Development of a Positron Production Target for the ILC Positron Source

Capture Optics

Positron beam pipe/NC rf cavity

Target wheel

Vacuum feedthrough

MotorPhotonbeam pipe

Water-cooled rotating wheel.

0.4 r.l. titanium alloy rim.

Radius ~1 m.

Rotates at ~1000 rpm.

The University of Liverpool, LLNL and SLAC are carry out design studies of the ILC e+source conversion target.

Project Overview

LLNL - draft design

Undulator Photon Beam (2) Minimum

ILC parameters

Nominal

Maximum ILC

parameters

Pulse frequency 5 5 5 Hz Pulse train length 0.2 1 2.6 ms Bunch length 0.5 1 1.7 ps Bunches / pulse 1330 2820 5640 Bunch spacing 154 308 461 ns Energy (*) 10.6 21.2 21.2 J/bunch Number of photons (*)

6.6 13.4 13.4 1012 photons/bunch

First harmonic photon energy

10 10 10 MeV

Number of polarised positrons required from source (no losses)

0.7 2.8 5.6 1014 positrons/s

Photon Beam power w/o coll. (*)

35 150 300 kW

Length of undulator (*)

100 100 100 m

* “Proportional to undulator length”

Target Systems •Key sub systems

•Target wheel

•Drive system

•Cooling system

•Vacuum system

•Remote-handling system

•Diagnostic and control systems

Not to scale! For illustration only.

Target Wheel Design

LLNL - draft designNumbers refer to LLNL study of earlier solid-disc design with 220 kW photon beam.

Eddy Current Simulations

LLNL - preliminary

LLNL - preliminary

Initial “Maxwell 3D” indicate:

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

•<20 kW power loss for current design.

•Simulations yet to be calibrated to SLAC rotating disc experiment.

Power Deposition & Cooling

Approximately 10% of photon beam power is deposited in target wheel

1.85E-03

5.21E+00

1.19E+03

1.20E+02

9.59E+01

1.02E+02

2.95E-05

9.90E-08

Bunch energy deposition (J/g) 2.39E+003.80E-06

Pulse energy deposition (J/g) 1.75E+021.08E+16Bunch (peak) deposited power density

(W/l)

Total volume of target struck by beam over pulse duration (m 3̂)

Total energy deposition of overlapping bunches (J)Total duration of overlapping bunches (s)

Degrees target rotates between bunchesDegrees target rotates over pulse duration

Number of overlapping consecutive bunches (95% energy containment)

Degrees target rotates between pulses

Total volume of target struck by beam over bunch duration (m 3̂)

Phase advance between start of consecutive pulses (degrees) LLNL - draft design

LLNL - draft design

Water fed into wheel via rotating water union on drive shaft.

Remote-Handling

Each hot cell consists of:• Super-structure and shielding• 2 lead glass windows (1m x 1m

viewing area, 1m thick)• 2 pairs of master-slave manipulators• In-cell crane • Ventilation system• Camera and sound system (8 videos

cameras)• Posting port• Miscellaneous tools…

Photon beam

•Full maintenance remote-handling concept.

•Two hot cells.

•Based on ISIS second target station.

Remote Handling (2)

Alternative single hot cell design.

Suited to two targets in series.

P. S

utcliffe, University o

f Liverpool.

Cheapest option may be to move any faulty target to a holding cell until ‘cool’ enough to be handled manually. Will depend on component reliability.

Summary and Outlook

Prototypes will be developed to demonstrate:

• Stability of rotating target• Reliability of drive

mechanism and vacuum seals.

• Rotation of target in B field of capture optics.

• Reliability of water-cooling system for required thermal load

• Engineering techniques for manufacture of water-cooling channels.

A design has been developed for a conversion target that satisfies the requirements of the ILC positron source.

Simulations and modelling of the target systems is ongoing.

A remote-handling design is being investigated.

Work supported by the Commission of the European Communities under the 6th Framework Programme “Structuring the European Research Area”, contract number RIDS-011899.

This work was performed under the auspices of the U.S. Department of Energy by the University of California,Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515.

Undulator Photon Beam •Undulator

•K=1, 1cm period, 100m

•Nominal ILC parameters.

•Neglect collimation.

•Target ~500 m downstream.

•Total photon beam power

•~145 kW

•Average photon energy

•~ 13MeV

•Beam spot rms

•~1 mm

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 1 2 3 4 5 6 7

radius (mm)

Po

wer

(kW

)

Power (kW)

Sim

ulations using SP

EC

TR

A

I.R. Bailey1,3 ,V. Bharadwa,j4 ,P. Cooke3,J.B. Dainton1,3, J. Gronberg2,D. Mayhall2,T. Piggott2,D.J. Scott1,3,J. Sheppard4,W. Stein2,P. Sutcliffe3

1 Cockcroft Institute, Daresbury Laboratory, Warrington, Cheshire, WA4 4AD, UK.

2 Lawrence Livermore National Lab, Livermore, CA 94551, USA.

3 Department of Physics, University of Liverpool, Liverpool, L69 7ZE, UK.

4 Stanford Linear Accelerator Cente, PO Box 20450, Stanford, CA 94309, USA.

Conversion Target (0.4X0 Ti)

Polarised Positrons(≈ 5 MeV)

Helical Undulat

or(≈ 200

m)

Photon Collimator

Photons(≈ 10 MeV )

Electrons(150 GeV)

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

Positron Source

Tim

Broo

me

, R

AL