Overview and Issues of the MEIC
Interaction Region
M. Sullivan
MEIC Accelerator Design Review
September 15-16, 2010
Review 09/2010
Page 1
Outline
• Interaction Region Design Concerns
• Accelerator Concerns
• Detector Concerns
• MEIC IR and detector
• Summary
Review 09/2010
Page 2
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*)
Review 09/2010
Page 3
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
Review 09/2010
Page 4
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
Review 09/2010
Page 5
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
Review 09/2010
Page 6
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
Review 09/2010
Page 7
Table of Parameters (electrons)
• Electron beam
• Energy range
• Beam-stay-clear
• Emittance (x/y)
• Betas
• x* = 100 cm
• y* =
2 cm
• Final focus magnets
• Name Z of face L (m)
• QFF1
3.5
0.5
• QFF2
4.2
0.5
• QFFL
6.7
0.5
Review 09/2010
3-11 GeV
12 beam sigmas
(1.02/0.20) nm-rad
x max = 435 m
y max = 640 m
k
-1.7106
1.7930
-0.6981
G (11 GeV)
-62.765
65.789
-25.615
Page 8
Table of Parameters (proton/ion)
• Proton/ion beam
• Energy range
• Beam-stay-clear
• Emittance (x/y)
• Betas
• x* = 100 cm
• y* =
2 cm
• Final focus magnets
• Name Z of face L (m)
• QFF1
3.5
0.5
• QFF2
4.2
0.5
• QFFL
6.7
0.5
Review 09/2010
20-60 GeV
12 beam sigmas
(2.25/0.45) nm-rad
x max = 2195 m
y max = 2580 m
k
-1.7106
1.7930
-0.6981
G (11 GeV)
-62.765
65.789
-25.615
Page 9
Interaction Region and Detector
Small angle
hadron detection
Central detector with endcaps
Low-Q2
Ultra forward
hadron detection
electron detection
ion quads
dipole
Large aperture
electron quads
dipole
IP
dipole
Small diameter
electron quads
~50 mrad crossing
Solenoid yoke + Muon Detector
EM Calorimeter
Hadron Calorimeter
Muon Detector
Tracking
RICH
RICH
HTCC
EM Calorimeter
Solenoid yoke + Hadronic Calorimeter
Courtesy
Pawel Nadel-Tournski
and Alex Bogacz
5 m solenoid
Review 09/2010
Page 10
Estimate of the detector magnetic field (Bz)
4
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.
3
Tesla
2
1
QFFP
QFFP
QFFL
QFF2 QFF1
QFF1 QFF2
QFFL
~2 kG
Review 09/2010
Page 11
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
Review 09/2010
Page 12
First look at backgrounds
50 mrad
Synchrotron radiation
photons incident on various
surfaces from the last 4
electron quads
38
P+ +
P
8.5x105
2.5W
4.6x104
240
2
FF2
FF1
40 mm
30 mm
50 mm
e-1
1
2
3
4
5
3080
Rate per bunch incident on the
surface > 10 keV
X
M. Sullivan
July 20, 2010
F$JLAB_E_3_5M_1A
Z
Beam current = 2.32 A
2.9x1010 particles/bunch
Review 09/2010
Rate per bunch incident on the
detector beam pipe assuming 1%
reflection coefficient and solid
angle acceptance of 4.4 %
Page 13
e-
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
Review 09/2010
Page 14
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
Review 09/2010
Page 15
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
Review 09/2010
Page 16