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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