MAGNETRON AS GENERATOR OF CENTIMETER WAVES 169 



discussion in PART II of the magnetrons developed at the Bell Laboratories 

 during the war. More complete presentations of the experimental and theo- 

 retical work done on the magnetron during the war are soon to be published 

 by other research groups. 



The material written up during the war has appeared as secret or confi- 

 dential reports issued by the British Committee on Valve Development 

 (CVD Magnetron Reports), by the Radiation Laboratories at the Massa- 

 chusetts Institute of Technology and at Columbia University, and by the 

 participating industrial laboratories. No attempt has been made in PART I 

 to indicate the specific sources of the work done since 1940. To fit the war- 

 time development of magnetrons into the sequence of previous developments, 

 specific references are made to publications appearing in the literature prior 

 to 1940. 



The nature and scope of PART II of the paper are discussed more fully 

 in its introductory Section, 11. General Remarks, 



PART I 



THE MAGNETRON OSCILLATOR 

 1. General Description 



1 . 1 Description: The multicavity magnetron oscillator has three principal 

 component parts: an electron interaction space, a multiple resonator system, 

 and an output circuit. Each of these is illustrated schematically in Fig. 1. 

 The electron interaction space is the region of cylindrical symmetry between 

 the cathode and the multisegment anode. In this region electrons emitted 

 from the cylindrical cathode move under the action of the DC radial electric 

 field, the DC axial magnetic field, and the RF field set up by the resonator 

 system between the anode segments. These electronic motions result in a 

 net transfer of energy from the DC electric field to the RF field. The RF 

 interaction field is the fringing electric field appearing between the anode seg- 

 ments, built up and maintained by the multicavity resonator in the anode 

 block. RF energy fed into the resonator system by the electrons is delivered 

 through the output circuit to the useful load. The output circuit shown in 

 Fig. 1 consists of a loop, inductively coupled to one of the hole and slot cavi- 

 ties, feeding a coaxial line. 



To operate such a magnetron oscillator, one must place it in a magnetic 

 field of suitable strength and apply a voltage of proper magnitude to its 

 cathode, driving the cathode negative with respect to the anode. This 

 voltage may be constant or pulsed. In the latter case, the voltage is applied 

 suddenly by a so-called pulser or modulator for short intervals, usually of 

 about one microsecond duration at a repetition rate of about 1000 pulses per 

 second. With suitable values of the operating parameters, the magnetron 



