mo.
We are hereSuperKEKB, the next step

SuperKEKBKEKB design

ILC??

Three factors to determine luminosity:
Stored current:

Beam-beam parameter:

1.2/1.65 A (KEKB)

0.057 (KEKB)→ 4.1/9.4 A (SuperKEKB)→ 0.14 (SuperKEKB)

Lorentz factor

σ *y ⎞ I±ξ± y ⎛ RL ⎞L=⎜1+ * ⎟ * ⎜ ⎟2ere ⎝ σ x ⎠ β y ⎝ Ry ⎠γ± ⎛Classical electron radiusBeam size ratio

Geometrical reduction factors due tocrossing angle and hour-glass effectLuminosity:

Vertical β at the IP:

0.14 ×1035 cm-2s-1 (KEKB)

5.2/6.5 mm (KEKB)

2.5×1035 cm-2s-1 (SuperKEKB)→ 3.0/3.0 mm (SuperKEKB)

Colliding Bunches at KEKB / SuperKEKB
Hor. Crossing Angle 22 /30 mrad
World’s smallest beam size inring colliders
7.8 / 11.8 ×1010
positrons/bunch

5.8 / 5.1 ×1010
electrons/bunch

Height: 2.1 / 1.4 μm

Width: 110 / 59 μm

Length: 7 / 3 mm
Revolution period: 10 μsec1293 / 5018 bunches / beam
6 - 8 / 2 ns bunch spacing

8GeV
Positron beam
4.1 A

3.5GeVElectron beam
9.4 A

Complicated Object

HOM ∝High-power RF

Beam Instabilities

N± I±σz

I± = N± N b frev

Heating, discharge, destruction…

Impedance ofcomponents
Belle backgroundγ ± I ±ξ± yL≈
2ere β *yσ z ≤ β *yElectron cloud
Fast ionprecise control oflinear optics
Orbit drift
shorter lifetime

higher chromaticity
Strong injector

smaller aperture

ARES Cavity•••••

Passive stabilization with huge stored energy.
Eliminates unnecessary modes by a coupling of 3cavities.
Higher order mode dampers and absorbers.
No need for longitudinal bunch-by-bunch feedback.
No transverse instability arises from the cavities.

StorageAccel.

Resonant

Superconducting Cavity•••

World’s highest current, 1.2 A.
Input coupler has been operated up to 380 kW.
Ferrite HOM absorber working at 10 kW.

ARES upgrade for SuperKEKB◆

Larger detuning⇒

Change energy ratio : Us/Ua = 9 →15

Small modification on the window size of A-cav-1 mode growth time :0.3 ms to 1.6 ms.
Then the -1 (and -2) modes related to the fundamental
mode will be suppressed by a FB system in the RFcontrol system.
(need bunch-by-bunch FB to suppress ARES HOM & 0/πmode instability )◆Higher HOM power
Upgrade of HOM damper◆

Higher input RF power
400 kW/cavity -> 800 kW/cavity
R&D of input coupler using new test-stand.
Talks by Kageyama, Abe

Superconducting Cavity
SuperKEKB
challenges:
Storing world’s
highest beam current of 1.2A.
The
expectedloadoperatedto the HOM
Input
coupler powerhas beenup to 380kW.
absorberis 50 kW/cavityat 4.1
A,Ferrite Higher
Order Mode(HOM)(even)
withworking
a largeratbeam
pipeof 220mmφ. 12kW atabsorber
10 kW(hasachieved1.2 A).
HOM damper upgrade may be needed.

Talk by Mitsunobu

Electron cloudSolenoid (800 m)

No Solenoid

Blow-up of the vertical beam size in LER has
been suppressed by more solenoid windings.
The coverred length of solenoids reached2,300 m, raised the threshold to 1.8 A.

Specific luminosity vs. LER current.
Solenoids are just so effective.

Winding more solenoids in the LER

Vacuum components:
Antechamber-type copper duct
Smaller SR Power Density
Lower Impedance
Lower photoelectron production

Prototype ducts were installed in the LER (Jan.2004)
Talk by Suetsugu

Fight forHigh Current- High luminosity always requires high storedcurrent.
- The history of KEK was a history of fight againsthigh current, which caused
Heating of components, by synchrotron lightand higher order modes

Heavy groove on the surface of a copper movable mask inHER.

Discharge and melt down
Vacuum leak
Damage on Belle detectors- Endless upgrades of components have been doneon vacuum chambers/movablemasks/bellows/pumps/abort windows, etc.
- Machine protection system with fast beam abort
has been developed to reduce the possible damage.

Thermal deformation of the fingers for rf shield ofbellows.

Vacuum components:
Bellows chamber with comb type RF-shield

High thermal strengthzLow impedancezNo sliding contact on thesurface facing the beamz

Comb-type bellows were installed in the LER (2004).
Talk by Suetsugu

C-Band Klystrons
Prototype C-band structure
installed and tested at linac
using actual beam (2003).
Measured field gradient of41 MV at 43 MW agrees withexpectation.

Talk by Kamitani

Damping Ring•

Positron emittance needs to be damped, to pass reduced
aperture of C-Band section and to meet IR dynamic aperture
restrictions.
– Electron DR may be considered later to reduce injection backgrounds inphysics detector, but for now only positron DR considered.

•Damping ring located downstream of positron target, before CBand accelerating section.

e+ production
e- gunBT
e+ Damping Ring

Talk by Kikuchi

J-ARC

How long should we run?

.6 /ab/mo.

ShutdownCrabData doubling period > 4yrs = unhealthy

How much do we need?

We may invite another detector.

… if you like it.

Summary• KEKB has been the front runner on theluminosity frontier.
• 1 /ab will be reached around 2007.
• A technically feasible design of SuperKEKB for
2.5×1035cm-2s-1 has been done.

Luminosity*:

Beam-beam tune
shift parameter*:
Beam current:

Luminosity
rewritten:*Assume both beams have the same sizes andβ*s.

N+ N− fL=RL**
4πσ xσ y

ξ± x,y =reGeometrical
reduction factors (σz,β∗, θx, εx, …)

N m β *x,y(2πγ ± σ *x,y σ *x + σ *y)Rx,yI± = N± ef

σ *y ⎞ I±ξ± y ⎛ RL ⎞L=
⎜1 + * ⎟ * ⎜ ⎟2ere ⎝ σ x ⎠ β y ⎝ Ry ⎠γ± ⎛γ ± I ±ξ± yL≈
2ere β *y(flat beam, short bunch)A jacket-type magnetic shield for the Crab Cavity.

The magnetic shield is made by 3mm thick permalloy sheet by spinning and forming.
The cell and beam pipe parts can divide into two peaces and assemble around thecrab cavity.

Parameters for SuperKEKB
bare latticewith beam-beamunit

Beam current (LER/HER)

I

9.4/4.1

9.4/4.1

A

Beam energy (LER/HER)

E

3.5/8.0

3.5/8.0GeVEmittance

εx24

77

nm

Horizontal beta at IP

βx*204.5cm

Vertical beta at IP

βy*32.3mmHorizontal beam size

σx*6959μm

Vertical beam size

σy*

0.7

1.4μm

Beam size ratior = σy*/σx*

1

2.4%

Crossing angle

θx00mradLuminosity reduction

RL

0.86

0.81

ξx reduction

Rξx0.990.97

ξy reductionRξy1.11

1.17

Horizontal beam-beam

ξx0.137

0.041

Vertical beam-beam

ξy0.218

0.108

RL/Rξy0.78

0.70

L4x1035

2.4x1035

Reduction ratio
Luminosity

cm-2s-1

Machine Parameters (June 3, 2004)

Machine parameters
Parameters

LER/HER

Unit

Beam energy

E

3.5/8.0

GeV

Beam currentI

9.4/4.1

A

Particles/bunchN

1.18´1011/ 5.13´1010

Number of bunches

nb5018Circumference

C3016.26m

Bunch spacing

σb0.6mHorizontal β at IP

βx200mm

Vertical β at IPβy3mm

Bunch length

σz3mm

Radiation loss

U01.23/3.48

MeV/mHorizontal beam-beam

ξx0.137

Vertical beam-beam

ξy0.14

Talk by Ohnishi

Tune Survey
Simulation by M. Tawada
10/29/2002
4/2/2003
5/9/2003

Reducing LER νx from 0.510 to0.506 increased the luminosity
by 20% in 2003, as thesimulation predicted.
20% more luminosity is expected by
reducing HER νx from 0.513 to 0.507.