This image below show the movement of an electron in a magnetic field, it's taken from the video [Histoire des sciences] La découverte de l'électron explaining the experience of J.J. Thompson when he discovered the electron.
I don't understand why electrons are going the way indicated the red dotted line. Below is how I understand this image with the right-hand rule:
Because the force $\vec{F}$ is oriented toward the top, a positively charged ion (or cation) should go toward the top as shown on the picture. But here, it's an electron, a negatively charged particle, so it should be going toward the bottom. So why is it going toward the top? What's wrong in my understanding?
Also, is it correct to mark a plus (+) and a minus (-) on the magnet?