CEPC and past CLIC studies Armen Apyan Northwestern University Evanston IL US 26052014 FCCee Accelerator meeting 6 1 Outline Polarized Positron Production Methods CLIC Main ID: 239051
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Slide1
Beam dump and positron production studies for CEPC and past CLIC studies
Armen Apyan
Northwestern UniversityEvanston, IL, US
26/05/2014
FCC-ee Accelerator meeting #6
1Slide2
Outline
__________________
Polarized Positron Production Methods
CLIC Main
Beam Dump
Summary
26/05/2014
FCC-ee Accelerator meeting #6
2Slide3
Polarized Positron Production
26/05/2014
FCC-ee Accelerator meeting #63Slide4
The Concept
+ decay of:naturally existing radioactive isotopes,
short – life isotopes produced by an accelerator Concerning polarization, positrons emitted from beta decays are longitudinally polarized but are subject to a large energy spread, a wide angular distribution
, low intensity, etc.
e+e
-
pair production of photons
Positron beam is longitudinally polarized at the upper limit of the e
+
energy.__________________26/05/2014FCC-ee Accelerator meeting #64Slide5
The Methods of Polarized Positrons Production
Circularly polarized g by bremsstrahlung of electrons (longitudinally polarized)
in amorphous or crystalline target and e+e-
production in converter target.
Circularly polarized
g
from high energy e-
(could be
unpolarized
)
beam passing through an helical undulator and e+e- production in converter target.Circularly polarized g from Compton backscattering of circularly polarized laser beam on e- (could be unpolarized) beam and e+e- production in converter target.
__________________
26/05/2014
FCC-ee Accelerator meeting #6
5Slide6
Conventional Scheme based on oriented crystal
Separate crystalline target for production of circularly polarized ’s by coherent bremsstrahlung of longitudinally polarized electrons
__________________
Step-1
:
Produce Circularly polarized
γ
Step 2:
Convert
γ
’s to e+
Separate amorphous target for e+ production:
Capture system
High intensity
Bending
Magnet
To beam dump
Pol. e
-
beam
Crystal
target
Pol.
’
s
e
+
Amorphous converter
e
-
Apyan, H. Braun, M. Velasco
for CLIC, 2005
Crystal increases the yield of the photons, not the polarization
26/05/2014
FCC-ee Accelerator meeting #6
6Slide7
Choice of Crystal Radiator and Converter
Circularly Polarized Photon
Sources:
__________________
High Z amorphous target
Tungsten
0.2 mm thick
Bremsstrahlung –
stable, proven method.
Crystal
Diamond
single crystal 1cm:
Tight lattice (small lattice constant 3.567Å
Low Z=6
Coherent Bremsstrahlung –
stable, proven method.
Polarized Positron Converter:
High Z material
Amorphous Tungsten 0.3 mm thick
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FCC-ee Accelerator meeting #6
7Slide8
Number of Photons and Positrons per Incident Electron
__________________
Proposed configurations give the following yield of photons
Tungsten radiator
0.007
g
/
e
-
Diamond single
crystal
0.03
g
/
e
-
T
he crystal
scheme
provides ~
3 times
larger photon
yield than
amorphous configuration
with the same beam parameters.
Tungsten was used as a positron converter for both configuratons
26/05/2014
FCC-ee Accelerator meeting #6
8Slide9
Polarized Positron Beam Production Based on Helical
UndulatorCircularly polarized g
from high energy e- beam passing through an helical undulator and e+e-
production in converter target.
__________________
high energy
e
-
beam
Helical
undulator
Bending
Magnet
Pol.
’
s
To beam dump
Converter target
Capture system
e
+
e
-
The electron
beam is coaxial with the
undulator
. The
highest energy
photons take on the polarization of the
undulator
field, so that a helical
undulator
leads to
circularly polarized photons. The
intensity of
undulator
photons depends
on the intensity of the virtual photons of the
undulator
,
and hence
on the square of its magnetic field strength.
The
photons
are
produced by scattering of virtual
photons of
a helical
undulator
with period λu off an electron beam. References:V.E. Balakin, A.A. Mikhailchenko, “The Conversion System for Obtaining High Energy Electrons and Positrons”, Preprinit BINP-79-85, 1979.26/05/2014
FCC-ee Accelerator meeting #6
9Slide10
Observation of Polarized Positrons from an Undulator
-Based Source: E166 ExperimentElectron beam
energy 46.6±0.1 GeVRepetition rate of 10 Hz with 1–4x109 e/pulseN
ormalized beam emittances 2.2(0
.5)X105
mradTransverse
spot
size
σ
x
σy 35 μm Helical undulator length 1mUndulator aperture 0.9mm__________________
References:
G. Alexander et al.
,
Observation of Polarized Positrons from an
Undulator
-Based Source
,Phys. Rev. Let.,
100, 210801 (2008)
The
photon beam impinged upon a 0.2-radiation-
length tungsten
target T1 to produce positrons and
electrons which
were separated in
spectrometer,
and the
polarization and
rate of the positrons were measured in
transmission
polarimeter
TP1.
The unconverted
photons were
monitored in a second transmission
polarimeter
, TP2.
26/05/2014
FCC-ee Accelerator meeting #6
10Slide11
Laser based Polarized Positrons Source
Circularly polarized g from Compton backscattering of laser beam on e- beam and e
+e- production in converter target.
__________________
CO
2
laser
Converter
target
Capture
system
High intensity
e
-
beam
Bending
Magnet
Pol. photons
To beam dump
Pol.
’
s
e
-
e
+
References:
T. Omori,
“
A Polarized Positron Beam for Linear Collider
”
, KEK Preprints 98-237 and 99-188.
The main advantages of the Compton scheme are that the positron source is
imposed independently
with respect to the main
linac
and the required drive
electron
beam energy is much lower as compared to the
undulator
scheme
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FCC-ee Accelerator meeting #6
11Slide12
Compton Source
R&D at ATF
__________________
References:
T. Omori et al.,
“
Efficient Propagation of Polarization from Laser Photons to
Positrons through
Compton Scattering and Electron-Positron Pair
Creation
“. Phys. Rev. Let., 96, 114801, 2006.A fundamental scheme of polarized positron production. Right-handed polarized laser photons are backscattered off relativistic electrons resulting in production of left handed polarized rays in the forward direction (in the high-energy part of the spectrum). Pair creation of the rays through a tungsten plate generates left-handed positrons in the high-energy part.
The magnitude of the positron polarization was calculated
as 73 ± 15 ±19%
, where the first error is a statistical
one
and the second error is systematic
one which
comes from the uncertainty in a Monte
Carlo simulation.
26/05/2014
FCC-ee Accelerator meeting #6
12Slide13
Polarized Positron Source for CEPC
__________________
Which scheme of polarized positron production is good for CEPC ?
The
three
concepts
have their own problems connected with the cost
and technical
complexity
.
Many investigations were done towards the polarized positron production in the last decade.Several existing Monte Carlo codes can help in simulation of the positron production with high accuracy. For example:Laser – electron interaction ------- CAIN, Guinea-PigEnergy deposition, particle interaction ---- GEANT4, FLUKAMagnetization of Iron ----------- POISSONAnd many other.26/05/2014
FCC-ee Accelerator meeting #6
13Slide14
Beam Dump Consideration
26/05/2014
FCC-ee Accelerator meeting #614Slide15
Design Consideration:
CLIC
post-collision line
Transport particles of all energies and intensities from IP to dump
Separation of the outgoing beams for diagnostics (luminosity monitoring)
Control beam losses in the magnets
Minimize background in the experiments
Stay clear of the incoming beam
__________________
26/05/2014
FCC-ee Accelerator meeting #6
15Slide16
Baseline Design
Separation of disrupted beam,
beamstrahlung
photons and
coherent
pairs
Back
-bending region to direct the beam onto the final dump
Allowing non-colliding beam to grow to acceptable size
intermediate dump
side view
27.5m
67m
1.5m
C-shape magnets
window-frame magnets
carbon based absorbers
ILC style
water dump
4m
315m
6m
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26/05/2014
FCC-ee Accelerator meeting #6
16Slide17
Some
Numbers
e
+
e
-
collision creates disrupted beam
Huge energy spread, large
x,y
div in outgoing
beam
total power of
~10MW
High power divergent
beamstrahlung
photons
2.2 photons/incoming
e+e
-
2.5 E12
photons/bunch train
total power of
~4MW
Coherent
e+e
- pairs
5E8
e+e
- pairs/
bunchX
170kW
opposite
charge
Incoherent
e+e
- pairs
4.4E5
e+e
- pairs/
bunchX
78 W
Right sign coherent beam
Beamstrahlung photons
Disrupted beam
Collided 1.5TeV Beam at water dump 315m from IP
Uncollided
beam:
s
x
= 1.56mm,
s
y
=2.73mm
5.6
mm
2
__________________
26/05/2014
FCC-ee Accelerator meeting #6
17Slide18
Particles distribution on the CLIC Main Beam Dump
__________________
Photons
Disrupted beam
Coherent beam
The CLIC post collision line is designed to transport the un-collided beams and the products of the collided beams with a total power of 14MW to the main beam dump.
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FCC-ee Accelerator meeting #6
18Slide19
Main Beam
Dump (History)
1966: SLAC beam dump
2.2 MW average beam power capacity
Power absorption medium is water
2000: TESLA
12 MW beam power capacity
Water dump
__________________
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FCC-ee Accelerator meeting #6
19Slide20
Concept of the Water based Beam Dump
The basic principle of water dump is to present the incoming beam with a region of cold water.
The beam dissipates its energy into water
. It is essential that the volume of water exposed to the core of the beam be moved transverse to the momentum vector of the beam to prevent “volume boiling”. To renew the
water volume in the central part of the shower, between successive bunch trains, a water flows transverse to the direction of the beam.
2.2 MW beam dump
D.R. Walz etal, 1965
This presents the following portion of the incoming beam with fresh cold water.
26/05/2014
FCC-ee Accelerator meeting #6
20Slide21
Baseline Main Dump
Design (CLIC)2010: CLIC 14 MW water dump
Cylindrical vesselVolume: 25m3, Length: 10mDiameter of 1.8mWater pressure at 10bar (boils at 180C)
Ti-window, 1mm thick, 60cm
diameter
baseline for CLIC 2010 main dump
CLIC
ILC
Beam energy
1500 GeV
500 GeV
# particles per bunch
3.7 x 10
9
2 x 10
10
# bunches per train
312
2820
Duration of bunch train
156 ns
950
m
s
Uncollided beam size at dump
s
x
,
s
y
1.56 mm, 2.73 mm
2.42 mm, 0.27 mm
# bunch trains per second
50
5
Beam power
14 MW
18 MW
Length 10.0 m
Diameter
1.8
m
60.0
cm
diameter window
(Ti
)
1.0 mm thick
20.0
mm thick s
tainless steel
vessel
Dump axis
ILC type
water dump
__________________
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FCC-ee Accelerator meeting #6
21Slide22
General Parameters of Water
Dump
1.The water beam absorber is a cylindrical vessel with an entrance and exit windows in both sides.
2. Volume of water around
25
m
3
3. Length of dump around 10 m (sufficient multiple of X
0
)
4. Diameter of dump about
1.8
m.
5. Pressure of water 10 bar, at which water boils at 180
0
C.
6. Water flow rate around 1 -1.5 m/s
7. Window made of
Ti
or other material, 1mm thick and
60
cm diameter.
__________________
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FCC-ee Accelerator meeting #6
22Slide23
Longitudinal and Transverse Distributions of
Paricles
The issue
for non-colliding beams are the small beam spot
and consequently the high
power density on a small point
of impact
on the dump window and the dump itself
.
Uncollided
beam:
E=1.5TeV,
s
x
= 1.56mm,
s
y
=2.73mm
5.6
mm
2
26/05/2014
FCC-ee Accelerator meeting #6
23Slide24
Main Beam Dump Issues
Maximum energy deposition per bunch train
: 270 J/cm
3
Remove heat deposited in the dump
Minimum water flow of 25-30
litre
/s with v=1.5m/s
Guarantee dump structural integrity
Almost instantaneous heat deposition generate a dynamic pressure wave inside the bath!
Cause overstress on dump wall and window (to be added to 10bar hydrostatic pressure).
dimensioning water tank, window, etc..
Radiolytical
/radiological effects
Hydrogen/oxygen
recombiners
, handling of
7
Be,
3
H
__________________
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FCC-ee Accelerator meeting #6
24Slide25
Simulation Tools
__________________
CAIN
Kaoru
Yokoya
ABEL 1984
Guinea Pig
Daniel Schulte
PhD Thesis 1996
T
hese
codes
are
fundamental tools
for R
&D on future linear
colliders. These
programs simulate beam-
beam interactions
in high-energy
e+
e
colliders
and the impact of the beam-beam effect on luminosity and background.
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FCC-ee Accelerator meeting #6
25Slide26
Beam-beam simulation by Guinea-PIG
__________________
TLEP
Armen’s
simulation
12M (multiplied by 30)
CERN simulation 360M
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FCC-ee Accelerator meeting #6
26
HF2012 workshop report, p. 42, Table 8.2Slide27
CAIN and Guinea-PIG simulations for
CEPC and TLEP
__________________
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FCC-ee Accelerator meeting #6
27Slide28
Conclusion (1)
__________________
Polarized or
unpolarized
e+e
- colliders
?
The schemes use different methods for production of circularly polarized gamma beams.
The schemes use the same method for converting gamma beam into electron-positron pairs.
There are many Monte-Carlo simulation and experimental research devoted to positron polarized production. It is time to think about CEPC positron production scheme.All mentioned schemes can be used to produce either polarized or unpolarized positron beams.26/05/2014FCC-ee Accelerator meeting #628Slide29
Conclusion (2)
__________________
Low positron yield.
Needs to be checked.
Conventional Scheme with crystal
Set of comparatively thin successive targets may
increase the yield of photons, positrons and ease
heating /stress problems for each
target
Small Multiple scattering angle
Well established physics of the processes of interaction of electrons with single crystal
Low cost and the simple technical solution make the conventional method attractive.
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FCC-ee Accelerator meeting #6
29Slide30
Conclusion (3)
__________________
Use electron main
linac
(150-250
GeV
).
Long helical
undulator
150-220m. Needs to be aligned.
Problem on design, construction, commissioning, maintenance.Undulator based SchemeLaser based Scheme
High Intensity
positron beam.
Highly polarized
positron beam
up to 7
0
%
.
Ease to switch laser polarization state
High intensity positron beam.
Highly polarized
positronbeam
up to 60%.
Required high intensity laser.
The positrons accepted
per one bunch crossing does not
fit
the high CLIC and ILC requirements.
For this
reason,
stacking of the positron bunches was
proposed.
The performance of the scheme is complicated.
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FCC-ee Accelerator meeting #6
30Slide31
Beam Dump
__________________
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31
It
was seen that the deposited energy through the shower spreads to the whole volume of water dump. Which can cause:
Heating of the water.
Radiolysis – water molecule is broken up into H+,(OH) and other radicals. The result will be H
2
O
2
and H
2
.
Production of radioactive isotopes –
photospallation
on oxygen
.
Each
of the two beam
dumps of CEPC must
be able to dissipate
360
k
J
of beam energy in
the 0.18
ms
circulation time, which equates to a power of
2
G
W
.
Beam
dump luminosity
monitor
based on detection of high energy
muons
is considered after the main beam dump
High energy
muons
escape the main dump nearly unaffected, except for small energy losses due to ionization.
Transverse distribution of
muons
depends on the offset of primary beams.Slide32
Beam Dump
__________________
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FCC-ee Accelerator meeting #6
32
It
was seen that the deposited energy through the shower spreads to the whole volume of water dump. Which can cause:
Heating of the water.
Radiolysis – water molecule is broken up into H+,(OH) and other radicals. The result will be H
2
O
2
and H
2
.
Production of radioactive isotopes –
photospallation
on oxygen
.
Each
of the two beam
dumps of CEPC must
be able to dissipate
360
k
J
of beam energy in
the 0.18
ms
circulation time, which equates to a power of
2
G
W
.
The luminosity monitoring system is considered at the CLIC b
eam dump. Luminosity
monitor
is based on detection of high energy
muons
High energy
muons
escape the main dump nearly unaffected, except for small energy losses due to ionization.
Transverse distribution of
muons
depends on the offset of primary beams.