How to trap particles
With Suzie Sheehy
About this video
In particle accelerators, beams of particles are focused and fired forward at almost the speed of light. But how are those particles controlled? With the help of two visual demonstrations, Suzie Sheehy explains.
Keeping a handle on particles is key to the huge range of applications particle accelerators have. The machines accelerate beams of particles using electric and magnetic fields. Suzie uses a ‘Paul trap’ to show how rapidly oscillating currents are used to keep particles on track. A ball on the saddle apparatus is kept in the centre by the rising sides. But that only controls the ball in one direction, meaning it can drop off. Magnetic or electric fields are similar, and can only direct particles in one plane at a time. When the kit begins to spin, though, the alternating position of the rising sides means the ball is contained in the center. This has the same effect that quadrupole magnets in an accelerator have, constantly alternating gradients to keep particles in line.
Using a more sophisticated setup, a quadrupole linear Paul trap, pollen grains can be held in place in a beam just as particles in an accelerator would be. Oscillating fields established across rods on opposite corners of the system keep the pollen particles trapped. Without the rapidly changing fields, the particles would just shoot off in one direction; it’s the changes that keep them from escaping in one or the other direction.
These simple analogies show how particle accelerators guide particles into focused beams, to be harnessed for a huge range of applications.
This video is supported by the Science and Technology Facilities Council.
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