Patent ID: 7235929

Claim:
A magnetron comprising: an anode cylindrical body having a plurality of radially arranged vanes; a cathode assembly having a filament provided on a central axis of the anode cylindrical body, the filament having a core wire and a carbonized layer around an outer circumference of the core wire, wherein, when an outer diameter D 1 of the filament including the carbonized layer is φ0.53 to 0.56 mm, assuming that a resistance value of the filament before forming the carbonized layer is R 1 and a resistance value of the filament after forming the carbonized layer is R 2 , the thickness of the carbonized layer of the filament is determined such that a carbonization rate Rx defined by the equation “R x {(R 2 −R 1 )/R 1 }×100” is in a range of from 30 to 50%.