Radiotherapy device and microwave source thereof

A microwave source, comprising:

• a cathode heater including one or more filaments, wherein each filament of the one or more filaments is of a cylindrical configuration;
• and
• a thermionic emitter configured to release electrons when the thermionic emitter is heated by the cathode heater;
• wherein when the cathode heater is disposed in a magnetic field, a direction of the magnetic field is parallel to an extending direction of the each filament of the one or more filaments.

A microwave source, comprising:

• a cathode heater;
• and
• a thermionic emitter configured to release electrons when the thermionic emitter is heated by the cathode heater, wherein the thermionic emitter includes:
• a substrate component, wherein the cathode heater is disposed inside the substrate component;
• and
• an electron emission layer disposed on an outer wall of the substrate component, wherein the electron emission layer includes at least one discontinuity.