MAGNETRON

PROBLEM TO BE SOLVED: To improve the output stability during operation.SOLUTION: A magnetron comprises a cylindrical positive electrode 1, a negative electrode 5 extending along its axis, pole pieces 8, 9 located at the opening at the end of the positive electrode 1, metal sealing bodies 10, 11 whose cylindrical parts extend from flanges which are joined to the pole pieces 8, 9, ferromagnetic yokes 23, 24 which are positioned so that they surround the cylindrical parts of the metal sealing bodies 10, 11, and a first permanent magnet 51 and a second permanent magnet 52 which are located between the yokes 23, 24 and the flanges of the metal sealing bodies 10, 11. The first permanent magnet 51 has coercive force whose temperature coefficient is positive and is positioned closer to the side of the metal sealing bodies 10, 11 than the second permanent magnet 52. The second permanent magnet 52 has a maximum energy product larger than that of the first permanent magnet 51.