Accelerating protons with electrons?

In the Fermilab Linac, a klystron creates high-power radio waves which are used to accelerate the H- beam. The klystron itself is also a “mini” accelerator, but instead of protons, it accelerates electrons to create radio waves. Here are the internals of a klystron, where one can see the electron beam pipe in the center of the exposed cutout, along with the electron bunching cavities in between the cutouts. Photo: Trevor Butleracc