the interaction region

1

5th SuperB Workshop May 9-11, 2007

Interaction Region

The Interaction Region

M. Sullivan

5th SuperB WorkshopParis

May 9-11, 2007

2


Interaction Region

Outline

• Design Issues

• IR Design

• Toward an improved design

• Summary

3


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

4


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

5


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

6


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

7


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

8


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

9


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

10


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

11


Interaction Region

LER SR fans

QD0 QD0

QD0H

QD0HB00LB00H

QF1 QF1

QF1QF1

B0L

B0H

B0H

B0L


0

10

20

-10

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

cm


12


Interaction Region

QD0 QD0

QD0H

QD0HB00LB00H

QF1 QF1

QF1QF1

B0L

B0H

B0H

B0L


0

10

20

-10

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

cm


HER SR fans

13


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

14


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

15


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

16


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

17


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


0

10

20

-10

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

cm


HER radiative bhabhas

18


Interaction Region

2 1.51

0.5

2.53

3.5

QD0 QD0

QD0H

QD0HB00LB00H

QF1 QF1

QF1QF1

B0L

B0H

B0H

B0L


0

10

20

-10

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

cm


LER radiative bhabhas

19


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

20


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

21


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

22


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

the interaction region

Documents