The Mad Scientist Diary

The ideas, experiences, and projects of a mad scientist-in-training.

Particle beams are cool!

The first picture above shows a particle beam spiraling through an apparatus used for an undergraduate experiment here at the University of Rochester (the apparatus is shown in better lighting in the second two photos).

When a charged particle (in this case an electron) moves through a magnetic field (provided by the two large coils on either side of the apparatus), it begins to curve, forming small circles. When this equipment is used by students in the lab, the electrons are emitted perpendicular to the magnetic field, so the “circles” of the beam stack on top of each other, producing a single circle of beam. However, when the tube is rotated a little bit (emitting the electrons with a slight component parallel to the magnetic field) The circles spread out, producing the beautiful spiral you can see above!

Normally, of course, a beam of electrons is invisible. However, the inside of this tube has been filled with traces of helium gas. When the electrons hit these gas molecules, they occasionally produce photons. These photons allow us to see the beam.

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