User Modeling for Domains without Explicit Design Theories

A magnetron comprises an anode cylinder, vanes extending from the inner surface of the anode cylinder toward the central axis of the anode cylinder, a cathode disposed at the central axis of the anode cylinder, an output antenna coupled in a high frequency coupling mode to the vanes, and a set of permanent magnets for creating a magnetic field having a line of magnetic force directed toward the axis of the anode cylinder. The set of permanent magnets constitutes a combination of, for example, an alnico magnet and rare earth magnet differing in coercive force.