Positron Source for ILC TeV Upgrade

Positron Source for ILC TeV Upgrade

Wanming LiuPosipol 2012

Posipol 2012, 09/04/2012 - 09/07/2012, DESY Zeuthen

Constrains

End of linac, => Drive beam energy =~500GeV Has to be compatible with the TDR site layout

– No change to be made on the target station and there after


Challenges Radiated Photo parameters from beam passing through a helical undulator:

1

222'2

2

220

26

))(][)((4

10]

1[ xJ

x

n

KxJ

K

hc

e

MeVmdE

dNphn

nn

functionsBesselJ

KKx

KK

n

n

n

n

)1(2

0]1)1(

[

21

22

12

1

)1(

4

][*][*934.0

2

2

11

K

K

cE

cmTBK

u

u

The 1st Harmonic critical energy is proportional g2

dq is inverse to g


Goals and Assumptions

Goal– A reasonable scheme for the 1 TeV option without

major impact on the ILC TDR configuration. Assumptions

– Drive beam energy: 500 GeV– Target: 0.4 X0 Ti– Drift from end of undulator to target: 400m– OMD: QWT and FC

Photon number spectrum for K=1 and different undulator period

0

0.005

0.01

0.015

0.02

0.025

0 50 100 150 200photon energy (MeV)

dNph

/dE

lu=1cmlu=2cmlu=4cmlu=8cm

lu( cm)

Nph/m E average (MeV)

Total photon energy per meter (MeV)

1 2.60323 139.381398

362.841814

2 1.301615 69.690699 90.710454

3 0.867743 46.460466 40.315757

4 0.650807 34.84535 22.677613

5 0.520646 27.87628 14.513673

6 0.433872 23.230233 10.078939

7 0.37189 19.911628 7.404935

8 0.325404 17.422675 5.669403



With Fixed K=1 and different undulator period length

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10l u (cm)

Pos

itron

yie

ld

0.00

0.05

0.10

0.15

0.20

0.25

Pol

ariz

atio

n

YieldPolarization

Based on the above plot, lu=4.3cm is used for a more detail simulation to evaluate the energy deposition and impact on drive beam


Photon beam power and energy deposition for generating 3e10 captured positrons

0.00

2.00

4.00

6.00

8.00

10.00

12.00

3 4 5 6 7 8l u (cm)

Ene

rgy

Dep

osi

ton

(kW

)

0.00

50.00

100.00

150.00

200.00

250.00

Ph

oto

n be

am p

ow

er (

kW)

Energy DepositionPhoton beam power

Parameters for 1.5 of positron yield using fixed K=1 with different undulator periodlu (cm) Photon beam

power (kW)Power deposition (kW)

Drive beam energy lost (GeV)

Undulator length required (m)

3 206 7.19 4.91 124

4 186 7.84 4.44 198

4.3 181 7.94 4.3 221

5 176 8.37 4.19 289

6 166 8.76 3.88 387

7 170 9.80 4.05 549

8 166 10.34 3.94 697



Using FC as OMD When FC is used as OMD instead of QWT, the yield increased

up to about 2.62 for 231m long undulator with K=1 and lu=4.3m and thus the undulator length is reduced to 132m


The impact on 500GeV drive beam from the chosen undulator parameters

Code used: elegant Lattice:

– Quads:Effective length 1mStrenth:0.09717 and -0.1109 alternating.Separation: 12m with space of quad excluded.

– Undulator:lu=4.3cm, K=1 Sections with effective length of ~11.0m between quads

Initial beam parameters:enx=10e-6 m.rad, eny=0.04e-6 m.radbx=46m, by=9mEnergy spread: 1GeV or 0.2% Average energy: 500GeV


Drive beam emittance

With no quad-bpm error included, the beam emittance is damping.

9.88E-06

9.90E-06

9.92E-06

9.94E-06

9.96E-06

9.98E-06

1.00E-05

1.00E-05

1.00E-05

0 100 200 300 400s (m)

e x (

m.r

ad)

3.95E-08

3.96E-08

3.97E-08

3.98E-08

3.99E-08

4.00E-08

4.01E-08

e y (

m.r

ad)

normalizedemittance x

Normalizedemittance y


Size of beam as it passing through the lattice

0.0E+00

5.0E-06

1.0E-05

1.5E-05

2.0E-05

2.5E-05

0 100 200 300 400s (m)

s x (

m)

0.0E+00

2.0E-07

4.0E-07

6.0E-07

8.0E-07

1.0E-06

1.2E-06

1.4E-06

s y (

m)

sigma_xsigma_y

The beam is well matched to the lattice


Beta of beam

0

5

10

15

20

25

30

35

40

45

50

0 100 200 300 400s (m)

Bet

a o

f bea

m

beta_xbeta_y


Drive beam energy and energy spread

0.195

0.2

0.205

0.21

0.215

0.22

0.225

0.23

0.00E+00 1.00E+02 2.00E+02 3.00E+02 4.00E+02s (m)

En

erg

y S

pre

ad

(%)

493.00

494.00

495.00

496.00

497.00

498.00

499.00

500.00

501.00

Be

am

Ene

rgy

(Ge

V)

Energy spread Beam Energy

Drive beam energy spread increased from about 0.2% up to about 0.23% with about 400m long undulator beam line.


Preliminary results about polarization

K=1, lu=3cm K=1.5, lu=4cm

30% polarization can be achieved by using a photon collimator with iris of about 0.9mm with K=1 and lu=3cm or about 1.1 with K=1.5 and lu=4cm


Preliminary results about polarization-Fixed K=1.5, different length of period

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14radius of collimator iris (cm)

Yie

ld

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

Pol

.

Yield, lu=5cmYield, lu=6cmYield, lu=7cmPol., lu=5cmPol., lu=6cmPol.,lu=7cm

Results are showing that the polarization doesn’t change much with the undulator period length. The criteria for choosing undulator period length will be depends on other parameters like energy deposition and the impact on the drive beam.


Summary

To upgrade to TeV ILC, the ILC undulator based positron source can be upgraded to take the ~500GeV drive beam by using an undulator having K=1 with lu=4.3m period without changing other part of positron source. There is no technical difficulty to build a longer period undulator with K=1.

To upgrade to TeV ILC with polarized positron source (>50% polarization), more studies and optimizations are needed.

Documents

Positron Source for ILC TeV Upgrade