Obergurgl, 20.06.2004Obergurgl, 20.06.2004
Damian Pliszka* , Grzegorz P. Karwasz, Roberto S. Brusa, Antonio Zecca,
Dipartimento di Fisica, Università Degli Studi di Trento, 38050 Povo (TN) Italia* Institute of Physics, Pomeranian Pedagogical University, 76-200 Slupsk, Poland
1. Slow positron apparatus
2. Testing
3. High energy mode
4. Deaccelerating mode
5. Benzene results
Schematics
INJECTION OPTICS
REMODERATOR STAGE
FIRST ACCELERATOR
DEFLECTOR
First accelerator - wide-angle electrostatic optics where slow positron beam is formed from Na22 source coupled with 1 m W monocrystal
90 electrostatic spherical deflector - used to prevent high-energy positrons from the source reaching the target
Remoderator stage – second accelerator equiped with electron gun which allows in situ conditioning Cu remoderator film
Injection optics - formed by three aperture electrodes, in focusing conditions a weak longitudinal magnetic field is used, and guides positrons through 10 cm long scattering cell.
Beam modellingFirst accelerator (SIMION simulation)
Testing
1. Electrons (focusing effect of magnetic field)
2 4 6 8 10
0
2000
4000
6000
8000
Elec
tron
bea
m c
urre
nt (
e- /s/1
0s)
Magnetic field B (G)
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
10
15
20
25
30
35
Kennerly convolution 130 meV tuning I tuning II
Tota
l cro
ss s
ectio
n (1
0-20 m
2 )
Electron energy (eV)
1. Electrons (cross sections)
2. Positrons (focusing effect of magnetic field)
4 6 8 10 120
100
200
300
400
500
600
700
Final energy of positrons 15 eV
C
ount
s (e
+/1
0sec
)
Magnetic field B (G)
64.8 65.0 65.2 65.4 65.6 65.8 66.00
200
400
600
800
1000
Positrons energy 4 eV
Cou
nts
(e+ /1
0sec
)
Deflector voltage (V)
2. Positrons (pass - band of deflector)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Nitrogen (N2)
T
otal
cro
ss s
ectio
n (1
0-20 m
2 )
Positron energy (eV)
Hoffman et al.
Present: preliminary
preliminary with energy correction
2.4 eV
Energy correction
Present
1 1020
30
40
50
60
70
8090
100
Benzene (C6H6)
T
otal
cro
ss s
ectio
n [1
0-20 m
2 ]
Positron energy [eV]
Experiment:
Sueoka 2003
Kimura 2000
Sueoka 2000
Sueoka 1988 x1.12
Benzene results – vs. experiments
Sueoka 1988 x1.12
Theory: Gianturco 2003
Present
1 1020
30
40
50
60
70
8090
100
Benzene (C6H6)
T
otal
cro
ss s
ectio
n [1
0-20 m
2 ]
Positron energy [eV]
Benzene results – vs. theory
Acknowledgements:
EPIC – made it possible!Trento is Rome subnode
Marco BettonteChiara Perazzolli