ILC site layout and location of e- and e+ sources

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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)

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Electron source parameters

Parameter Symbol Value Units

Electrons per bunch (at gun exit) N 3x1010 Number

Electrons per bunch (at DR injection) N 2x1010 Number

Number of bunches nb 1312 Number

Bunch repetition rate fb 1.8 MHz

Bunch train repetition rate frep 5 Hz

FW Bunch length at source Dt 1 ns

Peak current in bunch at source Iavg 3.2 A

Energy stability sE/E <5 % rms

Polarization Pe 80 (min) %

Photocathode Quantum Efficiency QE 0.5 %

Drive laser wavelength l 790±20 (tunable) nm

Single bunch laser energy ub 5 mJ

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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 dumpe- 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

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 dumpe- 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 dump

Nominal parameters of ILC positron source

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 UnitsQuadrupole spacing 14.538 mQuadrupole strength 0.06378 m-1

Quadrupole length 1 mPhase advance per cell 45 degreeCell length 29.075 mMaximum b funtion 46.93 mNumber of quadrupoles 23Total lattice length 319.828 m

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 ILC

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 energy

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.

Energy deposition/accumulation on Target

Centre-of-mass energy Ecm (GeV)

Parameter     200 230 250 350 500Positron pulse production rate Hz 5 5 5 5 5Electron beam energy (e+ prod.) GeV 150 150 150 178 252

Number of electron bunches nb 1312 1312 1312 1312 1312

Electron bunch population N+ ×1010 2 2 2 2 2Required undulator field B T 0.86 0.86 0.86 0.698 0.42undulator period length lu cm 1.15 1.15 1.15 1.15 1.15undulator K K 0.92 0.92 0.92 0.75 0.45Average photon power on target kW 91 100 107 55 42Incident photon energy per bunch J 9.6 9.6 9.6 8.1 6.0Energy deposition per bunch (e+ prod.) J 0.72 0.72 0.72 0.59 0.31Relative energy deposition % 7% 7% 7% 7.20% 5%Photon rms spot size on target mm 1.4 1.4 1.4 1.2 0.8

Peak energy density in target J/cm3 232.5 232.5 232.5 295.3 304.3    J/g 51.7 51.7 51.7 65.6 67.5

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.

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 1st 1.3m NC RF cavities.

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 LLNL

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 solenoids

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 dumpe- 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 PCAP

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 PPA

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 1st

section– 8C2Q which has 8 SCRF linacs and 2 quads. 8 units are used in the 2nd

section– 8C1Q which has 8 SCRF linacs and 1 quad. 12 units are used in the 3rd

section

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Matching section

PBSTR1: 400MEV TO 1082.5649MEV

PBSTR2: 1082.5649MEV TO 2507.0321 MeV

PBSTR3: 2507.0321 MeV to 5GeV

Matching to PTRANH

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: 934.23m

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Typical longitudinal distribution at end of PTRANH

Positron Linac to Damping Ring (PLTR) beamline

• PLTR beamline has two main functions: Energy compression and Spin rotation• At the beginning of PLTR, there is one horizontal chicane for introducing the needed chirp for

energy compressor.• The 1st 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

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Floor map of PLTR beamline

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)

Spin Rotator(8.3m long 3.16T SC solenoid)

Beamline Lattice • New lattice design has been done to comply with the new layouts as follow.

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Optics parameter of the new ILC positron source beamline lattice

TeV upgrade scenarios• Scenarios has been Studied by both DESY and ANL• Proposed that keep everything the same (Target, OMD), but the undulator change

to K=1, lu=4.3cm

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YieldPolarization

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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.

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.