# Why cannot electrons be accelerated by cyclotron?

I was reading about cyclotron and it's working. I found out that electrons cannot be accelerated by this device. The reason I found was that they are too light. But I want to know why exactly electron having mass(9.1*10^-31 kg) cannot be accelerated?

## 1 Answer

They can, but being light, they speed up with very little energy. This is when the cyclotron will stop being useful, since its frequency has to be tuned to the mass of the accelerated particle. Very soon, relativistic effects will become important (let's say that the apparent, or effective, mass will grow) and the cyclotron will be out of tune, unable to give more energy to the electron. You then obtain electrons with little energy, not very interesting.

• The question is about cyclotrons not synchrotrons. But yes, in principle you are right. As the synchrotron radius is "small" the electrons are losing "much" energy by radiation. Hence, the electron energy is "small". Thus, synchrotrons were the "natural" next step. – Semoi Jun 16 at 10:32
• @Semoi Sorry about that, I really meant "synchrotrons", cheers. Edited. – Matt Jun 16 at 10:39
• So did I. :) Of course I meant: "As the cyclotron radius is "small" the electrons are losing "much" energy by radiation. " Best. – Semoi Jun 16 at 10:43
• @Semoi We're both getting confused! ;) – Matt Jun 16 at 10:44
• Let's not say that the apparent mass grow and instead say that the relationship between momentum and speed changes. First because that identifies more exactly how to work out when the issue comes up and secondly because if you do use relativistic mass you will have to confront the distinction between longitudinal mass (needed to understand the electrostatic acceleration of the beam) and the transverse mass (needed to understand the radius of curvature and therefore the timing). – dmckee Jun 16 at 23:35