1. Positron Production at LI2FE
PLASMON X
MC-INFN Since Jan 2011
Positron Production at LI2FE
70 cm
Target
1-2-5 mm
4 mm
Beam spot (1 mm)
Eg = 4,10,20 MeV ; E/E=0
Ee- = 30, 150 MeV ; E/E=0
Meeting LI2FE Frascati mar-2011

2. Electrons are present too (a little bit more than positrons).
Protons are produced in air (g on N2), not in the target

3. Meeting LI2FE Frascati 16-mar-2011
Target Material
Eg = 10 MeV Target 1 mm thick
Meeting LI2FE Frascati mar-2011

4. Meeting LI2FE Frascati 16-mar-2011
Target Length
Higher production occurs at higher energy (because the cross section increases as the logarithm of the energy).
The best thickness for positrons (and electrons) is 2 mm, (effect more evident for E=20 MeV).
(This behaviour is probably due to a trade-off between the number of the target nuclei and the self absorption).
At 4 MeV the geometry of the target seems unessential for positrons.
Meeting LI2FE Frascati mar-2011

5. Positron produced (e+ pr-1)
Target Geometry (mm)
Positron produced (e+ pr-1)
± err%
Length
Radius
Forward
Side
Backward 1 2
6.9E-02 ± 6
5.4E-04 ± 0.6
2.5E-03 ± 0.3
9.2E-02 ± 4
5.7E-04 ± 0.1
3.1E-03 ± 0.3 5
7.6E-02 ± 5
===
3.2E-03 ± 0.3
Eg = 10 MeV
Having a primary photon flux of 109 photons/sec, about 108 forward positrons can be obtained.
What about the spectrum and the angular distribution of the positrons (users want “beam”)
Meeting LI2FE Frascati mar-2011

6. gmonochromatic +N  e+ + e- e- + N  gbremsstrahlung + N  e+ + e-
Photo/Electro production
PHOTOPRODUCTION
ELECTROPRODUCTION
NEEDS A LASER
(Hw, controls, maintenance)
NO EXTRA HW
DIRECT PROCESS
gmonochromatic +N  e+ + e-
e+ are secondaries
TWO STEP PROCESS
e- + N  gbremsstrahlung + N  e+ + e-
e+ are tertiaries
Photoproduction is expected more efficient
(depending on the energy)
Better beam quality
Meeting LI2FE Frascati mar-2011

7. Meeting LI2FE Frascati 16-mar-2011

8. Positron fw production at 1 Hz
Photo/Electro production
Positron fw production at 1 Hz
(0<q<5°)
Energy
Positrons ± err%
109 Photons 4
1.9 x 104 ± 2.6 10
9.6 x 104 ± 0.8 20
2.2 x 105 ± 0.8
1.1 nC Electrons 30
8.0 x 104 ± 8.8
150
4.5 x 105 ± 3.4
The photons available at LI2FE can be per shot
The primary electrons can be 1.1 nC  7x “
The repetition rate can increase to 10 Hz
Meeting LI2FE Frascati mar-2011

9. Meeting LI2FE Frascati 16-mar-2011
Different scales
DE =0.5 MeV
Meeting LI2FE Frascati mar-2011

10. Meeting LI2FE Frascati 16-mar-2011
DE =0.5 MeV
Same scales
The spectrum is continuous in both the situation, but photoproduction is more efficient (the energy of the maximum is relatively higher)
Meeting LI2FE Frascati mar-2011

11. Positron beam will be available at LI2FE
Production efficiency is about some % (considering the integral production)
Efficiency for fw and monochromatic beams is about 1/104
(Dq= 5°) (25% for g=4MeV < DE/E < 3% for g=20MeV beams)
The electro-production from the SPARC beam and photoproduction from PLASMON-X photons have almost the same efficiency (because of the limited charge of the electron beam, 1 nC electrons vs. 109 photons)
Meeting LI2FE Frascati mar-2011

12. Meeting LI2FE Frascati 16-mar-2011
Neutron Beams
n from g or e- beam on W are about a factor 100 less than e+
Alternative method is the photodissociation of the deuterons
(g +D2O  n + …)
Giving fw neutrons
F. Broggi, L. Serafini: "A Possible Neutron Source at "LIFE", EBD-09/003, 10/11/2009
Meeting LI2FE Frascati mar-2011