SLAC Accelerator Development Program:SuperB

Mike Sullivan

OHEP Accelerator Development Review

January 24-26, 2011

Outline

• The SuperB design

• Where SLAC expertise has and can contribute

• Summary

SLAC Accelerator Development Program Page 2

SuperB Design

• SuperB is an e+e- collider running at the Upsilon 4S resonance

• The design luminosity is 11036 cm-2s-1 (50 times higher)• This is achieved through:

– Ultra low-emittance beams– Very small y* values– Beam currents and bunch charge very similar to PEP-II and KEKB– Bunch length similar to present day B-factories (very important for

HOM issues)– Magnetic crabbed waist at the IP

• Can also run at the Tau/Charm region with 1035 luminosity• Electron beam is polarized

e+e- Colliders

1027

1029

1031

1033

1035

0.1 1 10 100 10001027

1029

1031

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1035L

um

ino

sit

y (

cm

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c.m. Energy (GeV)

ADONE

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ADONE

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SPEAR2

VEPP-4M PETRAPETRA

PEPDORIS2

BEPCII CESR

PEP-II

KEKB

LEP

LEP

LEP

LEP

ILC

CLIC

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SuperB

BINP c-

CESR -c

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-- straight sections

-- dipoles

-- quadrupoles

-- sextupoles

-- RF cavities

-- solenoids

IP

66 mrad

RF

HERarc

LERarcHER

arcLERarc

e-e+

Circ = 1254 m

SuperB Layout & Geometry

Projected peak and integrated luminosity

Superb Parameters

SLAC Contributions

• Interaction Region design– SLAC people have been involved in the design of the interaction region of

SuperB since 2005. This has been with close cooperation from people at INFN Pisa and INFN Frascati as well as groups from the detector community.

• Lattice– Some of the lattice topics we have studied are dynamic aperture, spin

rotator insertions, geometric constraints and detector solenoid compensation.

• RF parameters, HOM studies and stability– We have studied the RF parameters needed to sustain the required beam

currents. They have also looked into how we can use the PEP-II RF systems in the SuperB design.

• Polarization– We have put together a detailed design for the polarimeter needed to

measure the longitudinal polarization of the stored electron beam.

Interaction Region

• The design of the Interaction Region is one of the most difficult and crucial aspects of the collider

• A close association with the accelerator and the detector teams is a vital part of putting together a design that will work

• In close collaboration with INFN Frascati and INFN Pisa we have evolved an Interaction Region design that satisfies the accelerator and detector requirements

SuperB Interaction Region

0

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cm 3-Oct-09 M. Sullivan SB_I_ILC_R3_SR_3M

QF1QF1

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Solenoids

QD0

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Cryostat

Note the expanded left-hand scale

m

Interaction Region: Details

• One of the most challenging aspects of the SuperB IR design is the very low beta functions at the IP X* is 2.6 and 3.2 cm (PEP-II was 25-30 cm) 10

Y* is 0.25 and 0.21 mm (PEP-II was 8-12 mm) 50

– Light source rings never squeeze the beam down this much– The ILC design has similar values (2 cm and 0.4 mm) but that is a

single pass machine

• These very low values force the final focusing magnets to be as close as possible to the collision point– This puts all of the final focus magnets inside the detector

Interaction Region: Details

• Other design constraints– The detector needs as much total solid angle as the accelerator can

give it (300 mrad cones – same as PEP-II)– The detector beam pipe must be no larger than 10 mm radius in

order to maximize the physics

• We have incorporated a special dual quadrupole design in order to meet the design requirements– These magnets are super-conducting

• In addition, we have permanent magnets in the small region between the primary magnets and the junction of the beam pipes

Some of the Main IR Design Issues

• Control of the SR backgrounds– This drives much of the design as background rates can vary by orders of

magnitude with seemingly small changes in design

• Control of the local HOM power

• Developing a cryostat design compatible with detector acceptance and magnet requirements

• Developing magnet designs that can perform to the demanding specs of the accelerator

• Developing a complete assembly and access plan

Some IR Related Operational Issues

• Vibration control of the final focus elements– It is vital to understand this issue and adopt adequate correction

mechanisms. – We have already started work on this issue and, in particular,

with related aspects to the ILC IR design.– Some present light source experience will help but we have to bring

two very small beams into steady, reliable collision

• Luminosity measurement and maximization through beam position control– SuperB will need a fast, accurate luminosity detector– We have developed a preliminary design for a fast luminosity

feedback (ala PEP-II system) to keep the beams in collision

Lattice Work

• We have worked closely with the Italians (INFN Frascati) to develop a working lattice for the SuperB accelerator (2 examples)– Spin rotator sections

• The spin rotator sections are an integral piece of the lattice and are also lose to the IP. The matching of the spin rotator sections with the other constraints concerning the lattice near the IP (crab waist, chromaticity correction, etc.) has been a complicated balancing act. Together we have developed a realistic lattice for this area.

– Solenoid compensation• The compensation of the detector field is another complicated issue. The low

emittance of the beams and the low coupling (The final focusing elements in the SuperB design are permanent magnets that are too close the IP to allow the detector field to be canceled by compensating solenoids. We have developed a scheme for solenoid compensation that involves rotating the PMs as well as compensating the detector field as much as possible and including skew quads and compensating solenoids located outside of the detector.

Spin Rotator Section

• Similar layout as in HER except that matching section is shorter to provide space for spin rotator optics.

IP

Y-sext

X-sext

V12

Match & spinrotation

Crab

Solenoid compensation

QS1 QS3QS2QSDY QS4QSDPY

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[xy]1/2

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Correctors within ±7.5 m of IP (symmetric relative to IP)

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V2

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RF, HOMs, beam stability

• A lot of work has gone into finding the RF parameters needed to support the 1-2A beam currents of the SuperB

• The RF systems of PEP-II have been selected by the SuperB project. These stations delivered half of the wall plug power to the beam, one of the most efficient high-current RF systems ever built.

• Minimizing the ring impedence and maximizing the cavity coupling are just a couple of the constraints used to optimize the design

Phase transient

• We have also completed a very careful study of the phase transient induced by the ion gap in the ring current– PEP-II experience has told us that an ion gap of at least 1-2% is

necessary

• The phase transient is now an important issue since the collision has a large crossing angle (60-66 mrad)

• Control of the transient difference between the two beams has become an added constraint to the selection of beam current values and number of RF stations needed for each ring

Polarization

• The SuperB design calls for a polarized electron beam• This will significantly increase the physics potential of this

accelerator• We have found that the beam lifetime is too short for natural

polarization to build up• However, we can fill the ring from a polarized source and

the beam will stay polarized as long as the depolarizing time is long enough

• One therefore has to stay away from depolarizing resonances

Polarization vs Beam energy

With a 90% polarized injected beam and a 3.5 min. ring lifetime we can have nearly 80% polarization if we stay near the peak

Polarization Measurement

• Because we are constantly injecting polarized beam into the ring the measurement of the polarization of the beam becomes an interesting challenge

• We need to measure the polarization of each of the 978 beam bunches on a sub-minute time scale (the bunch frequency rate is over 200 MHz)

• The polarization measurement accuracy must be below 0.5% (at least as good as if not better than the measurement used for the SLC/SLD experiment)

• No one has done this

Polarimeter

We will use the bend magnets in the lattice as an energy spectrometer for the compton scattered electrons

By adding a port in the beam pipe, we can also capture the gammas from the compton scatter

The laser crosses the beam in a shallow vertical angle

Workshops/collaborations

• The SuperB team has four workshops each year and this has been of enormous benefit to the design effort

• We are able to meet with our collaborators in Italy, exchange notes concerning design progress and brainstorm ideas to overcome newly uncovered issues

• Eight papers have come out of this effort over the last two years

• We have also been a main contributor to the writing up of the accelerator for the CDR in 2007 and for the update to the CDR (CDR2) completed last summer (2010)http://arxiv.org/find/all/1/all:+AND+SuperB+Accelerator/0/1/0/all/0/1

Summary of what has been done

• The SuperB accelerator concept is quite exciting– Making a collider using very low-emittance beams, very small *

values, and high-currents (Similar to PEP-II currents)– The crab waist concept is what gives this collider the ability to

achieve nearly 100 times the luminosity of present day B-factories

• The simultaneous control of the low-emittance beams and the high-current effects on these beams will move accelerator technology into new territory

• The Interaction Region – one of the crucial aspects of the design – is an interesting balancing act of conflicting requirements. The design must cleanly mesh in order to maximize the chances of success.

Conclusion

• SLAC and other US laboratories can make significant and lasting contributions to the SuperB accelerator while enriching and improving the accelerator program here in the U.S.

• The knowledge gained from getting this collider designed, built and operational will be invaluable for future accelerators

• Finally, the physics that will come from this collider is quite exciting!