the interaction region

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5th SuperB Workshop May 9-11, 2007

Interaction Region

The Interaction Region

M. Sullivan

5th SuperB WorkshopParis

May 9-11, 2007

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5th SuperB Workshop May 9-11, 2007

Interaction Region

Outline

• Design Issues

• IR Design

• Toward an improved design

• Summary

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5th SuperB Workshop May 9-11, 2007

Interaction Region

Detector Considerations

• Reasonable angular acceptance– ±300 mrad

• Small radius beam pipe– 10 mm radius

• Thin beam pipe• SR backgrounds

– Rates comparable to PEP-II• Few hits per crossing on Be beam pipe• Little or no hits on nearby beam pipes

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5th SuperB Workshop May 9-11, 2007

Interaction Region

Detector Considerations (2)

• BGB backgrounds– Keep nearby upstream bending to a

minimum– Suggest upstream bending further away

from the detector (>10 m) to minimize the BGB integral

– Low vacuum pressure upstream of the detector

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5th SuperB Workshop May 9-11, 2007

Interaction Region

Detector Considerations (3)

• Luminosity backgrounds– Beam lifetimes– Radiative bhabhas– Beam-beam

• Local HOM power– Small diameter beam pipes trap higher

frequencies– Always get modes when two pipes merge

to one

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5th SuperB Workshop May 9-11, 2007

Interaction Region

Accelerator parameters

LER HEREnergy (GeV) 4.0 7.0Current (A) 3.95 2.17No. bunches 3466Bunch spacing (m) 0.63Beat x* (mm) 20 20Beta y* (mm) 0.2 0.2Emittance x (nm-rad) 1.6 1.6Emittance y (pm-rad) 4 4Full crossing angle (mrad) 34

These parameters constrain or define the IR design

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5th SuperB Workshop May 9-11, 2007

Interaction Region

Summary of Present Design• Crossing angle of ±17 mrad

• Beam pipe diameter of 20 mm at the end of QD0 for both beams (same size as IP pipe)

• This leaves enough room (~10 mm) to place a permanent magnet quadrupole and get the required strength (Using Br = 14 kG)

• We have placed small bending magnets between QD0 and QF1 on the incoming beam lines to redirect the QF1 SR

• The septum QF1 magnets for the outgoing beams are tilted in order to let the strong SR fans escape

• The outgoing beams B0 magnets are a C shape design in order to allow the strong SR fans to escape

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5th SuperB Workshop May 9-11, 2007

Interaction Region

IR design parameters

Length Starts at Strength CommentsL* 0.30 m 0.0 DriftQD0 0.46 m 0.30 m -820.6 kG/m Both HER and LERQD0H 0.29 m 0.76 m -820.6 kG/m HER onlyB00L 0.40 m -1.05 m -2.2 kG Incoming LER onlyB00H 0.40 m 1.05 m 1.5 kG Incoming HER onlyQF1L 0.40 m ±1.45 m 293.2 kG/m LER onlyQF1H 0.40 m ±1.45 m 589.1 kG/m HER onlyB0L 2.0 m ±2.05 m 0.3 kG LER only (sign?)B0H 2.0 m ±2.05 m 0.526 kG HER only (sign?)

QD0 offset 6.00 mm Incoming HERQD0 offset 7.50 mm Incoming LER

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5th SuperB Workshop May 9-11, 2007

Interaction Region

SR Power Numbers

SR power in QD0 (kW) for beam currents of 1.44A HER and 2.5A LER No QD0 offsets Ver. F1 Ver. G3 PEP-II 3A on 1.8AIncoming HER 41 9 4 49

Incoming LER 28 1 1 16

Outgoing HER 41 152 93 49

Outgoing LER 28 67 55 16

Total 138 230 153 130

The design (G3) has a total SR power comparable to PEP-II

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5th SuperB Workshop May 9-11, 2007

Interaction Region

QD0 QD0

QD0H

QD0HB00LB00H

QF1 QF1

QF1QF1

B0L

B0H

B0H

B0L

SuperB Interaction Region

0

10

20

-10

-200 1 2 3-1-2-3m

cm

M.SullivanNov. 13, 2006SB_IT_ILC_G3_300

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5th SuperB Workshop May 9-11, 2007

Interaction Region

LER SR fans

QD0 QD0

QD0H

QD0HB00LB00H

QF1 QF1

QF1QF1

B0L

B0H

B0H

B0L

SuperB Interaction Region

0

10

20

-10

-200 1 2 3-1-2-3m

cm

M.SullivanNov. 13, 2006SB_IT_ILC_G3_300

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5th SuperB Workshop May 9-11, 2007

Interaction Region

QD0 QD0

QD0H

QD0HB00LB00H

QF1 QF1

QF1QF1

B0L

B0H

B0H

B0L

SuperB Interaction Region

0

10

20

-10

-200 1 2 3-1-2-3m

cm

M.SullivanNov. 13, 2006SB_IT_ILC_G3_300

HER SR fans

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5th SuperB Workshop May 9-11, 2007

Interaction Region

SuperB Interaction Region

0

0 0.5 1-0.5-1

25

50

-25

-50

mm

mM. SullivanNov. 13, 2006SB_IT_ILC_G3_100

QD0 QD0

QD0 QD0

QD0H

QD0H

±1 meter

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5th SuperB Workshop May 9-11, 2007

Interaction Region

SuperB Interaction Region

0

0 0.5 1-0.5-1

25

50

-25

-50

mm

mM. SullivanNov. 13, 2006SB_IT_ILC_G3_100

QD0 QD0

QD0 QD0

QD0H

QD0H

SR fans

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5th SuperB Workshop May 9-11, 2007

Interaction Region

Some SR background details

• We are using a gaussian beam distribution with a second wider and lower gaussian simulating the “beam tails”

• The beam distribution parameters are the same as the ones used for PEP-II

• We allow particles out to 10 in x and 35 in y to generate SR

• Unlike in PEP-II the SR backgrounds in the SuperB are dominated by the particle distribution at large beam sigma, so we are more sensitive to the exact particle distribution out there

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5th SuperB Workshop May 9-11, 2007

Interaction Region

Radiative Bhabhas

• The outgoing beams are still significantly bent as they go through QD0

• Therefore the off-energy beam particles from radiative bhabhas will get swept out

• Knowing this, we will have to build in shielding for the detector

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5th SuperB Workshop May 9-11, 2007

Interaction Region

0.5 11.52

2.533.5

4

4.5 5

5.56 6.5

QD0 QD0

QD0H

QD0HB00LB00H

QF1 QF1

QF1QF1

B0L

B0H

B0H

B0L

SuperB Interaction Region

0

10

20

-10

-200 1 2 3-1-2-3m

cm

M.SullivanNov. 13, 2006SB_IT_ILC_G3_300

HER radiative bhabhas

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5th SuperB Workshop May 9-11, 2007

Interaction Region

2 1.51

0.5

2.53

3.5

QD0 QD0

QD0H

QD0HB00LB00H

QF1 QF1

QF1QF1

B0L

B0H

B0H

B0L

SuperB Interaction Region

0

10

20

-10

-200 1 2 3-1-2-3m

cm

M.SullivanNov. 13, 2006SB_IT_ILC_G3_300

LER radiative bhabhas

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5th SuperB Workshop May 9-11, 2007

Interaction Region

How to improve the design

• The best improvement would be to reduce the radiative bhabha background– Note that there is only a small gain in

beam separation from the strong outgoing bending because one has to allow the outgoing SR to escape (see slide 14)

– The only gain comes from the BSC moving away from the septum

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5th SuperB Workshop May 9-11, 2007

Interaction Region

Attempts to improve the design

• Three possibilities so far looked at– Reduce the strength of the shared element

• Difficult to control beta functions (Can’t let the beta functions get too big)

– Try a high strength but very short and close to the IP shared element (minimal off-axis trajectories)

• Need a VERY high strength field to control beta functions• High field still bends a beam even with a small off-axis traj.

– Eliminate the shared element• Wants a maximum crossing angle (±24 mrads?)• Can start one focusing magnet for one of the beams first

and then follow with the focusing magnet for the other beam as soon as possible

• Still need to control beta functions• Just got started on this option: no conclusion yet

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5th SuperB Workshop May 9-11, 2007

Interaction Region

More designs

• Other possibilities thought about– A longer, weaker shared element

• End up with more bending at the outboard end• Wants a minimal crossing angle • Difficult to control beta functions

– Asymmetric IR (more like ILC?)• Well controlled incoming beta functions• Outgoing beta functions allowed to get bigger• OK for ILC—not so good for storage rings

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5th SuperB Workshop May 9-11, 2007

Interaction Region

Summary

• We have an IR design that has acceptable SR backgrounds with a crossing angle of ±17 mrad and an energy asymmetry of 7x4

• The BGB and coulomb scattered beam particles as a background need to be calculated and controlled (been done?)

• Radiative bhabha backgrounds are still high due to the strong bending of the outgoing beams

• The total SR power generated by the IR is high for the same reason. This can cause emittance growth. Especially vertical emittance growth since this is in a coupled region.

• A through exploration of parameter space is needed to find the best IR design