# Ion engine: purpose of magnet rings

I have a question about the gridded electrostatic ion engine. In the ionisation chamber there are several magnet rings that create a magnetic field inside the chamber.

But what is the purpose of that magnetic field?

• +1 This is backed up by the label Magnetic Field Enhances Ionization Efficiency shown in the OP's figure. – uhoh Aug 24 '17 at 13:41