DC Electron beam acceleration with RF accelerator cavities without using buncher cavities Can a low-emittance (as low as necessary) dc electron beam (about 100keV energy) be directly loaded to an long (long enough to self bunching and accelerating) RF accelerartor structure without using any buncher cavities?
 A: If you inject a DC beam into an RF structure you will get that some particles get accelerated and other decelerated, depending on the RF phase. At $100$ KeV an electron is pretty far from being relativistic, this means that the velocities of the electrons in the beam can still vary substantially with the energy.
Therefore some bunching will start to take place spontaneously. The problem is that, without any further care, many particles will be outside the longitudinal acceptance and will get lost. This can be a radiation concern or even simply extra heating to be dissipated.
If you have more RF cavities and you optimize their phases you can improve on this, bunching the beam directly in the RF linac at the cost of the maximum energy reachable. This may or may not be a cost-effective solution depending on a number of external factors such as existing hardware, space availability, control system...
You may also consider a photocatode which, being controlled by a laser, will allow you to get any timing structure straight from the source.
