Giant Microwave Bursts Emitted from a Field-Emission, Relativistic-Electron-Beam Magnetron

Abstract

A magnetron operating at a wavelength of 10 cm has been constructed with six resonant cavities cut in a cylindrical anode block. A graphite cylinder acting as a field-emission cathode delivers ~12 kA in an accelerating radial potential of ~360 kV. .The magnetic field directed along the diode axis is ~8 kG. Linearly polarized microwaves of 30 nsec duration at powers of ~1.7 GW are achieved. The conversion efficiency of electron energy into microwave is ~35%.Advances in high-voltage pulse technology permit the generation of intense relativistic beams of electrons ranging in power from gigawatts to terawatts. Efficient conversion of this energy into electromagnetic radiation is a task pursued at several laboratories. In these studies one excites on the beam one of several known collective modes of oscillation and promotes wave growth at the expense of the beam's kinetic or potential energies. The techniques used to date fall into the following three categories. In the first, axial bunching 1 " 3 is induced on the relativistic beam. In the second, the electrons are made to bunch transversely 4 " 7 to a guiding axial magnetic field. And in the third, 8 * 9 one uses modes of oscillation which are typical of "crossed-beam" devices 10 ' 12 of which the magnetron is the best known example. Here the electron beam moves under the simultaneous action of a dc electric field and an orthogonal dc magnetic field. The well-known 11 efficiency of crossed-beam devices operating with convectional thermionic cathodes of relatively low current densities suggests that one apply them in the regime of high currents and high voltages characteristic of field-emission diodes. The magnetron described in this Letter yielded 13 a power of ~ 1.7 GW; the efficiency of converting beam energy to microwave energy was close to 35%.

Electron cyclotron maser emission mode coupling to the z-mode on a longitudinal density gradient in the context of solar type III bursts

“…Electron beam injection is common in many plasma situations. Examples are solar flares [1], cavity magnetrons that generate microwaves [2,3] or various radar applications. Beams of relativistic, hot electrons are also likely to be the source of solar type III radio bursts.…”

Numerical simulation of oscillating magnetrons

“…The simulation is also applicable to smooth bore magnetrons's, 1120 and to the study of magnetically insulated high-voltage transmission systems. 2 ' The code embodies several major improvements over an earlier magnetron simulation 2 2 which was electrostatic (in the moving wave frame), and which did not treat the anode geometry in detail.…”

“…These impressive results have reawakened an interest to better understand the interaction of the electromagnetic field and the dense space charge cloud in magnetron-type devices. Numerous attempts have been made over a span of forty years,"- 1 4 to calculate self-consistently the rf fields under the large signal conditions prevalent in the magnetron, and from these to predict the current, voltage, microwave power and efficiency.…”

S-band microwave radiation by a high-impedance diode with an A6 anode block

“…Here, let us note that the resonant frequencies of this RM differ very little from those obtained when the RM cathode diameter was 30 mm and the A6 anode block was not closed by end caps. 23,24 The time dependence of the microwave radiation frequency was determined using waveforms of the microwaves acquired using a 40 GS/s resolution digitizing oscilloscope. Namely, the frequency was calculated as an average value during the time interval of 10 microwave oscillation periods.…”

“…The first M-type microwave generator 23,24 was invented after successful research of low-impedance magnetically insulated high-power (several GW) electron diodes. 25 The design of this multi-resonator RM was very similar to the design of magnetically insulted diodes with a cylindrical anode.…”