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
A. Ushakov Update of e+ Source Parameters 14.09.2016 2 / 20
Schematic Layout of e+ Source (TDR, 2012)
Most important source parameters are summarized inILC Engineering Data Management System (EDMS) as
Excel document.
A. Ushakov Update of e+ Source Parameters 14.09.2016 3 / 20
Source Parameter List in EDMS (latest rev. 09-Aug-2012)
A. Ushakov Update of e+ Source Parameters 14.09.2016 4 / 20
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.
A. Ushakov Update of e+ Source Parameters 14.09.2016 5 / 20
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.
A. Ushakov Update of e+ Source Parameters 14.09.2016 6 / 20
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.
A. Ushakov Update of e+ Source Parameters 14.09.2016 7 / 20
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.
A. Ushakov Update of e+ Source Parameters 14.09.2016 8 / 20
150 GeV e− Beam Energy
A. Ushakov Update of e+ Source Parameters 14.09.2016 9 / 20
250 GeV e− Beam Energy
A. Ushakov Update of e+ Source Parameters 14.09.2016 10 / 20
Summary Table of Simulation Results
(Pe+ = 22% at 250 GeV and K = 0.92)
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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
]
A. Ushakov Update of e+ Source Parameters 14.09.2016 12 / 20
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
]
A. Ushakov Update of e+ Source Parameters 14.09.2016 13 / 20
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
A. Ushakov Update of e+ Source Parameters 14.09.2016 14 / 20
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
A. Ushakov Update of e+ Source Parameters 14.09.2016 15 / 20
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
A. Ushakov Update of e+ Source Parameters 14.09.2016 16 / 20
e+ Polarization for 231 m Undulator at 250 GeV e-
A. Ushakov Update of e+ Source Parameters 14.09.2016 17 / 20
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
A. Ushakov Update of e+ Source Parameters 14.09.2016 19 / 20
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]
A. Ushakov Update of e+ Source Parameters 14.09.2016 20 / 20