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