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 * E-mail : vivoli@lal.in2p3.fr

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 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

Compton Production Nd:YaG laser (l=1.064 mm) High Gain Fabry-Perot cavity Crossing angle : 8 degrees Distance between Compton interaction point and target : 10 m. Bunch charge : 1.5 nC RMS bunch length : 1 ps. e- bunch energy : 1.0 - 1.8 GeV. Simulations of Compton Scattering are made with CAIN 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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

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

Simulation: 1.3 GeV (III) Beam radius (rms): r = 10.4 mm (Photons) Without Diaphragm Beam radius (rms): r = 10.4 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 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 : 10.51 MeV Polarization : <x3> = 40% Simulation made with EGS4 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

Positron Polarization x3 Energy (MeV) 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 : 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 % 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

Captured Positron Beam 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 % 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 % 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

Polarization (I) Assumption : polarization is conserved in the transport line 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

RESULTS (I) 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

RESULTS (II) 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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) 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

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?) 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme

THANKS. The End 03/12/2018 A. Vivoli, Capture & Transmission of polarized positrons from a Compton Scheme