cpots2012.physics.uoc.gr Dept. of Physics, University of Crete Aug 19 – Sept 2, 2012
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Transcript of cpots2012.physics.uoc.gr Dept. of Physics, University of Crete Aug 19 – Sept 2, 2012
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: [email protected]
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