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CPOTS – 2 nd ERASMUS Intensive Program Introduction to Charged Particle Optics: Theory and Simulation UCMUCM http://cpots2012.physics.uoc.gr Dept. of Physics, University of Crete Aug 19 – Sept 2, 2012 Heraklion, Crete, GREECE
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Fringing fields of a parallel plate analyzer (PPA) Project 4 (for Unit 3) References: L3.1, L3.2, L3.4 Prof. Béla Sulik Univ. of Debrecen & MTA Institute of Nuclear Research (Atomki) E-mail: sulik@atomki.hu Dominik Schrempf Spiros Doukas Yasemin Gündoğdu
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Goals Learn the difference between ideal and real situations Learn what happens if the fıeld is not terminated by special electrodes Study the distorded 45 0 field analyser – Do we need a field termination for a good PPA?
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Ideal 45 0 PPA The development of fringing fields is prevented by the ideal grids in the slits E kin of electrons E 0 = 1000 eV Upper plate voltage V 0 = -600 V Plate length L = 15mm Plate distance D 0 = 3 mm Slit distance L 0 = 10 mm Slit size w 2 = 0.4 mm
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Energy spectrum of an ideal PPA with broad slits. Elevation angle varies from 40 0 to 50 o Plate length L = 15mm Plate distance D 0 = 3 mm Slit distance L 0 = 10 mm Slit size w 2 = 0.4 mm
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Ideal PPA with source outside We observe that if we move the source of the electrons lower, the focus point moves higher than the exit slit E kin of electrons E 0 = 1000 eV Upper plate voltage V 0 = -600 V Plate length L = 15mm Plate distance D 0 = 3 mm Slit distance L 0 = 10 mm Slit size w 2 = 0.4 mm
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Elevation angle varies from 40 0 to 50 o Energy spectrum of an ideal PPA with source outside and broad slits. Plate length L = 15mm Plate distance D 0 = 3 mm Slit distance L 0 = 10 mm Slit size w 2 = 0.4 mm
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In this analyzer we have removed the ideal grids and we observe fringing fields in the area around the slits Plate length L = 30 mm Plate distance D 0 = 6mm Slit distance L 0 = 20 mm Slit size w 2 = 0.8 mm E kin of electrons E 0 = 1000 eV Upper plate voltage V 0 = -600 V
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As an effect of the fringing field, the beam isn’t focused in the exit slit. 45 0 PPA with fringing fields E kin of electrons E 0 = 1000 eV Upper plate voltage V 0 = -600 V Plate length L = 30 mm Plate distance D 0 = 6mm Slit distance L 0 = 20 mm Slit size w 2 = 0.8 mm
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In the following figure we can see the distortion of the field near the exit slit and near the edge of the plate
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Elevation angle varies from 40 0 to 50 o Energy spectrum of a PPA with fringing fields. Plate length L = 30 mm Plate distance D 0 = 6mm Slit distance L 0 = 20 mm Slit size w 2 = 0.8 mm
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In this analyzer we have increased the size of the surrounding box and the distortion of the field becomes stronger
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45 0 PPA with fringing fields As an effect of the fringing field, the beam isn’t focused in the exit slit. Plate length L = 30 mm Plate distance D 0 = 6 mm Slit distance L 0 = 10 mm Slit size w 2 = 0.8 mm E kin of electrons E 0 = 1000 eV Upper plate voltage V 0 = -600 V
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In the following figure we can see the distortion of the field near the exit slit and near the edge of the plate
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Energy spectrum of a PPA with fringing fields. Plate length L = 30 mm Plate distance D0 = 6 mm Slit distance L0 = 20 mm Slit size w2 = 0.8 mm Elevation angle varies from 40 0 to 50 o
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Next, we reduce the size of the plates along the z-direction too. Plate width W = 5mm Plate distance D0 = 6 mm Slit distance L0 = 20 mm Slit size w2 = 0.8 mm E kin of electrons E 0 = 1000 eV Upper plate voltage V 0 = -625 V
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In order to have a focused beam on the exit slit with this item, we have to adjust the potential of the upper plate to V 0 =-623 V Plate width W = 5mm Plate distance D0 = 6 mm Slit distance L0 = 20 mm Slit size w2 = 0.8 mm E kin of electrons E 0 = 1000 eV Upper plate voltage V 0 = -625 V
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Thank you for your attention
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