Wei Gai for the ILC e and e collaboration PAC review 2012 KEK Japan ILC site layout and location of e and e sources Page 3 The Baseline ILC Electron Source Electron source provides polarized electron beam and consists of all systems from source laser to 5 GeV injection to damping ri ID: 370053
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Slide1
ILC Electron and Positron Sources
Wei Gai for the ILC e- and e+ collaboration
PAC review, 2012
KEK, JapanSlide2
ILC site layout and location of e- and e+ sourcesSlide3
Page
3
The Baseline ILC Electron Source
Electron source provides polarized electron beam and consists of all systems from source laser to 5 GeV injection to damping rings. ( 325 MHz SHB)
325
325Slide4
Electron source parameters
Parameter
Symbol
Value
Units
Electrons per bunch (at gun exit)
N
3x10
10
Number
Electrons per bunch (at DR injection)
N
2x10
10
Number
Number of bunches
n
b
1312
Number
Bunch repetition rate
f
b
1.8
MHz
Bunch train repetition rate
f
rep
5
Hz
FW Bunch length at source
D
t
1
ns
Peak current in bunch at source
I
avg
3.2
A
Energy stability
s
E
/E
<5
% rms
Polarization
P
e
80 (min)
%
Photocathode Quantum Efficiency
QE
0.5
%
Drive laser wavelength
l
790±20 (tunable)
nm
Single bunch laser energy
u
b
5
m
JSlide5
5
ILC TDR positron source location
Photon collimator for pol. upgrade
Optical Matching Device for e+ capture
Main e- beam from electron main linac
Target for e+ production
PTAPA
(~125MeV)
PPA
(125-400MeV)
PBSTR 400MeV-5GeV
g
dump
e- dump
Damping ring
147 m helical undulator for photon production
g
PCAP
PLTR: Energy compression and spin rotation
Main e- beam to IP
150 GeV beam to dumpSlide6
ILC Positron source schematic with key components
When Ecm is bellow 300GeV, the machine will be working in 10Hz mode where a dedicated 5Hz 150GeV positron production beam will be interlaced with 5Hz luminosity production beam
Photon collimator for pol. upgrade
Optical Matching Device for e+ capture enhancement
Main e- beam from electron main linac
Target for e+ production
Positron Target Area Pre-Accelerator (PTAPA ): L-band normal conducting RF accelerator to accelerate e+ beam up to ~125MeV
Positron Pre-Accelerator (PPA): Normal conducting L-band RF accelerator to accelerate e+ beam from 125MeV up to 400MeV
Positron Energy Booster (PBSTR): Cryo-modules to boost e+ energy from 400MeV up to 5GeV
g
dump
e- dump
Damping ring
147 m helical undulator for photon production
g
Positron separation and capture section:
To separate e+ from e- and
g
To clean up e+ which will not be accepted by damping
Positron Linac to damping Ring (PLTR): Energy compression and spin rotation
Main e- beam to IP
Used e+ production beam to dumpSlide7
Nominal parameters of ILC positron sourceSlide8
Helical undulator
The TDR baseline
undulator
has active length of 147m
The undulator will work at lower B field for
Ecm
=350GeV and 500GeV to bring the polarization back to ~30% while keep the positron yield at 1.5 (50% margin allowed for unexpected losses)
The lattice has reserved extra space for polarization upgrade(73.5m long active length)
The
undulator
magnet and crymodule has successfully prototyped at RAL
Basic parameters
Lattice parameter
Lattice (Layout) parameters
Value
Units
Quadrupole
spacing
14.538
m
Quadrupole
strength
0.06378
m
-1
Quadrupole
length
1
m
Phase advance per cell
45
degree
Cell length
29.075
m
Maximum
b
funtion
46.93
m
Number of
quadrupoles
23
Total lattice length
319.828
mSlide9
Undulator prototyping
RAL group has successfully fabricated two identical long undulators, each 1.75m in length, which have been magnetically tested and proven easily to achieve the field strength required
The RAL team has since incorporated both of these undulators into a single 4 m-long cryogenic module (which operates at -269 C) of the design required by ILCSlide10
Photon collimator
A photon collimator is not required for the TDR baseline
As part of positron source upgrade study, DESY team developed a photon collimator design. With the designed photon collimator, positron source polarization can be increased from ~30% up to 50-60% depending on the colliding beam energySlide11
Target system
The positron-production target is a rotating wheel made of titanium alloy (Ti6Al4V).
The diameter of the wheel is 1m and the thickness is 0.4 radiation lengths (1.4 cm).
During operation the outer edge of the rim moves at 100 m/s.Slide12
Energy deposition/accumulation on Target
Centre-of-mass energy
E
cm
(GeV)
Parameter
200
230
250
350
500
Positron pulse production rate
Hz
5
5
5
5
5
Electron beam energy (e+ prod.)
GeV
150
150
150
178
252
Number of electron bunches
n
b
1312
1312
1312
1312
1312
Electron bunch population
N
+
×10
10
2
2
2
2
2
Required
undulator
field
B
T
0.86
0.86
0.86
0.698
0.42
undulator
period length
l
u
cm
1.15
1.15
1.15
1.15
1.15
undulator
KK
0.92
0.920.92
0.75
0.45Average photon power on targetkW91100
107
5542Incident photon energy per bunchJ9.6
9.6
9.68.16.0Energy deposition per bunch (e+ prod.)J
0.720.720.720.590.31
Relative energy deposition%7%7%7%
7.20%
5%Photon rms spot size on targetmm1.4
1.41.4
1.20.8Peak energy density in targetJ/cm3
232.5
232.5232.5295.3304.3
J/g
51.751.751.765.6
67.5Slide13
Target system related issues
Vacuum seal
Two types of vacuum seals,
Rigaku
and FerroTech
, have been tested at LLNL.
Rigaku
seal wasn’t able
to
run at 2000RPM. FerroTech
seals each has its own individual personality; all have out gassing spike; off-the-shelf models do not seem to be well designed.Need to partner with FerroTech
to improve their design.
However, a differential pumping can be used as a back up scheme
Shockwaves and thermal dynamic
Energy deposition causes shockwaves in the material. If shock exceeds strain limit of material chunks can spall from the face
The SLC target showed spall damage after radiation damage had weakened the tungsten target material.
Initial calculations from LLNL had shown no problem in Titanium target
ANSYS simulation at DESY is underway and need to be further confirmed by experiment and/or simulation from different institute.
Future R&D Target system prototype and test will continue at LLNL
Shockwave damage simulation will continue and need to develop and carry out an experiment test.Slide14
Target area shielding and target remote handling
The target will be highly activated after one year of operation.
With the nominal150kW photon beam, after 5000 hours of operation and 1 week of shutdown, the equivalent dose rate at 1m from the target wheel will be approximately 170
mSv
/h. Concrete shielding of 0.8m thick around the target is sufficient fully to contain the radiation associated with the beam and with the subsequently activated materials.
A remote-handling system is used to replace the target, OMD and the 1
st
1.3m NC RF cavities.Slide15
Optical Matching Device (OMD)
ILC TDR baseline OMD is a flux concentrator.
It works by pulsing the exterior coil to enhance the magnetic field in the center.
Similar device built 40 years ago. Cryogenic nitrogen cooling of the concentrator plates.
A room temperature device has been designed and prototyped at LLNLSlide16
Positron source Target Area Pre-Accelerator(PTAPA)
The positron capturing region RF is consist of two 1.3m long L-band standing wave structure and three 4.3m long L-band travelling wave structure.
The background solenoid field is 0.5T
The center of positron beam will be accelerated up to 125MeV at the end of this section.
Typical longitudinal distribution of e+ at end of capturing section
PTAPA
RF and solenoidsSlide17
Photon collimator for pol. upgrade
Optical Matching Device for e+ capture
Main e- beam from electron main linac
Target for e+ production
PTAPA
(~125MeV)
PPA
(125-400MeV)
PBSTR 400MeV-5GeV
g
dump
e- dump
Damping ring
147 m helical undulator for photon production
g
PCAP
PLTR: Energy compression and spin rotation
Main e- beam to IP
150 GeV beam to dump
Positron separation
Positron separation beamline (PCAP section) is used to separate positrons beam from electrons and
g
beam.
The electron beam and
g
beam will be dumped into the e- dump and
g
dump.
The positrons with energy too low and too high will be cleaned up in this chicane using collimators.
The length of this section is 74m
Positron separation beamline
Typical longitudinal distribution after PCAPSlide18
Positron Pre-Accelerator (PPA)
ILC positron pre-accelerator is consist of eight 4.3m long L-band room temperature travelling wave structure surrounded by 0.5T solenoids.
PPA accelerate the positron beam from 125MeV up to 400MeV.
PPA
beamline
Typical longitudinal distribution at end of PPASlide19
Positron Booster Beamline (PBSTR)
Positron booster
beamline
is designed to accelerate positron beam energy from 400MeV up to 5GeV.
There are 3 type of cryomodules used in PBSTR.
4C4Q which has 4 SCRF
linacs
and 4 quads. 6 units are used in the 1
st
section8C2Q which has 8 SCRF linacs and 2 quads. 8 units are used in the 2
nd section8C1Q which has 8 SCRF linacs and 1 quad. 12 units are used in the 3rd section
19
Matching section
PBSTR1: 400MEV TO 1082.5649MEV
PBSTR2: 1082.5649MEV TO 2507.0321 MeV
PBSTR3: 2507.0321 MeV to 5GeV
Matching to PTRANHSlide20
Transfer
beamline
There are two positron transfer
beamline
400MeV transfer
beamline
(PTRAN). It is a 479m long FODO lattice between PPA and PBSTR
beamline
5GeV transfer
beamline (PTRANH). Total number of quads: 79
Total length of beamline: 934.23m20
Typical longitudinal distribution at end of PTRANHSlide21
Positron Linac to Damping Ring (PLTR)
beamline
PLTR
beamline
has two main functions: Energy compression and Spin rotationAt the beginning of PLTR, there is one horizontal chicane for introducing the needed chirp for energy compressor.
The 1
st
horizontal arc after the chicane will bend the beam by 23.8 degrees and rotates the spin axis by 270 degrees in horizontal plane.
An energy compressor using a 9C0Q
crymodule is installed to compress the beam energy spread into the damping acceptance window.Following the energy compressor, a spin rotator with 8.3m long 3.16T super conducting solenoid is used to rotate the spin into vertical so that it can be preserved in the damping ring
21
Floor map of PLTR
beamlineSlide22
Energy Compressor
TDR baseline energy compressor uses a
cryomodule
with 9 cavities and no quads. Each cavity has a voltage of 25MV.
The total length of cryomodule is 12.474m including flanges and interconnect pipes.
Typical longitudinal distribution before(a) and after(b) energy compressor
(a)
(b)Slide23
Spin Rotator(8.3m long 3.16T SC solenoid)Slide24
Beamline Lattice
New lattice design has been done to comply with the new layouts as follow.
24Slide25
Optics parameter of the new ILC positron source beamline latticeSlide26
TeV upgrade scenariosScenarios has been Studied by both DESY and ANL
Proposed that keep everything the same (Target, OMD), but the
undulator
change to K=1,
lu=4.3cmSlide27
27
Polarization upgrade
The ILC baseline positron source has an active
undulator
length of 147m while the
lattice/layout of ILC positron source have left enough space for 231m effective
undulator
length.
The
extra space can be used for additional undulator
modules for polarization upgrade
A multi stage photon collimator
design
for polarization upgrade has been
developed
at DESY
Simulation study at DESY has shown that with their multi stage photon collimator design, polarization of positron source can be increased up to 50-60% depends on the colliding beam energies.Slide28
Issues with ILC positron sources
Risk assessments for the e+ system:
Undulator
(OK, more RD needed for different scenarios other than Baseline)
Photon Collimators (good progress made, need a engineering design and prototyping)
Capturing magnets (design done, prototyping almost done)
Target (Rotating under magnetic field tested, vacuum seal being tested, shockwave damage simulation needs further confirmation)
Pre-accelerator (done)
RH (Engineering design done).
Lattice (Done, can be refined).
TeV
upgrade option is viable for positron
sources without
any change to other parts of machine except the
undulator
.