http://www.astec.ac.uk/id_mag/ID-Mag_Helical.htm

I.R. Bailey, J.B. Dainton, L.J. Jenner, L.I. Malysheva (University of Liverpool / Cockcroft Institute)

D.P. Barber (DESY / Cockcroft Institute)

G.A. Moortgat-Pick (IPPP, University of Durham / CERN / Cockcroft Institute)

A. Birch, J.A. Clarke, O.B. Malyshev, D.J. Scott (CCLRC ASTeC Daresbury Laboratory / Cockcroft Institute)

E. Baynham, T. Bradshaw, A. Brummit, S. Carr, Y. Ivanyushenkov, J. Rochford (CCLRC Rutherford Appleton Laboratory)

P. Cooke(University of Liverpool)

Helical Collaboration

Leo Jenner

University of Liverpool / Cockcroft Institute

Accelerator Science and Techology

EUROTeV: WP4 (polarised positron source) PTCD task

I. Bailey, J. Dainton, L. Zang (Cockcroft Institute / University of Liverpool)

D. Clarke, N. Krumpa, J. Strachan (CCLRC Daresbury Laboratory)

C. Densham, M. Woodward, B. Smith, (CCLRC Rutherford Appleton Laboratory)

J.L. Fernandez-Hernando, D.J. Scott (CCLRC ASTeC Daresbury Laboratory / Cockcroft Institute)

P. Cooke, P. Sutcliffe (University of Liverpool)

In collaboration with

Jeff Gronberg, David Mayhall, Tom Piggott, Werner Stein (LLNL)

Vinod Bharadwaj, John Sheppard (SLAC)

Ian Bailey

University of Liverpool / Cockcroft Institute

ILC Positron Source &

Spin Tracking

Daresbury Labs

Cockcroft Institute: Liverpool, Manchester, Lancaster, AsTeC

Most recent ILC layout…

• e+ e- linear collider

•Centrally located, stacked damping rings

•Single IR with push/pull detector

•The ILC requires of order 1014 positrons / s to meet its luminosity requirements.

•A factor ~60 greater than the ‘conventional’ SLC positron source.

•Undulator based source lower stresses in the production target(s) and less activation of the target station(s).

•Collimating the circularly-polarised SR from the undulator leads to production of longitudinally-polarised positrons.

Conversion Target (0.4X0 Ti)

Polarised Positrons(≈ 5 MeV)

Helical Undulat

or(≈ 100

m)

Photon Collimator

Photons(≈ 10 MeV )

Electrons(150 GeV)

Undulator-Based Polarised Positron Source for ILC

Original baseline layout of ILC with undulator at 150GeV position in main linac.

ILC Positron Source Layout

Baseline Positron Source R&D

Area Systems Group R&D topics

Undulator - CI

Topic Leader: Jim Clarke

Target station - CI

Topic Leader: Ian Bailey / Tom Piggott

OMD (capture optics) – CI

Target hall (eg layout, remote-handling) - CI

Capture rf cavity

Accelerator physics (eg production/ capture) - CI

Topic Leader: Gudi Moortgat-Pick

Polarisation (collimators, spin transport) - CI

Collaborating Institutes

DL

RAL

Cornell

SLAC

LLNL

ANL

DESY

BINP

CI - denotes a significant Cockcroft Institute contribution

Superconducting bifilar helix

First (20 period) prototype

Design field 0.8 T

Period 14 mm

Magnet bore 4 mm

Winding bore 6 mm

Winding section 4 4 mm2

Overall current density 1000 A/mm2

Peak field 1.8 T

Cut-away showing winding geometry

Parameters of first prototype

Superconducting undulator prototypes for ILC

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200 250 300 350

Position along axis, mm

Ra

dia

l fie

ld, T

Hall probe measurements of first prototype

Superconducting bifilar helix

First (20 period) prototype

Superconducting undulator prototypes for ILC

Section of second prototype, showing NbTi wires in Al former.

I II III IV V

Former material Al Al Al Iron Iron

Pitch, mm 14 14 12 12 11.5

Groove shape rectangular trapezoidal trapezoidal trapezoidal rectangular

Winding bore, mm 6 6 6.35 6.35 6.35

Vac bore, mm 4 4 4 4.5

(St Steel tube)

5.23*

(Cu tube)

Winding 8-wire ribbon,

8 layers

9-wire ribbon,

8 layers

7-wire ribbon,

8 layers

7-wire ribbon,

8 layers

7-wire ribbon,

8 layers

Sc wire Cu:Sc 1.35:1 Cu:Sc 1.35:1 Cu:Sc 1.35:1 Cu:Sc 1.35:1 Cu:Sc 0.9:1

Status Completed and tested

Completed, tested and sectioned

Completed and tested

Completed and tested

Manufacture in progress

Prototype Parameters

All completed prototypes have reached design field

Peak field specification of < +/- 1% demonstrated

Demonstrated predicted enhancement of field by ~0.44T using iron former

ILC Undulator Simulations

Energy spread increase in ILC electron beam due to

resistive wall impedance in undulator vacuum vessel. Red is room temperature,

blue is at 77K

Simulations of photon desorption of

absorbed gases from undulator beam pipe.

Collimation required to maintain vacuum of

10-8 Torr.

Undulator simulations showing winding bore and period of device needed

for ILC parameters.

Two sections of the undulator magnet

He bath vessel Thermal shield

Turret region

Cryostat wall – Thermal shield - He vessel - Magnetconnection

Long Prototype

Long prototype (4m) now under detailed design and will be manufactured by Summer ‘07.

Future Undulator ActivitiesFinalise design and construct long undulator prototype (4m)

Prototype beam tests

ERLP at Daresbury Laboratory

70 MeV electron beam visible light emitted

Pre-production prototype

Construct with UK industry

Module alignment issues

Module instrumentation

Collimation

Integrated vacuum system

Extend simulations

e.g. Geometric Wakefields

Capture Optics

Positron beam pipe/NC rf cavity

Target wheel

Vacuum feedthrough

MotorPhotonbeam pipe

Working in collaboration with SLAC and LLNL.

Developing water-cooled rotating wheel design.

0.4 radiation length titanium alloy rim.

Radius approximately 0.5 m.

Rotates at approximately 2000 rpm.

The CI plays a key role in the EUROTeV-funded task to carry out design studies of the conversion target and photon collimator for the polarised positron source.

Target Systems

LLNL - draft design

Target Wheel Design

LLNL - draft design

Iterative design evolution between LLNL and DL

Constraints:

• Wheel rim speed fixed by thermal load and cooling rate

•Wheel diameter fixed by radiation damage and capture optics

•Materials fixed by thermal and mechanical properties and pair-production cross-section (Ti6%Al4%V)

•Wheel geometry constrained by eddy currents.

DL - draft design

Eddy Current Simulations

LLNL - preliminary

LLNL - preliminary

Initial “Maxwell 3D” simulations by W. Stein and D. Mayhall at LLNL indicated:

•~2MW eddy current power loss for 1m radius solid Ti disc in 6T field of AMD.

•<20kW power loss for current 1m radius Ti rim design.

•However - Simulations do not yet agree with SLAC rotating disc experiment.

•8” diameter Cu disc rotating in field of permanent magnet.

•OPERA-3D simulations are starting at RAL.

Future Target ActivitiesPrototyping centred at Daresbury

• Proposing 3 staged prototypes over 3 years (LC-ABD funding bid)

• Measure eddy current effects• top priority• major impact on design

• Test reliability of drive mechanism and vacuum seals.

• Test reliability of water-cooling system for required thermal load

• Develop engineering techniques for manufacture of water-cooling channels.

• Develop techniques for balancing wheel.

• CI staff to work on design, operation and data analysis.

• Timeline integrated with our international collaborators.

Remote-handling design centred at RAL

• Essential that remote-handling design evolves in parallel with target design.

• Determines target hall layout and cost.

Related CI activities• Activation simulations (in

collaboration with DESY and ANL)• Positron production and capture

simulations (see spin tracking activities)

• Photon collimator design and simulation (CI PhD student + ASTeC expertise).

Capture Optics

z

• Two coil magnet gives focussing solenoid field

• Adding spin-tracking to ASTRA software

Damping Rings for ILCMachine pulse repetition rate is 5 Hz. Each bunch train consists of:

5782 bunches with 1010 particles per bunch.Bunch separation of 189 ns in the main linacs.Total bunch train length of 1.1 ms, or 328 km.

Positron and polarised electron sources produce bunches that are too large to generate much luminosity. We use damping rings to reduce the bunch emittances in the 200 ms between machine pulses.

particle trajectory

closed orbit

emitted photon

bending magnet

particle trajectoryclosed orbit

Andy Wolski,

Liverpool/Cockcroft

Other considerations…

• Wakefields

• Electron cloud effect in e+ line

Robust Spin Transport

• Developing reliable software tools that allow the machine to be optimised for spin polarisation as well as luminosity. Aiming to carry out full cradle-to-grave simulations.

• Currently carrying out simulations of depolarisation effects in damping rings, beam delivery system and during bunch-bunch interactions.

• Developing simulations of spin transport through the positron source.

•Will soon extend simulations to main linac, etc.

0E+00

5E+13

1E+14

2E+14

2E+14

3E+14

3E+14

0.0 20.0 40.0 60.0 80.0 100.0

Photon Energy (MeV)

Flu

x (p

ho

ton

s/s/

mA

/0.1

%)

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Cir

cula

r P

ola

risa

tio

n R

ate

20 x 20 urad flux2 x 2 urad flux20 x 20 urad polarisation2 x 2 urad polarisation

Energy spectrum and circular polarisation of photons from helical undulator.

Trajectories of electrons through helical undulator.

Example of SLICKTRACK simulation showing depolariation of electrons in a ring.

Collaborating with T. Hartin (Oxford) P. Bambade, C. Rimbault (LAL) J. Smith (Cornell)S. Riemann, A. Ushakov (DESY)

Both stochastic spin diffusion through photon emission and classical spin precession in inhomogeneous magnetic fields can lead to depolarisation.

1 mrad orbital deflection 30° spin precession at 250GeV.

Largest depolarisation effects are expected at the Interaction Points.

Depolarisation Processes

Photon emission

Spin precession

( 2)

2spin orbit

g

Undulator Collimator / Target Capture Optics

PhysicsProcess

Electrodynamics Standard Model T-BMT

(spin spread)

Packages

SPECTRA, URGENT

GEANT4, FLUKA ASTRA

Damping ring Main Linac / BDS

Interaction

Region

PhysicsProcess

T-BMT

(spin diffusion)

T-BMT Bunch-Bunch

Packages

SLICKTRACK,

(Merlin)

SLICKTRACK

(Merlin)

CAIN2.35

(Guinea-Pig)

Packages in parentheses will be evaluated at a later date.

e+ source

Software Tools

Positron Source Simulations

Polarisation of photon beam•Ongoing SPECTRA simulations (from SPRING-8) •Benchmarked against URGENT

•Depolarisation of e- beam•So far, review of analytical studies only •eg Perevedentsev etal “Spin behavior in Helical Undulator.” (1992)

•Target spin transfer• GEANT4 with polarised cross-sections provided by E166 experiment.• Installed and commissioned at University of Liverpool.

10MeV photons

Bunch-Bunch SimulationsOpposing bunches depolarise one another at the IP(s).

Studies of different possible ILC beam parameters (see table on right).

Much work ongoing into theoretical uncertainties.

Large Y

During Interaction

Before Interaction

After Interaction

Spread in Polarisation

Low Q

Before Interaction

During Interaction

After Interaction

SLICKTRACK Simulations

• Damping Rings– OCS and TESLA lattices

analysed for ILC DR group.– Depolarisation shown to be

negligible.– Ongoing rolling study.

• Beam Delivery System– First (linear spin motion)

simulations presented at EPAC ’06 conference.

– Ongoing rolling study.

• MERLIN development as a cross-check of main results– Andy Wolski training CI RA’s and PhD students

• Non-linear orbital maps interfaced to SLICKTRACK– Modelling sextupoles, octupoles, undulator, etc

• Integrated positron source simulations– Rolling study

• Beam-beam theoretical uncertainties– Incoherent pair production and EPA, T-BMT validity, etc…– Comparison with GUINEA-PIG

• Novel polarisation flipping in positron source– Flipping polarity of source without spin rotators (cost saving)

• Polarimetry and polarisation optimisation (University of Lancaster)– Developing techniques to optimise polarisation at the IP

• Optimising use of available computing resources at DL, Liverpool and on the GRID

Future Spin Transport Activities

• CI has leadership role in many areas of ILC positron source R&D

• Recent results presented at EPAC ’06, ICHEP ’06, SPIN ’06, …

• Proposed new prototyping programme to be based at Daresbury– Addressing key issues for undulator + target

• Establishing base of spin tracking expertise at CI

Summary and Outlook