Undulator Based ILC Positron Source Studies

Wei Gai

Argonne National Laboratory

CCAST ILC Accelerator Workshop

Beijing, Nov 5 – 7, 2007

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Acknowledgement:

The reported works are produced by the ILC positron collaborations:

SLAC, LLNL, ANL, ORNL, BNL, KEK, RAL, Daresbury/Cockcroft, DESY and others.

Most Recent Summaries can be found at:

www.hep.anl.gov/ILC-positron/

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Nominal Source Parameters

Parameter Symbol Value Units

Bunch Population Nb 2x1010 #

Bunches per pulse nb 2625 #

Bunch spacing tb 369 ns

Pulse repetition rate frep 5 Hz

Injection Energy (DR) E0 5 GeV

Beam Power (x1.5) Po 300 kW

Polarization e-(e+) P 80(30) %

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Positron Source Layout (undulator based scheme)

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Winding undulator on a custom built winding machine

Undulator winding (RAL/UK)

Courtesy Jim Clarke of CCRL/Daresbury

New tapering tested: conical transition from Iron to brass helix yoke New original technology of wire return testedNew iron spacing technologyNew winding machine

Right now the cold mass has diameter 1.5 inch. Designed cold mass with1 inch diameter6

Fabricated undulator with 6.35 mm Inner diameter (1/4”) available for the beam; 13.5 mm period K=1.48 measured

1 inAlexander Mikhailichenko/Cornell

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Target

Target– 100 m/s rim speed– 1-m diameter wheel– 1.4 cm– Ti-96%Al-4%V– 8% heat deposition

Stress from motion , stress from heating Vacuum seals that allow water flow and rotation Magnetic fields & moving metal

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Cockroft institute prototype experiment simulation

Technical drawing provided by I.Bailey

Simulation, Induced field, z-component, 2000RPM

z0

D – 1m, rim width – 30mm, rim thickness – 14mm, distance between magnet poles is 5cm, field – 1.5Tesla

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Photon Number Spectrum

Number of photons per e- per 1m undulator:Old BCD: 2.578UK1: 1.946; UK2: 1.556; UK3: 1.107Cornell1: 0.521; Cornell2: 1.2; Cornell3: 0.386

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Initial Polarization of Positron beam at Target exit(K=0.92 u=1.15)

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Initial Pol. Vs Energy of Captured Positron Beam

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Yield contribution from different harmonics – new baseline undulator, without collimator

High order harmonics are important

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Comparison of positron yield from different undulators

High K Devices Low K Devices

  BCD UK I UK II UK III Cornell I Cornell II Cornell III

Period (mm) 10.0 11.5 11.0 10.5 10.0 12.0 7

K 1.00 0.92 0.79 0.64 0.42 0.72 0.3

Field on Axis (T) 1.07 0.86 0.77 0.65 0.45 0.64 0.46

Beam aperture (mm) Not Defined

5.85 5.85 5.85 8.00 8.00

First Harmonic Energy (MeV)

10.7 10.1 12.0 14.4 18.2 11.7 28

Yield(Low Pol, 10m drift) ~2.4 ~1.37 ~1.12 ~0.86 ~0.39 ~0.75 ~0.54

Yield(Low Pol, 500m drift)

~2.13 ~1.28 ~1.08 ~0.83 ~0.39 ~0.7 ~0.54

Yield(Pol) ~1.1 ~0.7 ~0.66 ~0.53 ~0.32 ~0.49 ~0.44

Target: 1.42cm thick Titanium

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Immersed target works well in simulation, but can we use it?

Difficulties: Conventional magnets, ~ MW power supply.

Rotating in the magnetic field, people use this scheme for breaks.

What else we can do?

Build pulsed magnet; Lithium Lens(?) Use ¼ wave transformer scheme.

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

SLC OMD was a pulsed flux concentrator

It is a large extrapolation from SLC to ILC– 1s -> 1ms pulse width

Previous magnet for hyperon experiment was the closest thing we could find.– Cryogenic nitrogen cooling of the

concentrator plates.– ANL and LLNL did initial rough

electromagnetic simulations. Not impossible but an engineering challenge.

– No real engineering done so far.

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

¼ wave solenoid seems more feasible

Capture efficiency is only 25% less than flux concentrator

Low field at the target reduces eddy currents

This is probably easier to engineer than flux concentrator

SC, NC or pulsed NC?

ANL ¼ wave solenoid simulations

W. Liu

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Lithium lens Lithium Lens

– Will lithium cavitate under pulsed heating?• window erosion

– Will lithium flow adequately cool the windows?– Lens is defocusing for electrons

• Increased heating and radiation load in the capture section

P.G. Hurh & Z. Tang

A. Mikhailichenko

Alexander Mihkailchenko, Cornell Univ.

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

0

5

10

15

20

25

30

35

Shielded target & Quarter-wavetransformation(w/ collimation)

Shielded target & Quarter-wavetransformation

(w/o collimation)

Shielded target &Flux concentrator

(w/ collimation)

5T Immersedtarget & Flux

concentrator (w/ collimation)

Cap

ture

eff

icie

ncy

(%

)Capture Efficiency: FZ, YN SLAC; WL ANL

Sheppard, SLAC

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007

Summary

Systematic studies of the ILC positron source performed. Various issues addressed.

Basic-Basic (1/4 wave) scheme may work, but require 300 m long undulator and 3 GeV Linac to compensate the energy loss.

Challenges and further works:– Target design: Mechanical and materials. (Ti, W, Eddy current and

radiation damages).– Capturing Magnets (Lens): Small R&D investments may yield huge

savings.– Target Hall: Remote handling target and other beamline components.– Undulator: electron beam jitter tracking through the undulator,

polarizations, and other errors like undulator and alignments.– Electron beam properties after traversing the undulator, anything

changes except energy?