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ILC Electron and Positron Sources - PPT Presentation

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

beam positron target energy positron beam energy target undulator photon source ilc beamline length electron production dump bunch lattice main upgrade collimator

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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

.