Preparation for electron tube workshops

What happens during this workshop?

Students learn how to make and control a particle beam and study how electrically charged particles behave in magnetic fields. Students learn about synchrotrons like the LHC.

Before taking part in this workshop, students should already know about:

  • the properties of electrons and energy levels of electrons in atoms
  • electric and magnetic fields, e.g. the shape of the magnetic field of a bar magnet and of a simple coil 
  • the deflection of electrically charged particles in magnetic fields due to the Lorentz force
  • how to calculate the speed of electrons when they are accelerated by an electric field (optional)

Key concepts

  1. Magnetic field lines: Magnetic field lines can be used to visualise magnetic fields. By convention they are defined going from the magnetic north pole to the magnetic south pole of a magnet. 
  2. Electric charges and electric fields: Electric field lines can be used to visualise electric fields. By convention they are defined going from + to -. Negatively charged particles are attracted by positively charged objects.
  3. Lorentz force: Moving electrically charged particles can be deflected by magnetic fields. This is caused by the so-called Lorentz force.

Helpful material

  1. Visualize the magnetic field of a bar magnet by drawing magnetic field lines.
  2. What happens if an electron is placed in front of a positively charged metal plate?

a) The electron is attracted by the plate.
b) The electron is repelled by the plate.
c) The electron becomes a positron.
d) Nothing happens.

  1. What happens to a proton when moving through a magnetic field perpendicular to the direction of the proton?

a) The proton is deflected by a force.
b) The proton is not affected.
c) The proton transforms into an electron.

Summary and link to CERN physics

Electrically charged particles are deflected in magnetic fields. This is used in the LHC to make protons follow a circular path. To make particles faster, electric fields can be used.

In the LHC, protons gain kinetic energy when passing through high electric fields (RF cavities). To keep the protons on a circular track, 1232 special superconducting electromagnets are installed. The high magnetic field of the dipole magnets causes the deflection of these electrically charged particles due to the Lorentz force.