Overview and Issues of the MEIC Interaction Region

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

Outline

• MEIC IR and detector

• Backgrounds• SR• Radiative Bhabhas

• Summary

• Conclusion

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

Table of Parameters (electrons)

• Electron beam• Energy range 3-11 GeV• Beam-stay-clear 12 beam sigmas• Emittance (x/y) (5 GeV) (5.5/1.1) nm-rad• Betas

x* = 10 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

Table of Parameters (proton/ion)

• Proton/ion beam• Energy range 20-60 GeV• Beam-stay-clear 12 beam sigmas• Emittance (x/y) (60 GeV) (5.5/1.1) nm-rad• Betas

x* = 10 cm x max = 2195 my* = 2 cm y max = 2580 m

• Final focus magnets• Name Z of face L (m) k G (60 GeV)• QFF1 7.0 1.0 -0.3576 -71.570• QFF2 9.0 1.0 0.3192 63.884• QFFL 11.0 1.0 -0.2000 -40.028

Magnet apertures

• The magnet apertures are usually set by the required BSC

• Making the BSC generous forces larger aperture final focus magnets – usually these are more difficult magnets to build

• However, a large BSC improves machine flexibility by allowing for smaller beta* values (and hence larger beta max values) if the accelerator can operate with fewer beam sigmas than that defined by the BSC and backgrounds are acceptable

• The MEIC 12 sigma BSC definition is a reasonable compromise

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

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.

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 (for instance, only 30% of the final focus strength can be PM)

First look at SR 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/bunchX

P+

e-

ZElectron energy = 11 GeVx/y = 1.0/0.2 nm-rad

5 times larger beam emittances and lower beam energy

FF1 FF2

e-

P+

1 2 3 4 5-1

40 mm30 mm

50 mm

1.8x105

6.4x105

9.0x104

1.6x105

0.5W

7

4

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/bunchX

P+

e-

ZElectron energy = 5 GeVx/y = 5.5/1.1 nm-rad

Beam tails

0 10 20 30

yx

Gaussian beam profile (no tail)

Beam center

Nor

mal

ized

inte

nsity

10-6

10-3

10-9

100

x/x or y/y

d2Ndxdy

exp x 2

2x2

y2

2 y2

A exp

x2

2Sx2x

2 y2

2Sy2 y

2

A = 7.2 10 5

Sx = 3.3

Sy = 10

Assumed beam tail distribution is the same as was used in PEP-II background calculations

The tail distribution is primarily driven by the beam lifetime

The SR background is dominated by the beam tail particles

Backgrounds

• Initial look at synchrotron radiation indicates that this background should not be a problem but a more thorough study is needed

• Need to look at lost particle backgrounds for both beams• Proton beam has been studied extensively• 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

Radiative Bhabha Background

• There is a luminosity background from the electron beam

• During the collision the electron can radiate a photon

• This was a major source of neutrons in the B-Factory detectors

ion

e- / e+

B-Factory Radiative bhabhas

LER gammas

HER gammas

HER Radiative bhabhas

LER Radiative bhabhas

-7.5 -5 -2.5 0 2.5 5 7.5

0

10

20

30

-10

-20

-30

m

cm

PEP-II Interaction Region

M. SullivanFeb. 8, 2004API88k3_R5_RADBHA_TOT_7_5M

87.5

76.56

5.5

4

3.532.5

21.51

0.5

4.55

3.1 G

eV

3.1 G

eV

9 GeV

9 GeV

3

2.5

2 1.51

0.5

Off energy beam particles were swept out of the beam and then hit the local vacuum pipe

B-Factory Radiative Bhabhas

LER radiative gammas

0.511.5

22.5

3

LER radiative bhabhas

HER radiative gammas

7654

0.5

1

2

3

HER radiative bhabhas

KEKB Interaction Region

0

10

20

30

-10

-20

-300 2.5 5 7.5-2.5-5-7.5m

cm

HER

LER

8 GeV

3.5 GeV

M. Sullivan Nov. 9, 2004 B3$KEK2_IR_RADBHA

Detector

Detector

CSL CSR

QCSL QCSR

CSL CSR

QCSRQCSL

Q1EL

Q1ER

Q2PL

Q2PR

Both B-factories experienced this luminosity background

Super B-factories

• The super B-factories (SuperB and superKEKB) have designed the IR so that this background source is minimized

• This background has become one of the primary design drivers for the interaction region

• The other background that is close to being a design driver is the two-photon process where the produced background comes from low-energy e+/e- pairs produced from the interaction

• This background should not be a factor in the MEIC design (down by another factor of )

MEIC

• The radiative bhabha background may not be as important for the MEIC as it was for the B-factories but there will be beam induced backgrounds in the low angle detectors for the low-Q2 detectors and this reaction will be very similar to the physics signal looked for here

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

Summary

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

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

• The beam induced backgrounds many times control a large part of the design of the interaction region in order to allow the detector to operate in what can be a very hostile environment

Conclusion

• A careful study of the beam induced backgrounds is always an important aspect of any interaction region design

• As the accelerator design evolves one must constantly recheck backgrounds to make sure the changes do not have an adverse effect on rates

• There is always room for unexpected backgrounds so diligence in controlling and understanding backgrounds always tends to pay off

Overview and Issues of the MEIC Interaction Region

Documents

Transcript of Overview and Issues of the MEIC Interaction Region