SLAC Accelerator Department Super-B-Factory John T. Seeman Assistant Director of the Technical Division Head of the Accelerator Department Caltech Meeting

SLAC Accelerator Department

Super-B-Factory

John T. SeemanAssistant Director of the Technical Division

Head of the Accelerator DepartmentCaltech Meeting

December 3, 2004


Beam Lines

SBFSBF injector needs no changes


The PEP-II e+e- asymmetric collider

Location of new RF cavities


PEP-II HER RF cavities


Luminosity Equation y is the beam-beam parameter (~0.065)

Ib is the bunch current (1 to 3 mA)

n is the number of bunches (~1600) y

* is the IP lattice optics function (vertical beta) (10 mm)

E is the beam energy (3.1 and 9 GeV) Luminosity (1033 cm-2 s-1)

*341017.2

y

byEInxL


Achieving Super B Luminosities bnI Higher Currents:

o More rf power, cooling, injectoro More HOM heating (more bunches)o Beam instabilitieso Electron clouds, fast ions

* y Smaller y*:o Smaller physical/dynamic apertureo Shorter lifetime, more background

Shorter z:

o More HOM heatingo Coherent synchrotron radiationo Shorter lifetime, more background

y Higher tune shifts:

o Head-on collisions replaced by angled crossing

o Degrades maximum tune shift unless crabbing cavities used

34*

2.17 10 y b

y

n EIL


PEP-II/BaBar Roadmap: Super B-Factory Study

• The Roadmap Committee has studied the future of PEP-II and BaBar with a possible large upgrade at the end of the decade.

• A Super-PEP-II could produce 10 ab-1 per year with a peak luminosity of 7 x 1035/cm2/s.

• Accelerator parameter goals have been set and work towards a solid design has started.

• The long range time goal is to have a new upgraded accelerator running in 2011 or 2012.


PEP-II upgrades schemesLuminosity (x 1035)

1.5 2.5 7 57

RF frequency (MHz)

476 476 952 476952

Site power (MW)

75 85 100 70100

Crossing angle No Yes Yes Yes

Crab cavities No Yes Yes Yes

Replace LER Yes Yes Yes Yes

Replace HER No Yes Yes Yes

Upgradeable NoYes

(to 952MHz)Yes Yes

Detector requirements depend on projecting backgrounds for luminosities that are >20 times

larger than at present

Recommended


LER ring (no IR yet)

6 sextants, small negative momentum compaction,using present LER dipoles & quads (16 families),

3 sextupole families

Biagini


One sextant

Biagini


One half-arc + dispersion suppressor

Biagini


Super B-Factory Components Under Study

•

PEP-II 1036 B-Factory +/- 12 mrad xing angle Q2 septum at 2.5 m

30

20

10

0

-10

-20

-30

cm

-7.5 -5 -2.5 0 2.5 5 7.5m 31-JAN-2002

M. Sullivan

Q1

Q1Q1

Q1

Q2

Q4

Q5Q2

Q4Q5

IR SC magnets

New RF cavities New IR layout

New Arc magnets


New IR magnet design (Parker)


New IR magnet designQuadrupole, anti-

solenoid, skew quadrupole,

dipole and trims located in one

magnet.

All coils numerically wound on a bobbin.


Activities towards luminosity upgrade

crossing angle 22 mrad

Head-on(crab)

◊

◊◊

◊◊

y

(Strong-weak simulation)

(Strong-strong simulation)

Crab crossing may boost the beam-beam parameter up to 0.2!

Superconducting crab cavities are under development, will be installed in KEKB in 2005.

I.R. 20

I.R. 90

I.D. 188

I.D. 120

I.D. 30

I.D. 240

Input Coupler

Monitor Port

I.R.241.5

483

866Coaxial Coupler

scale (cm)

0 50 100 150

K. Ohmi

K. Hosoyama, et al


Electron Cloud Instability & multipacting


LER aluminum vacuum system: limit at 4.5A

Total LER SR power

= 2 MW

High powerphoton stops

AntechambersReduce Electron-Cloud-Instability

4.5 A at 3.1 GeV

Photon Stop limits


Vacuum system for Super B Factory

• Antechamber and solenoid coils in both rings.

• Absorb intense synchrotron radiation.

• Reduce effects of electron clouds.

Circular-chamber

Ante-chamber

Ante-chamberwith solenoid field

Build-up ofelectron clouds


HOM calculations: 476 MHz cavity

476 MHz cavity with a larger beam

opening

S.Novokhotski

Rbeam = 95.25 mmTotal loss = 0.538 V/pC

Loss integral above cutoff = 0.397 V/pC

HOM Power = 203 kW @ 15.5A


HOM calculations: 952 MHz cavity

952 MHz cavity with a larger beam

opening

S.Novokhotski

Rbeam = 47.6 mmTotal loss = 0.748 V/pC

Loss integral above cutoff = 0.472 V/pC

HOM Power = 121 kW @ 15.5A


87.57

6.56

5.5

4

3.532.5

21.51

0.5

4.55

HER Radiative Bhabhas

-7.5 -5 -2.5 0 2.5 5 7.5

0

10

20

30

-10

-20

-30

m

cm

M. SullivanFeb. 8, 2004API88k3_R5_RADBHA_TOT_7_5M

3.1 G

eV

3.1 G

eV

9 GeV

9 GeV

Luminosity-dependent backgrounds

o SR in bend & quadrupole magnets

o Current dependent terms due to residual vacuum

o Bhabha scattering at IP

PEP-II Head-On IR Layout


Achieving Super B Luminosities bnI Higher Currents:

o More rf power, cooling, injectoro More HOM heating (more bunches)o Beam instabilitieso Electron clouds, fast ions

* y Smaller y*:o Smaller physical/dynamic apertureo Shorter lifetime, more background

Shorter z:

o More HOM heatingo Coherent synchrotron radiationo Shorter lifetime, more background

y Higher tune shifts:

o Head-on collisions replaced by angled crossing

o Degrades maximum tune shift unless crabbing cavities used

34*

2.17 10 y b

y

n EIL


Power Scaling Equations

• Synch rad ~ I E4/• Resistive wall ~ I2

total/r1/frf/z3/2

• Cavity HOM ~ I2total/frf/z

1/2

• Cavity wall power = 50 kW

• Klystron gives 0.5 MW to each cavity

• Magnet power ~ gap~r1


Power scaling equations• Synch rad ~ I E4/• Resistive wall ~

I2total/r1/frf/z

3/2

• Cavity HOM ~ I2

total/frf/z1/2

• Cavity wall power = 50 kW

• Klystron gives 0.5 MW to each cavity

• Magnet power ~ gap ~ r1


Site power limits

476 MHz

952 MHz

(Linac, PEP-II magnets and campus power = 40 MW)

1.5x10342.5x1034 7x1034


Recommended scenario: 5 to 7 x 1035

• Replace present RF with 952 MHz frequency over period of time.

• Use 8 x 3.5 GeV with up to 15.5 A x 6.8 A.• New LER and HER vacuum chambers with antechambers

for higher power (x 4). • Keep present LER arc magnets but add magnets to soften

losses; replace HER magnets as well.• New bunch-by-bunch feedback for 6900 bunches (every

bucket) at 1 nsec spacing. (Presently designing feedback system being 0.6-0.8 nsec spacing.)

• Push y* to 1.5 mm: need new IR (SC quadrupoles) with

15 mrad crossing angle and crab cavities


Important Factors in Upgrade Direction• Project is “tunable”

– Can react to physics developments

– Can react to changing geopolitical situation

• Project anti-commutes with linear collider

• Will emerge from BABAR and Belle, but could be attractive to wider community in context of other opportunities

– As we learn more about machine and detector requirements and design, can fine tune goals and plans within this framework

• Project has headroom

– Major upgrades to detector and machine, but none contingent upon completing fundamental R&D

– Headroom for detector up to 5 x 1035; with thin pixels beyond

– Headroom for machine up to 8.5 x 1035; requires additional rf, which can be staged into machine over time


Luminosity Equation • When vertical beam-beam parameter is limited. y ~ 0.06 in PEP-II and KEKB.

• To raise luminosity: lower y*, raise I & y.

)(2 **

*0 flatbeamsNr

xy

yby

*341017.2

y

byEInxL


Early SBF with 3 x 1035

• E+ = 8 GeV• E- = 3.5 GeV• RF frequency = partial 476 and partial 952.• I+ = 5.3 A• I- = 12.0 A y

* = 3 mm x

* = 25 cm• Emittance = 42 nm• Bunch length = 3.3 mm• Crossing angle = ~15. mrad• Beam-beam parameters = 0.11• N = 3450 bunches• L = 3 x 1035 cm-2s-1

• Site power with linac and campus = ~90 MW.


Final SBF with 8.4 x 1035

• E+ = 8 GeV• E- = 3.5 GeV• RF frequency = 952 MHz• I+ = 10.1 A• I- = 22.8 A y

* = 2 mm x

* = 15 cm• Emittance = 39 nm• Bunch length = 2.2 mm• Crossing angle = ~15. mrad• Beam-beam parameters = 0.11• N = 6900 bunches• L = 8.4 x 1035 cm-2s-1

• Site power with linac and campus = ~120 MW.


Possible Timeline for Super B Program

LOI

Construction of upgrades to L = 5-7x1035

-1~10 ab / yrLdt

Super-B Program

CDR Installation

R&D, Design, Proposals and

Approvals

P5

Construction

2001 2003 2010200820062005

Planned PEP-II Program

-1140 f bLdt -1500 f bLdt -1~1 2 abLdt

(June 30, 2003) (End 2006) (PEP-II ultimate)

Commission

2012

Super B Operation

2011


Simulation: head-on vs finite-crossing

• Beam-beam limit is ~0.05 for finite-crossing collision from the both simulations. (Not much difference between 11 & 15 mrad)

• Head-on collision much improves beam-beam parameter.• Discrepancy between Weak-Strong and Strong-Strong

simulation is a factor of 2 for head-on collisions.

Weak-Strong Strong-Strong

11 mrad = half crossing angle

[bunch current]

[bunch current]


Coherent synchrotron radiation

• Numerical simulations with mesh (T.Agoh and K.Yokoya)

– Analytic formula is not reliable due to strong shielding.

• Loss factor estimation :– 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 ring

Energy change as a function of z/zKEKB LER/ 2.6A (5120)

c h3 2.5 mm

bunch length dependence

chamber height dependence


S-KEKB Choice of x, x

• x=30, 20, 15 cm

• x=24, 18, 12 nm

Strong-Strong Beam-BeamSimulations by K. Ohmi

Our choice

Achievable beam-beam parameters depends on x and x.


Super KEKB machine parameters

Beam-beam parameter is obtained from simulations: strong-strong (weak-strong)

Documents

SLAC Accelerator Department Super-B-Factory John T. Seeman Assistant Director of the Technical Division Head of the Accelerator Department Caltech Meeting