A 10GeV mono energetic electron beam (with au gaussian distribution in x and y
-in root : gRandom->Gaus(0,2.5e-3)/sqrt(2.)-) impinging on 0.1 cm amorphous tungsten produced gamma with this phase space (yield=#gamma/#e-=138966/50000~2.78)

Those gamma are using to produce positron by impinging on 0.8 cm of amorphous tungsten
(distance between the two amophous target is 2m).
Positron phase space distribution(yield=#positron/#electron=143443/50000 ~2.86)

(Robert Chehab’s graphic and summary)
In the following we took:

For both case (10 GeV and 5 GeV) the inital x and y electron distribution follow (ROOT syntax)

x=gRandom->Gaus(0,2.5e-3)/sqrt(2.); // gaussian centered x=0 with rms_x=2.5mm
y=gRandom->Gaus(0,2.5e-3)/sqrt(2.); // gaussian centered y=0 whith rms_y=2.5mm

Electron beam energy : 10 GeV

Crystal thickness : 0.1 cm
Distance between amorphous and amorphous : 2m
Amorphous thickness [...]

Initial parameters :

e- beam 80-50 MeV normal incidence, stat. 10^6
100% longitudinal electron polarisation S(0,0,1)
Tungsten target of 1×X0 = 3.5 mm (Z=74, ρ = 19.3 g/cm3)

Positron Yield = Ne+/Ne- ~ 15 %
Energy deposited in the tungsten target per initial incident electron ~ 14 MeV
Mean positron polarisation : Sz ~ 30 %
Modification of the positron yield, positron polarisation [...]