Development of a 10 kw 4 mm magnetron

Under a development contract between Bomac Laboratories, Inc. and the Signal Corps Electronic Laboratories, the BL-221, a 4.3 mm packaged magnetron with pulsed power in excess of 10 kw was designed and fabricated. This tube has been successfully operated at duty cycles up to .0005 over a range of pulse widths from .03 to .3 microseconds, and at pulse repetition rates from 1670 to 16,700 c.p.s. This paper discusses the design in moderate detail, the techniques employed in its fabrication, and test results of typical samples. In achieving this accomplishment, the state of the art has been extended in a number of directions simultaneously. The BL-221 development resulted in a more rugged tube, lighter weight, smaller overall size, and higher power output than any 4 mm magnetron previously produced in this country. This development concentrated on certain inherently desirable features of tube construction which tend to make it more shock and vibration resistant, and contribute to longer life, higher power, and more compactness. Features of construction include: (1) Replacement of all glass members with ceramics, except for the output window. (2) Design of a compact "E" magnet and improved magnetic circuit. (3) Use of Phillips type emitter. (4) Application of internal getters. (5) Ingenious method of electrical centering of cathode during operation.