How Do Electrons Induce Different Electric Fields in Magnetrons and Klystrons?

[CL39]

Please explain "inducing electric field" which I found from reading about magnetron and klystron.

This is what I found from a book.

Magnetron: e- from cathode, forced by the pulsed voltage, go to the anode (in a sweeping motion due to mag. field) induce oscillating electric field at the ends of the anode opening.

Klystron: e- from the e-gun gets bunched in the initial buncher cavity and drifts to the catcher cavity where it induces retarding electric field (which forces the e- to slow down and the loss of KE is given off as microwave)

Why/how does electrons approaching something "induce" electric field.

And why for the magnetron the book says "oscillating E field" and for Klystron "retarding E field"

Thank you.

 

[Vailanor]

Inducing electric field means that when electrons move in the vicinity of a conductor, they create an electric field in the vicinity of the conductor. This electric field can be used to accelerate the electrons, or slow them down. In the case of the magnetron, the electric field created by the electrons is oscillating (alternating between positive and negative). This is because the electrons move in a sweeping motion due to the magnetic field. In the case of the klystron, the electric field created by the electrons is retarding, which means it slows them down. This is because the electrons are bunched up in the initial buncher cavity and then drift to the catcher cavity, where the electric field created by the electrons forces them to slow down and lose kinetic energy, which is then given off as microwaves.