1. A Teaching Laboratory on Electron Optics
Zhang Ye-qing, Xia Hui, Hu Li-peng, Liu Jie-meng, Le Yong-kang
Fudan Physics Teaching Lab, Shanghai, People’s Republic of China
We started with the investigation on the focus of electron beam in a single trace oscilloscope CRT. SIMION software was employed to simulate the focus effect in dependence of different parameters, such as the local distribution and energy distribution of the initial electrons, voltage of the lens electrodes, etc.
I. Background: Electron Optics of the Cathode Ray Tube (CRT) [1]
SIMION 8 Interface
Electron Gun Structure
Oscillograph Operation Panel
II. SIMION Result [2]
Theoretical Formula:
Fig. 1 The focal length decreases with the electron-emission off-axial distance increases. Mutation occurs when the off-axial distance exceeds a limit, which causes aberration.
Fig. 2 By controlling anodes voltages, the focal effect would change. Focal length decreases with increasing voltage on Anode I. Focal length decreases with decreasing voltage on Anode II. Variation of the voltage on Anode II serves as rough tuning, while that on Anode I as fine tuning.
Fig. 4 Current distribution at the screen: experimentally observed and simulated. The distribution consists of a bright middle spot and halation around the middle spot.
Fig. 3 Electron trace at different grid voltage. Proper grid voltage could increase the beam current density, but may "cost" the filed angle of the beam.
III. Future Work: Fabrication of a Focused Ion Gun [3] [4]
IV. References
[1] SIMION 8 Manual.
[2] Hua Zhong-yi, Gu Chang-xin “Electron Optics” 1993.
[3] The Extractor Ion Source IQE 11/35 Product Information.
[4] Li Li “30 minutes Quick Guide for SolidWorks Cavity Design” 2010.
Immersion Lens Simulation
Initial Ion Energy: 5keV
Electrodes Voltage: 4.5kV
Detector Distance: 22mm
Initial Radius: 3mm
Focus Radius: 0.36mm
Focal Radius Ratio: 12%
Designing a Device for Experiment
Designed Focal Device Structure
SIMION 8 Simulation