Experimental investigations of a millimeter wave relativistic magnetron

Results of an experimental study of a 48-resonator relativistic magnetron (RM48) operating in the 8 mm waveband have demonstrated a fair agreement with theoretical calculations and a 3D numerical simulation. With cathode-anode gap sizes of 3 to 5 mm the magnetron generated in the range of 36-39 GHz, featuring oscillations close to the π-mode of the fundamental spatial harmonic. Meanwhile, the width t
_MW
of the generated pulse was, in practically all operation regimes, t
_MW
=3 ns to 8 ns, which is much shorter than the driving pulse width t
_P
= 35 ns. This is evidence for the existence of some agents producing a negative effect on the magnetron performance. The traces of microwave breakdowns detectable between the EDS and the cathode, as well as extension of the operative area (in terms of U
₀
and B
₀
) beyond Hull's cut-off indicate an extremely high level of electric fields in the interaction space, which fields are excited by the high current of the electron flow. It is logical to conclude that during intense generation the beam particles are subjected, along with the dc fields E
₀
and B
₀
, to the action of commensurate r.f. wave fields and those due to the space charge. All of these may alter essentially excitation modes of the EDS.