-2mm Update of ILC Positron Source Parameters · A. Ushakov Update of e+ Source Parameters 14.09.2016 7 / 20. Simpliﬁcations of Capture RF Section Length of capture RF section (1.3

Update of ILC Positron Source Parameters

Andriy Ushakov1 and Sabine Riemann2

1University of Hamburg, 2DESY (Germany)

POSIPOL 2016

14 September 2016Laboratoire de l’Accélérateur Linéaire (LAL), Orsay, France

A. Ushakov Update of e+ Source Parameters 14.09.2016 1 / 20

Outline

Undulator-based source parameters in ILC Engineering DataManagement System (EDMS)

Source model used in simulations

Simulation results for 125 GeV, 150 GeV, 175 GeV and 250 GeVe− beams

Comparison with EDMS parameter list

Impact of E-field phase on e+ yield

e+ yield for different longitudinal bunch length cuts and emittancecuts

Is a longer undulator with lower K is much better for e+

polarization?

Summary


Schematic Layout of e+ Source (TDR, 2012)

Most important source parameters are summarized inILC Engineering Data Management System (EDMS) as

Excel document.


Source Parameter List in EDMS (latest rev. 09-Aug-2012)


Optimization of Positron Capture

Wanming Liu and Wei Gai (ANL) made the great job on positron capturesimulations and tracking up to DR summarized in TDR and EDMSsource parameters tables.

Since 2012 some optimization studies have been done.

Energy Deposited in Target and Temperature Rise per Pulse

⇒ Re-check of photon power, peak energy deposition density (PEDD) intarget and etc. was needed in whole energy range of e− drive beam.


General Remarks and Fixed in Simulation Parameters

Start-to-end simulations give the most correct results. Such simulationsare time consuming and usually require using two or more differentcodes for modeling of undulator/e+ production/e+ capture/e+ tracking upto DR.Optimization of undulator-source lattice is not finished yet.

⇒ Only positron capture section is included in our simulations.Simulations have been done by help of a single relatively quickGeant4-based application (PPS-Sim). DR acceptance is emulated asa series of cuts at the end of capture section (125 MeV):

Energy spread: (±0.75% at DR)⇒ ±2.2% after capture section⇔±11 mm long. bunch length cut;Normalized emittance: εnx + εny < 70 mm rad.

Photon radiation in real/measured field of helical undulator is ongoing(Khaled Alharbi talk today).

⇒ (Kincaid) ideal model of undulator radiation is used.⇒ Field, undulator geometry imperfections, e− energy losses and smalldeflections of e− trajectories in undulator were not taken into account.


Fixed/Free Parameters: e+ Beam, Undulator and FCe+ Beam: 125÷ 250 GeV, 2 · 1010 e+/bunch, 1312 bunches/pulse with 554 nsbunch spacing, 5 Hz rep. rate.

Helical Undulator

Source has to provide 1.5 e+/e− at DR.

Maximal undulator magnet length is limited (fixed) by

147 m for Ee− ≥ 150 GeV,231 m for Ee− < 150 GeV.

Undulator field (or K-value) is adjustable. B ≤ 0.86 T (K ≤ 0.92).

Flux Concentrator (FC)

Min. aperture radius: 6 mm.

Max. field of FC: 3.2 T, 2 cm downstream the target.

Min. field of FC: 0.5 T, 14 cm downstream the target.

FC has no any dipole field component.

FC field is constant during the beam pulse.


Simplifications of Capture RF Section

Length of capture RF section (1.3 GHz) downstream FC is 15.44 m.

For simplification, the capture section consists from one module and theE-field amplitude is constant over whole capture section.

Both accelerated and decelerated phases of E-field at the beginning ofcapture RF section have been considered.

Positron energy at the end of capture RF section has to be 125 MeV.Therefore, the average positron energy gain is the same for both fieldphases.


150 GeV e− Beam Energy


250 GeV e− Beam Energy


Summary Table of Simulation Results

(Pe+ = 22% at 250 GeV and K = 0.92)


E-Phase Scan for 150 GeV e− Beam

147 m Undulator with K = 0.92, E0 = 18.5 MV/m

e+ Yield and Polarization vs E-Field Phase

-150 -100 -50 0

1.5

1.6

1.7

1.8

1.9

2.0

Yie

ld [e

+ /e- ]

E-Phase [degree]

110

120

130

140

150

160

Ene

rgy

[MeV

]


E-Phase Scan for 250 GeV e− Beam

147 m Undulator with K = 0.45, E0 = 18.5 MV/m

e+ Yield and Polarization vs E-Field Phase

-150 -100 -50 0

1.35

1.40

1.45

1.50

Yie

ld [e

+ /e- ]

E-Phase [degree]

105

110

115

120

125

130

135

140

145

150

155

160

165

Ene

rgy

[MeV

]


250 GeV: Longitudinal Bunch Length Cut

0 3 6 9 12 15 180.0

0.3

0.6

0.9

1.2

1.5

e Y

ield

[e/e

]

Long. Bunch Length Cut [mm]

16

20

24

28

32

36

e P

olar

izat

ion

[%]

Solid curves: accelerated E-phase, K = 0.47Dotted curves: decelerated E-phase, K = 0.45


250 GeV: Longitudinal Profile of Positron Bunch

K = 0.47, accel. E-phase

Mean 7.015

RMS 4.805

z [mm]0 2 4 6 8 10 12 14 16 18 20 22 24

[a.u

.]e+

N

0

50

100

150

200

250

300

350

400

450 Mean 7.015

RMS 4.805

K = 0.45, decel. E-phase

Mean 80.18

RMS 2.576

z [mm]70 75 80 85 90

[a.u

.]e+

N0

200

400

600

800

1000Mean 80.18

RMS 2.576


250 GeV: Emittance Cut

0 20 40 60 80 100 120 140

0.4

0.8

1.2

1.6

2.0 Yaccel Ydecel

e Y

ield

[e/e

]

Emittance Cut [mm rad]

20

25

30

35

40

Paccel Pdecel

e P

olar

izat

ion

[%]

Solid curves: accelerated E-phase, K = 0.47Dotted curves: decelerated E-phase, K = 0.45


e+ Polarization for 231 m Undulator at 250 GeV e-


Summary

Most of parameters included in EDMS list of source parametershave been checked.

Simulations were done for accelerated and decelerated phases atthe beginning of positron capture accelerator section.

Deceleration of positrons after FC reduces long. bunch length andhelps to increase the captured e+ yield.

Source with 231 m undulator can generate the required number ofpositrons at 125 GeV drive e− beam.

Increasing of undulator length from 147 m to 231 m for 250 GeVe− beam and reduction of undulator K-value does not increase e+

polarization significantly.

TO DO ItemsSimulations based on the measured undulator field.

Power deposition / radiation damage of FC at “low” energies.A. Ushakov Update of e+ Source Parameters 14.09.2016 18 / 20

Backup Slides


250 GeV: e+ Yield vs Target Thickness

2 4 6 8 10 12 14 16

0.9

1.0

1.1

1.2

1.3

1.4

1.5Y

ield

[e+ /e

- ]

Target Thickness [mm]


Documents

-2mm Update of ILC Positron Source Parameters · A. Ushakov Update of e+ Source Parameters 14.09.2016 7 / 20. Simpliﬁcations of Capture RF Section Length of capture RF section (1.3