M. Sullivan
Mini-workshop on the MEIC design
Nov 2, 2012
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Introduction
Accelerator Parameters
Previous Synchrotron Radiation estimates
Other SR issues
Other detector backgrounds
Points of Interest
Summary
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Motherhood statements first
◦ IR is one of the most important regions of a collider
◦ Detector requirements and accelerator
requirements must coexist
◦ Usually the detector and accelerator constraints
conflict
◦ Compromises must be made on both sides without
jeopardizing either side’s design goals
◦ (I hope the following machine parameters are still
accurate)
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Electron beam
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Energy range
Beam-stay-clear
Emittance (x/y) (5 GeV)
Betas
 x* = 10 cm
 y* = 2 cm
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x max = 435 m
y max = 640 m
Final focus magnets
◦
◦
◦
◦
Name
QFF1
QFF2
QFFL
Z of face
3.5
4.2
6.7
3-11 GeV
12 beam sigmas
(5.5/1.1) nm-rad
L (m)
0.5
0.5
0.5
k
-1.7106
1.7930
-0.6981
G (11 GeV)
-62.765
65.789
-25.615
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Proton/ion beam
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◦
◦
◦
Energy range
Beam-stay-clear
Emittance (x/y) (60 GeV)
Betas
 x* = 10 cm
 y* = 2 cm
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x max = 2195 m
y max = 2580 m
Final focus magnets
◦
◦
◦
◦
Name
QFF1
QFF2
QFFL
Z of face
7.0
9.0
11.0
20-100 GeV
12 beam sigmas
(5.5/1.1) nm-rad
L (m)
1.0
1.0
1.0
k
-0.3576
0.3192
-0.2000
G (60 GeV)
-71.570
63.884
-40.02
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
5 m solenoid
EM Calorimeter
Hadron Calorimeter
Muon Detector
Tracking
RICH
RICH
HTCC
EM Calorimeter
Solenoid yoke + Hadronic Calorimeter
Copied from
an old talk
Courtesy
Pawel Nadel-Tournski
and Alex Bogacz
Q3P
100
P+
Q2P
75
cm
D1P
Q1P
50
25
Q3e
e-
0
Q1e Q2e
0
Q4e Q5e
5
10
Meters
15
M. Sullivan
JLAB_EP_3M_4R
July 30, 2012
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
e1
-1
2
4
3
5
3080
Beam current = 2.32 A
2.9x1010 particles/bunch
X
M. Sullivan
July 20, 2010
F$JLAB_E_3_5M_1A
Z
Electron energy = 11 GeV
x/y = 1.0/0.2 nm-rad
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 %
e-
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Local forward and back scattering rates from
nearby beam pipe surfaces
◦ The electron beam current is comparable to the Bfactories and to the super B-factories
◦ This may still NOT be very important for the MEIC
 The central beam pipe is large which helps a lot
 Still it needs to be checked – especially for various
running conditions
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The large set of running conditions for the
MEIC means that several IR lattice designs
need to be checked for SR backgrounds
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The MEIC detector design with a suite of very
forward detectors means that we will have to
trace SR fans from bend magnets to see
where the power goes and how this interacts
with the beam pipe design in front of these
detectors
The proton/ion beam does not have this
issue but it has another issue that is also a
concern for the electron beam that the super
B-factory designs are struggling with right
now
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The high current super B-factories (Superb and
superKEKB) are working quite hard to identify
and shield sources of neutrons
In general, these sources occur after the beam
has been bent going through a dipole and this is
essentially what the MEIC detector wants to do to
study the very low Q2 physics region
The low angle detectors for these events will
become neutron source points from the shower
development in these detectors as well as other
regions of the beam line on either side of the
detector
The super B-factories are simulating the beam
line (full GEANT4) out to at least 20 m from the IP
This topic is mentioned in the most recent MEIC report
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Beam-beam interactions do affect the
accelerator performance and preliminary
studies have been made in this regard
But beam-beam effects also produce nongaussian tails in the transverse beam
dimensions and these tails can create
backgrounds
Tails are not studied much in accelerators
except for lifetime estimate calculations
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Machine flexibility (mentioned in the MEIC
report)
◦ First is the energy range of each beam together
with possible extreme combinations
 Are there any lattice changes just outside of the
detector region?
 What are the machine parameters of these different
cases?
 How does the machine change?
 What are the performance requirements for the physics
These have already been thought about at some level
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More on machine flexibility
◦ What possible upgrades are being envisioned
 From the accelerator
 From the detector
 From the physics
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Initial startup scenerios
◦ Machine commissioning time without the detector
◦ Vacuum scrubbing for the electron beam
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HERA experience
◦ (I believe this has been mentioned before)
◦ Is there anything we can learn from HERA?
 Physics range
 Backgrounds uncovered and fixed
 Accelerator experience
◦ Energy range is very much higher than MEIC
 28 GeV e- on 920 GeV P+
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The crab cavities as a possible upgrade seem to
be located fairly close to the IP
These cavities are sensitive to SR fans of
radiation and a careful study for these cavities is
called for
Special masking may be needed
PEP-II experience is that SR from the last bend
magnet affected the first RF cavity in the RF
straights
The cavities may be in or near the low angle
detector areas
Need to keep in touch with accelerator folks
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The effect of the solenoid on the beams will
need to be studied in detail
Solutions to accelerator problems created by
the detector field may affect the detector
design and/or solid angle acceptance
Skew quads, compensating solenoids, etc. are
some examples
Close integration with both teams will be
needed
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Perhaps we can make a list of things that
need further study
Then set some priorities (there are never
enough people to do everything you would
like to do)
Also identify which areas need close
cooperation with accelerator and detector
people
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The MEIC design is a good starting point
The design looks solid and further study
should reinforce this
Effort now is to look for weak points or
overlooked issues
◦ Many times these studies can uncover something
that forces a design change – the sooner these are
found the better
We want to get to the point where we actually
think this thing can be built and it has a good
chance of working!