1. Capture and Transmission of polarized positrons from a Compton Scheme
A. VIVOLI*, B. MOUTON, A. VARIOLA, O. DADOUN (LAL/IN2P3-CNRS), R. CHEHAB (IPNL &LAL/IN2P3-CNRS), Orsay, France *

2. CONTENTS General scheme of the positron source
Scheme of the Capture Section
Working of the elements
Simulations of different cases of positrons production and capture
Comparison of results
Conclusions & Future tasks
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

3. Positron Source g Target Diaphragm ERL Scheme e- e+ e-,g e- e+
Compton cavities
Up to 5 GeV
superconducting linac
with quadrupole focusing
Target
1.3 to 1.8 GeV
superconducting linac
Capture Section with solenoid
(+ Bunch Compressor)
Up to 150 MeV
Damping Ring
e- injector +
Bunch Compressor
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

4. Compton Production Nd:YaG laser (l=1.064 mm)
High Gain Fabry-Perot cavity
Crossing angle : degrees
Distance between Compton interaction point and target : 10 m.
Bunch charge : 1.5 nC
RMS bunch length : ps.
e- bunch energy : GeV.
Simulations of Compton Scattering are made with CAIN
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

5. Diaphragmation Target Maximum angle allowed : Jp = 0.4 mrad 3 m 3 m
Target : f = 3 cm
5 mm
5 mm
Collision point
Target
Energy
Acceptance
1.0 GeV
0.51
1.3 GeV
0.61
1.5 GeV
0.67
1.8 GeV
0.73
Maximum angle allowed : Jp = 0.4 mrad
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

6. Simulation: 1.3 GeV (I) Without Diaphragm With Diaphragm 03/12/2018
A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

7. Simulation : 1.3 GeV (II) Without Diaphragm With Diaphragm 03/12/2018
A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

8. Simulation: 1.3 GeV (III) Beam radius (rms): r = 10.4 mm
(Photons)
Without Diaphragm
Beam radius (rms): r = mm
Mean Energy : E = 14,7 MeV
With Diaphragm
Beam radius (rms) : r = 2.3 mm
Mean Energy : E = 20.9 MeV
Number of photons simulated : 10000
Polarization agreement : x3 = +1 indicates right circular polarization
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

9. Positron Production (1.3 GeV no D)
Target material : W
Target thickness : l = 0.4 X0 = 1.4 mm
Number of e+ : 549
Mean energy : MeV
Polarization : <x3> = 40%
Simulation made with EGS4
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

10. Positron Polarizationx3
Energy (MeV)
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

11. Capture Section (+ B.C.) g Adiabatic Matching Device Bunch Compressor
Pre-accelerator
Target
From
Compton
Cavities e-
To the accelerator g g e+
Bending
Magnets
Drifts
Solenoid
Cavities
Magnetic field
Electric field
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

12. Adiabatic Matching Device
Length: L = 50 cm
Magnetic field at the target : B0 = 6 T
Magnetic field at the end : B(L) = 0.5 T
Magnetic Field Behaviour :
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

13. Beam parameters n. e+ ex (rms) mm mrad ey (rms) mm mrad <E> MeV
Parameters of the positron beam at the exit of the target (z = 0 cm)
and at the exit of the AMD (z = 50 cm)
n. e+
ex (rms) mm mrad
ey (rms) mm mrad
<E> MeV
DE/<E> %
DL (rms) mm
<x3>
410
2140
3400
11.79
46.52
0.30
46.94
291
765
769
11.46
47.64
9.16
48.01
Z = 0
Z = 50
Capture efficiency : 71,0 %
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

14. Captured Positron Beam
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

15. Pre-accelerator Solenoid Magnetic Field = 0.5 T Length = ~ 31 m
Accelerating Cavities:
Length = 1.25 m
Aperture = 2.3 cm
Average accelerating Field = ~ 7 MV/m
Number of cavities = 22
Drift length between cavities = 13 cm
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

16. Beam parameters II n. e+ ex (rms) mm mrad ey (rms) mm mrad
Parameters of the positron beam at the exit of the AMD (z = 50 cm)
and at the exit of the solenoid (z = 3085 cm)
n. e+
ex (rms) mm mrad
ey (rms) mm mrad
<E> MeV
DE/<E> %
DL (rms) mm
<x3>
291
765
769
11.46
47.64
9.16
48.01
215 34 32
152.43
7.55
10.34
49.43
Z = 50
Z = 3085
Loss percentage : 26,12 %
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

17. Bunch Compressor Bending Magnets Length = 35 cm
Bending angle = 18,50 deg.
Magnetic field intensity = 4.6 KG
Straight edges
Drift length between magnets = 20 cm
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

18. Beam parameters III n. e+ ex (rms) mm mrad ey (rms) mm mrad
Parameters of the positron beam at the exit of the solenoid (z = 3085 cm) and of the Capture Section (z = 3436 cm)
n. e+
ex (rms) mm mrad
ey (rms) mm mrad
<E> MeV
DE/<E> %
DL (rms) mm
<x3>
215 34 32
152.43
7.55
10.34
49.43
205 31
152.34
7.39
5.85
48.94
Z= 3085
Z= 3436
Total capture efficiency ~ 2,05 %
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

19. Polarization (I)
Assumption : polarization is conserved in the transport line
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

20. Polarization (II) Energy cut (MeV) Capture eff. (%) Polarization (%)
2.05
48.9 5
1.86
55.6 10
1.26
70.1 15
0.62
85.0 20
0.18
93.1
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

21. 5 GeV superconducting LINAC
Quadrupoles length : L = 10 – 20 cm
Field at pole tip : B = 3 – 8 KG
Quadrupoles aperture : R = 5 cm
Cavities length : l = 1.25 m
Mean accelerating field : E = 10 MV/m
Cavities aperture : r = 3.5 cm
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

22. RESULTS (I)
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

23. RESULTS (II)
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

24. Conclusions
Increasing the energy of the e- beam for the Compton scattering the capture efficiency increases nearly linearly (from 0.9% for 1.0 GeV to 4% for 1.8 GeV) but the total polarization is affected. (from ~60% to ~ 30%)
At 5 GeV (injection in the Damping Ring) the energy spread is ~ 0.2 %, bunch length ~ 6-7 mm, emittance < 1 mm mrad.
Gamma photon diaphragm does not seems to be determinant.
Bunch compression ~ 2.
Further improvement in optimization will be studied.
Energy selection of the e+ may be considered to increase polarization at expenses of capture efficiency.(5-10 MeV)
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

25. Future tasks Parameters optimization
Polarization selection (diaphragm in the bunch compressor?)
Thin target (for CW ERL multiple stacking injection)
Polarization transport
Longitudinal phase space capture optimisation (capture cavity closer?)
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

26. THANKS.
The End
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A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme