CPOTS – 2nd ERASMUS Intensive ProgramIntroduction to Charged Particle Optics:

Theory and Simulation

UCM

http://cpots2012.physics.uoc.grDept. 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 SulikUniv. of Debrecen &

MTA Institute of Nuclear Research (Atomki)E-mail: sulik@atomki.hu

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 450 field analyser– Do we need a field termination for a good PPA?

Ideal 450 PPAThe development of fringing fields is prevented by the ideal grids

in the slits

Ekin of electrons E0 = 1000 eVUpper plate voltage V0 = -600 V

Plate length L = 15mmPlate distance D0 = 3 mm

Slit distance L0 = 10 mmSlit size w2 = 0.4 mm

Energy spectrum of an ideal PPA with broad slits.

Elevation angle varies from 400 to 50o

Plate length L = 15mmPlate distance D0 = 3 mm

Slit distance L0 = 10 mmSlit size w2 = 0.4 mm

Ideal PPA with source outsideWe observe that if we move the source of the electrons lower, the focus point

moves higher than the exit slit

Ekin of electrons E0 = 1000 eVUpper plate voltage V0 = -600 V

Plate length L = 15mmPlate distance D0 = 3 mm

Slit distance L0 = 10 mmSlit size w2 = 0.4 mm

Elevation angle varies from 400 to 50o

Energy spectrum of an ideal PPA with source outside and broad slits.

Plate length L = 15mmPlate distance D0 = 3 mm

Slit distance L0 = 10 mmSlit size w2 = 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 mmPlate distance D0 = 6mmSlit distance L0 = 20 mm

Slit size w2 = 0.8 mm

Ekin of electrons E0 = 1000 eVUpper plate voltage V0 = -600 V

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

450 PPA with fringing fields

Ekin of electrons E0 = 1000 eVUpper plate voltage V0 = -600 V

Plate length L = 30 mmPlate distance D0 = 6mmSlit distance L0 = 20 mm

Slit size w2 = 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 400 to 50o

Energy spectrum of a PPA with fringing fields.

Plate length L = 30 mmPlate distance D0 = 6mmSlit distance L0 = 20 mm

Slit size w2 = 0.8 mm

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

450 PPA with fringing fieldsAs an effect of the fringing field, the beam isn’t focused in the exit slit.

Plate length L = 30 mmPlate distance D0 = 6 mm

Slit distance L0 = 10 mmSlit size w2 = 0.8 mm

Ekin of electrons E0 = 1000 eVUpper plate voltage V0 = -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 mmPlate distance D0 = 6 mm

Slit distance L0 = 20 mmSlit size w2 = 0.8 mm

Elevation angle varies from 400 to 50o

Next, we reduce the size of the plates along the z-direction too.

Plate width W = 5mmPlate distance D0 = 6 mm

Slit distance L0 = 20 mmSlit size w2 = 0.8 mm

Ekin of electrons E0 = 1000 eVUpper plate voltage V0 = -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 V0=-623 V

Plate width W = 5mmPlate distance D0 = 6 mm

Slit distance L0 = 20 mmSlit size w2 = 0.8 mm

Ekin of electrons E0 = 1000 eVUpper plate voltage V0 = -625 V

Thank you for your attention