Cyclotron engines as a means of thrust for interplanetary travel?

Question

How feasible is it to use a cyclotron in this manner for space propulsion?

Inject small amounts (aliquots) of ionized matter into cyclotron at some high integer multiple n of the cyclotron frequency $\omega=qB/m$ so that there are n aliquots at each radius in the cyclotron. Since the time it takes to complete one revolution is the same for all of these aliquots, one could use the frequency $2n\omega$ of the alternating electric field to accelerate all these aliquots in a synchronous manner. This would give essentially a continuous stream of very high speed plasma or material to accelerate spacecraft. Of course, the aliquots could move at relativistic speeds which would affect the cyclotron frequency by $\gamma$. But one could design a magnetic field that gets stronger with increasing radius especially toward outer portions where relativistic effects would be more prominent. There would also be electrostatic repulsions between aliquots that would need to be taken into account. The spacecraft would likely need nuclear power source. Is this a feasible idea? Has this been thought of already?

Answer 1

A cyclotron is a type of Ion engine. Cyclotrons (in the classical sense of the word) haven't been used because they have a very low power-to-weight ratio (tons of magnet to accelerate tiny amounts of matter).

There are ion engines that use the Electron cyclotron Resonance principle; these use the cyclotron princple at a tiny scale to create ions that are then accelerated in a linear accelerator.

Answer 2

You certainly can build a form of ion thruster this way. You will also need an electron source (such as a simple hot cathode, or more sophisticated devices) to emit an equal number of electrons as ions (assuming you use positive ions) to keep from building up a charge.

This sort of engine will lend itself to extremely high Isp, many times higher than most currently existing ion engines, and using (proportionately) very large amounts of electric power while generating very, very low thrust. It is arguably "overpowered" (in an Isp sense) enough to be inefficient unless it can be matched with an extremely high power density and lightweight power source -- existing solar panels and nuclear reactors, or those that we could feasibly build with plausibly extrapolated future technology -- don't really fit the bill.