CPOTS – 2 nd ERASMUS Intensive Program Introduction to Charged Particle Optics: Theory and Simulation UCMUCM Dept. of Physics, University of Crete Aug 19 – Sept 2, 2012 Heraklion, Crete, GREECE

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) Dominik Schrempf Spiros Doukas Yasemin Gündoğdu

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?

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

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

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

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

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

As an effect of the fringing field, the beam isn’t focused in the exit slit 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

In the following figure we can see the distortion of the field near the exit slit and near the edge of the plate

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

In this analyzer we have increased the size of the surrounding box and the distortion of the field becomes stronger

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

In the following figure we can see the distortion of the field near the exit slit and near the edge of the plate

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

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

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

Thank you for your attention