Page 1Review 09/2010

Overview and Issues of the MEIC Overview and Issues of the MEIC Interaction Region Interaction Region

M. Sullivan

MEIC Accelerator Design ReviewSeptember 15-16, 2010

Page 2Review 09/2010

Outline

• Interaction Region Design Concerns• Accelerator Concerns• Detector Concerns

• MEIC IR and detector

• Summary

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Interaction Region Design

• There are several conflicting constraints that must be balanced in the design of an Interaction Region

• The design must accommodate the requirements of the detector in order to maximize the physics obtained from the accelerator

• At the same time, the design must try to maximize accelerator performance which usually means having the final focusing elements in as close as possible to the collision point (minimize L*)

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Interaction Region Design (2)

• Beam related detector backgrounds must be carefully analyzed and mitigation schemes developed that allow the detector to pull out the physics• For electron (positron) beams this means

controlling synchrotron radiation backgrounds and lost beam particles

• For proton (ion) beams this means primarily controlling the lost beam particles

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Interaction Region Design (3)

• An adequate beam-stay-clear must be defined

• If possible, the definition should permit beam injection while the detector is taking data (for the electron beam)• Modern light sources, the B-factories and (of

course) the super B-factory designs use continuous injection

• Machine performance with continuous injection is vastly improved

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Interaction Region Design (4)

• The detector acceptance for the physics is a very important constraint

• Usually all detectors want 4 solid angle coverage

• This wish has to be tempered with the needs of the accelerator and the requirements of the final focusing elements

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MEIC Interaction Region Design

• The MEIC Interaction Region Features• 50 mrad crossing angle

• Detector is aligned along the electron beam line

• Electron FF magnets start/stop 3.5 m from the IP

• Proton/ion FF magnets start/stop 7 m from the IP

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Table of Parameters (electrons)

• Electron beam• Energy range 3-11 GeV• Beam-stay-clear 12 beam sigmas• Emittance (x/y) (1.02/0.20) nm-rad• Betas

x* = 100 cm x max = 435 my* = 2 cm y max = 640 m

• Final focus magnets• Name Z of face L (m) k G (11 GeV)• QFF1 3.5 0.5 -1.7106 -62.765• QFF2 4.2 0.5 1.7930 65.789• QFFL 6.7 0.5 -0.6981 -25.615

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Table of Parameters (proton/ion)

• Proton/ion beam• Energy range 20-60 GeV• Beam-stay-clear 12 beam sigmas• Emittance (x/y) (2.25/0.45) nm-rad• Betas

x* = 100 cm x max = 2195 my* = 2 cm y max = 2580 m

• Final focus magnets• Name Z of face L (m) k G (11 GeV)• QFF1 3.5 0.5 -1.7106 -62.765• QFF2 4.2 0.5 1.7930 65.789• QFFL 6.7 0.5 -0.6981 -25.615

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Interaction Region and Detector

EM

Cal

orim

eter

Had

ron

Cal

orim

eter

Muo

n D

etec

tor

EM

Cal

orim

eter

Solenoid yoke + Hadronic Calorimeter

Solenoid yoke + Muon Detector

HT

CC

RIC

H

RICH

Tracking

5 m solenoid

IP

Ultra forwardhadron detection

dipole

dipole

Low-Q2

electron detection

Large apertureelectron quads

Small diameterelectron quads

ion quads

Small anglehadron detection

dipole

Central detector with endcaps

~50 mrad crossing

CourtesyPawel Nadel-Tournski and Alex Bogacz

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Estimate of the detector magnetic field (Bz)

QFF1 QFF1QFF2 QFF2QFFL QFFL

QFFP QFFP

~2 kG

4

3

2

1

Tesla

The detector magnetic field will have a significant impact on the beams. Some of the final focusing elements will have to work in this field.

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Energy range

• Both beam energies have a fairly large energy range requirement

• The final focus elements must be able to accommodate these energy ranges

• An attractive alternative for some of the final focusing elements (especially the electron elements) is to use permanent magnets – they have a very small size and do not need power leads

• However, any PM design has to be able to span the energy range

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First look at backgrounds

FF1 FF2

e-

P+

1 2 3 4 5-1

40 mm30 mm

50 mm

240

3080

4.6x104

8.5x105

2.5W

38

2

Synchrotron radiation photons incident on various surfaces from the last 4 electron quads

Rate per bunch incident on the surface > 10 keV

Rate per bunch incident on the detector beam pipe assuming 1% reflection coefficient and solid angle acceptance of 4.4 %

M. SullivanJuly 20, 2010F$JLAB_E_3_5M_1A

50 mrad

Beam current = 2.32 A 2.9x1010 particles/bunch

X

P+

e-

Z

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Backgrounds

• Initial look at synchrotron radiation indicate that this background should not be a problem

• Need to look at lost particle backgrounds for both beams• Generally one can restrict the study to the region

upstream of the IP before the last bend magnet• A high quality vacuum in this region is sometimes

enough

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Summary

• The IR is one of the more difficult regions to design

• There are multiple constraints, however, balancing the various requirements to maximize the physics should be the primary goal of any design

• The MEIC IR design shows good promise and initial studies of SR backgrounds show that this background looks ok

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Conclusion

• The MEIC IR design has tried to accommodate the requirements of the detector and the requirements of the accelerator

• The design has benefited from input from both the accelerator and the detector community

• A reasonable compromise has been struck and the design can deliver the needed accelerator performance while allowing the detector to collect the important physics