Mode Switching in Relativistic Magnetrons and Hysteresis

Electron flow in relativistic magnetrons has been studied for decades. It is responsible for
the generation of very high power levels of microwave radiation, and the physics of this
type of crossed‐field flow has also been used to describe the cylindrical electrosphere in
pulsars. The A6 relativistic magnetron invented by Bekefi at MIT in the mid‐to‐late 1970’s
is known to suffer from mode competition. For the accelerator parameters available at
the University of New Mexico, at a fixed cathode radius mode competition in an A6 magnetron
takes place between the ‐mode and 2/3‐mode when the applied DC magnetic
field is near the critical field of about 4.5 kG. Using particle‐in‐cell computer simulations
we show that the introduction of a relatively low‐power external RF signal can eliminate
this mode competition to achieve stable single mode operation. The mechanical analogy
of the situation at the critical magnetic field is the bifurcation of modes that occurs for a
system of two stable states separated by a saddle point. In addition, the introduction of
an external RF signal during magnetron operation leads to mode switching during the
pulse, adding frequency agility to the source. Furthermore, hysteresis is observed to be
associated with mode switching during magnetron operation. These processes and the
electron flow associated with them will be discussed.
Dr. Edl Schamiloglu is the Gardner‐Zemke Professor of Electrical and Computer
Engineering at the University of New Mexico. He received his Ph.D. at Cornell University’s
Laboratory of Plasma Studies in 1988. He has coauthored 80 articles in archival journals and two
books. He is a Fellow of the IEEE, a Senior Editor of the IEEE Transactions on Plasma Science, and
an Associate Editor of the Journal of Electromagnetic Waves and Applications. He was the General
Chair of the 2007 IEEE Pulsed Power and Plasma Science Conference (combined Pulsed
Power and ICOPS).