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Navigate between the simulations
0. Synchrotron > 1. Electron Gun > 2. The Linac > 3. Dipole Magnets > 4. Vacuum > 5. Undulator > 6. Beamlines
Instructions
- Heat the cathode by pressing the '+' button on the cathode heater and note what happens.
- Now apply a positive voltage by pressing the '+' button on the anode. Note how the electric field lines change.
- Adjust the anode voltage again to see what happens when the voltage is so low the electrons do not enter the electric field.
Think about:
- What do you need in order to get a large current from the gun (large number of electrons flowing)?
- What do you need to do to get the electrons flowing faster?
In Summary
The electrons used by Diamond begin their journey at the Electron Gun. When metals get very hot they start to lose electrons from the surface through a process called thermionic emission. Normally the electrons simply fall back, so that no net current flows away from the metal surface. When an electric field (a positively charged surface) is brought close to the surface that is emitting electrons, the electrons are attracted away and no longer return to the filament. The stronger the electric field (the more positive the anode is made) the faster the electrons are accelerated away.
In more depth
The kinetic energy acquired by the electrons is equal to the electric work done by the field in ripping them away from near the surface of the filament.
So we can say:
Kinetic energy = electrical work done
½ mv2 = eV
Where m is the electron mass,
v is its velocity as it leaves the gun,
e is the charge of the electron, and
V is the Voltage on the anode.
Electrons are so light that very quickly they reach speeds close to the speed of light. Trying to accelerate electrons much further starts to bring in relativistic effects: the velocity doesn't increase much more but the electron mass starts to increase instead! Sounds quite complicated, but that's relativity for you!
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
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