Microwave coupler for electron cyclotron resonance accelerator

An apparatus comprising:

• a radio-frequency (RF) waveguide comprising:
• a pair of parallel rectangular waveguides including a first waveguide and a second waveguide;
• and
• a mode converter coupled to respective ends of the pair of parallel rectangular waveguides, the mode converter comprising and outer body and two coaxial cylinders;
• an electron source configured to provide a beam of electrons;
• and
• an accelerator including:
• a RF cavity having a longitudinal axis, a cylindrical outer wall, an inlet, and an outlet;
• an electro-magnet surrounding the RF cavity and configured to produce an axial magnetic field.

A method, comprising:

• feeding, via an RF waveguide, microwaves from an RF source into a mode converter comprising and outer body and two coaxial cylinders, the mode converter configured to transform a radiation pattern of the microwaves into a rotating TE-11 coaxial mode between the two coaxial cylinders;
• exciting, by the mode converter, a rotating TE-111 mode in an RF cavity coupled to respective ends of the two coaxial cylinders;
• generating an axial magnetic field in the RF cavity with a first magnet surrounding the RF cavity;
• emitting a beam of electrons into the RF cavity through a passage within an inner cylinder of the two coaxial cylinders;
• and
• accelerating the beam of electrons axially entering the RF cavity with non-linear cyclotron resonance acceleration.